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Growth process of the lava dome/flow complex at Sinabung Volcano during 2013–2016
Abstract
Mount Sinabung, North Sumatra, Indonesia, erupted for the first time in 2010 and reactivated again in 2013. The eruption started with a phreatic phase, changed to phreatomagmatic, and then andesite lava appeared at the summit crater in late December 2013. Lava effusion continued and has been associated with partial to complete collapses of the lava complex, which successively generated pyroclastic density currents (PDCs). The lava complex grew first as a lava dome and then developed into a lava flow (lava extension stage). It extended up to about 3 km in horizontal runout distance by late 2014. When the front of the lava complex moved onto the middle and lower slope of the volcano, PDC events were initially replaced by simple rock falls. Inflation of the upper part of the lava complex began in mid-2014 when the movement of the lava flow front stagnated. The inflation was associated with hybrid seismic events and frequent partial collapses of the upper part of the lava complex, generating PDC events with long travel distances. From mid-September 2014, new lobes repeatedly appeared near the summit and collapsed. Cyclic vulcanian events began in August 2015 when hybrid events peaked, and continued > 1.5 years (vulcanian stage). These events sometimes triggered PDCs, whose deposits contained vesiculated lava fragments. The distribution of PDC deposits, which extended over time, mostly overlapped in areal extent with that of the 9th–10th century eruption. Eruption volumes were estimated based on measurements with a laser distance meter during 6 periods, digital surface model (DSM) analysis of satellite images during one period, and the cumulative number of seismically detected PDC events, assuming a constant volume of each PDC event. The total volume of eruption products reached about 0.16 km³ DRE as of the end of 2015. The lava discharge rate was largest during the initial stage (> 7 m³/s) and decreased exponentially over time. The discharge rate during the vulcanian stage was ≪ 1 m³/s. The trend of decreasing discharge rate is in harmony with that of ground deflation recorded by a GPS measurement. The chemical composition of lava slightly evolved with time. Cyclic vulcanian events may have been triggered by limited degassing conditions in the upper conduit and by unloading of the conduit by lava dome collapses.
... The younger part lacks pumice fall, suggesting effusive eruptions forming lava domes and flows rather than Plinian eruptions. The last significant eruption occurred in the 9th or 10th century, with pyroclastic density currents (PDCs) extending approximately 4.5 km from the summit (Nakada et al., 2019), resembling the 2014-2018 eruptions. ...
... The activity ceased temporarily in September 2010, with the dormant period lasting until September 15, 2013, when a second phreatic eruption occurred. A new lava dome appeared at the summit on December 18, 2013, gradually growing until it collapsed at the end of the month, triggering PDCs that destroyed the 3-Mm 3 lava dome Nakada et al., 2019;Pallister et al., 2019). ...
... Lava effusion in the form of flows began on January 10, 2014, reaching the volcano base by March 2014 (Nakada et al., 2019). From the end of September 2014 to February 2018, lava effusion alternated with dome growth, rockfall, and PDC events. ...
... For example, Sinabung volcano, erupted the first time in 810±70 years ago and reoccurrence in 1881 [8]. After a very long time of gap (129 years), it erupted back in 2010 and continued until 2015 [9]. Currently, it has dropped to warning level activity from alert. ...
... The chemical composition of the magma describes the characteristics of past and future volcanic eruptions. It is obtained from chemical tests on magma samples or erupted rocks [9,, as given in Table 2. The volcano in Sumatra has two types of magma, basaltic and andesitic. ...
... Chemical composition of the magma in active volcanoes based on previous work[9,[13][14][15][16][17][18]. ...
The characteristics of active volcanoes in Sumatra have been summarized based on the analysis of the relationship between seismicity, morphology, magma chemical composition, and eruption history. The level of volcano activity is linked to how partial melting depth, continuity distribution of hypocentre beneath each volcano to the trench line (magma dyke), visual activity seen on craters, chemical magma content, and reoccurrence of eruption analysis. The analysis result showed the current status of the volcano is inverted linear with partial melting depth. The scatter point of the hypocentre beneath the alert and warning volcano is continued to the trench line, but normal volcano status is discontinued. It was similar to volcanic activity seen in craters. It may relate to the quantity and activity of magma flow in dyke. According to reoccurrence analysis, Mt. Krakatau, Mt. Marapi, and Mt. Kerinci are highly vulnerable because they have the shortest accumulated eruption interval. However, all of active volcanoes have the potential for repeated massive eruptions, like what happened to Sinabung. Mix eruption is their eruption because magma types tend to be basaltic and andesitic. Only on Mt. Dempo is detected rhyolitic (SiO2 more than 65%).
... One particularly important dataset recorded by observers at the observatory was a time series of explosive events occurring at the volcano's summit. Explosions occurred frequently, particularly after the volcano entered a phase of cyclic Vulcanian events in August 2015 Nakada et al., 2019). In 2016, the Sinabung monitoring network was expanded to include three scanning Differential Optical Absorption Spectrometers (DOAS) (Primulyana et al., 2019). ...
... In fact, similar emissions have been sustained for over a decade at Sinabung (Primulyana et al., 2019), indicating a relatively constant magma supply rate. The petrologic degassing behavior of sulfur is complex and has not been explicitly studied for Sinabung's andesitic (Nakada et al., 2019) magmas. However, research from other andesitic arc magmas (hydrous, relatively oxidized) suggests that sulfur degassing occurs throughout the mid-and upper-crust, where many magmas are saturated in a H 2 O-and CO 2 -rich multicomponent vapor phase (Métrich and Wallace, 2008;Fiege et al., 2014). ...
... Secondly, the decrease in SO 2 emission rates in the days preceding explosive events ( Figure 3A) suggests that the established degassing pathways can become sealed by the viscous, degassed dome material, which causes pressurization and eventual explosive rupture. The potential for a protracted phase of repeating explosive events at Sinabung caused by magma densification through degassing and vesicle collapse of the lava dome and upper conduit was already recognized by Primulyana et al. (2019) and Nakada et al. (2019), and this prediction appears to hold true based on recent years of observations. One possible trigger for sealing of the system is a short-term reduction in magma supply rate from depth, which could lead to a slight cooling and reduction in gas streaming through the peripheral lava dome cracks, thus allowing ductile dome material to seal the pathways. ...
Dome-building volcanic eruptions are often associated with frequent Vulcanian explosions, which constitute a substantial threat to proximal communities. One proposed mechanism driving such explosions is the sealing of the shallow volcanic system followed by pressurization due to gas accumulation beneath the seal. We investigate this hypothesis at Sinabung Volcano (Sumatra, Indonesia), which has been in a state of eruption since August 2010. In 2013, the volcano began erupting a lava dome and lava flow, and frequent explosions produced eruptive columns that rose many kilometers into the atmosphere and at times sent pyroclastic density currents down the southeast flanks. A network of scanning Differential Optical Absorption Spectrometers (DOAS) was installed on the volcano’s eastern flank in 2016 to continuously monitor SO2 emission rates during daytime hours. Analysis of the DOAS data from October 2016 to September 2017 revealed that passive SO2 emissions were generally lower in the 5 days leading up to explosive events (∼100 t/d) than was common in 5-day periods leading up to days on which no explosions occurred (∼200 t/d). The variability of passive SO2 emissions, expressed as the standard deviation, also took on a slightly wider range of values before days with explosions (0–103 t/d at 1-sigma) than before days without explosions (43–117 t/d). These observations are consistent with the aforementioned seal-failure model, where the sealing of the volcanic conduit blocks gas emissions and leads to pressurization and potential Vulcanian explosions. We develop a forecasting methodology that allows calculation of a relative daily explosion probability based solely on measurements of the SO2 emission rate in the preceding days. We then calculate forecast explosion probabilities for the remaining SO2 emissions dataset (October 2017—September 2021). While the absolute accuracy of forecast explosion probabilities is variable, the method can inform the probability of an explosion occurring relative to that on other days in each test period. This information can be used operationally by volcano observatories to assess relative risk. The SO2 emissions-based forecasting method is likely applicable to other open vent volcanoes experiencing dome-forming eruptions.
... Lava dome growth at Sinabung began in December 2013 Pallister et al., 2019). Effusion of lava over the next 4 years resulted in thousands of collapse-generated PDCs and the emplacement of a 3 km long andesitic lava flow (Carr et al., 2019a;Nakada et al., 2019;Pallister et al., 2019;Kriswati and Solikhin, 2020). Nakada et al. (2019), Pallister et al. (2019), and Carr et al. (2019a); Carr et al. (2019b) FIGURE 1 | Location of Sinabung Volcano. ...
... Effusion of lava over the next 4 years resulted in thousands of collapse-generated PDCs and the emplacement of a 3 km long andesitic lava flow (Carr et al., 2019a;Nakada et al., 2019;Pallister et al., 2019;Kriswati and Solikhin, 2020). Nakada et al. (2019), Pallister et al. (2019), and Carr et al. (2019a); Carr et al. (2019b) FIGURE 1 | Location of Sinabung Volcano. (A) Sinabung Volcano is located in the Karo Regency of North Sumatra, Indonesia (modified from Carr et al., 2019a). ...
... A similar series of collapses occurred in June 2015 on the northeast side of the upper flow as that ridgeline was also overtopped. The collapses of the upper part of the flow in September-October 2014 and June 2015 ended lava flow emplacement and initiated a new phase of dome growth and collapse at the summit vent ( Figure 2) (Carr et al., 2019b;Nakada et al., 2019;Pallister et al., 2019). ...
Lava domes form by the effusive eruption of high-viscosity lava and are inherently unstable and prone to collapse, representing a significant volcanic hazard. Many processes contribute to instability in lava domes and can generally be grouped into two categories: active and passive. Active collapses are driven directly by lava effusion. In contrast, passive collapses are not correlated with effusion rate, and thus represent a hazard that is more difficult to assess and forecast. We demonstrate a new workflow for assessing and forecasting passive dome collapse by examining a case study at Sinabung Volcano (North Sumatra, Indonesia). We captured visual images from the ground in 2014 and from unoccupied aerial systems (UAS) in 2018 and used structure-from-motion photogrammetry to generate digital elevation models (DEMs) of Sinabung’s evolving lava dome. By comparing our DEMs to a pre-eruption DEM, we estimate volume changes associated with the eruption. As of June 2018, the total erupted volume since the eruption began is 162 × 10⁶ m³. Between 2014 and 2018, 10 × 10⁶ m³ of material collapsed from the lava flow due to passive processes. We evaluate lava dome stability using the Scoops3D numerical model and the DEMs. We assess the passive collapse hazard and analyze the effect of lava material properties on dome stability. Scoops3D is able to hindcast the location and volume of passive collapses at Sinabung that occurred during 2014 and 2015, and we use the same material properties to demonstrate that significant portions of the erupted lava potentially remain unstable and prone to collapse as of late 2018, despite a pause in effusive activity earlier that year. This workflow offers a means of quantitatively assessing passive collapse hazards at active or recently active volcanoes.
... Volcanic activity at Sinabung was relatively unknown, and had been absent for the last 400 years, before its first historical eruption occurred in 2010 . After 3 years of repose, the volcano again erupted in 2013, this time evolving into a long-term (~5 years) eruption, which included initial phreatic and phreatomagmatic phases, several periods of lava-dome growth and collapse, andesitic lava flows and (cyclic) Vulcanian explosions Nakada et al. 2019;Pallister et al. 2019). ...
... Also eruption-style data plays a role in the volcano analogy but the data for Sinabung are not properly recorded in the version of the GVP database used in this analysis. That is, no lava flows or water-sediment flows are reported in the ID profile ( Fig. 3) even though they did occur during the 2013-2018 eruption Nakada et al. 2019). ...
... comm., October 12, 2018) when using two different ID profiles for the target volcano. a, b: ID profile stored in the GVP database, version 4.6.7 (see Fig. 3); c, d: ID profile obtained after upgrading the 2013-2018 to VEI 4 and adding lava flows and lahars as phenomenology that happened during the aformentioned eruption Nakada et al., 2019;GVP database, version 4.7.4) those in morphology linked with the partial or total destruction of the edifice (Cioni et al. 1999;Belousov et al. 2007). Eruption size and style data will depend more strongly on under-recording (Mead and Magill 2014;Sheldrake 2014;Rougier et al. 2016), under-/mis-reporting and data discovery (Loughlin et al. 2015). ...
The definition of a suite of analogue volcanoes, or volcanoes that are considered to share enough characteristics as to be considered exchangeable to a certain extent, is becoming a key component of volcanic hazard assessment. This is particularly the case for volcanoes where data are lacking or scarce. Moreover, volcano comparisons have often been based on similarities and differences inferred through expert judgement and not necessarily informed by volcano characteristics from global datasets. These similarities can be based on a range of features, from very simplified (e.g. statrovolcanoes) to very specific (e.g. detailed eruption chronologies), and may be strongly influenced by the personal experience of individuals or teams conducting the analogue analysis. In this work, we present VOLCANS (VOLCano ANalogues Search)—an objective, structured and reproducible method to identify sets of analogue volcanoes from global volcanological databases. Five overarching criteria (tectonic setting, rock geochemistry, volcano morphology, eruption size and eruption style), and a structured combination of them, are used to quantify overall multi-criteria volcano analogy. This innovative method is complementary to expert-derived sets of analogue volcanoes and provides the user with full flexibility to weigh the criteria and identify analogue volcanoes applicable to varied purposes. Some results are illustrated for three volcanoes with diverse features and significant recent and/or ongoing eruptions: Kı̄lauea (USA), Fuego (Guatemala) and Sinabung (Indonesia). The identified analogue volcanoes correspond well with a priori analogue volcanoes derived from expert knowledge. In some cases, single-criterion searches may not be able to isolate a reduced set of analogue volcanoes but any multi-criteria search can provide high degrees of granularity in the sets of analogue volcanoes obtained. Data quality and quantity can be important factors, especially for single-criterion searches and volcanoes with very scarce data (e.g. Sinabung). Nevertheless, the method gives stable results overall across multi-criteria searches of analogue volcanoes. Potential uses of VOLCANS range from quantitative volcanic hazard assessment to promoting fundamental understanding of volcanic processes.
... As there was no geologic map of this volcano, the joint team of Indonesia and Japanese geologists conducted a field survey soon after the eruption in 2010 [13,16]. The eruption at Sinabung resumed in September 2013; a lava dome appeared in December 2013 and grew to a lava flow complex [17,18]. This erup-tion continued in June 2018. ...
... When the event tree was prepared by our team [11], it was considered that juvenile particles appear in the volcanic ash of phreatic events once the magmatic stage is entered. Indeed, the presence of juvenile particles in the volcanic ash from the 11 November 2013 Vulcanian events was confirmed [17]. This event tree did not include the sequence from the lava dome/flow event to a more explosive event. ...
... This event tree did not include the sequence from the lava dome/flow event to a more explosive event. In reality, the explosive stage was accompanied by repeated Vulcanian events beginning in the summer of 2015 [17]. It is common that lava dome eruptions are simply and dominantly effusive throughout eruptions, except for short-lived explosive events in the beginning or midway through the sequences, where the magma discharge rate suddenly increases or a large collapse of the dome occurs. ...
Eruption scenarios were prepared as possible sequences in event trees for six active volcanoes in Indonesia, that are located near populated areas or have erupted in recent years (Galunggung, Guntur, Kelud, Merapi, Semeru, and Sinabung). The event trees prepared here show sequences of possible eruption phenomena without probabilities on branches and cover sequences experienced in historical and pre-historical eruptions based on archives and field research results. Changing magma discharge rates during eruption sequences were considered for the event tree of Merapi. This conceptual event tree can also be used as a short-term event tree in which forecasting the coming eruption became possible with geophysical and geochemical monitoring data. Eruption event trees prepared for selected time windows cannot illustrate all plausible hazards and risks associated with an eruption. Therefore, hazards and risks generated from an eruption should be considered in different domains from the event tree.
... From April through September 2014 the lava flow grew in both length and thickness, although PDC activity decreased (Sinabung Volcano Observatory, pers. comm.; Nakada et al., 2017). On September 6, 2014, the lava flow was 2.9 km long (Global Volcanism Program, 2014b). ...
... On September 6, 2014, the lava flow was 2.9 km long (Global Volcanism Program, 2014b). Large collapses of the upper part of the lava flow began on September 30, 2014, and June 2, 2015, resulting in renewed PDC activity (Global Volcanism Program, 2014b, 2016Nakada et al., 2017). Two new lava lobes broke out at the collapse sites and redirected the flow of fresh lava away from the original flow axis such that, despite continued effusion, the main flow was no longer active and remains 2.9 km long (Global Volcanism Program, 2015). ...
... well to the lava flow volume estimate of 1.1 ± 0.11 × 10 8 m 3 byNakada et al. (2017) who used laser distance meter surveys to create digital surface models of the flow and 1.1 ± 0.22 × 10 8 m 3 byPallister et al. (this issue). Using January 10, 2014, as the starting point of the effusive eruption(Pallister et al., this issue), the time-averaged discharge rate at Sinabung for those nine months was 4.8 ± 0.6 m 3 s −1 . ...
An effusive eruption at Sinabung Volcano in Indonesia began in December 2013. We use structure-from-motion (SfM) photogrammetric techniques to create digital elevation models (DEMs) of the active lava flow. We build DEMs from photographs taken during two separate time periods and from two separate low-cost handheld cameras and compare them with a pre-eruption DEM to assess the quality and accuracy of photogrammetric DEMs created using different cameras, calculate flow volume and long-term average effusion rate, and document changes in flow morphology. On September 22nd, 2014, the lava flow was 2.9 km long and had a volume of 1.03 ± 0.14 × 10⁸ m³, leading to an estimated time-averaged discharge rate of 4.8 ± 0.6 m³ s⁻¹. Differencing the photogrammetric DEMs shows that during the two-week field campaign, topographic changes of the flow occurred in zones along the flow front and on the upper flank, a finding supported by relatively high temperatures in corresponding thermal images. The deformation can be explained by active advance at the flow front and development of instabilities and collapse on the upper flanks. Large pyroclastic density currents associated with gravitational collapse of upper-flank instabilities in October 2014 and June 2015 were caused by lava growing over ridges that had initially confined the flow to a pre-existing channel. This work demonstrates the ability of SfM photogrammetry to measure or identify the lava flow volume, time-averaged discharge rate, flow emplacement rate and style, as well as the development of gravitational instabilities. Our results show the potential of SfM photogrammetry as a cost- and time-effective method of repeatedly measuring active volcanic features and monitoring hazards at Sinabung and during similar eruptions.
... Voight et al. 2000), Sinabung Volcano, Indonesia (e.g. Nakada et al. 2019) and Soufrière Hills Volcano on Montserrat, UK (e.g. Watts et al. 2002;Wadge et al. 2014). ...
