The volcanic provinces are embedded between the NE margin of b56 /Lennon-Picasso basin and high terrain bounding structures. Resulting plains are interested by endogenic pits associated with pyroclastic activity, in agreement with the observation that Mercury's explosive volcanic vents tend to be located along major fold and thrust belts (Byrne et al 2014) and around large impact basins. Recent large scale mapping defined them intercrater plains partly covered by smooth plains (Malliband et al 2019; Whitten et al 2020). In addition to endogenic pits, these provinces display several 10-km diameter prominent cones, sometimes aligned forming high-relief ridges, resembling  constructional edifices. In colour composite images, cone tops are peculiarly darker (blue) or, alternatively, brighter (and yellow) with respect to the surrounding material. On the surface Mercury, Wright et al. (2019) interpreted two randomly located constructional edifices of similar size, attributing their origin to a late highly viscous  stage of volcanism that followed lower-viscous stage that are thought to provide typical smooth plains. Wider et al. (2016) proposed that the encounter of highly-viscous lavas with C-rich material during the magma ascent can easily provide volatiles (Zolotov et al. 2011) that progressively accumulate and lead to explosive eruptions. The resulting high reflectance of pyroclastic deposits would arise from removal of graphite as it was consumed during oxidation. The study aims to reveal the nature of cones at the margin of the Lennon-Picasso basin and to explain the relationship between a potential long-lasting volcanic activity and the concurrent global contractional regime.

Authors received funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47 and from European Union’s Horizon 2020 research grant under agreement 776276- PLANMAP.

How to cite: Ferrari, S., Massironi, M., Pozzobon, R., and Bedon, S.: The volcanic provinces of the Lennon-Picasso basin (Mercury), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15987, https://doi.org/10.5194/egusphere-egu21-15987, 2021.

Aligned volcanism is very common in many monogenetic volcanic fields around the world, which can reveal volcano-tectonic interactions at different scales. For instance, volcanic distribution discloses the tectonic stress orientation on regional scales. On more local scales, preexisting faults or fractures may control magma intrusions and their propagation through the upper crust, as faults are zones of crustal weakness that magma intrusions can intercept during its ascent, partly controlling the volcanic vent spatial distribution. But it is not quite understood how do these alignments occur; if they erupted at the same time (within a few dozens of years), if they erupted during a short time interval (hundreds of years) or during a long time interval (thousands of years); if the eruptive style and magma volumes are controlled by these faults and the regional tectonic stress regime, etc.

This study aims to understand the magmatic and structural conditions that favored the emission of a lava plateau followed by Strombolian explosions that built 13 aligned and six dispersed scoria cones through preexisting E-W– to ENE-striking faults in the Queréndaro area. Our results indicate that volcanism in the Michoacán-Guanajuato Volcanic Field occurs as intermittent magma fluxes, sometimes represented by independent volcanic vents and sometimes by clustered or aligned volcanoes. Moreover, preexisting faults exert a strong influence on volcanic spatial and temporal distribution, volcanic morphology, magma volume, and eruptive dynamics in this area.

How to cite: Gómez Vasconcelos, M. G., Macías, J. L., Avellán, D. R., Sosa-Ceballos, G., and Garduño-Monroy, V. H.: Tectonic control on monogenetic volcanism in the Michoacán-Guanajuato Volcanic Field, México, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8497, https://doi.org/10.5194/egusphere-egu21-8497, 2021.

The Reykjanes Peninsula in south-west Iceland straddles the North-America - Eurasia plate boundary and hosts several active volcanic systems, including the Svartsengi volcanic system. The last eruption in this area took place around 1240 CE, with eruptive episodes recurring every 800-1000 years, affecting one volcanic system at a time, but spanning multiple systems  with activity spaced ~100 to 200 years. In January 2020, unrest was identified in Svartsengi, characterized by intense seismicity and inflation at a rate of 3-4 mm per day. This area is located within 5 km of several important infrastructures: a) the town of Grindavík; b) the Svartsengi geothermal power plant; c) and the Blue Lagoon geothermal spa, which had over a million annual visits before the Covid pandemy.

Two continuously recording GNSS stations were installed in the Svartsengi geothermal area in 2013-2015 to monitor geothermally-induced subsidence.  Coinciding with the onset of an earthquake swarm starting on January 21 (M<4), uplift of about 3-4 mm/day was noticed in automated GNSS and InSAR results. The uplift rates in this first inflation phase decreased after January 31 and reverted to slight subsidence in early February. Interestingly, the most intense seismicity was offset from the uplift center by about 2-4 km to the southeast. Geodetic source models from the initial two weeks indicate the deformation is the result of a sill intrusion at a depth of about 4 km  with a volume change of approximately 3  million m³. The resulting stress changes from this intrusion act to increase seismicity at the sill edges, thus offering an explanation for why the seismicity is offset from the center of uplift. The location of the sill coincides roughly with a crustal volume with a high V_p/V_s ratio.

