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![(a) Map of southeast Iceland showing central volcanoes and associated fissure swarms [modified after Gudmundsson and H€ ognad ottir, 2007]. The Holuhraun eruption site lies within the Askja fissure swarm, but seismicity prior to the eruption traced a propagating dyke from B arðarbunga volcano. The seismic trace was first radial from the B arðarbunga caldera margin, but soon changed direction to align with the regional fissure trends. Dyke propagation was accompanied by caldera subsidence in the B arðarbunga caldera. (b) Map of eruption vents (dark triangles), sampling locations (yellow stars) and the extent of the Holuhraun lava field on the sampling date (12 September 2014; cream colored area), as well as the final extent of the Holuhraun lava field after the eruption ceased on the 27 February 2015 (85 km 2 , red area) [after G ıslason et al., 2015].](profile/Tobias-Mattsson/publication/304027348/figure/fig2/AS:877258164162564@1586166053896/a-Map-of-southeast-Iceland-showing-central-volcanoes-and-associated-fissure-swarms.png)
(a) Map of southeast Iceland showing central volcanoes and associated fissure swarms [modified after Gudmundsson and H€ ognad ottir, 2007]. The Holuhraun eruption site lies within the Askja fissure swarm, but seismicity prior to the eruption traced a propagating dyke from B arðarbunga volcano. The seismic trace was first radial from the B arðarbunga caldera margin, but soon changed direction to align with the regional fissure trends. Dyke propagation was accompanied by caldera subsidence in the B arðarbunga caldera. (b) Map of eruption vents (dark triangles), sampling locations (yellow stars) and the extent of the Holuhraun lava field on the sampling date (12 September 2014; cream colored area), as well as the final extent of the Holuhraun lava field after the eruption ceased on the 27 February 2015 (85 km 2 , red area) [after G ıslason et al., 2015].
Source publication
The 2014-15 Holuhraun eruption on Iceland was located within the Askja fissure swarm, but was accompanied by caldera subsidence in the Bárðarbunga central volcano 45 km to the southwest. Geophysical monitoring of the eruption identified a seismic swarm that migrated from Bárðarbunga to the Holuhraun eruption site over the course of 2 weeks. In orde...
Contexts in source publication
Context 1
... the case of the 2014-2015 Holuhraun eruption, seismicity and ground deformation indicated a connection between the Holuhraun eruption site and the neighboring B arðarbunga central volcano (Figure 1) [Riel et al., 2015;Sigmundsson et al., 2015], which would imply that the fissure eruption was laterally fed from a reservoir beneath B arðarbunga. In this paper, we aim to further assess the nature of this lateral connection through a first-order mineralogical and geochemical investigation. ...
Context 2
... 8 km, the seismic activity underwent a significant change, indicating dyke propagation toward the northeast. Approximately two weeks after this change in propagation direction, on the 29 August 2014, seismicity reached the Holuhraun site (45 km to the northeast of B arðarbunga) and lava outpouring commenced ( Figure 1) [Sig- mundsson et al., 2015]. The Holuhraun eruption began along a fissure that opened within the Askja fissure swarm in Iceland's North Volcanic Zone, and continued until the 27 February 2015 (Figure 1) [G ıslason et al., 2015;Sigmunds- son et al., 2015]. ...
Context 3
... two weeks after this change in propagation direction, on the 29 August 2014, seismicity reached the Holuhraun site (45 km to the northeast of B arðarbunga) and lava outpouring commenced ( Figure 1) [Sig- mundsson et al., 2015]. The Holuhraun eruption began along a fissure that opened within the Askja fissure swarm in Iceland's North Volcanic Zone, and continued until the 27 February 2015 (Figure 1) [G ıslason et al., 2015;Sigmunds- son et al., 2015]. The volume of erupted lava (1.6 6 0.3 km 3 ) marks the Holuhraun event as the most voluminous fissure eruption since the Laki fires of 1783-1784 [G ıslason et al., 2015]. ...
Context 4
... samples were collected on 20 September 2014 from the flow front at three sites. Sample set 1 was collected at 16.85748W, 64.87728N and sample set 2 at 16.83338W, 64.88338N (Figure 1b). These two sets of Gudmundsson and H€ ognad ottir, 2007]. ...