... Andesitic to rhyolitic magmas with a significant silica content have a higher viscosity than basaltic magmas. Spine-shaped (or obelisk-shaped) structures are formed at low DR (normally < 1 m 3 s −1 ), whereas lavas develop lobe-and pancakeshaped structures on the surface at the higher rates (see Fig. 1, Watts et al. 2002;Bernstein et al. 2013;Nakada et al. 2019). Spineshaped domes are tall (up to a few hundred metres) with steep sides and wide (ranging from metres to tens of metres) exogenous bodies (Figs 1a and b), which form normally directly above an active The black curved arrow marks the symmetry along the axis x 1 = 0. Different conditions are prescribed to the differently coloured parts of the model boundary (see the text for the boundary conditions). ...
Lava domes form when highly viscous magmas erupt on the surface. Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma. Here, we develop a 2-D axisymmetric model of magma extrusion on the surface and lava dome evolution and analyse the dome morphology using a finite-volume method implemented in Ansys Fluent software. The magma/lava viscosity depends on the volume fraction of crystals and temperature. We show that the morphology of domes is influenced by two parameters: the characteristic time of crystal content growth (CCGT) and the discharge rate (DR). At smaller values of the CCGTs, that is, at rapid lava crystallization, obelisk-shaped structures develop at low DRs and pancake-shaped structures at high DRs; at longer CCGTs, lava domes feature lobe- to pancake-shaped structures. A thick carapace of about 70 per cent crystal content evolves at smaller CCGTs. We demonstrate that cooling does not play the essential role during a lava dome emplacement, because the thermal thickness of the evolving carapace remains small in comparison with the dome's height. A transition from the endogenic to exogenic regime of the lava dome growth occurs after a rapid increase in the DR. A strain-rate-dependent lava viscosity leads to a more confined dome, but the influence of this viscosity on the dome morphology is not well pronounced. The model results can be used in assessments of the rates of magma extrusion, the lava viscosity and the morphology of active lava domes..
... The eruptive activity with frequent pyroclastic flows and/or vertical eruptions continued until February 2018. The total volume of eruption products reached approximately 0.16 km 3 DRE as of the end of 2015 [18]. Lahars frequently occurred along the Borus River. ...
... Lahar potential increases when eruptions oc- cur. The large pyroclastic flow on May 21, 2016, reaching a distance of 4.5 km [18], was among the rapid-increase events in terms of lahar potential. When rain triggers lahars, the lahar potential decreases. ...
An estimation method for debris flow potential is proposed to evaluate the possibility of the occurrence of rain-triggered debris flows. Sakurajima volcano has repeatedly erupted (Vulcanian type) and has continuously emitted volcanic ash at the Minamidake summit crater or Showa crater east of the summit since 1955, and debris flows have frequently occurred at rates of 10 to 111 events per year. Ground deformation associated with debris flows along the Arimura River were analyzed for the period from 2009 to 2016. Downward tilt (10–450 nrad) in the direction of the river and extensional strain (3–138 nstrain) were detected during occurrence of the debris flows. The tilt and strain changes were modeled using a point load caused by debris flow deposition beside a sabo dam. Depositional weights of individual debris flow events were estimated to range from 6 to 276 kt. The total weight of the debris flows was 2,154 kt, which is approximately 5% of the total weight of volcanic ash ejected from the craters during the study period. Debris flow potential (DFP) was defined as the difference in the volcanic ash deposits along the upper stream of the river (5% of the total) and the lower stream of the river, and the temporal change of the debris flow potential was investigated. When the debris flow potential reached a level of 0.4 Mt resulting from an increase in eruptive activity, debris flows frequently occurred or large debris flows were induced during rainy seasons. The concept of debris flow potential was applied to volcanoes in Indonesia as lahar potential. After the 2010 eruption at Merapi volcano, lahar potential, perhaps, quasi-exponentially decays during the dormant period. The lahar potential of Sinabung volcano complicatedly varies because of long-term eruptivity beginning in 2014.
... Unzen (Nakada et al. 1999) and Mt. Sinabung (Nakada et al. 2017). ...
... Due to the high viscosity of the ascending magma, shallow earthquake swarms preceding eruptions of Kizimen can last for more than a year as the magma slowly breaks a pathway to the surface. Similar processes possibly occur at other persistently degassing volcanoes with highly evolved magmas, as at Tatun in Taiwan and Gede in Java, Indonesia (Belousov et al. 2010(Belousov et al. , 2015b, Sinabung (Nakada et al. 2017) and Mayon (Global Volcanism Program 2016). ...
Kizimen volcano in Kamchatka is well known as a source of highly heterogeneous poorly mingled magmas ranging from dacites to basaltic andesites. In 2010–2013, the volcano produced its first historical magmatic eruption with the deposition of 0.27 km³ of block and ash pyroclastic flows accompanied by slow extrusion of a 200-m-thick, highly viscous (10¹⁰–10¹¹ Pa s) block lava flow with a volume of 0.3 km³. The total volume of erupted magma comprised approximately 0.4 km³ DRE. We provide description of the eruption chronology, as well as the lithology and petrology of eruptive products. The erupted material is represented by banded dacite and high-silica andesite. The dacitic magma was formed during a long dormancy after the previous magmatic eruption several hundred years ago with mineral compositions indicating average pre-eruptive temperatures of ~ 810 °C, fO2 of 0.9–1.6 log units above the nickel–nickel oxide (NNO) buffer and shallow crustal storage conditions at ~ 123 MPa. The silica-rich andesite represents a hybrid magma, which shows signs of recent thermal and compositional disequilibrium. We suggest that the hybrid magma started to form in 1963 when a swarm of deep earthquakes indicated an input of mafic magma from depth into the 6–11-km-deep silicic magma chamber. It took the following 46 years until the magma filling the chamber reached an eruptible state. Poor mingling of the two melts is attributed to its unusually high viscosity that could be associated with the pre-eruptive long-term leakage of volatiles from the chamber through a regional tectonic fault. Our investigations have shown that shallow magma chambers of dormant volcanoes demonstrating strong persistent fumarolic activity can contain highly viscous, degassed magma of evolved composition. Reactivation of such magma chambers by injection of basic magma takes a long time (several decades). Thus, eruption forecasts at such volcanoes should include a possibility of long time lag between a swarm of deep earthquakes (indicating the recharge of basic magma from depth) and the following swarm of shallow earthquakes (indicating final ascent of the hybrid magma towards the surface). Due to the high viscosity of the magma, the shallow swarm can last for more than a year. The forthcoming eruption can be of moderate to low explosivity and include extrusion of viscous lava flows and domes composed of poorly mingled magmas of contrasting compositions.
... Lava dome growth has been monitored at several volcanoes (e.g. Nakada et al. 1999Nakada et al. , 2019Watts et al. 2002 ;Harris et al. 2003 ;Wadge et al. 2014 ;Zobin et al. 2015 ). Monitoring allows mapping the spatial and temporal development of lava domes and determining the morphological changes during the growth as well as the changes in the lava volume over time. ...
Lava domes form during effusive eruptions due to an extrusion of highly viscous magmas from volcanic vents. In this paper we present a numerical study of the lava dome growth at Volcán de Colima, Mexico during 2007-2009. The mathematical model treats the lava dome extrusion dynamics as a thermo-mechanical problem. The equations of motion, continuity, and heat transfer are solved with the relevant boundary and initial conditions in the assumption that magma viscosity depends on the volume fraction of crystals and temperature. We perform several sets of numerical experiments to analyse the internal structure of the lava dome (i.e., the distributions of the temperature, crystal content, viscosity, and velocity) depending on various heat sources and thermal boundary conditions. Although the lava dome growth at Volcán de Colima during short (a few months) dome-building episodes can be explained by an isothermal model of lava extrusion with the viscosity depending on the volume fraction of crystals, we show here that cooling plays a significant role during long (up to several years) episodes of dome building. A carapace develops as a response to a convective cooling at the lava dome-air interface. The carapace becomes thicker if the radiative heat loss at the interface is also considered. The thick carapace influences the lava dome dynamics preventing its lateral advancement. The release of the latent heat of crystallization leads to an increase of the temperatures in the lava dome interior and to a relative flattening of the dome. Meanwhile, the heat source due to viscous dissipation inside the lava dome is negligible, and it does not influence the lava dome growth. The developed thermo-mechanical model of the lava dome dynamics at Volcán de Colima can be used elsewhere to analyze effusive eruptions, dome morphology, and carapace evolution including its failure potentially leading to pyroclastic flow hazards.
... In contrast, the extrusions of lava domes tend to be localized at the summit. However, because summit regions are typically steep (Sigurdsson, 2000), lava domes are prone to collapsing, which often results in a highly destructive pyroclastic density current (PDC, observed as block and ash flow deposits) as was observed for the Unzen volcano in Japan and the Sinabung and Merapi volcanoes in Indonesia (Noguchi et al., 2008a(Noguchi et al., , 2008bNakada et al., 2019;Wibowo et al., 2018). Moreover, the presence of a lava dome at the vent might lead to gas accumulation in the conduit, thus increasing the probability of future explosive volcanic eruptions such as the 2008 eruption of Chaiten, Chile, 2010 eruption of Merapi, and 2014 eruption of Kelud, Indonesia (Alfano et al., 2011;Cronin et al., 2013;Maeno et al., 2019). ...
In this study, we combined the results of petrography [pheno-crystallinity (ϕ_PC)] and magma compositions (bulk and melt compositions) to calculate the magma viscosity (μ_(eff.)) of the lava flows and domes that erupted from Mount Ungaran, Central Java, Indonesia. The lava flows were characterized by slightly larger SiO2 variations than those of lava domes, with a large overlap between each phase (46.7 – 57.8 and 53.2 – 59.8 wt. % SiO2, respectively). However, lava flows were typically less crystalline than the lava domes (average ϕ_PC of 33 % and 40 %, respectively). Because lava flows share an identical composition to lava domes and temperature is inversely proportional to SiO2 content, it is inferred that magma composition and temperature did not play a substantial role in controlling magma viscosity. Instead, we found that pheno-crystallinity was the most important parameter. Specially, for a ±7 % difference of pheno-crystallinity (at a given SiO2), magma viscosity could differ by one order of magnitude, ultimately controlling lava morphology: high-viscosity magma (5.6 – 7.8 log Pa s) formed lava domes, whereas low-viscosity magma (4.6 – 6.6 log Pa s) produced lava flow. Moreover, we found that lava dome samples exhibited gentler phenocryst size distribution (CSD) slopes than lava flow samples (2.1–3.4 and 2.7–6.9, respectively). Because the CSD slope was inversely proportional to the magma residence time (CSD slope = –1/Gt), we suggest that lava dome formation, which requires a high magma viscosity, originates from a longer-lived and more crystalline magma, whereas lava flow with low magma viscosity originates from a young and less crystalline magma. Thus, in the case of mafic-to-intermediate magma, as in the present case, we think that the resultant lava morphology is strongly controlled by the abundance of phenocrysts and magma residence time.
... Lava dome growths have been monitored at several volcanoes (e.g. Swanson et al., 1987;Daag et al., 1996;Nakada et al., 1999;Watts et al., 2002;Harris et al., 2003;Wadge et al., 2014;Zobin et al., 2015;Nakada et al., 2019). Monitoring allows mapping the spatial and temporal development of lava domes and determining the morphological changes during the growth as well as the changes in the lava volume over time. ...
Many contemporary problems within the Earth sciences are complex, and require an interdisciplinary approach. This book provides a comprehensive reference on data assimilation and inverse problems, as well as their applications across a broad range of geophysical disciplines. With contributions from world leading researchers, it covers basic knowledge about geophysical inversions and data assimilation and discusses a range of important research issues and applications in atmospheric and cryospheric sciences, hydrology, geochronology, geodesy, geodynamics, geomagnetism, gravity, near-Earth electron radiation, seismology, and volcanology. Highlighting the importance of research in data assimilation for understanding dynamical processes of the Earth and its space environment and for predictability, it summarizes relevant new advances in data assimilation and inverse problems related to different geophysical fields. Covering both theory and practical applications, it is an ideal reference for researchers and graduate students within the geosciences who are interested in inverse problems, data assimilation, predictability, and numerical methods.
... The activity has been continuing and increasingly intensive. In 2013, lava flows began to appear and lasted about three years (Nakada et al. 2017). Currently, the activity of Mount Sinabung is relatively low (at the time of writing this article, at the Alert Level II). ...
Volcano disaster risk management during a crisis requires continuous and intensive risk communication with the public. However, to have the desired public response during a crisis, it is necessary to improve the community’s understanding of volcanoes. Knowledge, experience, risk perception, communication, and drills shape good community responses. These require a bottom-up process of communication and involvement of the community in decision-making and engagement with the government. Thus, proper crisis management requires top-down and bottom-up communication and joint work between the scientists, decision-makers, and the community. The response from the community can be improved through community-based preparedness with a culturally sensitive approach that facilitates a strong relationship and participation of community members according to their customs. The Wajib Latih Penanggulangan Bencana (WLPB: Compulsory Disaster Management Training Program) and the SISTER VILLAGE Program in the Merapi Volcano community are good examples of community-based preparation in Indonesia.
An effective volcano early warning protocol includes risks analysis, volcano monitoring, hazards analysis and forecasting, dissemination of alerts and warnings, and community response according to the warning. Alert levels can also be increased during the unrest, so actions are also associated with this and not just related to the impacts of an eruption. Therefore, the alert level alone is not helpful if it is not appropriately communicated with an action plan in place to improve community awareness. Moreover, personal communication between scientists and decision-makers and between scientists and the community is essential to instill self-responsibility and a sense of belonging. Personal communication describes the trust of community members or certain decision-makers to scientists to obtain more detailed explanations of volcanic activity. Such communication is already occurring in communities that have experienced a long history of eruptions, and/or continuous eruptions, such as at Merapi and Sinabung volcanoes.
The disaster management system in Indonesia includes institutions that manage science and institutions responsible for social aspects, such as evacuations, refugee handling, rehabilitation, and reconstruction. The National Disaster Management Agency (NDMA, Badan Nasional Bencana, BNPB in Bahasa Indonesia) of Indonesia coordinates all disasters to integrate management of and facilitate communication between stakeholders.
In addition to a well-established system, effective and good disaster management needs to be supported by policies related to public needs before, during, and after the disaster. After disasters, a review of previous strategies is also necessary to develop a better strategy and obtain a better result. Establishing SISTER VILLAGES is an excellent strategy to meet the needs during a crisis. However, this needs to be supported by regulations related to collecting data, the evacuation process and facilitation, and infrastructure, communication, and coordination.
Here, we present good risk communication practices around Indonesia's volcanoes related to how people receive and understand early warning information and take action with the support of the government through capacity improvement and learning from experiences.
... Many volcanoes have produced PDCs this way, referred to as dome-collapse PDCs. Recent examples of such PDCs include Unzen in Japan (1991)(1992)(1993)(1994)(1995) [4][5][6][7], Volcán de Colima in Mexico (1991-1992, 1998-1999, 2004, and 2015) [8][9][10], Merapi in Indonesia (1994, 1997-1998, 2006, 2010, and 2018-2019) [11][12][13][14][15], Soufrière Hills in Montserrat (1995Montserrat ( -1999 [16][17][18][19], and Sinabung in Indonesia (2013-) [20][21][22]. PDCs can devastate urban areas and cause fatalities owing to their high dynamic pressures and high temperatures [23][24][25]. To conduct hazard assessments of PDCs, it is necessary to understand and correctly estimate internal flow dynamics and the resulting run-out area (especially, the run-out distance). ...
Pyroclastic density currents (PDCs) are one of the most dangerous but least understood phenomena of volcanic eruptions. An open-source numerical depth-averaged model of dense granular currents controlled by physical processes such as energy dissipation, basal deposition, and erosion (faSavageHutterFOAM) was applied to investigate the basal concentrated region of a dome-collapse PDC generated on June 3, 1991 at Unzen volcano (Japan) to assess the effects of the physical processes (and their interplay) on the flow dynamics and run-out area of the PDC. Numerical simulations show that energy dissipation process decreases the flow velocity and increases the basal deposition rate, which reduces the run-out distance. The simulations also reveal that erosion process during flow propagation decreases the flow velocity and increases the run-out distance. The numerical results are sensitive to the parameters of energy dissipation (dry friction coefficient μ and collisional or turbulent friction coefficient χ) and erosion (specific erosion energy e b ). The results are fitted to field data for run-out distance and flow velocity when μ is between 0.01 and 0.1 with χ∼10 ³ m ⁻¹ s ⁻² (or when χ is between 10 ⁴ and 10 ⁵ m ⁻¹ s ⁻² with μ∼0.2) and e b ∼10 ² m ² s ⁻² . The estimated value of e b suggests that re-entrainment of deposit mass played an important role in controlling the flow dynamics and run-out area of the PDC. The estimated values of μ and χ are correlated, but the estimation of these parameters might be improved by further constraints from field data. The presented results serve as a basis to make further quantitative estimations of the model parameters (μ, χ, and e b ) for applying the faSavageHutterFOAM model to hazard assessments of PDCs.
... These four volcanoes alone constitute around half of the total inventory. They are sustained by different magma compositions, i.e., basaltic andesite to andesite on Sinabung 13 between 50 and 100 Mg/d that together represent 11% of the budget, seven with SO 2 emission rates between 10 and 50 Mg/d, representing 5% of the budget, and finally 14 volcanoes whose SO 2 degassing is below 10 Mg/d. ...
Indonesia hosts the largest number of active volcanoes, several of which are renowned for climate-changing historical eruptions. This pedigree might suggest a substantial fraction of global volcanic sulfur emissions from Indonesia and are intrinsically driven by sulfur-rich magmas. However, a paucity of observations has hampered evaluation of these points—many volcanoes have hitherto not been subject to emissions measurements. Here we report new gas measurements from Indonesian volcanoes. The combined SO2 output amounts to 1.15 ± 0.48 Tg/yr. We estimate an additional time-averaged SO2 yield of 0.12-0.54 Tg/yr for explosive eruptions, indicating a total SO2 inventory of 1.27-1.69 Tg/yr for Indonesian. This is comparatively modest—individual volcanoes such as Etna have sustained higher fluxes. To understand this paradox, we compare the geodynamic, petrologic, magma dynamical and shallow magmatic-hydrothermal processes that influence the sulfur transfer to the atmosphere. Results reinforce the idea that sulfur-rich eruptions reflect long-term accumulation of volatiles in the reservoirs.
... We conducted a similar UAS survey to the one described here at Sinabung Volcano (North Sumatra, Indonesia) (Supplementary Table S1). Starting in late 2013, an effusive eruption at Sinabung emplaced a 3 km long andesite lava flow and generated hundreds to thousands of PDCs caused by both lava dome collapse and Vulcanian-style explosions (Nakada et al., 2019). The deposits from the eruption cover approximately 10 km 2 (Pallister et al., 2019). ...
