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(A) Illustration of the geometry of typical feeder dike, where w is the opening or thickness of the dike and L is the along strike length of the dike. Po is the overpressure of magma in the dike. E and ν is the Young’s modulus and Poisson’s ratio of the host rock, respectively. (B) Schematic cross section along an eruption fissure. Height of the feeder dike (h) is the depth to the magma chamber. Fissure eruption starts when a feeder dike intersects the ground surface. The fissure eruption will propagate in both directions as the growth of feeder dike progresses. When the feeder dike changes direction horizontally, the eruption fissure can propagate laterally.
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Buoyant magmas abundant in exsolved volatiles (bubbles) drive the rapid upward-propagation of feeder dikes from magma chambers. The consequence of a feeder dike reaching the surface can result in an explosive volcanic eruption depending, partly, on the retention of volatiles. Therefore, timely detection of the vesicularity and overpressure of the m...
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Citations
... The analysis of textures provides insights into the evolutionary history of the conduit and the magmatic processes that occurred during its formation. We interpret the outcrop as a fossilised volcanic conduit that has a fan-like shape suggesting that magma was approaching the surface (Geshi et al., 2020;Unwin et al., 2023), which is also supported by the low total water content (<1%) of all the conduit domains, indicating low confining pressure (Gonnermann and Manga, 2013). We consider the yellow domain as a product of primary fragmentation processes within the shallow conduit. ...
... The exposed conduit studied on the SW flank of Nevados de Chillan is at least an order of magnitude thinner, at around 1 m wide, than the other three examples discussed here. However, dykes of similar thickness (between 1 and 10 m wide) have been shown to commonly feed flank eruptions (Geshi and Neri, 2014;Browning et al., 2015;Ruz et al., 2020;Geshi et al., 2020). As such, the similarity of textural observations observed across the scales mentioned indicates the universality of shallow conduit processes. ...
... The only comparable cases are those from the East Rift and Timna Igneous Complex, which however exceed 3 and 1 km in length, respectively, whereas the exposed TSF dike is less than 1 km. Furthermore, a thickness >20 m would require significant magma overpressure (Geshi et al., 2020), but volcanological and petrographic observations suggest that the magma was only moderately vesiculated, both in the solidified lava and the ballistic juvenile material, likely indicating low magma overpressure, following the relationship proposed by Geshi et al. (2020). ...
... The only comparable cases are those from the East Rift and Timna Igneous Complex, which however exceed 3 and 1 km in length, respectively, whereas the exposed TSF dike is less than 1 km. Furthermore, a thickness >20 m would require significant magma overpressure (Geshi et al., 2020), but volcanological and petrographic observations suggest that the magma was only moderately vesiculated, both in the solidified lava and the ballistic juvenile material, likely indicating low magma overpressure, following the relationship proposed by Geshi et al. (2020). ...
... On the other hand, the absence of diagnostic structures, such as multiple joint rows or internal chilled margins, indicates that such large thickness could not result from multiple magma injections (sensu Gudmundsson, 1984). Therefore, we propose that the unusually large thickness of the TSF dike is related to a spectrum of factors that include the lack of constraints at the free surface (Geshi et al., 2010(Geshi et al., , 2020, the effect of dilatant component of normal faults during rifting (Weismuller et al., 2019), and the pre-existing very-low rigidity damage zone of NE-SW faults, that magma re-used in localized oblique opening during propagation, as suggested by the deviation from E-W to NE-SW orientation, and already observed in monitored rifting events (Ruch et al., 2016). ...