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Citations
... Water contents in matrix glasses and melt inclusions have been measured by FTIR and calculated, accounting for diffusive re-equilibration of melt inclusions, to be in the range of 0.13-0.7 wt.% Hartley et al., 2018). If water contents are constrained to a specific range, we can use the H 2 O- (Geiger et al., 2016) using Equation 25a (Putirka, 2008), plagioclasesaturated melt barometry (mean of both matrix glass and melt inclusion pressures estimated from both H 2 O-dependent and H 2 O-independent melt barometers), OPAM barometry , and clinopyroxene-liquid barometry (Neave et al., 2019) using iterative thermobarometric calculations of Equation 1 of Neave and Putirka (2017) and Equation 33 of Putirka (2008). dependent barometer differently by testing various water values as inputs. ...
Compositions of plagioclase‐melt pairs are commonly used to constrain temperatures (T), dissolved water contents (H2O) and pressures (P) of pre‐eruptive magma storage and transport. However, previous plagioclase‐based thermometers, hygrometers, and barometers can have significant errors, leading to imprecise reconstructions of conditions during plagioclase growth. Here, we explore whether we can refine existing plagioclase‐based hygrothermobarometers with either plagioclase‐melt or melt‐only chemistry (±T/H2O), calibrated using random forest machine learning on experimental petrology data (n = 1,152). We find that both the plagioclase‐melt and melt‐only models return similar cross‐validation root‐mean‐square errors (RMSEs), as the melt holds most of the P‐T‐H2O information rather than the plagioclase. T/H2O‐dependent melt models have test set RMSEs of 25°C, 0.70 wt.% and 76 MPa for temperature, H2O content and pressure, respectively, while T/H2O‐independent models have RMSEs of 38°C, 0.97 wt.% and 91 MPa. The melt thermometer and hygrometer are applicable to a wide range of plagioclase‐bearing melts at temperatures between 664 and 1355°C, and with H2O concentrations up to 11.2 wt.%, while the melt barometer is suitable for pressures of ≤500 MPa. An updated plagioclase‐melt equilibrium model has also been calibrated, allowing the equilibrium anorthite content to be predicted with an error of 5.8 mol%. The new P‐T‐H2O‐An models were applied to matrix glasses and melt inclusions from the 1980 Mount St Helens (USA) and 2014–2015 Holuhraun (Iceland) eruptions, corroborating previous independent estimates and observations. Models are available at https://github.com/kyra‐cutler/Plag‐saturated‐melt‐P‐T‐H2O‐An, enabling assessment of plagioclase‐melt equilibrium and characterization of last‐equilibrated P‐T‐H2O conditions of plagioclase‐saturated magmas.
... Holuhraun, similarly to the Fimmvörðuháls eruption, had a relatively deep source at 17-18 km (Geiger et al. 2016), with the most primitive melt inclusions indicating equilibration pressures equivalent to around 25 km depth ). However, the magma was likely stored in the mid-crust (6-7 km) prior to eruption , which would have allowed the gases to modify from equilibrium with the deep source magma towards equilibrium at this shallower level. ...
The eruptions of Eyjafjallajökull volcano in 2010 (including its initial effusive phase at Fimmvörðuháls and its later explosive phase from the central volcano) and Bárðarbunga volcano in 2014–2015 (at Holuhraun) were widely reported. Here, we report on complementary, interdisciplinary observations made of the eruptive gases and lavas that shed light on the processes and atmospheric impacts of the eruptions, and afford an intercomparison of contrasting eruptive styles and hazards. We find that (i) consistent with other authors, there are substantial differences in the gas composition between the eruptions; namely that the deeper stored Eyjafjallajökull magmas led to greater enrichment in Cl relative to S; (ii) lava field SO2 degassing was measured to be 5–20% of the total emissions during Holuhraun, and the lava emissions were enriched in Cl at both fissure eruptions—particularly Fimmvörðuháls; and (iii) BrO is produced in Icelandic plumes in spite of the low UV levels.
Supplementary Information
The online version contains supplementary material available at 10.1007/s11069-023-06114-7.