The deposits from volcanic eruptions represent the record of activity at a volcano. Identification, classification, and interpretation of these deposits are crucial to the understanding of volcanic processes and assessing hazards. However, deposits often cover large areas and can be difficult or dangerous to access, making field mapping hazardous and time-consuming. Remote sensing techniques are often used to map and identify the deposits of volcanic eruptions, though these techniques present their own trade-offs in terms of image resolution, wavelength, and observation frequency. Here, we present a new approach for mapping and classifying volcanic deposits using a multi-sensor unoccupied aerial system (UAS) and demonstrate its application on lava and tephra deposits associated with the 2018 eruption of Sierra Negra volcano (Galápagos Archipelago, Ecuador). We surveyed the study area and collected visible and thermal infrared (TIR) images. We used structure-from-motion photogrammetry to create a digital elevation model (DEM) from the visual images and calculated the solar heating rate of the surface from temperature maps based on the TIR images. We find that the solar heating rate is highest for tephra deposits and lowest for ʻaʻā lava, with pāhoehoe lava having intermediate values. This is consistent with the solar heating rate correlating to the density and particle size of the surface. The solar heating rate for the lava flow also decreases with increasing distance from the vent, consistent with an increase in density as the lava degasses. We combined the surface roughness (calculated from the DEM) and the solar heating rate of the surface to remotely classify tephra deposits and different lava morphologies. We applied both supervised and unsupervised machine learning algorithms. A supervised classification method can replicate the manual classification while the unsupervised method can identify major surface units with no ground truth information. These methods allow for remote mapping and classification at high spatial resolution (< 1 m) of a variety of volcanic deposits, with potential for application to deposits from other processes (e.g., fluvial, glacial) and deposits on other planetary bodies.
... In basaltic, andesitic, and dacitic lavas, there have been many opportunities for the direct observations, and their eruption, flow dynamics, and potential hazards are relatively well understood [e.g. Gregg 2017;Nakada et al. 2019]. However, it seems to be difficult for volcanologists to predict the flow behavior and the envisaged hazards precisely during effusion of rhyolite lava. ...
This study presents a description of a rhyolite lava-forming eruption, including the conduit system, degassing history during the lava flow dynamics. We examined the Pleistocene Shiroyama rhyolite lava on Himeshima Island, Japan. The lava is mainly characterized by locally developed obsidian. Based on the structural variation, the obsidian lithofacies correspond to the shallow conduit. The geological investigation and FTIR analyses showed that gas removal from the conduit magma proceeded via vesiculation, fracturing, and brecciation, allowing formation of the dense obsidian. Since the lava originally maintained some extent of water, the lava effervesced just after the effusion. This vesiculation resulted in pervasive bubble coalescence and the formation of abundant permeable pathways. The volcanic gasses escaped via those pathways, allowing collapse of the bubbles and deflation of the lava. AMS (anisotropy of magnetic susceptibility) results indicate that the lava spread concentrically.
... At NChVC, this stage lasted less than a year, but its duration and intensity varies between volcanoes. For example, the reawakening of Sinabung eruption began with phreatic events in 2010 that lasted for about three months, but then there was a lull of activity of three years until August 2013 (Nakada et al., 2019). Another example is the reawakening of Unzen volcano in 1991, where volcanic unrest consisted of one year of increased seismicity, followed by four months of phreatic events until the magmatic phase started (Nakada et al., 1999). ...
Volcanoes are often monitored by geophysical and geochemical instruments that aim to track and anticipate their eruptive activity. However, assessment of the state of the volcano at any given time, and its evolution towards eruption or change in eruptive activity is notoriously difficult. Once explosive activity has begun, the study of volcanic ash can provide crucial insights on whether the activity is mainly driven by the hydrothermal system, shallow gas accumulation, or/and a new stalled intrusion close to the surface. We present the results of a study of ash componentry from part of the current volcanic crisis that started in December 2015 at Nevados de Chillán Volcanic Complex (Chile) which we integrate with seismic and visual data. We identified three main stages: (i) an early one that lasted for about a year and includes two months of increased seismicity and significant amount of juvenile ash fragments, and thus suggesting some explosions were fed by a shallow magma intrusion. (ii) A second one which lasted for about six months with cycles of quiescence and explosions, and a predominance of lithic particles in the ash, suggesting that the explosions were probably driven by the dynamics in the upper part of the system, including shallow gas accumulation or/and the hydrothermal system, rather than by fresh magma intrusion. (iii) Finally, after about two years of unrest and intermittent explosions, seismicity increased again and the ash became dominated by juvenile particles, and led to the extrusion of a dome. The timing and sequence of events that we report is broadly similar to other volcanoes that have produced dome eruptions such as Soufriere Hills (Montserrat), Unzen (Japan) and Sinabung (Indonesia). Our study highlights the usefulness of integration of volcanic ash studies with other monitoring data and importance of integration of many case studies to gain a more comprehensive understanding of the processes and evolution of dome-forming eruptions.
... Detailed monitoring of lava domes has been conducted at several volcanoes, such as the Mount St. Helens in the United States (Swanson et al., 1987), Mount Pinatubo in the Philippines (Daag et al., 1996), Mount Unzen in Japan (Nakada et al., 1999), Santiaguito (Santa Maria) in Guatemala (Harris et al., 2003), Merapi and Sinabung in Indonesia Nakada et al., 2019), Soufrière Hills on Montserrat (Watts et al., 2002;Wadge et al., 2014) (Zobin et al., 2015). Monitoring allows mapping the spatial and temporal development of lava domes, and determining the morphological changes during the dome growth as well as the changes in the lava volume over time (to assess the discharge rate). ...
Lava domes form when a highly viscous magma erupts on the surface. Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma: obelisks, lava lobes, and endogenic structures. The viscosity of magma nonlinearly depends on the volume fraction of crystals and temperature. Here we present an approach to magma viscosity estimation based on a comparison of observed and simulated morphological forms of lava domes. We consider a two-dimensional axisymmetric model of magma extrusion on the surface and lava dome evolution, and assume that the lava viscosity depends only on the volume fraction of crystals. The crystallization is associated with a growth of the liquidus temperature due to the volatile loss from the magma, and it is determined by the characteristic time of crystal content growth (CCGT) and the discharge rate. Lava domes are modeled using a finite-volume method implemented in Ansys Fluent software for various CCGTs and volcanic vent sizes. For a selected eruption duration a set of morphological shapes of domes (shapes of the interface between lava dome and air) is obtained. Lava dome shapes modeled this way are compared with the observed shape of the lava dome (synthesized in the study by a random modification of one of the calculated shapes). To estimate magma viscosity, the deviation between the observed dome shape and the simulated dome shapes is assessed by three functionals: the symmetric difference, the peak signal-to-noise ratio, and the structural similarity index measure. These functionals are often used in the computer vision and in image processing. Although each functional allows to determine the best fit between the modeled and observed shapes of lava dome, the functional based on the structural similarity index measure performs it better. The viscosity of the observed dome can be then approximated by the viscosity of the modeled dome, which shape fits best the shape of the observed dome. This approach can be extended to three-dimensional case studies to restore the conditions of natural lava dome growth.
... Some researchers have calculated the volume of material discharge during the eruption of Sinabung Volcano since 2013. Nakada et al. (2018) calculated the lava discharge rate during 2013-2015 eruption. The volume was calculated by combining topographic measurement and remote sensing imagery data as well as thermal camera. ...
To find out the long term data of Sinabung magma discharge rate and how long a series of eruption will be ended, time series of the volume of magma discharge is required. The dominant eruption product is pyroclastic flow that begins with the growth of the lava dome, so it is important to determine the volume of the lava dome over time.
The method of determining the volume of magma issued is carried out by using hotspot data to resolve the problem of prevented visual observations and ground measurements. The heat and volume flux data expressed within a long period for a better view of variations in the Sinabung volcanic activity are based on thermal satellite data. Related lava dome volume and seismic data are also displayed to be compared with the heat and volume flux data. The numbers of
thermally anomalous pixels and sum of radiance for all detected pixels at Sinabung during an overpass in the period of 2014 to 2018 have a downward trend. The discharge rates in the period of January 2014 to April 2015, Mei 2015 to March 2016, April 2016 to March 2017, and June 2017 to February 2018 are 0.86 m 3/sec, 0.59 m3/sec, 0.36 m3/sec, and 0.25 m3/sec, respectively. Assuming no new intrusion or deformation rate changes, the lava discharge will
be in the lowest rate in the early 2020s.
... Pyroclastic density current distribution was controlled by the geometry of the volcano (e.g. Sinabung 2013; Nakada et al. 2018). This behaviour produced multiple interbedded BAF and pyroclastic surge episodes with long runouts and thick monolithologic BAF deposits in valleys. ...
A volcanic regime classifies a specific volcanic hazard state during which eruption episodes and events share similar frequency, magnitude, composition, and style. The post-AD 960 Maero Eruptive Period (MEP) at Mt. Taranaki (New Zealand) exemplifies such a distinctive eruptive period of volcanism. The deposits from intermittent eruptive episodes during this period built a pyroclastic fan on the northwestern flanks of the volcano. These deposits correlate to fall and thin pyroclastic density current deposits on other flanks. We have defined a sequence of 11 events via stratigraphy, radiocarbon dating, and geochemical studies. Each MEP episode involved lava dome growth and destruction from the summit crater. The deposits of the first MEP eruption episode cover deep palaeosols formed during a ~ 7000-year gap in activity on the NW volcano flanks. The first lava domes breached the western crater rim, and a large portion of the rim collapsed during the Newall episode c. AD 1360. This gave rise to increasingly hot and widespread block-and-ash flows. During the MEP, changes in magma composition reflect magma injection and mixing processes in small reservoirs. The episodes are classified into four scenarios, from high to low hazard impact: (1) dome collapse leading to Subplinian eruption, (2) explosive dome destruction and directed blast, (3) repeated rapid dome growth and large-scale hot dome collapse, and (4) slow dome effusion and partial collapse. The MEP defines a distinct volcanic regime, with the interval between the most recent MEP eruption and present > 50 years longer than any previous gaps between MEP episodes. As such, volcanic mitigation and forecasting at Taranaki must consider changes in hazard type if the current regime comes to an end.
... The DEM temporal sampling is more problematic for optical data such as Pléiades (Nakada et al., 2017) and WorldView (Dai and Howat, 2017) because these images are also limited by cloud coverage, a systematic problem at many volcanoes. On the other hand, there are many stereo optical satellites, and if their observations could be coordinated over erupting volcanoes, better time series could be possible. ...
The 9 month long 2011-2012 eruption of Cordón Caulle (Southern Andes, Chile) is the best instrumentally recorded rhyolitic eruption to date and the first time that the effusion of a rhyolitic flow has been observed in detail. We use Interferometric Synthetic Aperture Radar (InSAR), with time-lapse digital elevation models (DEMs) and numerical models to study the dynamics of coupled magma reservoir deflation and lava effusion. InSAR recorded 2.2-2.5 m of subsidence after the first three days of the eruption, which can be modeled using a spheroidal magma reservoir at a depth of ∼5 km, ∼20 km long, and with a pressure drop of 20-30 MPa. The source is elongated in the NW-SE direction and its large dimensions imply a large plumbing system active throughout the eruption and spanning neighboring volcanoes, with a slight change in the geometry halfway through the effusive phase. TanDEM-X and Pléiades DEMs record the extrusion of both the rhyolitic lava flow and the intrusion of a shallow laccolith around the eruptive vent after the third day of the eruption, with a total volume of ∼1.45 km3 DRE. The laccolith was emplaced during the first month of the eruption, during both the explosive and effusive stages of the eruption. Both the reservoir pressure drop and the extruded volume time series follow quasi-exponential trends, and can be explained by a model that couples the reservoir pressure decrease, time- and pressure-dependent variations in the magma properties inside of the reservoir, and conduit flow. This model predicts both the temporal evolution and amplitude of both time series during the effusive phase, and a magma compressibility of ∼10−10 Pa−1, half the reported compressibility of the magma of the sub-Plinian explosive phase. Further, we estimate that the reservoir contained 1-3 wt.% dissolved H2O at the onset of lava effusion, with no exsolved CO2 and H2O in the reservoir throughout the effusive phase. This implies that the magma was significantly degassed after the explosive phase. The remaining volatiles in the magma after the explosive stage might have caused magma fragmentation, consistent with the hybrid explosive-effusive style observed during the waning of the eruption.
... Following the phreatic eruption in 2010, the magmatic eruptions have been initiated at September 15 th , 2013 and continued until recently Nakada et al., 2017). A new phase of Mount Sinabung eruptions has forced people around the volcano to evacuate from the hazardous zones. ...
Mount Sinabung was re-activated at August 28th, 2010 after a long repose interval. The early stage of a phreatic eruption was then followed by magmatic eruptions at September 15th, 2013 for years until now. To understand the ground surface changes accompanying the eruption periods, comprehensive analyses of surface and subsurface data are necessary, especially the condition in pre- and syn-eruption periods. This study is raised to identify ground surface and topographical changes before, intra, and after the eruption periods by analyzing the temporal signature of surface roughness, moisture, and deformation derived from Synthetic Aperture Radar (SAR) data. The time series of SAR backscattering intensity were analyzed prior to and after the early eruption periods to know the lateral ground surface changes including estimated lava dome roughness and surface moisture. Meanwhile, the atmospherically corrected Differential Interferometric SAR (D-InSAR) method was also applied to know the vertical topographical changes prior to the eruptions. The atmospheric correction based on modified Referenced Linear Correlation (mRLC) was applied to each D-InSAR pair to exclude the atmospheric phase delay from the deformation signal. The changes of surface moistures on syn-eruptions were estimated by calculating dielectric constant from SAR polarimetric mode following Dubois model. Twenty-one Phased Array type L-band SAR (PALSAR) data on board Advanced Land Observing Satellite (ALOS) and nine Sentinel-1A SAR data were used in this study with the acquisition date between February 2006 and February 2017. For D-InSAR purposes, the ALOS PALSAR data were paired to generate twenty interferograms. Based on the D-InSAR deformation, three times inflation-deflation periods were observed prior to the early eruption at August 28th 2010. The first and second inflation-deflation periods at the end of 2008 and middle 2009 presented migration of magma batches and dike generations in the deep reservoir. The third inflation-deflation periods in the middle of 2010 served as a precursor signal presenting magma feeding to the shallow reservoir. The summit was inflated about 1.4 cm and followed by the eruptions. The deflation of about 2.3 cm indicated the release pressure and temperature in the shallow reservoir after the early eruption at August 28th, 2010. The last inflation-deflation period was also confirmed by the increase of the lava dome roughness size from 5,121 m2 on July to 6,584 m2 on August. The summit then inflated again about 1.1 cm after the first eruption and followed by unrest periods presented by lava dome growth and destruction at September 15th, 2013. The volcanic products including lava and pyroclastics strongly affected the moisture of surface layer. The volcanic products were observed to reduce the surface moisture within syn-eruption periods. The hot materials are presumed responsible for the evaporation of the surface moisture as well.
... Eruption dynamics for Kelud are elucidated through the study of pyroclastic deposits (Goode et al., 2019), and the dynamics of the high-altitude Kelud umbrella cloud is studied through work on volcanic lightning by Hargie et al. (2019). The mass eruption rate at Kelud is determined through numerical modeling of the volcanic plumes and at Sinabung through differencing of digital elevation models by Nakada et al. (2019) and Pallister et al. (2019) as well as by structure-frommotion analysis of oblique photographs (Carr et al., 2019b). An overview of the Sinabung eruption, including the 2010 phreatomagmatic phase, is presented by Gunawan et al. (2019). ...
1. Introduction
Explosions and ash emissions at Sinabung volcano (Sumatra; Fig. 1) in 2010 marked a renewal of activity after hundreds of years of quiescence. Following a three-year period without significant eruptions, phreatomagmatic eruptions began again in late 2013 and were followed by extrusion of lava domes, lava flows, and by multiple explosive and dome-collapse eruptions that produced block-and-ash type pyroclastic density currents (PDCs). These eruptions continue to the present. Individual explosions and collapse events have been short in duration, typically lasting a day or less and have had Volcano Explosivity Indices (VEI; Newhall and Self, 1982) of VEI 3 or less. Fifteen students and their professor were killed on 1 February 2014, when collapse of the flank of a lava flow generated a deadly pyroclastic flow and surge that swept through the access-prohibited area into which they had ventured (Andreastuti et al., 2019). On 21 May 2016, nine additional fatalities took place in the village of Gamber, within the danger zone, when a dome collapse sent a pyroclastic density current into the area. These fatalities at Sinabung stand in contrast to the few fatalities at Kelud volcano in Java during the more powerful singular explosive eruption (VEI 4) of 14 February 2014.
The Sinabung eruption is unusual, not only because it occurred at a newly awakening volcano, but also because the newly erupted summit lava dome evolved into a lava flow and flowed for several kilometers down the steep-sided volcano, while collapsing from the flow front and margins to produce pyroclastic density currents (Fig. 2). The flow was then abandoned, and lava dome and PDC eruptions resumed at Sinabung and continue at the time of this writing. The most recent eruption through the time of this report took place on 19 February 2018 (Fig. 3, Fig. 4). This explosive eruption destroyed the summit lava dome, created a new summit crater and generated PDCs to 4.2 km. Ash plumes from the eruption were as high or higher (14 km)1 than previous phreatomagmatic eruptions in 2013 (e.g. 23 Nov 2013: PDCs to 2 km radius, plume to 12 km) and previous dome collapse and explosive eruptions (e.g. 19–20 February 2015: PDCs to 4.4 km radius, plume to 14 km). Because of a lack of eruption experience among the local population and the long-duration of the eruption, the Sinabung eruption has been challenging. More than 25,000 people were repeatedly evacuated, many permanently relocated, and alert levels and evacuation zones have been revised several times to take into account not just potential hazards, but also risk to the remaining population.
In contrast, the 2014 eruption of Kelud (alternate spelling is Kelut) was short in duration (~6 h, on 13–14 February 2014), but large in explosivity (VEI 4). This powerful eruption produced a spectacular vertical ash column that penetrated the equatorial troposphere and reached an altitude of 26 km into the stratosphere (Fig. 5). Ash from the ensuing eruption cloud blanketed central Java, closed airports and disrupted regional aviation. A commercial A-320 airliner en-route from Australia to Indonesia encountered the ash cloud. Damage from ash ingestion required replacement of both engines at a cost of approximately US$20 million. The 14 February eruption destroyed a lava dome that had erupted passively within the volcano's crater in 2007, leaving a 200-m-deep pit crater in its place and raising questions as to the future of the 90-year-old drainage tunnels that maintained the crater lake at low levels, thereby preventing the very large and devastating lahars, for which Kelud is known (such as those in 1919 that killed 5000 people). The 2014 eruption produced PDC deposits in nearby drainages, and relatively small rainfall-induced lahars followed. Due to well-known eruption precursors at Kelud, timely monitoring and warnings by local authorities, public familiarity with eruption hazards, extensive education and evacuation planning, and a cultural acceptance of hazards and government authority, an organized evacuation of 200,000 people took place in a period of only a few hours preceding the nighttime eruption. There were only three fatalities, and people were able to return to areas near the volcano within a week.
This special issue of the Journal of Volcanology and Geothermal Research describes and evaluates the volcanology and geophysics of these two remarkable eruptions, as well as addresses the societal responses to the eruptions.