The Roccamonfina volcano is located within the Garigliano Graben (southern Apennines, Italy) and has been active throughout the Middle‐Late Pleistocene. Along its polyphase volcanic history (630–55 ka), including several caldera‐forming eruptions (385–230 ka), several effusive/mildly explosive monogenetic events occurred along the volcano slopes, within the summit caldera, and along the graben‐bounding carbonate reliefs. In this paper, we present a multidisciplinary study of a mafic magmatic feeder dike intruded within the Meso‐Tertiary carbonates and overlying Lower Pleistocene breccias of Mt Cesima, northeast of the Roccamonfina volcano. We performed a stratigraphic and structural survey of the area and petrographic analyses on several samples of the dike. Results indicate that a ∼1 km long fissure fed an eruption that also emplaced a Strombolian pyroclastic sequence. Petrological data show that an open‐system mafic recharge fueled the tephritic magma that fed the eruption, whereas no evidence of significant pre/syn‐eruptive assimilation of carbonate has been identified. Stratigraphic and petrological data do not allow to firmly constrain the timing of the eruption, which could belong both to the pre‐Brown Leucitic Tuff (>354 ka) and to the post‐White Trachytic Tuffs (<230 ka) epochs of activity of the Roccamonfina volcano. Structural data show that the dike is broadly oriented E‐W and changes direction toward NE‐SW in correspondence with a pre‐existing fault damage zone. We suggest that magma was intruded during an N‐S trending extensional event in the Middle Pleistocene, whose prolonged activity resulted in regional uplift and exhumation of regional significance.
... Volcanic eruptions can occur when a magmafilled fracture (a dike, sill, or inclined sheet) propagates from a magma source through the crust to the surface (Rivalta et al., 2015, Acocella, 2021. Magma emplacement deforms the crust, resulting in surface uplift or subsidence signals that can be measured and used to infer information about intrusion depth, volume, shape, and orientation and which may be useful for determining potential eruption characteristics (Geshi et al., 2020). However, the vast majority of models used in volcano monitoring to infer the deformation associated with magmatic emplacement assume that the crust is either isotropic (an elastic half-space) (e.g., Okada, 1985;Mantiloni et al., 2020) or mechanically stratified with horizontal layers (Masterlark, 2007;Gudmundsson, 2019, 2020). ...
Constraints on the amount and pattern of ground deformation induced by dike emplacement are important for assessing potential eruptions. The vast majority of ground deformation inversions made for volcano monitoring during volcanic unrest assume that dikes are emplaced in either an elastic half-space (a homogeneous crust) or a crust made of horizontal layers with different mechanical properties. We extend these models by designing a novel set of two-dimensional finite-element method numerical simulations that consider dike-induced surface deformation related to a mechanically heterogeneous crust with inclined layers, thus modeling a common geometry in stratovolcanoes and crustal segments that have been folded by tectonic forces. Our results confirm that layer inclination can produce localized ground deformation that may be as much as 40× higher in terms of deformation magnitude than would be expected in a non-layered model, depending on the angle of inclination and the stiffness of the rock units that host and are adjacent to the dike. Generated asymmetrical deformation patterns produce deformation peaks located as much as 1.4 km away from those expected in non-layered models. These results highlight the necessity of accurately quantifying both the mechanical properties and attitude of the geology underlying active volcanoes.
... Based on the measurements of the aspect ratio of continental dykes, a few workers have quantitatively estimated magma chamber depths of Cretaceous (Babiker and Gudmundsson, 2004;Ray et al., 2007) and Tertiary dykes (Gudmundsson, 1983(Gudmundsson, , 1985Mège and Korme, 2004;Elshaafi and Gudmundsson, 2016). Similarly, overpressures and magma chamber depth of selected Quaternary (Holocene) dykes, associated with active volcanoes have also been estimated to study their potential explosivity and to predict future volcanic hazards (e.g., Becerril et al., 2013;Scudero et al., 2019;Geshi et al., 2020;Ruz et al., 2020). Quantitatively, these methods involve several assumptions, which may lead to poorly constrained depth estimates. ...
... It is also noticed that a few longer dykes (>11 km) from each of these dyke swarms show higher aspect ratios and display no similarity with the other dykes in length vs. width plots . This is perhaps a result of lateral magma injection in propagating fissures at shallow depths (Fialko and Rubin, 1999;Gudmundsson, 2020;Geshi et al., 2020). ...