... Previous studies investigating Icelandic volcanic systems using these barometers have established multi-tiered magmatic plumbing systems (Budd et al., 2016;Burney et al., 2020;Geiger et al., 2016;Hartley et al., 2018;Kahl et al., 2021;Keiding & Sigmarsson, 2012;Kelley & Barton, 2008;Neave et al., 2013;Schiellerup, 1995). Barometry has been used to argue for a model where the mid-lower crust is an important site for magma storage, mixing mantle melts, and magma evolution (Maclennan, McKenzie, Grönvold, et al., 2003;Maclennan, McKenzie, Hilton, et al., 2003;Neave & Putirka, 2017;Neave et al., 2013;Nikkola et al., 2019;Winpenny & Maclennan, 2011). ...
The compositions of volcanic materials are sensitive to physical conditions in the underlying magmatic system. When basaltic melts are saturated in olivine‐plagioclase‐augite prior to eruption, their compositions can be used to estimate the pressure at which they last equilibrated. We developed PyOPAM, an open‐source tool that runs in Python, and use this refreshed liquid‐barometer to investigate the relationship between final depths of magma storage and magma flux. We first tested PyOPAM using 312 experimental glasses compiled from literature and found that the 1σ uncertainty is 1.13 kbar (±3 km). PyOPAM was then applied to a data set of 13,400 analyses from Iceland, where suspected controls on magma flux are well constrained. Of these, 3807 analyses return robust pressure estimates, constraining final pre‐eruptive magma storage depths for 23 of the 30 Icelandic volcanic systems. Our results indicate that magma storage pressures on Iceland are linked to melt‐flux from the mantle. This finding is consistent with previous models linking storage depths and spreading rates on the global mid‐ocean ridge system. In addition, we provide clear evidence that the magma flux, rather than spreading rate alone, is the key control on the distribution of melt at spreading centers. Increased melt flux is associated with shoaling of pre‐eruptive storage depths, indicating that mantle melt fluxes dictate the long‐term stabilization of extensive magmatic storage regions at depths shallower than 10 km. Quantitative relationships between mantle melt flux and storage depths can be used to test computational models of transcrustal magmatic systems.
... In comparison, other flows from the Askja Volcanic system from the twentieth century and the 2015 Holuhraun eruption have lower Fe/Mg ratios of 1.0-1.3 (Hartley and Thordarson 2013;Geiger et al. 2016). Nýjahraun, in the North Volcanic Zone, has a recorded maximum Fe/Mg of 2.0 (Hartley and Thordarson 2013) (Additional file 5: Fig. S1). ...
We examine the morphology and chemistry of the Vikrahraun basaltic eruption emplaced at Askja Volcano, Iceland, from Oct. 26–Dec. 17, 1961. The eruption had three eruptive events, initiating with aʻa and followed by alternating aʻa and pahoehoe lava flow emplacement. We determine that while the eruption is chemically homogenous (Fe/Mg = 1.9–2.2, 47–52 wt.% SiO2), it demonstrates transitions from high to low viscosity lava flow morphologies. Aʻa flows have a total crystallinity (phenocryst and microlite abundance by area) ranging from 85–100%, which increases by 1% per km from the vents, while pahoehoe flows range from 55–86% and increase at a higher rate of 5% per km. Vesicularity systematically decreases with distance from the vent by 3% per km. Pahoehoe and vent samples have calculated temperatures 50 °C higher than aʻa samples, which we interpret to be due to the difference between tube fed pahoehoe and open channel aʻa lavas. The homogenous nature of the Vikrahraun lava makes it an excellent testbed to study the effects of observational scale and satellite resolution on the interpretation of surficial textures. Festoons, which are downslope pointed convex ridges from 1 to 5 m high and ~ 10 m long, are observed in event 2 aʻa lavas in satellite imagery and topographic profiles. Features of this scale have previously only been documented in terrestrial rhyolitic lavas, leading planetary researchers to infer that festooned lava flows on Venus and Mars may be silicic. The diverse morphologies and homogenous composition make Vikrahraun an important planetary analog, where morphological complexity is over-attributed to chemical variation and suggests the need to re-evaluation planetary lava flow interpretations.