... Based on the eruption nature and circumstances of the Sinabung volcano, then the potential eruption hazards that may occur are 1) pyroclastic flow (hot clouds); 2) pyroclastic falls (the bursts of incandescent rock and ash rain); and 3) lava flows [18][19][20][21][22][23]. [24] adds based on the hazard level of Sinabung volcano eruption that might happen, the region of the disaster-prone of Sinabung volcano can be divided into three of the vulnerability level from low to high, however based on the analysis of the eruption hazard indicator according to Head Regulation, Agency of National Disaster Management (BNPB) No. 02 of 2012 the volcano eruption risk level of Sinabung belongs on the medium and high hazard levels (Tabel 1). 3% every year. ...
The purpose of this research was to determine the level of volcano eruption risk and compile a disaster risk mitigation model for the Sinabung volcano eruption. Analysis technique of volcano eruption disaster risk of Sinabung uses scoring techniques for all indicators. The volcano eruption disaster risk of Sinabung refers to eruption hazard level, vulnerability level, and disaster prevention capacity index. The level of volcano eruption hazard and vulnerability of Sinabung volcano was analyzed by GIS approach using ArcGIS 10.1 software, based on units of sub-district administration. The capacity index was analyzed based on the Hyogo Framework for Action-HFA 2005-2015. While the disaster mitigation and policy model of adaptation of volcano eruption Sinabung were analyzed with FGD and AHP. The level of volcano eruption disaster risk of Sinabung is high > 49 (614). As for the mitigation model of the eruption risk of Sinabung volcano and model of adaptation policy based on alternative priorities for disaster risk reduction has 4 main priorities, i.e: 1) Relocation for identify, assess and monitor of disaster risk and implement an early warning system; 2) Utilize of knowledge, innovation and education to build a culture of safety and resilience at all levels; 3) Make of disaster risk reduction a priority of national and region implemented through strong institutions; and 4) the reducing of underlying factors that increase disaster risk.
... They may occur in individual episodes over a long period of a volcano's eruptive record or in quick succession over a short span of activity as in the cases of Mt. Sinabung since 2013 [Nakada et al. 2017] and of Soufrière Hills volcano from 1996 to 1998 . In both these cases, block-andash flows and eruptions triggered by the dome collapse necessitated major, largely successful evacuations, but still resulted in casualties [Robertson et al. 2000;Andreastuti et al. 2017]. ...
Temperature can be an important characteristic used to distinguish primary pyroclastic density currents or block-and-ash flows from other collapses not primarily related to an eruption, and also governs the type and level of hazard presented by these mass flows. We examined several mass-flow deposits within the AD1000-1800 Maero Formation at Mt. Taranaki, New Zealand, for field characteristics of hot emplacement-such as the presence of charcoal, baking of soils, or gas-elutriation piping-and conducted a paleomagnetic study of their thermoremanent magnetization (TRM) to determine emplacement temperatures. Results show that the majority of the deposits result from block-and-ash flows emplaced over ∼500 • C. Some of these deposits were indistinguishable in the field from a reworked or low-temperature emplaced lahar or landslide deposit, indicating that sedimentary features are not a clear determinant of high emplacement temperature. The high emplacement temperatures suggest that the time between dome emplacement and collapse during this period was usually brief (<30 years), with some events consisting of rapid and repeated growth and collapse of lava domes, possibly within the same prolonged lava effusion episode.
... Miyabuchi, 1999 Tarawera 1305 CE 9.4 Nairn et al., 2001;Hanenkamp, 2011Chaiten 19-Feb-20096 Major et al., 2013Soufriere Hills ⁎⁎ 19957 10 Cole et al., 2002Sparks et al., 2002Sinabung 20104.9 Yulianto et al., 2016Nakada et al., 2017;Pallister et al., 2017 Augustine ⁎⁎ Jan-Mar 2006 5 4.42 ⁎ Vallance et al., 2010Colima 19-Jan-191315 0.07 Saucedo et al., 2005 ⁎ Area includes all deposit components (block and ash flow plus surge). ⁎⁎ Flows entered the sea, therefore, runout distances are minimum values. ...
For the years 2001 to 2013 of the ongoing eruption of Shiveluch volcano, a combination of different satellite remote
sensing data are used to investigate the dome-collapse events and the resulting pyroclastic deposits.
Shiveluch volcano in Kamchatka, Russia, is one of the world's most active dome-building volcanoes, which has
produced some of the largest known historical block-and-ash flows (BAFs). Globally, quantitative data for deposits
resulting from such large and long-lived dome-forming eruptions, especially like those at Shiveluch, are
scarce. We use Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) thermal infrared
(TIR), shortwave infrared (SWIR), and visible-near infrared (VNIR) data to analyze the dome-collapse scars
and BAF deposits that were formed during eruptions and collapse events in 2001, 2004, 2005, 2007, 2009,
2010, and two events in 2013. These events produced flows with runout distances of as far as 19 km from the
dome, and with aerial extents of as much as 22.3 km2
. Over the 12 years of this period of investigation, there is
no trend in deposit area or runout distances of the flows through time. However, two potentially predictive features
are apparent in our data set: 1) the largest dome-collapse events occurred when the dome exceeded a relative
height (from dome base to top) of 500 m; 2) collapses were preceded by thermal anomalies in six of the
cases in which ASTER data were available, although the areal extent of these precursory thermal areas did not
generally match the size of the collapse events as indicated by scar area (volumes are available for three collapse
events). Linking the deposit distribution to the area, location, and temperature profiles of the dome-collapse scars
provides a basis for determining similar future hazards at Shiveluch and at other dome-forming volcanoes. Because
of these factors, we suggest that volcanic hazard analysis and mitigation at volcanoes with similar BAF emplacement
behavior may be improved with detailed, synoptic studies, especially when it is possible to access and
interpret appropriate remote sensing data in near-real time.
TerraSAR-X (TSX), TanDEM-X (TDX), and PAZ Synthetic Aperture Radar data have been used at over 120 volcanoes to assess surface characteristics and change over time. We examine previous work, adding additional examples to understand where and when these data are most useful for volcanology. We focus on volcanoes as part of the Committee on Earth Observation Satellites (CEOS) Volcano Demonstrator Project. TSX/TDX/PAZ data provide a valuable means of detecting small surface changes from amplitude images and topographic changes from bistatic TSX/TDX data. For short temporal and perpendicular baselines, TDX/TSX/PAZ can also provide useful deformation data, even in presence of vegetation. No global background mission currently acquires TSX/TDX/PAZ data at volcanoes: 70 % of CEOS volcanoes have no repeat high spatial resolution data, limiting their suitability for studying pre-eruptive unrest. Coordinated targeting by SAR constellations of priority volcanoes would provide data and insights valuable for forecasting eruptions and associated hazards.
Shifts in activity at long-active, open-vent volcanoes are difficult to forecast because precursory signals are enigmatic and can be lost in and amongst daily activity. Here, we propose that crater and vent morphologies, along with summit height, can help us bring some insights into future activity at one of Ecuador’s most active volcanoes El Reventador. On 3 November 2002, El Reventador volcano experienced the largest eruption in Ecuador in the last 140 years and has been continuously active ever since with transitions between and coexistence of explosive and effusive activity, characterized by Strombolian and Vulcanian behavior. Based on the analysis of a large dataset of thermal and visual images, we determined that in the last 20 years of activity, the volcano faced three destructive events: A. Destruction of the upper part of the summit leaving a north-south breached crater (3 November 2002), B. NE border crater collapse (2017), and C. NW flank collapse (2018), with two periods of reconstruction of the edifice: Period 1. Refill of the crater (2002-early 2018) and Period 2. Refill of the 2018 scar (April 2018–December 2022). Through photogrammetric analysis of visual and thermal images acquired in 11 overflights of the volcano, we created a time-series of digital elevation models (DEMs) to determine the maximum height of the volcano at each date, quantify the volume changes between successive dates, and characterize the morphological changes in the summit region. We estimate that approximately 34.1x10⁶ m³ of volcanic material was removed from the volcano due to destructive events, whereas 64.1x10⁶ m³ was added by constructive processes. The pre-2002 summit height was 3,560 m and due to the 2002 eruption it decreased to 3,527 m; it regained its previous height between 2014 and 2015 and the summit crater was completely filled by early April 2018. Event A resulted from an intrusion of magma that erupted violently; we proposed that Events B and C could be a result of an intrusion as well but may also be due to a lack of stability of the volcano summit which occurs when it reaches its maximum height of approximately 3,590 and 3,600 m.
Up‐to‐date topography data sets are essential for forecasting volcanic hazards and monitoring deformation. Digital elevation models are used to quantify eruption rates, used in flow modeling programs, and are necessary to accurately process interferometric synthetic aperture radar data for surface deformation. We can track topographic change at volcanoes through fieldwork, airborne instruments, and satellite data, with the last providing the greatest potential for global coverage. Despite this global coverage, we do not know the characteristics of topographic change at volcanoes over a given time interval. We define the specific acquisition needs for topography data using topographic change detected from recent eruptions. We review existing literature and compile a data set of eruptive products (121 lava flows, 99 domes and 163 pyroclastic density currents (PDCs)) from eruptions between 1980 and 2019. We find that different sensing capabilities are required for different use cases. A vertical accuracy of 1 m would detect 92% of all eruptive products including 100% of lava domes and lava flows, but only 78% of PDCs. A horizontal resolution of 13 × 13 m pixels is the minimum necessary to detect 90% of all eruptive products. Explosive eruptions (with PDC products) typically lasted less than 1 day and would need a temporal resolution of 1 day while a longer repeat interval is acceptable at effusive eruptions (lava domes and flows), which could last weeks to years. We find a lack of consistent data acquisition, with 45% of the 383 eruptive products reported not having published spatial dimensions.
This study aims to provide the first general typology of Indonesian stratovolcano (number of analyses=154), including various types of rock compositions and diverse volcanic hazards. Several parameters were evaluated, including average radius (r), average slope (S), surface roughness (RMS), rock compositions, mineralogy, and deposit characteristics. Four types were identified as follows: (1) small-least dissected cones, (2) broad-dissected cones, (3) extremely broad-dissected cones with caldera, and (4) residual-highly dissected cones. Type I is typically small (r=2.1 km), steep (S=19.8ᵒ), rough (RMS=88.8), less evolved (predominantly basic to intermediate), having abundant mafic (olivine, clinopyroxene) and minor hydrous (amphibole, biotite) minerals, with rare pumice and lava domes (mostly scoria and lava flows). Type II has moderate values of r, s, and RMS (8.8 km, 15.2ᵒ, and 47.7, respectively) with predominantly intermediate rocks, minor olivine with abundant hydrous minerals, and abundant pumice and lava domes. Type III is typically large (r=18.1 km), gentle (S=9.2ᵒ), smooth (RMS=40.1), producing abundant felsic rocks and felsic minerals (quartz and sanidine), and characterized by the occurrence of thick ignimbrite deposits. Type IV has relatively similar size to type II (r=8.2 km), but the slope is gentler with coarser surface textures (S=10.7ᵒ and RMS=56.8), includes more portion of ultrabasic rocks and mafic minerals, and has no feature of lava domes with common exposure of intrusions (e.g., dyke). We suggest that the evolution from type I to type III corresponds to maturation stage, whereas the formation of type IV represents erosional stage.
Andesitic blocky lava flows are characterized by the surfaces that consist of large angular blocks of lava. They move slowly downhill the slope of volcano. These flows often travel only a few kilometres from the vent. In this paper, we first describe the possibility to apply the seismic signals, recorded during the blocky lava flows discharge, for reconstruction of the lava flow emplacement during the 2004 and 2016 eruptions at Volcán de Colima, México. There were shown the characteristic properties of lavafalls in comparison with the pyroclastic flows and igneous rockfalls (PFIRs), generated during Vulcanian explosions. It was shown that the waveforms of lavafalls are similar generally to the waveforms of PFIRs but are characterized by higher frequencies. The dominance of the short-duration seismic signals of lavafalls, comparative with the signals of PFIRs, indicates relatively smaller dimensions of lavafalls. We introduced the power spectral density curves of one-hour seismic signals as a tool to reconstruct the emplacement dynamics. It was shown that the lava outflowed from the crater in two ways, as lava pulses or as lava large-volume collapses.
Petrological analysis of the 2020-21 La Soufrière lava dome reveals ubiquitous oxidation textures. Comparison of the natural dome rock to subsequent explosive scoria phases highlights the lack of any oxidation features in the latter, indicating that oxidation processes affected only the dome-forming magma, either during pre-eruptive storage or upon emplacement. To investigate the causes of oxidation we present a series of one-atmosphere experiments, using fresh natural basaltic andesite scoria as a starting material. Experiments were performed at 900 and 1020°C and at oxygen fugacities between NNO-2 and air. Experimental results show that iron oxide nanolites nucleate on the rims of pyroxene microlites and phenocrysts under all experimental conditions except at NNO−2. Orthopyroxene phenocrysts become unstable at 1020°C, at and above NNO+2. Olivine symplectites form in all experiments at and above NNO. Titanomagnetite co-exsolves titanohematite and an Mg-Fe-Al spinel (pleonaste-magnesioferrite) at and above NNO+2. Well-developed Mg-Fe-Al spinel trellis exsolution lamellae in titanomagnetite phenocrysts, as seen in the dome, only form in the presence of air at 900°C. The combination of textures and compositions observed in the natural dome indicates that oxidation of the dome magma occurred during emplacement at Earth's surface, with air percolating through the dome at temperatures ≤ 900°C.
Recent eruptions of the Shinmoedake volcano, Japan, have provided a valuable opportunity to investigate the transition between explosive and effusive eruptions. In October 2017, phreatic/phreatomagmatic explosions occurred. They were followed in March 2018 by a phase of hybrid activity with simultaneous explosions and lava flows and then a transition to intermittent, Vulcanian-style explosions. Evolution of surface phenomena, temporal variations of whole-rock chemical compositions from representative eruptive material samples, and rock microtextural properties, such as the crystallinity and crystal size distribution of juvenile products, are analyzed to characterize the eruption style transition, the conduit location, and the shallow magma conditions of the volcanic edifice. The 2017–2018 eruptive event is also compared with the preceding 2011 explosive–effusive eruption. The chemical and textural properties of the 2018 products (two types of pumice, ballistically ejected lava blocks, and massive lava) are representative of distinct cooling and magma ascent processes. The initial pumice, erupted during lava dome formation, has a groundmass crystallinity of up to 45% and the highest plagioclase number density of all products (1.9 × 10 ⁶ /mm ³ ). Conversely, pumice that erupted later has the lowest plagioclase number density (1.2 × 10 ⁵ /mm ³ ) and the highest nucleation density (23/mm ⁴ in natural logarithm). This 2018 pumice is similar to the 2011 subplinian pumice. Therefore, it was likely produced by undegassed magma with a high discharge rate. Ballistics and massive lava in 2018 are comparable to the 2011 Vulcanian ballistics. Conversely, the high plagioclase number density pumice that occurred in 2018 was not observed during the 2011 eruption. Thus, such pumice might be specific to hybrid eruptions defined by small-scale explosions and lava dome formation with low magma discharge. The observed transitions and temporal variations of the activities and eruption style during the 2017–2018 Shinmoedake eruptions were primarily influenced by the ascent rate of andesitic magma and the geological structure beneath the summit crater.
Graphical Abstract
Volcanism is one of the main mechanisms transferring mass and energy between the interior of the Earth and the Earth's surface. However, the global mass flux of lava, volcanic ash and explosive pyroclastic deposits is not well constrained. Here we review published estimates of the mass of the erupted products from 1980 to 2019 by a global compilation. We identified 1,064 magmatic eruptions that occurred between 1980 and 2019 from the Smithsonian Global Volcanism Program database. For each eruption, we reported both the total erupted mass and its partitioning into the different volcanic products. Using this data set, we quantified the temporal and spatial evolution of subaerial volcanism and its products from 1980 to 2019 at a global and regional scale. The mass of magma erupted in each analyzed decade ranged from 1.1–4.9 × 10¹³ kg. Lava is the main subaerial erupted product representing ∼57% of the total erupted mass of magma. The products related to the biggest eruptions (Magnitude ≥6), with long recurrence times, can temporarily make explosive products more abundant than lava (e.g., decade 1990–1999). Twenty‐three volcanoes produced ∼72% of the total mass, while two different sets of 15 volcanoes erupted >70% of the total mass of either effusive or explosive products. At a global scale, the 10 and 40‐year average eruptive rates calculated from 1980 to 2019 have the same magnitude as the long‐term average eruptive rates (from thousand to millions of years), because in both cases rates are scaled for times comparable to the recurrence time of the biggest eruptions occurred.
Volcanoes have been found to display periodicities or cyclic trends in a wide range of phenomena. These include the eruptive activity itself, but also in the time series of geophysical and geochemical monitoring data such as volcanic degassing. Here, we test the existence of periodicities of volcanic degassing at 32 volcanoes using the time series of sulfur dioxide (SO2) emission rates from data of the Network for Observation of Volcanic and Atmospheric Change (NOVAC). We use the Lomb‐Scargle periodogram to analyze the SO2 data which allows efficient computation of a Fourier‐like power spectrum from unevenly sampled data. We were able to calculate False‐Alarm Probabilities in 28 of the 32 volcanoes, and we identified significant periodicities in the SO2 emission rates in 17 of the 28 volcanoes. However, we find that most of these periodicities are also present in the plume speeds used to determine SO2 emission rates. Periodicities at about 30–70, ∼120, and ∼180 days were identified at volcanoes located between 16°N and 16°S and are related to intraseasonality and interseasonality in global trade winds and not volcanic in origin. Periodicities between 30 and 70 days in both plume speed and SO2 emission rates are associated to the Madden‐Julian Oscillation that is responsible for intraseasonal variability in the tropical atmosphere. Our study highlights the importance of using local wind data for deriving realistic SO2 emissions and the identification of short‐term periodicity in volcanic behavior.
Mount Sinabung is a Pleistocene-to-Holocene stratovolcano, and its 2010 eruption was the first active activity after having been dormant for a long time. Enhanced pressure, intensity, and thermal energy of Sinabung activities hit several geothermal resources and triggered Tinggi Raja geofluid in Simalungun. This study aims to identify Sinabung eruption influences the appearance and point-transfer movement of geothermal features in Tinggi Raja. This research method builds a field model analysis (FMA) by integrating the quantitative and qualitative approaches focused on historic earthquakes activities (HEA) from the Center of Volcanology and Geological Hazard Mitigation (CVGHM), time-series satellite observation of land surface change, and land surface temperature, the residual anomaly of the geothermal reservoir, high altitudes and chemical-drop in pH, and point-transfer movement. HEA shows fluctuating activities in eruption level or Volcanic Eruption Index (VEI) scale. FMA offers fewer residual anomalies from Southwest to Northeast in 100 m–600 m coverage 5 km² underground than pre-hypothesis indicates the anomaly zone associated with the fracture zone; however, the lithology of the geothermal system is categorized as limestone rock and has no active faults. It indicates a low magnetic field anomaly in geothermal resources that does not correlate volcanic manifestation to geothermal trigger. Distance, type, and felt volcanic earthquake and eruption are less direct impact between the eruption of Mount Sinabung and the displacement of springs at Tinggi Raja.