Understanding emplacement mechanism and depth of origin of continental mafic dyke swarms is pivotal in resolving outstanding questions regarding magma flow dynamics, plumbing system architecture, and amount of crustal dilation related to large igneous provinces. Paleoproterozoic mafic dyke swarms are often deemed as suitable candidates to establish the crustal evolution of cratonic regions. Here, we present the geometric and statistical
analyses of five distinct Paleoproterozoic mafic dyke swarms and associated fracture systems in the Eastern Dharwar Craton (EDC) to constrain their magmatic overpressures and magma chamber depths. The geometric analysis is further validated with field evidence and measurements. It is suggested that mafic dykes of different swarms are formed primarily due to vertical magma injection from deep-seated magma reservoirs, followed by
lateral magma flow at shallower depths. This study suggests a direct derivation of magma from deep-seated magma reservoirs, extending from lower crustal depths (~17 km) to the crust-mantle boundary (~36 km). It is also suggested that the emplacement of mafic dykes at ca. 2.37–2.36 Ga, ca. 2.26–2.25 Ga, ca. 2.22 Ga, and ca. 2.21 Ga can be traced back to the development of fracture system formed during and subsequent to the
Neoarchean accretion event of Eastern and Western Dharwar Cratons (< 2.52 Ga). Therefore, the emplacement systems of the studied mafic dyke swarms have been largely controlled by the regional stress field and large-scale structural architecture of the Dharwar Craton.
... Taguchi et al. (2018) investigated these ratios for shallow long-period Kusatsu-Shirane sources using a frequency analysis. The (Geshi et al. 2020). Based on these observations, we assumed W /L = 0.7 and L/�d = 3000 to investigate the length, width, and aperture change of the tensile cracks at candidates (d), (e), (g), (i), and (j). ...
We conducted waveform inversions of an ultra-long-period (~ 240-s) event associated with the phreatic eruption of Mount Kusatsu–Shirane on January 23, 2018. We used broadband seismic and tilt records from three stations surrounding the eruption site. The horizontal components of the broadband seismic records were severely contaminated by tilt motions. We applied a waveform inversion algorithm to account for both the translational and tilt motions. To reduce the number of free parameters, we assumed a tensile crack source and conducted grid searches for the centroid location and orientation of the crack. The results showed a rapid inflation of 10 ⁵ m ³ of the crack, followed by a slow deflation starting 8–11 s prior to the onset of the eruption. The source location and crack orientation were not uniquely determined. The most likely source is a north–south-opening sub-vertical crack near the eruptive craters. This ultra-long-period event may represent volcanic fluid migration from depth to the surface through a vertical crack during the eruption.
Graphical abstract
... propagates from a magma source through the crust to the surface (Gudmundsson et al., 1999;Rivalta et al., 2015, Acocella, 2021. Magma emplacement deforms the crust resulting in surface uplift or subsidence signals that can be measured and used to infer information about intrusion depth, volume, shape and orientation, and which may be useful for determining potential eruption characteristics (Geshi et al., 2020). However, the vast majority of models used in volcano monitoring to infer the deformation associated with magmatic emplacement assume that the crust is either isotropic (an elastic half-space) (e.g., Okada, 1985;Mantiloni et al., 2020), or mechanically stratified with horizontal layers (Masterlark, 2007;Bazargan and Gudmundsson, 2019;2020). ...
Constraints on the amount and pattern of ground deformation induced by dike emplacement are important for assessing potential eruptions. The vast majority of ground deformation inversions made for volcano monitoring during volcanic unrest assume that dikes are emplaced in either an elastic-half space (a homogeneous crust) or a crust made of horizontal layers with different mechanical properties. Here, we extend these models by designing a novel set of two-dimensional Finite Element Method numerical simulations that consider dike-induced surface deformations related to a mechanically heterogeneous crust with inclined layers, thus modelling a common geometry in stratovolcanoes and crustal segments that have been folded by tectonic forces. Our results confirm that layer inclination can produce localized ground deformations which may be up to 40 times higher in terms of deformation magnitude than would be expected in a non-layered model, depending on the angle of inclination and the stiffness of the rock units that host, and are adjacent to the dike. Generated asymmetrical deformation patterns produce deformation peaks located as much as 1.4 km away from those expected in non-layered models. These results highlight the necessity to accurately quantify both the mechanical properties and attitude of the geology underlying active volcanoes.