Graphical Abstract
... The sample contains numerous microglomerocrysts of anhedral clinopyroxene, plagioclase, minor subhedral olivine and skeletal Fe-Ti oxides, and small vesicles (0.2-0.5 mm) set in a microlithic groundmass consisting of the same previous mineral assemblage. The identified textural and mineralogical features is similar to that of typical Icelandic tholeiites associated with the Bárðarbunga volcanic system as observed inGeiger et al. (2016)Kolzenburg et al. (2017), andHalldórsson et al. (2018). ...
Temperature is a key parameter controlling the rheology of lava flows. However, the unpredictable hazard of eruptions prevents direct measurements of hot volcanic bodies. Thus, the temperature of lava products is mostly retrieved by remote sensing techniques (ground- or satellite-based detectors) build on measuring infrared (IR) radiance. These well-established techniques are however subjected to important errors related to the poor knowledge of one of the most critical parameters, namely spectral emissivity. The aim of our study is to fill this gap by exploring the emissivity–temperature relationship of three different basalts. We performed in situ emissivity measurements at high temperatures (up to 1800 K) over a wide spectral range (350–8000 cm⁻¹; 1.25–28.6 μm), using a non-contact IR apparatus. To unravel the complex radiative behavior of the samples with temperature, structural, chemical and textural analyses using Raman spectroscopy, XRD, DSC, SEM, EMPA and TEM were systematically performed. Our results show that spectral emissivity varies with temperature, wavenumber, and the sample degree of polymerization combined with total FeO content. Spectral emissivity is greatly affected by the crystallization of Fe-Mg-rich crystals at the micro-scale. Consequently, this study proves that spectral emissivity cannot be assumed constant for a single magmatic composition. Finally, our laboratory-measured values of spectral emissivity allowed refining the remote sensing temperature of the 2014–2015 Holuhraun eruption (Bárðarbunga, volcano) by 50 K in average. These new insights will ultimately reduce uncertainties in temperature estimates based on IR technology, information that are crucial to improve hazard assessment in volcanic crisis.
... Additionally, we apply the cpx only ERT barometer to the analyses reported by Caricchi et al. (2020) and Geiger et al. (2016) for the 2014-2015 Holuhraun eruption (Barðarbunga volcanic system; Figure 11a). Observing Figure 11, it emerges that (1) clinopyroxenes registered crystallization pressures mostly in the range 1-6 kbar; (2) combining all pressure estimates (Figure 11b), the pressure range with the highest probability (i.e., 74%) is 1-3 kbar; and (3) the average of all pressure estimations for the Barðarbunga volcanic system by the ERT barometer is 2.3 ± 1.1 kbar. ...
... Definitely, cutting-edge polyhedral views of volcanic processes can be only conceived through merging of manifold disciplines (e.g., Fernández et al., 2017). Encouraging researches with this rationale have been already launched at some volcanoes on Earth, especially where products of the eruptive activity can be contextualized within the framework of data coming from high-quality monitoring networks (e.g., Carey et al., 2015;Cassidy et al., 2019;Geiger et al., 2016;Hibert et al., 2015;Magee et al., 2018;Martí et al., 2013). ...
The 24–27 December 2018 flank eruption at Mount Etna (Southern Italy) has been investigated through a multidisciplinary approach in which olivine chemical zoning and diffusion chronometry data were integrated with models inferred by GNSS (Global Navigation Satellite System) measurements. Inspection of the olivine chemical zoning from core to rim allowed the identification of some dominant ways of transfer and interaction between magmas pertaining to different magmatic environments. Most of crystal cores are representative of crystallization at pressure of 290–230 and 160–120 MPa. Olivine rims suggest re‐equilibration at shallow pressure (≤30 MPa). Geodetic‐based models indicate pressurization of near‐vertical prolate spheroidal sources centered at ∼7.2 km below sea level (bsl) between 9 June 2017 and 28 June 2018 and later at ∼5.1 km bsl between 28 June 2018 and the eruption onset. Geodetic data also highlight a change in the inflation rate since late June 2018 and later around November 2018, which has been here related to both replenishment phases and magma uprising across the plumbing system. Timescales of magma replenishment are in agreement with prolonged recharge from deep levels upward to shallow environments started about 6 months before the eruption, with further replenishment involving the upper magmatic environments just 3–16 days before the eruption. At present, the eruptive activity at the volcano is primarily controlled by pressure imbalances affecting extensive sections of the plumbing system, with possibility to develop persistent eruptive activity at the summit versus flank eruptions depending on fortuitous interruptions of the steady magma recharge/discharge rate at shallow levels.