Over the past two decades, the availability of satellite measurements of volcanic gas emissions and heat flux has driven the development of new methodologies to improve global-scale volcano monitoring. In this work we explored the relationship between volcanic sulfur dioxide (SO2) emissions and radiant heat flux (RHF) measurements from NASA’s Ozone Monitoring Instrument (OMI) and Moderate Resolution Imaging Spectroradiometer (MODIS), respectively, to gain insight into how it associates to volcanic processes and eruption styles. The OMI SO2 emissions data are derived from existing databases developed by using the methodology in Fioletov et al. (2016), which contain global, passive volcanic SO2 degassing fluxes (PVF) for approximately 90-100 active volcanoes calculated at annual and seasonal intervals from 2005-2019 and 2005-2016, respectively. Volcanoes with available SO2 flux datasets and measurable MODIS RHF data were identified using the University of Hawaii’s near-time thermal monitoring of global hot-spots (MODVOLC) thermal alert system. The MODIS data was then integrated to match the annual and seasonal intervals at which the SO2 fluxes were calculated and converted from RHF to Volcanic Radiative Energy (VRE). Both parameters were analyzed quantitatively by building seasonal and annual timeseries and studying how they changed together. This successfully allowed us to see a variety of activity patterns, including but not limited to identifying endogenic and exogenic behavior and transitions between the two states in certain volcanoes. In addition, the VRE and SO2 annual and seasonal data was subjected to a simple linear regression analysis, through which we assessed the strength of the relationship given different types of activity, silica compositions and temporal scales. For example, we looked at six felsic dome/flow volcanoes with higher silica content products whose regressions using annual data returned a strong correlation that weakened when using their seasonally integrated data. Seven of the volcanoes with stronger correlations were used to extrapolate SO2 values from 2000-2005 (prior to the launch of the OMI satellite) based on 2000-2005 MODIS heat emissions data. Given the general lack of SO2 data for that period, it was not possible to corroborate the values and additional studies must be conducted to determine this method’s feasibility. Finally, we conducted an “excess” sulfur analysis where we quantitatively compared melt inclusion-derived sulfur content and total degassed sulfur estimates from 15 volcanoes which also returned high VRE-SO2 correlations. Our results show that there is no clear relationship between tectonic environments, magma composition or activity type (individually) and the amount of “excess” sulfur emitted by a volcano. Additional analyses are needed to determine if any specific combination between these could produce a higher correlation.
This discussion concerns the flowage of the 1991 lava lobes at Unzen that were suggested by Goto et al. (2020) to be moving rigidly. Pictorial evidence of flowage of the 1991 lava lobe of Unzen, such as morphological change of the lava lobe, protrusion of the front of lava lobe, crease structure, and wrinkle surface of lava blocks, are presented. Differences in the interpretation of flow mechanisms may reflect slight difference in temperature and glass composition of the lavas. Temperatures used by Goto et al. (2020) were 780–880 °C, whereas those estimated by Venezky and Rutherford (1999) were 900 ± 30 °C. The groundmass glass compositions of 1991 blocks of Unzen dacite used by Goto et al. (2020) are 1–2 wt% higher in SiO2 than those of Nakada and Motomura (1999) and ours, suggesting that the samples used by Goto et al. (2020) represent the cooler rigid parts of the lava lobes. The lava viscosity is delicately influenced by cooling, dewatering, and crystallization during eruption. The direct application of experimental results to understanding the rheological behavior of natural lavas needs much more careful consideration.
Lava dome collapses are a major threat to the population living near such volcanoes. However, it is not possible to forecast collapses reliably because the mechanisms are not clearly understood, due partly to the lack of continuous observations of such events. To address this need for field data, we have developed new monitoring stations, which are adapted to the volcanic environment. The stations tracked the complete evolution of the 2018−2019 lava dome of Merapi volcano (Indonesia) and the associated pyroclastic density currents. During the fourteen months of activity, the stations acquired thermal, high-resolution visual images and movies in stereoscopic configurations. The dome developed on a plateau flanked by steep sides (~40°−50°) inside the crater, which was open to the SE. We observed that the dome behaved in a viscous manner (with a viscosity of 109 Pa s for the interior to 1013 Pa s for external parts of the dome) on gentle slopes, and in a brittle way (friction angle ~35°, cohesion <100 kPa) on slopes steeper than 35°. Thus, the lava dome was unable to grow on the outer slopes of the plateau and a significant volume of lava (350−750×103 m3) accumulated and collapsed daily to the SE in relatively small volumes (<10 000 m3), preventing the lava dome from reaching the critical volume necessary for pyroclastic density currents to form and threaten the surrounding population. The cause of the small and frequent collapses was purely gravitational during the dome activity. This suggests that relatively small differences in the summit morphology can control dome evolution, favouring either a lava dome restricted to a small volume and leading to only a minor crisis, or more voluminous dome growth and a catastrophic collapse.
In this article I present a review of InSAR observations of ground deformation at Cordón Caulle volcano, whose 2011–2012 VEI 4-5 eruption is the best scientifically observed and instrumentally recorded rhyolitic eruption to date. I document a complete cycle of pre-eruptive uplift, co-eruptive subsidence and post-eruptive uplift with InSAR data between March 2003 and May 2020, and produced by a complex interplay of magmatic processes. Pre-eruptive data show ~0.5 m of ground uplift in three distinct episodes between 2003 and 2011, with uplift rates between ~3 and ~30 cm/yr. The uplift was likely caused by magma injection resulting in pressurization of the magmatic system at depths of 4–9 km. Data spanning the first 3 days of the eruption show ~1.5 m of deflation produced by two distinct sources at 4–6 km depth located 18 km from each other and up to 10 km from the eruptive vent -- suggesting hydraulic connectivity of a large magma mush zone. A third source of deformation was recorded during the rest of the eruption at a depth of ~5 km, resulting in a total subsidence of ~4.2 m during the whole eruption. On a much smaller spatial scale (~25 km²), InSAR-derived digital elevation models recorded ~250 m of uplift in the area of the eruptive vent interpreted as the intrusion of a shallow laccolith during the first 2.5 months of the eruption and time averaged lava discharge rates up to ~150 m³/s. The co-eruptive time series of reservoir pressure drop and extruded volume follow exponential trends that can be explained by a model of magma reservoir depressurization and conduit flow. Since the end of the eruption, the surface of the volcano was uplifted ~1 m in a sequence of three transient episodes of unrest during 2012 and 2019, with uplift rates between 6 and 45 cm/yr and lasting between 0.5 and 3.2 years. These pulses can be modeled by the same source, a sub-horizontal sill at a depth of ~6 km. Viscoelastic relaxation is not significant on these time scales, hence I interpret these uplift signals as being produced by episodic pulses of magma injection in the crystal mush that likely underlies the volcano. The episodic and abrupt changes of the ground deformation suggest a restless trans-lateral magmatic system at depths of 4–9 km, and active across multiple spatial and temporal scales. Finally, I also discuss challenges of the InSAR technology that should be addressed to detect ground deformation on short time scales, particularly under the low coherence conditions of Cordón Caulle.
During the past two decades, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on the Terra satellite has acquired nearly 320,000 scenes of the world’s volcanoes. This is ~10% of the data in the global ASTER archive. Many of these scenes captured volcanic activity at never before seen spatial and spectral scales, particularly in the thermal infrared (TIR) region. Despite this large archive of data, the temporal resolution of ASTER is simply not adequate to understand ongoing eruptions and assess the hazards to local populations in near real time. However, programs designed to integrate ASTER into a volcanic data sensor web have greatly improved the cadence of the data (in some cases, to as many as 3 scenes in 48 h). This frequency can inform our understanding of what is possible with future systems collecting similar data on the daily or hourly time scales. Here, we present the history of ASTER’s contributions to volcanology, highlighting unique aspects of the instrument and its data. The ASTER archive was mined to provide statistics including the number of observations with volcanic activity, its type, and the average cloud cover. These were noted for more than 2000 scenes over periods of 1, 5 and 20 years.
Routine volcano monitoring increasingly involves multiparameter datasets. Databases that include multi-disciplinary datasets have great potential to contribute to the evaluation of ongoing volcanic eruptions and unrest events. Here, we examine the characteristics of a multiparameter dataset from Shinmoedake volcano (Kirishima) in Japan for the period of 2010–2018 to examine how the chronology of volcanic activity can be traced. Our dataset consists of global navigation satellite system (GNSS), seismic, tilt, infrasound, sulfur dioxide (SO 2 ) column amount, and video records. We focus mainly on the period after 2012, particularly a series of ash emissions in 2017 (hereafter the 2017 eruption), lava effusion, and Vulcanian eruptions in 2018 (hereafter the 2018 eruption). Our dataset shows that the GNSS observations successfully captured the gradual inflation of the volcano edifice, suggesting magma intrusion or pressure buildup in the magma storage region prior to the 2017 and 2018 eruptions. The number of volcanic earthquakes also gradually increased from 2016 toward the eruptions, particularly events occurring beneath Shinmoedake. Tilt data captured a precursor tilt event prior to the 2017 eruption and a magma chamber deflation during the lava effusion of the 2018 eruption. Tilt, seismic, infrasound, SO 2 gas column, and video data record signals accompanying periodic degassing during the lava effusion and explosive degassing accompanying the Vulcanian eruptions, which have similar characteristics to those reported for past eruptions at Shinmoedake and other volcanoes. This similarity suggests that multidisciplinary databases will be an important reference for future evaluations of ongoing volcanic activity and unrest.
During the ongoing (2013–present) eruption of Sinabung volcano, north Sumatra, we have routinely used a variety of satellite remote sensing data to observe and forecast lava dome and lava flow collapse events, to map the resulting pyroclastic deposits, and to estimate effusion rates. In this paper, we focus on the first two years of the current eruption (September 2013–December 2015), and we summarize major events in 2016. We divide the eruption into 5 major phases: 1) phreatomagmatic (July 2013–18 December 2013), 2) first dome growth and collapse (18 December 2013–10 January 2014), 3) lava-flow (10 January 2014–mid-September 2014), 4) second lava dome and collapse (mid-September 2014–July 2015), 5) lava dome collapse and ash explosion phase (August 2015–present). Throughout the eruption, remotely sensed information has been instrumental in assessing the stability of the lava dome and flow and to forecast collapse events that produce pyroclastic density currents (PDCs: block-and-ash flows, co-ignimbrite surges, and blasts). Forecasts based on remote sensing data in combination with seismic, geodetic and gas-monitoring data have also helped inform decisions related to alert levels and evacuations. Relatively unusual aspects of the Sinabung eruption include the transition from dome to flow morphology (phase 2 to phase 3 transition) and the frequent occurrence during phase 3 of collapses from the lava flow-front and flow-margins—collapses that produced extensive pyroclastic density currents. By analogy to the well-known “Merapi type” collapses and pyroclastic deposits, we propose that lava flow-front and flow-margin collapses with associated PDCs be known as “Sinabung type.” Although detailed study of deposits has not been possible due to continuing hazards, our observations suggest that the transition from lava dome to lava flow and the occurrence of flow-front and flow-margin collapses reflect a particular combination of lava viscosity and steepness of slope. Our observations also show clear evidence of at least one slope-parallel high-velocity and dilute PDC (a “blast”) that emanated from a lava-margin collapse site 500 m downslope from the vent. This 1 February 2014 blast downed and singed a forest out to at least 3.9 km from the collapse site and killed 16 people. We also use a combination of field and remotely sensed data to map the distribution of Sinabung deposits. We estimate eruptive volumes and extrusion rates by combining sequential measurements of lava surface and pyroclastic flow areas with thickness estimates derived from simple geometric assumptions, oblique photographs and Digital Elevation Models (DEMs) derived from remotely sensed data. Our estimates of short-term effusion rates vary widely on a daily to weekly basis, from <1 to >20 m³ s⁻¹. In a few cases, periods of increased extrusion precede lava flow-front collapses by a few days to a week, suggesting delays in transmittance of effusion pulses as lava moves from vent to flow front. We find that, as of 1 January 2016, the total area of deposits is 10⁷ m², and their approximate deposit volume is about 0.3 km³, equivalent to 0.2 km³ Dense Rock Equivalent (DRE). We anticipate that our deposit maps will be valuable in the future as a framework for the study of the magmatic and textural evolution of eruptive products through time.
Eruptions of Sinabung volcano, Indonesia have been ongoing since 2013. Since that time, the character of eruptions has changed, from phreatic to phreatomagmatic to magmatic explosive eruptions, and from production of a lava dome that collapsed to a subsequent thick lava flow that slowly ceased to be active, and later, to a new lava dome. As the eruption progressed, event trees were constructed to forecast eruptive behavior six times, with forecast windows that ranged from 2. weeks to 1. year: November 7-10, December 12-14, and December 27, 2013; and January 9-10, May 13, and October 7, 2014. These event trees were successful in helping to frame the forecast scenarios, to collate current monitoring information, and to document outstanding questions and unknowns. The highest probability forecasts closely matched outcomes of eruption size (including extrusion of the first dome), production of pyroclastic density currents, and pyroclastic density current runout distances. Events assigned low probabilities also occurred, including total collapse of the lava dome in January 2014 and production of a small blast pyroclastic density current in February 2014.
ABSTRACT
Sinabung volcano has a new magmatic eruptive period in September 2013 where its first historic eruption started on August 27th, 2010 since the latest eruption about 1150 ± 50 BP. Magmatic eruptions are characterized by dome growth and collapsed-type pyroclastic flow (block-and-ash flow). Rock samples from 2016 Sinabung eruption showed the andesite composition, contain plagioclase, pyroxene, and hornblende phenocrysts in the groundmass of volcanic glass, microliths of plagioclase, and opaque minerals. There are two (2) type of crystal clots in all samples i.e. crystal clots of plagioclase, hornblende, opaque and plagioclase, pyroxene, opaque. There are no evidance that the crystals intergrowth of hornblende and pyroxene in the same crystal clots. Its suggest that there are magma mixing in Sinabung volcano before erupted. Geothermometry of coexisting pyroxene (clinopyroxene and orthopyroxene) indicated that the magma has temperature of 1079o-1103o C and the other magma has temperature of 850o-855o C based on geothermometry of coexisting hornblende and plagioclase. The presence of several disequilibrium textures such as sieve texture and reverse zoning in plagioclase phenocrysts, reaction-rim of clinopyroxene in hornblende phenocrysts suggests that there are injections of basaltic melts (replenishment) and mixing with pre-exiting magma during 2016 eruption with andesite composition.
Keyword: Sinabung volcano, mixing, magma, crystal clots, geothermometry.
We analyzed continuous Global Positioning System (GPS) data from Sinabung to capture and model the migration of magma from the pre-eruptive and syn-eruptive time period between June 2013 and January 2016. We divided this time into four periods of significant deformation: two extensional stages followed by two contractional stages. Using a grid search method, we determined the location and volume change of a Mogi source for each deformation stage. Cumulative volume changes during the contraction periods were approximated by an exponentially decaying function with time. Period 1 began in June 2013 with slight extension, for which an inflation source was modeled at a depth of 3-8km below sea level (bsl) and a volume change of 0.3-1.8Mm³. Seismicity in period 1 was marked by a notable increase in deep high frequency volcano tectonic earthquakes (VTs) beginning in July 2013 and shallow VTs in September 2013. Period 2 began in late October 2013 with accelerated extension, with at least 1cm extension in the baseline length. During period 2 the modeled inflation source ascended to a shallower depth of 0.9 (0.4-2.1) km below sea level (bsl) beneath Sinabung with a change in volume of +0.39 (+0.18-+0.60) Mm³, and with accelerated rates of volume increase during the time period when the magma migrated to the surface. Seismicity during period 2 was marked first by an increase in the incidence of shallow volcano-tectonic (VT) earthquakes and later by repetitive self-similar hybrid events as the magma migrated to the surface. Period 3 began in January 2014, after the appearance of the lava dome, and was marked by rapid steady contraction of ∼3cm through March 2014. The modeled source located at 8.4 (7.4-9.9) km bsl beneath the eastern flank of Sinabung with a volume change of -20.51 (-26.89 to -14.12) Mm³. Period 4 began in April 2014 with decelerating contraction, and the modeled deformation center shifted to the northeast, reaching a depth of 12.2 (10.1-14.8) km bsl between Sinabung and Sibayak volcanoes and a change in volume of -88.26 (-123.87 to -52.66) Mm³. Approximately 2/3 of the total volume change related to contraction occurred between January 2014 and May 2016, and the current activity of Sinabung is expected to decrease gradually and almost terminate in the early 2020s, assuming no new intrusion or deformation rate changes. Both of the eruptions at Sinabung in 2010 and Unzen in 1991-1995 show characteristics of ground inflation and subsequent deflation, indicating magma migration and effusion processes similar to the current Sinabung activity. The inflation before the 2010 Sinabung eruptions likely started before 2007 and is an indication of magma intrusion before the 2010 and 2013 eruptions.
During the ongoing (2013–present) eruption of Sinabung volcano, north Sumatra, we have routinely used a variety of satellite remote sensing data to observe and forecast lava dome and lava flow collapse events, to map the resulting pyroclastic deposits, and to estimate effusion rates. In this paper, we focus on the first two years of the current eruption (September 2013–December 2015), and we summarize major events in 2016. We divide the eruption into 5 major phases: 1) phreatomagmatic (July 2013–18 December 2013), 2) first dome growth and collapse (18 December 2013–10 January 2014), 3) lava-flow (10 January 2014–mid-September 2014), 4) second lava dome and collapse (mid-September 2014–July 2015), 5) lava dome collapse and ash explosion phase (August 2015–present). Throughout the eruption, remotely sensed information has been instrumental in assessing the stability of the lava dome and flow and to forecast collapse events that produce pyroclastic density currents (PDCs: block-and-ash flows, co-ignimbrite surges, and blasts). Forecasts based on remote sensing data in combination with seismic, geodetic and gas-monitoring data have also helped inform decisions related to alert levels and evacuations. Relatively unusual aspects of the Sinabung eruption include the transition from dome to flow morphology (phase 2 to phase 3 transition) and the frequent occurrence during phase 3 of collapses from the lava flow-front and flow-margins—collapses that produced extensive pyroclastic density currents. By analogy to the well-known “Merapi type” collapses and pyroclastic deposits, we propose that lava flow-front and flow-margin collapses with associated PDCs be known as “Sinabung type.” Although detailed study of deposits has not been possible due to continuing hazards, our observations suggest that the transition from lava dome to lava flow and the occurrence of flow-front and flow-margin collapses reflect a particular combination of lava viscosity and steepness of slope. Our observations also show clear evidence of at least one slope-parallel high-velocity and dilute PDC (a “blast”) that emanated from a lava-margin collapse site 500 m downslope from the vent. This 1 February 2014 blast downed and singed a forest out to at least 3.9 km from the collapse site and killed 16 people. We also use a combination of field and remotely sensed data to map the distribution of Sinabung deposits. We estimate eruptive volumes and extrusion rates by combining sequential measurements of lava surface and pyroclastic flow areas with thickness estimates derived from simple geometric assumptions, oblique photographs and Digital Elevation Models (DEMs) derived from remotely sensed data. Our estimates of short-term effusion rates vary widely on a daily to weekly basis, from <1 to >20 m³ s⁻¹. In a few cases, periods of increased extrusion precede lava flow-front collapses by a few days to a week, suggesting delays in transmittance of effusion pulses as lava moves from vent to flow front. We find that, as of 1 January 2016, the total area of deposits is 10⁷ m², and their approximate deposit volume is about 0.3 km³, equivalent to 0.2 km³ Dense Rock Equivalent (DRE). We anticipate that our deposit maps will be valuable in the future as a framework for the study of the magmatic and textural evolution of eruptive products through time.