... Internal stresses within a volcanic edifice are induced by magmatic overpressures (Huppert and Woods 2002). At ocean islands, the magnitude of this stress is a result of the buoyancy force of a magma reservoir, which is related to magma density (Pinel and Jaupart 2000) and exsolution of volatiles (Geshi et al. 2020). External stresses are generated by local and regional topography, diminishing as a function of increased magma storage depth. ...
Isla Santa Cruz is a volcanic island located in the central Galápagos Archipelago. The island’s northern and southern flanks are deformed by E–W-trending normal faults not observed on the younger Galápagos shields, and Santa Cruz lacks the large summit calderas that characterize those structures. To construct a chronology of volcanism and deformation on Santa Cruz, we employ ⁴⁰ Ar/ ³⁹ Ar geochronology of lavas and ³ He exposure dating of fault scarps from across the island. The combination of Ar–Ar dating with in situ - produced cosmogenic exposure age data provides a powerful tool to evaluate fault chronologies. The ⁴⁰ Ar/ ³⁹ Ar ages indicate that the island has been volcanically active since at least 1.62 ± 0.030 Ma (2SD). Volcanism deposited lavas over the entire island until ~ 200 ka, when it became focused along an E–W-trending summit vent system; all dated lavas < 200 ka were emplaced on the southern flank. Structural observations suggest that the island has experienced two major faulting episodes. Crosscutting relationships of lavas indicate that north flank faults formed after 1.16 ± 0.070 Ma, but likely before 416 ± 36 ka, whereas the faults on the southern flank of the island initiated between 201 ± 37 and 32.6 ± 4.6 ka, based on ³ He exposure dating of fault surfaces. The data are consistent with a model wherein the northeastern faults are associated with regional extension owing to the young volcano’s location closer to the Galápagos Spreading Center at the time. The second phase of volcanism is contemporaneous with the formation of the southern faults. The expression of this younger, low-volume volcanic phase was likely related to the elongate island morphology established during earlier deformation. The complex feedback between tectonic and volcanic processes responsible for southward spreading along the southern flank likely generated persistent E-W-oriented magmatic intrusions. The formation of the Galápagos Transform Fault and sea-level fluctuations may be the primary causes of eruptive and deformational episodes on Santa Cruz.
... As explained in Appendix B, this assumption in the conduit flow model does not preclude radiation, which of course requires elasticity of the solid surrounding the conduit and deformation of the conduit walls. For other conduit geometries, such as a dike-like conduit, elastic compliance must be accounted for in the conduit flow model (Costa et al., 2007(Costa et al., , 2009Geshi et al., 2020). We model the magma chamber using a lumped parameter model that assumes spatially uniform pressure changes within the chamber, derived from the chamber mass balance with outflow from the chamber to conduit. ...
Explosive volcanic eruptions radiate seismic waves as a consequence of pressure and shear traction changes within the conduit/chamber system. Kinematic source inversions utilize these waves to determine equivalent seismic force and moment tensor sources, but relation to eruptive processes is often ambiguous and nonunique. In this work, we provide an alternative, forward modeling approach to calculate moment tensor and force equivalents of a model of eruptive conduit flow and chamber depressurization. We explain the equivalence of two seismic force descriptions, the first in terms of traction changes on conduit/chamber walls, and the second in terms of changes in magma momentum, weight, and momentum transfer to the atmosphere. Eruption onset is marked by a downward seismic force, associated with loss of restraining shear tractions from fragmentation. This is followed by a much larger upward seismic force from upward drag of ascending magma and reduction of magma weight remaining in the conduit/chamber system. The static force is upward, arising from weight reduction. We calculate synthetic seismograms to examine the expression of eruptive processes at different receiver distances. Filtering these synthetics to the frequency band typically resolved by broadband seismometers produces waveforms similar to very long period seismic events observed in strombolian and vulcanian eruptions. However, filtering heavily distorts waveforms, accentuating processes in early, unsteady parts of eruptions and eliminating information about longer (ultra long period time scale depressurization and weight changes that dominate unfiltered seismograms. Our workflow can be utilized to directly and quantitatively connect eruption models with seismic observations.