... Additionally, we apply the cpx only ERT barometer to the analyses reported by Caricchi et al. (2020) and Geiger et al. (2016) for the 2014-2015 Holuhraun eruption (Barðarbunga volcanic system; Figure 11a). Observing Figure 11, it emerges that (1) clinopyroxenes registered crystallization pressures mostly in the range 1-6 kbar; (2) combining all pressure estimates (Figure 11b), the pressure range with the highest probability (i.e., 74%) is 1-3 kbar; and (3) the average of all pressure estimations for the Barðarbunga volcanic system by the ERT barometer is 2.3 ± 1.1 kbar. ...
We introduce a new approach, based on machine learning, to estimate pre‐eruptive temperatures and storage depths using clinopyroxene‐melt pairs and clinopyroxene‐only chemistry. The model is calibrated for magmas of a wide compositional range, it complements existing models, and it can be applied independently of tectonic setting. Additionally, it allows the identification of the main chemical exchange mechanisms occurring in response to pressure and temperature variations on the base of experimental data without a priori assumptions. After the validation process, performances are assessed with test data never used during the training phase. We estimate the uncertainty using the root‐mean‐square error (RMSE) and the coefficient of determination (R²). The application of the best performing algorithm (trained in the range 0–40 kbar and 952–1882 K) to clinopyroxene‐melt pairs from primitive to extremely differentiated magmas of both subalkaline and alkaline systems returns a RMSE on the order of 2.6 kbar and 40 K for pressure and temperature, respectively. We additionally present a melt‐ and temperature‐independent clinopyroxene barometer in the range 0–40 kbar, characterized by a RMSE of the order of 3 kbar. Tested for tholeiitic compositions in the range 0–10 kbar, the melt‐ and temperature‐independent clinopyroxene barometer has a RMSE of 1.7 kbar. We finally apply the proposed approach to clinopyroxenes from Iceland, providing new, independent, insights about pre‐eruptive storage depths of Icelandic volcanoes. The general applicability of this model will promote the comparison between the architecture of plumbing systems across tectonic settings and facilitate the comparison between petrologic and geophysical studies.
... As Iceland has been subject to several landscape-shaping volcanic eruptions during the time span that is covered by remote sensing data, we included aerial imagery dating back to the 1950s provided by the National Land Survey of Iceland in our preliminary remote sensing. Some examples of young volcanic eruptions include the Krafla fires (Hjartardóttir et al., 2012;Tryggvason, 1986) with nine eruptions between 1975(Thordarson and Larsen, 2007, the 1991 and 2000 eruptions of Hekla ( Gudmundsson et al., 1992;Rose et al., 2003) or the Holuhraun eruption during 2014-2015, the largest Icelandic eruption in more than two centuries (Geiger et al., 2016;Müller et al., 2017;Schmidt et al., 2015). Published mappings of faults and fissures of the NVZ ( Hjartardóttir et al., 2012) and the Reykjanes Peninsula ( Clifton and Kattenhorn, 2006) were further used to identify possible sites. ...
Normal faults in basalts develop massive dilatancy in the upper few hundred
meters below the Earth's surface with corresponding interactions with
groundwater and lava flow. These massively dilatant faults (MDFs) are
widespread in Iceland and the East African Rift, but the details of their
geometry are not well documented, despite their importance for fluid flow in
the subsurface, geohazard assessment and geothermal energy. We present a
large set of digital elevation models (DEMs) of the surface geometries of
MDFs with 5–15 cm resolution, acquired along the Icelandic rift zone using
unmanned aerial vehicles (UAVs). Our data present a representative set of
outcrops of MDFs in Iceland, formed in basaltic sequences linked to the mid-ocean ridge.
UAVs provide a much higher resolution than aerial/satellite imagery and a
much better overview than ground-based fieldwork, bridging the gap between
outcrop-scale observations and remote sensing. We acquired photosets of
overlapping images along about 20 km of MDFs and processed these using
photogrammetry to create high-resolution DEMs and orthorectified images. We
use this dataset to map the faults and their damage zones to measure length,
opening width and vertical offset of the faults and identify surface tilt in
the damage zones. Ground truthing of the data was done by field
observations.