We analyzed continuous Global Positioning System (GPS) data from Sinabung to capture and model the migration of magma from the pre-eruptive and syn-eruptive time period between June 2013 and January 2016. We divided this time into four periods of significant deformation: two extensional stages followed by two contractional stages. Using a grid search method, we determined the location and volume change of a Mogi source for each deformation stage. Cumulative volume changes during the contraction periods were approximated by an exponentially decaying function with time. Period 1 began in June 2013 with slight extension, for which an inflation source was modeled at a depth of 3-8km below sea level (bsl) and a volume change of 0.3-1.8Mm³. Seismicity in period 1 was marked by a notable increase in deep high frequency volcano tectonic earthquakes (VTs) beginning in July 2013 and shallow VTs in September 2013. Period 2 began in late October 2013 with accelerated extension, with at least 1cm extension in the baseline length. During period 2 the modeled inflation source ascended to a shallower depth of 0.9 (0.4-2.1) km below sea level (bsl) beneath Sinabung with a change in volume of +0.39 (+0.18-+0.60) Mm³, and with accelerated rates of volume increase during the time period when the magma migrated to the surface. Seismicity during period 2 was marked first by an increase in the incidence of shallow volcano-tectonic (VT) earthquakes and later by repetitive self-similar hybrid events as the magma migrated to the surface. Period 3 began in January 2014, after the appearance of the lava dome, and was marked by rapid steady contraction of ∼3cm through March 2014. The modeled source located at 8.4 (7.4-9.9) km bsl beneath the eastern flank of Sinabung with a volume change of -20.51 (-26.89 to -14.12) Mm³. Period 4 began in April 2014 with decelerating contraction, and the modeled deformation center shifted to the northeast, reaching a depth of 12.2 (10.1-14.8) km bsl between Sinabung and Sibayak volcanoes and a change in volume of -88.26 (-123.87 to -52.66) Mm³. Approximately 2/3 of the total volume change related to contraction occurred between January 2014 and May 2016, and the current activity of Sinabung is expected to decrease gradually and almost terminate in the early 2020s, assuming no new intrusion or deformation rate changes. Both of the eruptions at Sinabung in 2010 and Unzen in 1991-1995 show characteristics of ground inflation and subsequent deflation, indicating magma migration and effusion processes similar to the current Sinabung activity. The inflation before the 2010 Sinabung eruptions likely started before 2007 and is an indication of magma intrusion before the 2010 and 2013 eruptions.
A small phreatic eruption of Sinabung Volcano, North Sumatra on 28 August 2010, at 18:30 local time marked the first eruption in the past ~ 1200 years. The eruption took place from two small vents in the south crater area. Explosions and ash emissions from these vents generated multiple ash plumes that reached altitudes of up to 5 km during early- to mid-September. By the end of September 2010, only low level steam plumes were visible and the alert level was reduced from Level 4 (highest) to Level 3. The 2010 eruption effectively ended at this time. Beginning two days after the initial 2010 eruption, activity of the eruption has been monitoring continuously by a telemetered seismic network surrounding the volcano and by remotely sensed observations. This monitoring system was supplemented with a near-field continuous GPS network, beginning in February 2011. Persistent fumarolic emissions continued for almost 3 years following the 2010 eruption, before a new eruption began on 15 September 2013. This eruption continues to the present. The ongoing eruption is divided into 5 major phases: 1) phreatomagmatic phase (July 2013–18 December 2013); 2) first dome and collapse phase with pyroclastic density currents (PDCs; block-and-ash flows and related surges) to south (18 December 2013–10 January 2014); 3) lava-flow and collapse phase (10 January 2014–mid-September 2014); 4) second lava dome and collapse phase with PDCs to south (mid-September 2014–July 2015); 5) lava dome collapse and ash explosion phase with PDCs to southeast and east (August 2015–present). The volcano erupted intermittently during the early phreatomagmatic phase with small vertical ash explosions. Then the eruption became increasingly vigorous with more repetitive and intense vertical ash explosions during late October through November. The first small pyroclastic density currents (PDCs) began on November 1. These pyroclastic flows descended the southeastern flank to a distance of 2 km.
Swarms of volcano-tectonic (VT) earthquakes and volcanic tremor lasting hours occurred repeatedly during the phreatomagmatic phase and some of these VT-swarms were following by explosions. In early December 2013, during the transition between phreatomagmatic and dome-collapse phases, swarms of hybrid earthquakes took place preceding and accompanying dome growth. The first lava dome was observed in satellite images on 18 December near the main crater rim. Partial collapses of the dome produced pyroclastic density currents (PDCs) beginning on 30 December. Growth of this first lava dome continued into January and was accompanied by additional collapses and PDCs. By about 10 January, the lava had transitioned from a summit dome morphology into a lava flow morphology. The resulting lava flow descended the southeast flank of the volcano, producing flow-front and marginal collapses with associated PDCs. One such flow-flank collapse on 2 February 2014 resulted in a PCD that killed 16. The lava flow phase continued through mid-September 2014, when a second summit lava dome began to grow and collapse, producing PDCs initially to the south and southeast, and then beginning in July 2015 to the east and southeast.
The eruption of Sinabung resulted in major impacts on the population of the resort and farming area near the volcano and in the Ginting and Karo Regencies of North Sumatra. Local communities, having not experienced eruptions were initially curious and credulous of any information and various institutions providing information to the public with little coordination, resulting in confusion. With time communications have improved and communities and the responsible governments have become more prepared in dealing with the persistent eruption. The Government of Indonesia has provided funding to support villagers who lived within a 5 km radius danger zone to stay in relocation camps as a permanent relocation area is being determined. Unfortunately, on 21 May 2016, 9 additional fatalities took place in the village of Gamber, within the danger zone, when a dome collapse sent a pyroclastic density current into the area.
Throughout the eruption, the volcano has been monitored by the Indonesian Center for Volcanology and Geologic Hazard Mitigation (CVGHM) in partnership with the USGS-USAID Volcano Disaster Assistance Program and the Disaster Prevention Research Institute of Kyoto University. Monitoring techniques have included seismic, geodetic, gas, satellite and field observations, as well as occasional sampling of ash and lava for geochemical analyses. In this paper, we summarize key aspects of the monitoring data, their interpretations and their use in forecasting eruptive behavior and in issuance of alerts and warnings. More detailed interpretations of the monitoring data and their use are found in the other papers of this special issue.
Most volcanoes worldwide are not monitored in real-time; for those that are, patterns of pre-eruptive earthquakes coupled with conceptual models of magma ascent enable short-term forecasting of eruption onset. Basic event locations, characterization of background seismicity, and recognizing changes in earthquake types and energy release are most important to successful eruption forecasting. During renewed activity at Sinabung Volcano, Indonesia, this approach was used by the Center for Volcanology and Geological Hazards Mitigation (CVGHM) and the USGS Volcano Disaster Assistance Program to forecast eruption onset, identify changes in eruptive styles and raise or lower alert levels and extend or contract evacuation zones. After > 400 years of quiescence, Sinabung Volcano began erupting in August 2010. The volcano was unmonitored at the onset of phreatic eruptions in 2010, but soon had a monitoring network. Patterns of seismicity, primarily increasing swarms of high frequency volcano tectonic (VT) seismicity were used to forecast the continuing phreatic eruptions. Volcanic activity decreased in mid-September 2010, while additional intrusions accompanied by distal VT swarms continued through September 2013, when explosive phreatic eruptions recurred. Explosive eruptions were forecast based on increases in the real-time seismic amplitude measurement (RSAM) and VT seismicity. Seismicity changed markedly in late November and early December 2013 with the occurrence of deep seismicity and an overall transition from low frequency (LF) dominated irregular (in time and magnitude) to regular seismicity – a transition that accompanied the continued rise, eventual emergence and growth of a lava dome in the summit crater. In late December 2013 to early January 2014, the eruptive style changed as additional ascending magma deformed the summit and the dome grew beyond the capacity of the summit crater, resulting in the collapse of the summit lava dome (0.002 km³) on 11 January and producing the largest pyroclastic flow to date. The collapse was forecast by a several order of magnitude increase in RSAM, continued strong distal VT seismicity, an increase in proximal seismicity, and by large-scale observed deformation of the summit area. Similarly a second collapse was forecast based on increases in distal seismicity. We propose a process-based volcano seismicity model, that when applied to real volcanic data, helps to forecast eruption timing, size and changes in eruption style.
DOI: 10.17014/ijog.v8i1.155
Mount Sinabung, located in Karo Regency, North Sumatra Province, is a strato volcano having four active craters. Since its latest eruption about 1,200 year ago, a phreatic eruption occurred on August 27th, 2010. The eruption took place in Crater-I, which was initiated by a greyish white plume and then followed by black plumes as high as 2000 m above the crater. Altered rock fragments and ash were erupted during this event. The altered rocks show a development of argillic alterations which was formed in the hydrothermal system in depth. The alteration zone is formed along the northeast-southwest and northwest-southeast trend across the three craters. All of the craters are actively discharging solfataric gases, of which sulphur deposits are resulted, and they have been quarried by the local people. The age of the latest magmatic eruption was dated by 14C method from the charcoal sample found in the pyroclastic flow deposits near Bekerah Village.
In this research, remotely sensed data has been used to estimate the volume of pyroclastic deposits and analyze morphological changes that have resulted from the eruption of Sinabung volcano. Topographic information was obtained from these data and used for rapid mapping to assist in the emergency response. Topographic information and change analyses (pre- and syn- eruption) were conducted using digital elevation models (DEMs) for the period 2010–2015. Advanced spaceborne thermal emission and reflection radiometer (ASTER) global digital elevation model (GDEM) data from 2009 were used to generate the initial DEMs for the condition prior to the eruption of 2010. Satellite pour l’observation de la terre 6 (SPOT 6) stereo images acquired on 21 June 2015 and were used to make a DEM for that time. The results show that the estimated total volume of lava and pyroclastic deposits, produced during the period 2010 to mid-2015 is approximately 2.8 × 108 m3. This estimated volume of pyroclastic deposits can be used to predict the magnitude of future secondary lahar hazards, which are also related to the capacity of rivers in the area. Morphological changes are illustrated using cross-sectional analysis of the deposits, which are currently deposited to the east, southeast and south of the volcano. Such analyses can also help in forecasting the direction of the future flow hazards. The remote sensing and analysis methods used at Sinabung can also be applied at other volcanoes and to assess the threats of other types of hazards such as landslides and land subsidence.
DOI: 10.17014/ijog.v8i1.155Mount Sinabung, located in Karo Regency, North Sumatra Province, is a strato volcano having four active craters. Since its latest eruption about 1,200 year ago, a phreatic eruption occurred on August 27th, 2010. The eruption took place in Crater-I, which was initiated by a greyish white plume and then followed by black plumes as high as 2000 m above the crater. Altered rock fragments and ash were erupted during this event. The altered rocks show a development of argillic alterations which was formed in the hydrothermal system in depth. The alteration zone is formed along the northeast-southwest and northwest-southeast trend across the three craters. All of the craters are actively discharging solfataric gases, of which sulphur deposits are resulted, and they have been quarried by the local people. The age of the latest magmatic eruption was dated by 14C method from the charcoal sample found in the pyroclastic flow deposits near Bekerah Village.
In studies of volcanic tephra, it is usual that the overall volume of tephra is estimated ashfall volumes based on representative locations within the ashfall area. The precision of the volume estimation largely depends on the number of the locations. However, in the case of ongoing eruptions on island volcanoes, such as Sakurajima volcano, the observation locations are usually limited. We therefore have developed a practical method for estimating ashfall volume and distribution in such case. The method approximates the distribution of ashfall as ellipses, with the distribution area (A) and thickness or weight of deposit (T) determined by A=αT-1. The ellipse-approximated isopachs can be determined by using the direction of the ellipse axis and ashfall data at two points. In determing the
ellipse axis exactly, we usually need additional ashfall amounts from the other locations. We set 37 samplers around Sakurajima volcano, and retrieved the samplers 15 times, from April to December, 2008. Using the propose method, we are able to determine the volume of ash produced by small, continuous eruptions.
Dome-forming eruption is a frequent eruptive style and a major hazard on numerous volcanoes worldwide. Lava domes are built by slow extrusion of degassed, viscous magma and may be destroyed by gravitational collapse or explosion. The triggering of lava dome explosions is poorly understood: here we propose a new model of superficial lava-dome explosivity based upon a textural and geochemical study (vesicularity, microcrystallinity, cristobalite distribution, residual water contents, crystal transit times) of clasts produced by key eruptions. Superficial explosion of a growing lava dome may be promoted through porosity reduction caused by both vesicle flattening due to gas escape and syn-eruptive cristobalite precipitation. Both processes generate an impermeable and rigid carapace allowing overpressurisation of the inner parts of the lava dome by the rapid input of vesiculated magma batches. The relative thickness of the cristobalite-rich carapace is an inverse function of the external lava dome surface area. Explosive activity is thus more likely to occur at the onset of lava dome extrusion, in agreement with observations, as the likelihood of superficial lava dome explosions depends inversely on lava dome volume. This new result is of interest for the whole volcanological community and for risk management.
Investigation of the global eruptive records of particular types of volcanoes is a fundamental and valuable method of understanding what style of activity can be anticipated in the future, and can highlight what might be expected or unusual in particular settings. This paper investigates the relationship between major explosive activity (VEI ≥ 4) and lava dome-growth from 1000 AD-present and develops the DomeHaz database. DomeHaz contains information from 367 dome-forming episodes, including duration of dome-growth, duration of pauses in extrusion, extrusion rates, and the timing and magnitude of associated explosions. Large explosive activity, when associated with dome-growth, is more likely to occur before dome-growth rather than during, or at the end of, dome-forming eruptions. In most cases where large explosive activity has been associated with dome-growth, the eruptions occurred at andesitic volcanoes (the most common type of dome-forming volcano), but a greater percentage of dacitic and rhyolitic dome-growth episodes were associated with large explosions. Higher extrusion rates (> 10 m^3 s^(-1)) generally seem to be associated with large explosions; high extrusion rates may inhibit degassing or destabilize existing domes, leading to explosive decompression. Large explosions may, alternatively, be followed by dome-growth, which represents the clearing of residual magma from the conduit. Relationships extracted from the global record can be used to construct probability trees for new and ongoing dome-forming eruptions, or can be used in conjunction with other types of event trees to aid in forecasting volcanic hazards during a crisis, especially for volcanoes where data are sparse.
We use geologic field mapping and sampling, photogrammetrlc analysis of oblique aerial photographs, and digital elevation models to document the 2008-2009 eruptive sequence at Chaitén Volcano and to estimate volumes and effusion rates for the lava dome. We also present geochemical and petrologic data that contribute to understanding the source of the rhyolite and its unusually rapid effusion rates. The eruption consisted of five major phases: 1. An explosive phase (1-11 May 2008); 2. A transitional phase (11-31 May 2008) in which low-altitude tephra columns and simultaneous lava extrusion took place; 3. An exogenous lava flow phase (June-September 2008); 4. A spine extrusion and endogenous growth phase (October 2008-February 2009); and 5. A mainly endogenous growth phase that began after the collapse of a prominent Peléean spine on 19 February 2009 and continued until the end of the eruption (late 2009 or possibly earliest 2010). The 2008-2009 rhyolite lava dome has a total volume of approximately 0.8 km³. The effusion rate averaged 66 m³s-1 during the first two weeks and averaged 45 m³s-1 for the first four months of the eruption, during which 0.5 km³ of rhyolite lava was erupted. These are among the highest rates measured world-wide for historical eruptions of silicic lava. Chaitén's 2008-2009 lava is phenocryst-poor obsidian and microcrystalline rhyolite with 75.3±0.3% SiO2. The lava was erupted at relatively high temperature and is remarkably similar in composition and petrography to Chaitén's pre-historic rhyolite. The rhyolite's normative composition plots close to that of low pressure (100-200 MPa) minimum melts in the granite system, consistent with estimates of approximately 5 to 10 km source depths based on phase equilibria and geodetic studies. Calcic plagioclase, magnesian orthopyroxene and aluminous amphibole among the sparse phenocrysts suggest derivation of the rhyolite by melt extraction from a more mafic magmatic mush. High temperature and relatively low viscosity enabled rapid magma ascent and high effusion rates during the dome-forming phases of the 2008-2009 eruption.
We present precise geodetic and satellite observation-based estimations of the erupted volume and discharge rate of magma during the 2011 eruptions of Kirishima-Shinmoe-dake volcano, Japan. During these events, the type and intensity of eruption drastically changed within a week, with three major sub-Plinian eruptions on January 26 and 27, and a continuous lava extrusion from January 29 to 31. In response to each eruptive event, borehole-type tiltmeters detected deflation of a magma chamber caused by migration of magma to the surface. These measurements enabled us to estimate the geodetic volume change in the magma chamber caused by each eruptive event. Erupted volumes and discharge rates were constrained during lava extrusion using synthetic aperture radar satellite imaging of lava accumulation inside the summit crater. Combining the geodetic volume change and the volume of lava extrusion enabled the determination of the erupted volume and discharge rate during each sub-Plinian event. These precise estimates provide important information about magma storage conditions in magma chambers and eruption column dynamics, and indicate that the Shinmoe-dake eruptions occurred in a critical state between explosive and effusive eruption.
We present a model of effusive silicic volcanic eruptions which relates magma chamber and conduit physics to time-dependent data sets, including ground deformation and extrusion rate. The model involves a deflating chamber which supplies Newtonian magma through a cylindrical conduit. Solidification is approximated as occurring at fixed depth, producing a solid plug that slips along its margins with rate-dependent friction. Changes in tractions acting on the chamber and conduit walls are used to compute surface deformations. Given appropriate material properties and initial conditions, the model predicts the full evolution of an eruption, allowing us to examine the dependence of observables on initial chamber volume, overpressure, and volatile content. Employing multiple data sets in combination with a physics-based model allows for better constraints on these parameters than is possible using kinematic idealizations. Modeling posteruptive deformation provides an improved constraint on the rate of influx into the magma chamber from deeper sources. We compare numerical results to analytical approximations and to data from the 2004-2008 eruption of Mount St. Helens. For nominal parameters the balance between magma chamber pressure and frictional resistance of the solid plug controls the evolution of the eruption, with little contribution from the fluid magma below the idealized crystallization depth. While rate-dependent plug friction influences the time-dependent evolution of the eruption, it has no control on the final chamber pressure or extruded volume.