... Volcanic eruptions can occur when a magma-filled fracture (a dike if it is vertical, a sill if horizontal, or an inclined sheet if it is neither vertical nor horizontal) propagates from a magma source through the crust up to the surface (Gudmundsson et al., 1999;Rivalta et al., 2015, Acocella, 2021. The emplacement of the magma deforms the crust which may result in ground deformation signals that can be measured and used to infer information about the intrusion such as depth, volume, shape and orientation which may be useful for determining potential eruption characteristics (Geshi et al., 2020). However, the vast majority of models used in volcano monitoring to infer the deformation associated with magmatic emplacement assume that the crust is either isotropic (an elastic half-space) (Okada, 1985), or mechanically stratified with horizontal layers (Masterlark, 2007;Bazargan and Gudmundsson, 2019;2020). ...
Constraints on the amount and pattern of ground deformation induced by dike emplacement are important for assessing potential eruptions. The vast majority of ground deformation inversions made for volcano monitoring during volcanic unrest assume that dikes are emplaced in either an elastic-half space (a homogeneous crust) or a crust made of horizontal layers with different mechanical properties. Here, we extend these models by designing a novel set of two-dimensional Finite Element Method numerical simulations that consider dike induced surface deformations related to a mechanically heterogeneous crust with inclined layers, thus modelling a common geometry in stratovolcanoes and crustal segments that have been folded by tectonic forces. Our results confirm that layer inclination can produce localized ground deformations which may be up to 30 times higher in terms of deformation magnitude than would be expected in a purely homogeneous model, depending on the angle of inclination and the stiffness of the rock units that host and are close to the dike, generating asymmetrical deformation patterns with peaks located as much as 1.4 km away from the expected in the homogeneous model. These results highlight the necessity to accurately quantify both the mechanical properties and attitude of the geology underlying active volcanoes.
... As a result, Nealtican lavas were extruded along the NE-SW Atexca fault through the aligned El Ombligo flank vents suggesting that the magma was transported from a shallow reservoir to the surface through a dike system (Fig. 13B). Such a system probably had a low overpressure during magma ascent, which according to Geshi et al. (2020) also promotes an effusive eruption (e.g., Miyakejima volcano, Japan). The less viscous andesitic magma propagated first through dikes and erupted before the more viscous phenocrystrich dacitic magma, because low-viscosity mag-mas have a higher eruptibility than viscous ones (Takeuchi, 2011). ...
Popocatépetl, one of the most hazardous volcanoes worldwide, poses significant threats for nearby populations in central Mexico. Therefore, it is important to reconstruct its eruptive history, including estimates of lava-flow emplacement times and their rheological properties. These studies define possible future eruptive scenarios and are necessary to mitigate the risk. Stratigraphic studies of the cal 350−50 B.C. Lorenzo Plinian pumice sequence indicate that effusive activity (Nealtican lava-flow field) occurred shortly after explosive activity, reflecting drastic changes in the eruptive dynamics. It was likely due to the efficient degassing of the magma during the Plinian phase and a decrease of magma ascent and decompression rates. Magma mixing, fractional crystallization, and a minor crust assimilation are the processes controlling the differentiation of the Nealtican lavas. We used lava chemical and mineralogical composition to estimate lava-flow viscosities, and used high-resolution elevation data to estimate emplacement times. Results indicate that lava viscosities of andesites and dacites ranged from 109 to 1012 Pa·s and emplacement durations were between ∼1 and ∼29 years, depending on the flow unit and morphological method employed. Considering the entire volume of emitted lava (4.2 km3) and a mean output rate of ∼1 m3/s to ∼15 m3/s, we estimated that the effusive phase that produced the Nealtican lava-flow field may have lasted ∼35 years. This eruption had a considerable impact on pre-Hispanic settlements around the volcano, whose population exodus and relocation probably contributed to the rise of important cities in central Mexico, such as Teotihuacán and Cholula.