Mapped vertical offsets show typical trends of normal fault growth by
segment coalescence. However, opening widths in map view show variations at
much higher frequency, caused by segmentation, collapsed relays and tilted
blocks. These effects commonly cause a higher-than-expected ratio of
vertical offset and opening width for a steep normal fault at depth.
Based on field observations and the relationships of opening width and
vertical offset, we define three endmember morphologies of MDFs: (i) dilatant
faults with opening width and vertical offset, (ii) tilted blocks (TBs) and
(iii) opening-mode (mode I) fissures. Field observation of normal faults
without visible opening invariably shows that these have an opening filled
with recent sediment. TB-dominated normal faults tend to have the largest
ratio of opening width and vertical offset. Fissures have opening widths up
to 15 m with throw below a 2 m threshold. Plotting opening width versus
vertical offset shows that there is a continuous transition between the
endmembers. We conclude that for these endmembers, the ratio between
opening width and vertical offset R can be reliably used to predict fault
structures at depth. However, fractures associated with MDFs belong to one
larger continuum and, consequently, where different endmembers coexist, a
clear identification of structures solely via the determination of R is
impossible.
... As Iceland has been subject to several landscape shaping volcanic eruptions during the time span that is covered by remote sensing data, we included aerial imagery dating back to the 1950s provided by the National Land Survey of Iceland in our preliminary remote sensing. Some examples of young volcanic eruptions include the Krafla Fires (Hjartardóttir et al., 2012;Tryggvason, 10 1986) with nine eruptions between 1975-1984(Thordarson and Larsen, 2007, the 2000 eruption of Hekla (Gudmundsson et al., 1992;Rose et al., 2003), or the Holuhraun eruption during 2014 -2015, the largest Icelandic eruption since more than two centuries (Geiger et al., 2016;Müller et al., 2017;Schmidt et al., 2015). Published mappings of faults and fissures of the NVZ (Hjartardóttir et al., 2012) and the Reykjanes Peninsula (Clifton and Kattenhorn, 2006) were further used to identify possible sites. ...
Normal faults in basalts develop massive dilatancy up to several tens of meters close to the Earth's surface and show corresponding interactions with groundwater and lava flow. These massively dilatant faults (MDF) are widespread in extensional settings like Iceland or the East African Rift, but their detailed geometry is not well understood, despite their importance for fluid flow in the subsurface, geohazards or geothermal energy. We present a large set of digital elevation models (DEM) of the surface geometries of MDF with 5–15 cm resolution, acquired along the Icelandic Rift zone using unmanned aerial vehicles (UAV). UAV provide a much higher resolution than aerial/satellite imagery and a much better overview than ground-based fieldwork, thus bridging the gap between outcrop scale and regional observations.
Our data present representative outcrops of MDF, formed in basaltic sequences linked to the Mid Ocean Ridge. We acquired photosets of overlapping images along about 20 km of MDF and processed these using photogrammetry to create high resolution DEMs and ortho-rectified images. We use this dataset to map the faults and their damage zones to measure length, opening width and vertical offset of the faults and identify surface tilt in the damage zones. Ground truthing of the data was done by field observations.
Mapped vertical offsets show typical trends of normal fault growth by segment coalescence. However, opening widths in map-view show variations at much higher frequency, caused by segmentation, collapsed relays and tilted blocks. These effects cause a commonly higher than expected ratio of vertical offset and opening width for a steep normal fault at depth.
Based on field observations and the relationships of opening width and vertical offset, we define three endmember morphologies of MDF: (i) dilatant faults with opening width and vertical offset, (ii) tilted blocks (TB), and (iii) opening mode (mode I) fissures. Field observation of normal faults without visible opening invariably shows that these have an opening filled by recent sediment. TB dominated normal faults tend to have a largest opening width with respect to vertical offsets. Fissures have opening widths up to 15 m with throw below a 2 m threshold. Plotting opening width versus vertical offset of the fractures shows that there is a continuous transition between the endmembers. We conclude that fractures associated with MDF belong to one larger continuum and the three endmembers are thus not necessarily indicative for fracture maturity.