The M-w 7.8 October 2010 Mentawai, Indonesia, earthquake was a "tsunami earthquake," a rare type of earthquake that generates a tsunami much larger than expected based on the seismic magnitude. It produced a locally devastating tsunami, with runup commonly in excess of 6 m. We examine this event using a combination of high-rate GPS data, from instruments located on the nearby islands, and a tsunami field survey. The GPS displacement time series are deficient in high-frequency energy, and show small coseismic displacements (<22 cm horizontal and <4 cm subsidence). The field survey shows that maximum tsunami runup was >16 m. Our modeling results show that the combination of the small GPS displacements and large tsunami can only be explained by high fault slip at very shallow depths, far from the islands and close to the oceanic trench. Inelastic uplift of trench sediments likely contributed to the size of the tsunami. Recent results for the 2011 M-w 9.0 Tohoko-Oki earthquake have also shown shallow fault slip, but the results from our study, which involves a smaller earthquake, provide much stronger constraints on how shallow the rupture can be, with the majority of slip for the Mentawai earthquake occurring at depths of <6 km. This result challenges the conventional wisdom that the shallow tips of subduction megathrusts are aseismic, and therefore raises important questions both about the mechanical properties of the shallow fault zone and the potential seismic and tsunami hazard of this shallow region.
In 1997 Soufriére Hills Volcano on Montserrat produced 88 Vulcanian explosions: 13 between 4 and 12 August and 75 between 22 September and 21 October. Each episode was preceded by a large dome collapse that decompressed the conduit and led to the conditions for explosive fragmentation. The explosions, which occurred at intervals of 2.5 to 63 hours, with a mean of 10 hours, were transient events, with an initial high-intensity phase lasting a few tens of seconds and a lower-intensity, waning phase lasting 1 to 3 hours. In all but one explosion, fountain collapse during the first 10-20 seconds generated pyroclastic surges that swept out to 1-2 km before lofting, as well as high-concentration pumiceous pyroclastic flows that travelled up to 6 km down all major drainages around the dome. Buoyant plumes ascended 3-15 km into the atmosphere, where they spread out as umbrella clouds. Most umbrella clouds were blown to the north or NW by high-level (8-18 km) winds, whereas the lower, waning plumes were dispersed to the west or NW by low-level (<5 km) winds. Exit velocities measured from videos ranged from 40 to 140 ms-1 and ballistic blocks were thrown as far as 1.7 km from the dome. Each explosion discharged on average 3 x 105m3 of magma, about one-third forming fallout and two-thirds forming pyroclastic flows and surges, and emptied the conduit to a depth of 0.5-2 km or more. Two overlapping components were distinguished in the explosion seismic signals: a low-frequency (c. 1 Hz) one due to the explosion itself, and a high-frequency (2 Hz) one due to fountain collapse, ballistic impact and pyroclastic flow. In many explosions a delay between the explosion onset and start of the pyroclastic flow signal (typically 10-20 seconds) recorded the time necessary for ballistics and the collapsing fountain to hit the ground. The explosions in August were accompanied by cyclic patterns of seismicity and edifice deformation due to repeated pressurization of the upper conduit. The angular, tabular forms of many fallout pumices show that they preserve vesicularities and shapes acquired upon fragmentation, and suggest that the explosions were driven by brittle fragmentation of overpressured magmatic foam with at least 55 vol% bubbles present in the upper conduit prior to each event.
Between 3 January 1996 and 1 December 1998 at Soufrière Hills Volcano, Montserrat, there were 27150 seismic signals attributable to rockfalls and pyroclastic flows. Large (1-4 x 106m3) and major (4 x 106m3) dome collapses began to occur after the extrusion rate reached 2 m3 s-1 and the lava dome exceeded 30 x 106m3 in volume. Large to major collapses occurred on 26 occasions and were usually associated with periods of elevated extrusion rate (6 13 m3 s-1), intense hybrid earthquake swarms and/or inflation-deflation cycles of crater-rim ground deformation. During these cycles, gas-rich pulses of magma, 140 000 320 000 m3 in volume, were intruded into the dome and, soon thereafter, dome collapses from the headwalls of shear lobes were generated. Large dome collapses also occurred after 10 March 1998, when magma extrusion ceased, but these had no seismic precursors. These events represent structural failures from over steepened canyon-like walls and were followed by intense degassing, suggesting that gas pressure build-up within the relict dome may have played some role. Rockfall counts and durations established from seismic data show variations that correlate with extrusion rate. Using pyroclastic flow runout and rockfall duration data as proxies for event magnitude, power law relationships between frequency (total number of events) and magnitude have been found. Seismic signals associated with rockfalls and pyroclastic flows commonly comprise both high-frequency and long-period components. Intense degassing from the dome is interpreted as the source for the long-period component. These results indicate that rockfalls and pyroclastic flows generated by dome collapse at Montserrat are not simply the result of passive dome failure, but are intimately related to discharge of pressurized gas and pulses of magma extrusion. Pyroclastic flows were usually sourced from lobe headwalls, where lava was hot and gas-rich and where fragmentation of the micro vesicular andesite lava occurred more readily.
Eruption of the Soufrière Hills Volcano on Montserrat allowed the detailed documentation of a Pélean dome-forming eruption. Dome growth between November 1995 and March 1998 produced over 0.3 km3 of crystal-rich andesitic lava. Discharge rates gradually accelerated from >1 m3 s-1 during the first few months to >5 m3 s-1 in the later stages. Early dome growth (November 1995 to September 1996) was dominated by the diffuse extrusion of large spines and mounds of blocky lava. A major dome collapse (17 September 1996) culminated in a magmatic explosive eruption, which unroofed the main conduit. Subsequent dome growth was dominated by the extrusion of broad lobes, here termed shear lobes. These lobes developed through a combination of exogenous and endogenous growth over many weeks, with movement accommodated along curved shear faults within the dome interior. Growth cycles were recognized, with each cycle initiated by the slow emplacement of a large shear lobe, constructing a steep flank on one sector of the dome. A growth spurt, heralded by the onset of intense hybrid seismicity, pushed the lobe rapidly out, triggering dome collapse. Extrusion of another lobe within the resulting collapse scar reconstructed the steep dome flanks prior to the next cycle.
Single-grain laser-fusion 40Ar/39Ar analyses of individual sanidine phenocrysts from the two youngest Toba (Indonesia) tuffs yield mean ages of 73 ±4 and 501 ±5 ka. In addition, glass shards from Toba ash deposited in Malaysia were dated at 68 ±7 ka by the isothermal plateau fission-track technique. These new determinations, in conjunction with previous ages for the two oldest tuffs at Toba, establish the chronology of four eruptive events from the Toba caldera complex over the past 1.2 m.y. Ash-flow tuffs were erupted from the complex every 0.34 to 0.43 m.y., culminating with the enormous (2500-3000 km3) Youngest Toba tuff eruption, caldera formation, and subsequent resurgence of Samosir Island. Timing of this last eruption at Toba is coincident with the early Wisconsin glacial advance. The high-precision 40Ar/39Ar age for an eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exception-ally large explosive eruptions.
During the eruption of the Soufrière Hills volcano, Montserrat (1995-99), and several other dome eruptions, shallow seismicity, short-lived explosive eruptions and ground deformation patterns indicating large overpressures (of several megapascals) in the uppermost few hundred metres of the volcanic conduit have been observed. These phenomena can be explained by the nonlinear effects of crystallization and gas loss by permeable flow, which are here incorporated into a numerical model of conduit flow and lava dome extrusion. Crystallization can introduce strong feedback mechanisms which greatly amplify the effect on extrusion rates of small changes of chamber pressure, conduit dimensions or magma viscosity. When timescales for magma ascent are comparable to timescales for crystallization, there can be multiple steady solutions for fixed conditions. Such nonlinear dynamics can cause large changes in dome extrusion rate and pulsatory patterns of dome growth.
Effusive eruption of dacite magma (2.1×108 m3) during 1991–1995 formed a lava dome at the summit of Unzen Volcano, Japan. The effusion rate was highest at the beginning, 4.0×105 m3/day (4.6 m3/s), and decreased roughly with time, to almost zero before this pattern was repeated with a second pulse of magma supply. The whole-rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance; the more mafic, the more abundant the phenocrysts. The pattern of chemical variation with time shows some difference from that of the effusion rate. All phenocrysts in dacite (plagioclase, hornblende, biotite, quartz and magnetite) show evidence of disequilibrium with melt. Although a glomerophyric aggregation of phenocrysts suggests coexistence with each other, phenocrysts are isotopically heterogeneous from species to species. The calculated initial melt composition was rhyodacite, and was nearly constant throughout the activity. In contrast, the bulk phenocryst population is andesite. A model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments (or xenocrysts) by parental rhyodacite magma. It is suggested that, when effusion rate was high, less viscous crystal-poor magma exited from the reservoir. Groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate; the higher the effusion rate, the more evolved the compositions. Groundmass crystallinity increased with decreasing effusion rate; from 33% to 50%. Textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top. The Fe–Ti oxide temperature (880–780°C) was low when the crystallinity was high. Micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit. Porosity of dome lavas was lower at lower effusion rates. Collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low-frequency earthquakes. Phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction. When effusion waned, degassing and the resultant crystallization proceeded more completely, so that the magma became too viscous to flow in the conduit top and behaved as a plug, resulting in a temporary halt of effusion. In turn, groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling. The plug was scavenged when rising excess pressure overcame its effective strength. Then, the second pulse of magma supply began. Strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason.
Vulcanian eruptions are common at many volcanoes around the world. Vulcanian activity occurs as either isolated sequences of eruptions or as precursors to sustained explosive events and is interpreted as clearing of shallow plugs from volcanic conduits. Breadcrust bombs characteristic of Vulcanian eruptions represent samples of different parts of these plugs and preserve information that can be used to infer parameters of pre-eruption magma ascent. The morphology and preserved volatile contents of breadcrust bombs erupted in 1999 from Guagua Pichincha volcano, Ecuador, thus allow us to constrain the physical processes responsible for Vulcanian eruption sequences of this volcano. Morphologically, breadcrust bombs differ in the thickness of glassy surface rinds and in the orientation and density of crack networks. Thick rinds fracture to create deep, widely spaced cracks that form large rectangular domains of surface crust. In contrast, thin rinds form polygonal networks of closely spaced shallow cracks. Rind thickness, in turn, is inversely correlated with matrix glass water content in the rind. Assuming that all rinds cooled at the same rate, this correlation suggests increasing bubble nucleation delay times with decreasing pre-fragmentation water content of the melt. A critical bubble nucleation threshold of 0.4–0.9wt% water exists, below which bubble nucleation does not occur and resultant bombs are dense. At pre-fragmentation melt H2O contents of >∼0.9wt%, only glassy rinds are dense and bomb interiors vesiculate after fragmentation. For matrix glass H2O contents of ≥1.4wt%, rinds are thin and vesicular instead of thick and non-vesicular. A maximum measured H2O content of 3.1wt% establishes the maximum pressure (63MPa) and depth (2.5km) of magma that may have been tapped during a single eruptive event. More common H2O contents of ≤1.5wt% suggest that most eruptions involved evacuation of ≤1.5km of the conduit. As we expect that substantial overpressures existed in the conduit prior to eruption, these depth estimates based on magmastatic pressure are maxima. Moreover, the presence of measurable CO2 (≤17ppm) in quenched glass of highly degassed magma is inconsistent with simple models of either open- or closed-system degassing, and leads us instead to suggest re-equilibration of the melt with gas derived from a deeper magmatic source. Together, these observations suggest a model for the repeated Vulcanian eruptions that includes (1) evacuation of the shallow conduit during an individual eruption, (2) depressurization of magma remaining in the conduit accompanied by open-system degassing through permeable bubble networks, (3) rapid conduit re-filling, and (4) dome formation prior to the subsequent explosion. An important part of this process is densification of upper conduit magma to allow repressurization between explosions. At a critical overpressure, trapped pressurized gas fragments the nascent impermeable cap to repeat the process.
Following 198 years of dormancy, a small phreatic eruption started at the summit of Unzen Volcano (Mt. Fugen) in November 1990. A swarm of volcano-tectonic (VT) earthquakes had begun below the western flank of the volcano a year before this eruption, and isolated tremor occurred below the summit shortly before it. The focus of VT events had migrated eastward to the summit and became shallower. Following a period of phreatic activity, phreatomagmatic eruptions began in February 1991, became larger with time, and developed into a dacite dome eruption in May 1991 that lasted approximately 4 years. The emergence of the dome followed inflation, demagnetization and a swarm of high-frequency (HF) earthquakes in the crater area. After the dome appeared, activity of the VT earthquakes and the summit HF events was replaced largely by low-frequency (LF) earthquakes. Magma was discharged nearly continuously through the period of dome growth, and the rate decreased roughly with time. The lava dome grew in an unstable form on the shoulder of Mt. Fugen, with repeating partial collapses. The growth was exogenous when the lava effusion rate was high, and endogenous when low. A total of 13 lobes grew as a result of exogenous growth. Vigorous swarms of LF earthquakes occurred just prior to each lobe extrusion. Endogenous growth was accompanied by strong deformation of the crater floor and HF and LF earthquakes. By repeated exogenous and endogenous growth, a large dome was formed over the crater. Pyroclastic flows frequently descended to the northeast, east, and southeast, and their deposits extensively covered the eastern slope and flank of Mt. Fugen. Major pyroclastic flows took place when the lava effusion rate was high. Small vulcanian explosions were limited in the initial stage of dome growth. One of them occurred following collapse of the dome. The total volume of magma erupted was 2.1×108 m3 (dense-rock-equivalent); about a half of this volume remained as a lava dome at the summit (1.2 km long, 0.8 km wide and 230–540 m high). The eruption finished with extrusion of a spine at the endogenous dome top. Several monitoring results convinced us that the eruption had come to an end: the minimal levels of both seismicity and rockfalls, no discharge of magma, the minimal SO2 flux, and cessation of subsidence of the western flank of the volcano. The dome started slow deformation and cooling after the halt of magma effusion in February 1995.
High-resolution, digital topographic maps of the Mount St. Helens dome derived from aerial photographs are used here to make a quantitative assessment of the partitioning of magma into endogenous intrusion and exogenous lobes. The endogenous growth is found to be predictable, which shows that the cooling dome controls its own development independently of such deep-seated factors as magma overpressure and extrusion rate. The observed regular decrease in exogenous growth rate also allows volume prediction. Knowledge of the volume can be used to determine when an ongoing eruptive event should end. Finally, the observed transition from predominantly exogenous to predominantly endogenous growth reflects the increase in crust thickness, which in turn seems to depend on long repose periods rather than some fundamental change in the character of the dome.
This chapter deals with the morphology and rheology of terrestrial basaltic and silicic lava flows. Here we take a facies-based approach, describing each lava type in terms of its typical geometry, texture, structures, movement patterns and incorporation of alien objects. Using such an approach we distinguish the three classically defined types of lava: ‘a‘ā, pāhoehoe and block, as well as their sub-types. Inflation is a widespread phenomenon at both ‘a‘ā and pāhoehoe flows. Indeed there is no part of the extensive pāhoehoe flow fields of Kīlauea that is not inflated. We thus also classify and describe the main inflation features, as well as the components of the distribution systems that feed lava flows, namely channels and tubes. We finish by considering the control lava rheology, cooling and cooling-driven groundmass crystallisation has on flow dynamics. We base our review on the classical studies, classification schemes and definitions whose modern roots span the 1970s through 1980s, following formalisation of the ‘a‘ā, pāhoehoe and block lava distinction in 1953. These basic, fundamental schemes were based on careful observations and descriptions which still hold today. It is our opinion that modern volcanology now needs to focus on improved measurement of the emplacement dynamics and mechanics associated with each flow type.
Nine dominantly nonexplosive episodes of dome growth at Mount St. Helens during 1981-83 added about 40 x 106 m3 of dacitic lava to the active composite dome in the volcano's 1980 crater. Endogenous and exogenous growth, the latter mostly in the form of stubby lava flows that accumulated on the dome, combined to build an edifice 880 m long, 830 m wide, and 224 m high by December 1983; the total volume (1980-1983) was about 44 x 106 m3 . Every 1-5 months during 1981-82, periods of increasing seismicity and ground deformation lasting 1-3 weeks culminated in extrusions lasting a few days. Endogenous growth became increasingly important during this interval, and in February 1983, the style of activity changed from episodic to essentially continuous endogenous and exogenous growth. In March 1982 and February 1983, extrusions were preceded by lateral explosions that triggered snow avalanches from the crater wall and mudflows down the volcano's north flank. Collapse of part of the north face of the dome during rapid endogenous growth in April 1982 produced a hot rock avalanche and small mudflow. Ejections of gas and comminuted dome rock from the top of the dome were frequent throughout 1981-83, and averaged several per day in 1983. As the dome continues to grow, its capacity to accommodate newly supplied magma without rupturing, and hence the ratio of endogenous to exogenous growth, will probably continue to increase. Endogenous growth will be especially favored when magma supply is continuous and slow; extrusive activity will be favored if the short-term supply rate becomes significantly higher than the current rate of about 0.9 x 106 m3/month. Future explosive activity is possible and perhaps even likely in view of Mount St. Helens' history and the histories of similar contemporary domes at other volcanoes, but at this time we can foresee no change from the pattern of mostly nonexplosive dome growth that characterized activity during 1981-83.
The dacite dome at Mount St. Helens grew episodically between October 18, 1980, and October 22, 1986, chiefly by extrusion of thick flows but also by endogenous growth resulting from intrusion into its molten core. Typical growth episodes lasted several days and produced volumes of 1.2–4.5×10⁶m³, but growth was continuous from February 1983 to February 1984. By the end of October 1986, the volume of the dome and its talus apron was about 74.1×10⁶ m³, and the volume of all erupted material (including tephra and debris removed from the dome by explosions and rockfalls) was about 77.1×10⁶m³.
During the ongoing eruption at Mount St. Helens, Washington, lava has extruded continuously at a rate that decreased from ∼7-9 m3/s in October 2004 to 1-2 m3/s by December 2005. The volume loss in the magma reservoir estimated from the geodetic data, 1.6 -2.7×107 m3, is only a few tens of percent of the 7.5×107 m3 volume that had erupted by the end of 2005. In this paper we use geodetic models to constrain the size and depth of the magma reservoir. We also ask whether the relations between extruded volume and geodetic deflation volume are consistent with drainage of a reservoir of compressible magma within a linearly elastic host rock. Finally, we compare the time histories of extrusion and geodetic deflation with idealized models of such a reservoir. Critical parameters include erupted volume Ve, dome density ?e, reservoir volume VC, initial reservoir overpressure p0ex, pressure drop during the eruption Δp, reservoir compressibility K?C = (1/VC)(dVC / dp), magma density ?PM, and magma compressibility ?κM = (1/pM)(d?M /dp). Seismic velocity and reservoir geometry suggest κC ≈ 2×10 -11 Pa-1, but mechanical considerations suggest κC = 7-15×10 -11 Pa-1. The geodetic data are best fit with an ellipsoidal source whose top is 5 ±1 km deep and whose base is ∼10 -20 + km deep. In the absence of recharge, the decrease in magma-reservoir volume dVC is theoretically related to the erupted volume Ve by Ve / dVC = (ρM /ρe)(1+ κM /κC). For κC = ∼7-15×10 -11 Pa-1 and ρM ≈ ρe, estimates of Ve and dVC suggest that ?κM = 1.4 -3.0×10 -10 Pa-1, corresponding to a magmatic gas content in the reservoir of vg = 0 to 1.8 percent by volume. If we assume that effusion rate is linearly related to reservoir pressure and that the recharge rate into the reservoir is constant, the effusion rate should decrease exponentially with time to a value that equals the recharge rate. Best-fit curves of this form suggest recharge rates of 1.2 -1.3 m3/s over the first 500 days of the eruption. The best-fit constants include the product VcPoex(κc+κm) , making it possible to constrain reservoir volume using values of κC and κM constrained from ratios of erupted volume to geodetic deflation volume. If, on the other hand, we assume a logarithmic pressure-effusion rate relation and a constant recharge rate, the dome volume-time curve should follow a modified logarithmic relation, with the total erupted volume at a given time proportional to V cΔP(κc+κm) Using κC = 7-15×10 -11 Pa-1, results from log and exponential curves suggest a reservoir volume of at least several cubic kilometers if Δp or p0ex is less than ∼30 MPa. Similar results are obtained from numerical calculations that consider temporal changes in (1) magma compressibility, (2) the weight of the lava dome suppressing effusion, and (3) recharge rate. These results are consistent with the notion that the reservoir volume is at least a few times larger than the largest Holocene eruption of Mount St. Helens (4 km3 dense-rock-equivalent + volume for the 3.4-ka Yn eruption). Both the exponential and logarithmic models predict a history of reservoir decompression that imperfectly matches displacement data at GPS station JRO1. Neither model, for example, predicts the rapid radially inward movement at JRO1 during the first month of the eruption. Such movement, followed by long-term linear deflation, suggests that erupted magma has been replaced in increasing proportions by recharge, but that the recharge rate remains somewhat less than the current (early 2006) effusion rate.
We report methods, based on geophysical observations and geological surveys, for the prediction of eruptions and the evaluation of the activity of 4 volcanoes in Indonesia. These are Semeru, Guntur, Kelud and Sinabung volcanoes. Minor increases in tilt were detected by borehole tiltmeters prior to eruptions at the Semeru volcano depending on the seismic amplitude of explosion earthquakes. The results show the possibility of prediction of the type and magnitude of eruption and the effectiveness of observation with a high signalto-noise ratio. The establishment of background data is important for evaluating volcanic activity in longterm prediction. Typical distributions of volcanic and local tectonic earthquakes were obtained around the Guntur volcano, where geodetic monitoring by continuous GPS observation is valuable. The cumulative volume of eruptive products is valuable for evaluating the potential for future eruption. The eruptive rate of the Kelud volcano is ca 2×10 6 m 3/y (dense rock equivalent), but the volume of the 2007 eruption was only 2×10 7 m 3, suggesting a still high potential for eruption. Based on geological surveys and dating, an eruption scenario is proposed for the activity of Mt. Sinabung, where phreatic eruptions occurred in 2010 after a historically long dormancy.
Eruptive activity at the Showa crater of the Sakurajima volcano has steadily increased since it resumed in June 2006, and 2718 vulcanian eruptions occurred during the period from 2008 to 2011. In this paper, we clarify the characteristics of vulcanian eruptions at the Showa crater based mainly on ground deformation. A long-term extension of the ground of the Aira caldera and Sakurajima, repeating quasi-annual cycles of minor inflation-deflation, were obtained by GPS, tilt and strain observations. The inflation event that started in October 2009 was the largest. Major pressure source was estimated to be located at a depth of 12 km beneath the Aira caldera for the inflation and a minor source was obtained a depth of 5 km at the northern flank of Kitadake in addition to a source beneath Minamidake which has been know by previous studies. The magma plumbing system is composed of a major magma reservoir at a depth of ≈ 10 km beneath the Aira caldera and additional magma reservoirs at depths of around 5 km beneath the summit area from the north flank of Kitadake to Minamidake. Strain changes which indicate inflation were detected prior to explosions and the inflation strain lasted mostly 1 h. The strain changes were caused by a shallow pressure source less than 1.5 km. The inflation occasionally continued for more than 7 h with an addition of inflation of a deep source (4 km), which corresponds to the magma reservoir beneath Minamidake. The conduit to the Showa crater may be branched from the magma reservoir beneath Minamidake or from the major conduit connected to it. When inflationary ground deformation progressed at a high rate, the eruptive activity reached a peak from December 2009 to March 2010. This suggests that the accumulation of magma beneath the central cones of the Sakurajima volcano progressed simultaneously to a discharge of magma. The simultaneous progress of the accumulation and discharge of magma and the frequent occurrence of small vulcanian eruptions may be related to the small open conduit.
An unusual feature of the 2004-6 eruptive activity of Mount St. Helens has been the continuous growth of successive spines that are mantled by thick fault gouge. Fault gouge formation requires, first, solidification of ascending magma within the conduit, then brittle fragmentation and cataclastic flow. We document these processes through field relations, hand samples, and thin-section textures. Field observations show that the gouge zone is typically 1-3 m thick and that it includes cataclasite and, locally, breccia in addition to unconsolidated (true) gouge. The gouge contains multiple slickenside sets oriented subparallel to each other and to the striation direction, as well as surface striations parallel to extrusion direction. Hand specimens show the cataclasite and gouge to be composed of a wide size range of broken dome and wall-rock fragments. This grain-size heterogeneity is even more pronounced in thin section, where individual samples contain fragments that span more than four orders of magnitude in size (from more than 10 to less than 10-3 mm). Textures preserved within the gouge zone provide evidence of different processes operating in time and space. Most individual fragments are holocrystalline, suggesting that crystallization of the ascending magma preceded gouge formation. Cataclasite samples preserve a wide range of clast sizes; pronounced rounding of many clasts indicates extensive abrasion during transport. Within the gouge, crystals and lava fragments adjacent to finely comminuted shear zones (slickensides) are shattered into small, angular fragments that are either preserved in place, with little disruption, or incorporated into shear trains, creating a well-developed foliation. Together, evidence of initial grain shattering, followed by shear, grinding, and wear, suggests extensive transport distances (large strains). Textural transitions are often abrupt, indicating extreme shear localization during transport. Comparison of groundmass textures from dome lavas and fault gouge further suggests that brittle fracture was confined to the upper 400-500 m of the conduit. Observed magma extrusion (ascent) rates of ∼7 m/d (8×10 -5 m/s) permit several weeks for magma ascent from ∼1,000 m (where groundmass crystallization becomes important) to ∼500 m (where solidification nears completion). Brittle fracture, cataclastic flow, and shear localization (slickenside formation) probably dominated in the upper 500 m of the conduit. Comparison of eruptive conditions during the 2004-6 activity at Mount St. Helens with those of other spine-forming eruptions suggests that magma ascent rates of about 10-4 m/s or less allow sufficient degassing and crystallization within the conduit to form large volcanic spines of intermediate composition (andesite to dacite). Solidification deep within the conduit, in turn, requires transport of the solid plug over long distances (hundreds of meters); resultant large strains are responsible for extensive brittle breakage and development of thick gouge zones. Moreover, similarities between gouge textures and those of ash emitted by explosions from spine margins indicate that fault gouge is the origin for the ash. As the comminution and generation of ash-sized particles was clearly a multistep process, this observation suggests that fragmentation preceded, rather than accompanied, these explosions.
The physical condition of the 1 February, 2011, vulcanian explosion at Shinmoedake volcano, Japan, is estimated based on the size of impact craters created by ballistic ejecta, using a ballistic trajectory model and a scaling law for impact crater formation. The initial velocity, impact velocity and mass of ejecta were estimated at 240–290 m/s, 140 ± 20 m/s and 1–3 ton, respectively. The gas mass fraction at the source was calculated to be 0.04–0.1, using the initial velocity and a theoretical model of vulcanian explosion. This gas mass fraction is higher than the petrologically estimated value for pre-eruptive magma. Low-angle jets from the explosion and the estimated depth and size of a pressurized gas region suggest a shallow source inside the lava dome. The observation and results imply that segregation and accumulation of gas in a shallow conduit played a role in an increase of excess pressure immediately below the dome surface, prior to the vulcanian explosion.
We present a simple tool to evaluate the dominant dynamical regime of a lava flow and to estimate the order of magnitude of the main rheological parameter (viscosity or yield strength) controlling the length of the lava flow with time. We consider three dynamical regimes: a Newtonian viscous regime, a yield strength-dominated regime and a crust-dominated regime. For each of these regimes, we present a scaling analysis to derive relationships between front position and time, emitted volume, slope, width of the flow and rheological properties. We apply the resulting equations to published data from eruptions of 10 lava flows with a range of compositions and conditions. Comparisons of the fits of the models to the data reveal that short-lived, high effusion rate eruptions are dominated by the internal viscosity of the lava, whereas low effusion rate or long-lived eruptions are dominated by the yield strength in the growing crust. Finally, blocky lavas with very high initial crystal contents are dominated by the internal yield strength. The evolution of some flows can be approximated with only two viscosity values: an early low lava viscosity stage and a later higher viscosity stage. The increase in viscosity is attributed to the initial disequilibrium conditions of the magma at the vent with further degassing and cooling triggering crystallisation of the lava flow. For yield strength-dominated flows yield strength is always within an order of magnitude of 105 Pa. This study provides a practical framework for predicting the evolution of the length of lava flows from estimates of the crystal content of the erupting lava and its effusion rate.
An active volcano, Mt. Asama, located in the central part of the Honshu island of Japan, erupted on September 1, 2004. Since then, thick volcanic fumes have prevented monitoring of the topography on the summit crater floor by standard optical methods. To detect geomorphic changes of the volcano, GSI repeatedly carried out Airborne Synthetic Aperture Radar (AirSAR) measurements including interferometry between September 2004 and March 2005. The comparison of AirSAR results with a digital elevation model (DEM) by Airborne Laser Scanning measurements in October 2003 revealed that a pancake shape lava mound had formed on the crater floor, and the volume of the lava mound amounted to 2.1×106 m3. From this, AirSAR measurement is recognized as an effective method for monitoring the topographic change of active volcano craters, and for foreseeing crises.
The eruption on Montserrat during 1995-1999 was the most destructive in the Caribbean volcanic arc since that of Mont Pelee (Martinique) in 1902. It began on 18 July 1995 at the site of the most recent previous activity, on the flank of a c. 350-year-old lava dome within a sector-collapse scar. Phreatic explosivity occurred for 18 weeks before the onset of extrusion of an andesitic lava dome. Dome collapses produced pyroclastic flows that initially were confined by the sector-collapse scar. After 60 weeks of unsteadily accelerating dome growth and one episode of sub-Plinian explosivity, the dome eventually overtopped the confining scar. During 1997 almost two-thirds of the island was devastated following major dome collapses, two episodes of Vulcanian explosivity with fountain-collapse pyroclastic flows, and a flank failure with associated debris avalanche and explosive disruption of the lava dome. Nineteen people were killed directly by the volcanic activity and several were injured. From March 1998 until November 1999 there was a pause in magma ascent accompanied by reduced seismic activity, substantial degradation of the dome, and considerable degassing with venting of ash.The slow progress and long duration of the volcanic escalation, coupled with the small size of the island and the vulnerability of homes, key installations and infrastructure, resulted in a style of emergency management that was dominantly reactive. In order to minimize the disruption to life for those remaining on the island, following large-scale evacuations, scientists at the Montserrat Volcano Observatory had to anticipate hazards and their potential extents of impact with considerable precision. Based on frequent hazards assessments, a series of risk management zone maps was issued by administrative authorities to control access as the eruption escalated. These were used in conjunction with an alert-level system. The unpreparedness of the Montserrat authorities and the responsible UK government departments resulted in hardship, ill feeling and at times acrimony as the situation deteriorated and needs for aid mounted. Losses and stress could have been less if an existing hazards assessment had registered with appropriate authorities before the eruption.
A physical model is developed to determine factors which influence the dynamics of non-explosive lava eruptions. In the model, magma rises in a laminar regime from an overpressured chamber surrounded by elastic rock and erupts at the surface, where the accumulation of lava may alter the vent pressure. In a flow rate versus volume diagram, an eruption follows a path which is sensitive to relative changes in flow variables such as viscosity, conduit dimensions and thickness of lava over the vent. The path does not depend on the unknown elastic properties of the country rock or the chamber dimensions. With appropriate volcanological data, an observed flow rate versus volume path can be interpreted. The approach is applied to three well-documented eruptions. In each case the eruption rate was partially influenced by decreasing chamber pressure. The 1988-1990 eruption of Lonquimay (Chile) exhibits an early phase of conduit shrinkage which lasted about 100 days, probably due to magma solidification against country rock. The 1979 eruption of La Soufrière de Saint Vincent (West Indies) was initially affected by lava dome growth and later passed through a phase possibly caused by constriction of the conduit. The 1943-1952 eruption of Paricutín (Mexico) was affected by changes of lava level in the cinder cone and magma properties. In these three eruptions, the pre-eruptive chamber overpressures were similar (10-20 MPa) even though the erupted volumes differed by as much as two orders of magnitude.
Eruptions of intermediate magma may be explosive or effusive. The development of open system degassing has been proposed as a pre-requisite for effusion of intermediate magma, however processes leading to open system degassing are poorly understood. To better understand degassing processes during lava dome extrusion we report high temporal-resolution SO2 emission rate measurements collected with an ultra violet imaging camera at Santiaguito, Guatemala. Santiaguito is an ideal case study as the dome lava is compositionally very similar to products of the 1902 Plinian eruption of the parental Santa María volcano. We find that degassing is weak (0.4–1 kg s− 1) but continuous, and explosions are associated with small increases in emission rates (up to 2–3 kg s− 1). Continuous repose degassing occurs through a shallow cap rock which likely represents a proto-crust on the block lava flow which is extruded from the same vent. The continual permeability of the upper conduit argues against a mechanism of explosion triggering in which gas pressure builds beneath a viscous cap rock or plug. Rather, we consider degassing data better consistent with a model of shear-fracturing at the conduit margins. Using field constraints, we model the viscosity of Santiaguito magma as a function of depth and show that conditions for shear-fracturing are met from 150–600 m to the surface. This is in line with independent estimates of explosion initiation depth. We show that repose timescales are orders of magnitude longer than the timescale for shear fracture, and suggest that explosions are triggered when a continuous network of smaller-scale fractures develops, at which point decompression occurs and an explosion is triggered. Fracture healing occurs by viscous relaxation however near to the surface where viscosity is highest, an unconsolidated gouge layer may develop. Our model implies that the observed explosions are a by-product of extrusion. Shear-fracturing can drive open system degassing of crystal rich intermediate magma at shallow levels in the conduit, as high magma viscosity is able to overcome the low strain rates associated with slow ascent of magma.Research Highlights► Santiaguito explosions are triggered by shear fracturing at the conduit margins. ► Conditions for shear fracturing met over top 150–600 m of conduit. ► Eruptions are triggered by connectivity of a network of small shear fractures. ► Shear fracturing can drive open system degassing of crystal-rich intermediate magma.
The 1980–1986 eruption of Mount St. Helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale. Groundmass plagioclase size measurements are coupled with measured changes in matrix glass, plagioclase and Fe–Ti oxide chemistry to document increasing groundmass crystallinity, and thus to better constrain proposed physical models of the post-May 18, 1980 magmatic reservoir. Measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth (approximately 10-9 cm/s) of groundmass plagioclase occurred immediately subsequent to May 18. Relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10-11 cm/s; plagioclase growth rates then decreased to -11 cm/s through 1986. Changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst-rim chemistry, although the matrix glass composition appears to have remained approximately constant from 1981–1986 after a rapid compositional change from May 18 until the end of 1980. Plagioclase microphenocrysts show increasingly more complex zoning patterns with time; microphenocryst-core compositions are commonly positively correlated with crystal size. Both of these observations indicate continuous groundmass plagioclase growth through 1986. Magmatic temperatures estimated from Fe–Ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930C and at log fO2 of -10.8; by 1985–1986 oxide temperatures decreased to 870C. Chemical and textural changes can be explained by: (1) rapid degassing and crystallization in response to the intrusion of magma into a shallow (
The lava dome collapse of 12–13 July 2003 was the largest of the Soufrière Hills Volcano eruption thus far (1995–2005) and the largest recorded in historical times from any volcano; 210 million m3 of dome material collapsed over 18 h and formed large pyroclastic flows, which reached the sea. The evolution of the collapse can be interpreted with reference to the complex structure of the lava dome, which comprised discrete spines and shear lobes and an apron of talus. Progressive slumping of talus for 10 h at the beginning of the collapse generated low-volume pyroclastic flows. It undermined the massive part of the lava dome and eventually prompted catastrophic failure. From 02:00 to 04:40 13 July 2003 large pyroclastic flows were generated; these reached their largest magnitude at 03:35, when the volume flux of material lost from the lava dome probably approached 16 million m3 over two minutes. The high flux of pyroclastic flows into the sea caused a tsunami and a hydrovolcanic explosion with an associated pyroclastic surge, which flowed inland. A vulcanian explosion occurred during or immediately after the largest pyroclastic flows at 03:35 13 July and four further explosions occurred at progressively longer intervals during 13–15 July 2003. The dome collapse lasted approximately 18 h, but 170 of the total 210 million m3 was removed in only 2.6 h during the most intense stage of the collapse.
The study of active vent dynamics is hindered by the difficulty of directly observing features and processes during eruptive periods. Here, we describe some recent observations of the summit dome activity of Santiaguito volcano, Guatemala, from the vantage point of its parent, Santa Marı́a. We have taken 12 h of digital video of activity over a 3-year period, which includes 28 eruptions and numerous smaller gas exhalations. Santiaguito persistently extrudes a dacitic lava flow, and produces strombolian eruptions on the order of every 0.5 to 2 h; we have documented many of these eruptions as emitting from a ring-shaped set of fractures in the dome surface. The ring has apparently grown from 70 m diameter in 2002 to 120 m in 2004, which could reflect an increasing conduit opening. Eruptions typically consist of 30–60 s of vigorous emissions; measurements of emission exit velocities have ranged from 5 to 30 m/s. The observed ash bursts, correlated with measured extrusion rates, suggest an incremental plug flow through the conduit. Bubble generation and shearing at the conduit boundaries produce the ring-shaped ash and gas pulses. Continued field studies from this unique observation site may help relate summit emission characteristics to conduit geometry and eruption processes.
Report on Sinabung (Indonesia)
- Global Volcanism Program
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Catastrophic lava dome failure at Soufrière Hills Volcano
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Geologic map of Sinabung Volcano, North Sumatra Province (1:25.000). Center for Volcanology and Geological Hazard Mitigation
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phreatic eruption of Mount Sinabung
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Volume estimation of 1991-1992 eruption of Unzen Volcano, and initiation mechanisms of pyroclastic flows on
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