Two more inflation-deflation episodes have occurred at Svartsengi in 2020 and the total uplift amounts to approximately 12 cm. Additionally, at least one inflation episode occurred in the Reykjanes system, in February 2020, and inflation started in the Krýsuvík system in mid-July 2020, culminating in a M5.6 earthquake on October 20. The Fagradalsfjall system, between Krýsuvík and Svartsengi, has shown high seismicity in 2020, but does not display detectable inflation nor deflation. Therefore, the volcano-tectonic activity in 2020 spans the entire western part of the Reykjanes Peninsula. The stress changes for each of these events are too small to explain the cross-system activity, hence we suggest the entire unrest is  by deep magma migration beneath the entire western Reykjanes Peninsula.  

How to cite: Geirsson, H., Parks, M., Vogfjörd, K., Einarsson, P., Sigmundsson, F., Jónsdóttir, K., Drouin, V., Ófeigsson, B. G., Hreinsdóttir, S., and Ducrocq, C.: The 2020 volcano-tectonic unrest at Reykjanes Peninsula, Iceland: stress triggering and reactivation of several volcanic systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7534, https://doi.org/10.5194/egusphere-egu21-7534, 2021.

From 1993 to 1998, the Hengill volcanic area in SW-Iceland was subjected to a volcano-tectonic event which caused a local uplift of the crust of 8 cm and triggered over 90.000 earthquakes. Relocating a sub-set of 12.000 earthquakes in the direct vicinity of the uplift centre improved resolution and enabled the mapping of 25, mostly NNE-SSW and ENE-WSW oriented sub-vertical groups of earthquake which are interpreted as faults. Focal mechanisms were calculated, using the best fitting plane through a group of earthquakes as additional constraint. Slip on the interpreted faults could be estimated averaging slip of all earthquakes within that group. Most faults show strike-slip movement with a small normal component. Right-lateral slip prevails. We modelled Coulomb stress changes that the uplift would have caused and compared them to out results. The Coulomb stress changes can only explain the observed movement on some of the faults but on others fault movements is impeded, that is, the Coulomb stress change is negative. Varying the location of the uplift within its error margin increases the number of faults on which the observed movement is promoted but the slip on a number of faults remains unexplained.  

How to cite: Blanck, H., Vogfjörd, K., Geirsson, H., and Hjörleifsdóttir, V.: Mapping and dynamic analysis of faults in the Hengill volcanic area, SW-Iceland , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9052, https://doi.org/10.5194/egusphere-egu21-9052, 2021.

Deformation models are an important tool to study and monitor active volcanoes. However, in many cases models are strongly simplified either due to a lack of data or for the sake of speed and computational demands. The assumption of a magma body embedded in a homogeneous elastic half-space for example neglects the topography and heterogeneous crustal structures found at some volcanoes. This oversimplification can lead to a poor representation of individual systems and result in erroneous estimates of deformation source parameters like the location and geometry of a magma chamber.  The Finite Element Method (FEM) is a powerful tool to include complex heterogeneous structures and existing data sets into deformation models in order to create more realistic representations of individual volcanic systems.
In this study, the FEM-software COMSOL was used to build a three-dimensional elastic model of the subglacial volcano Grímsvötn, Iceland, accounting for the steep topography at the caldera rim, using a digital elevation model, as well as crustal heterogeneity. The elastic structure developed for this model is based on a density-structure, a seismic-velocity-structure and a pressure-dependent relation between the dynamic and static elastic moduli. The main feature of the elastic structure is a weak material (static shear modulus of G_stat=0.6-9.8 GPa from 1 km above to 2 km below sea level) filing the caldera, which is surrounded by a stiffer, ring-like structure underneath the caldera rim (G_stat=1.6-18 GPa from 1 km above to 2 km below sea level). The source parameters and geometry of forward models including the topography and elastic structure (individually and combined) were varied to fit the deformation observed at the nunatak GPS station GFUM, located at the caldera rim, during the last eruption (2011). While the topography has limited influence at the deformation at GFUM, the elastic structure requires the magma chamber to be significantly deeper than previous models suggested.

How to cite: Greiner, S. H. M. and Geirsson, H.: An elastic 3D Finite-Element-Model for Grímsvötn, Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5571, https://doi.org/10.5194/egusphere-egu21-5571, 2021.

Laccoliths play a significant role in the transport and storage of magma in sub-volcanic systems. The construction and geometry of laccoliths can influence host rock and surface deformation patterns that may precede and provide warning of active magmatism and impending eruptions. Yet how laccolith construction and internal magma dynamics controls the location and form of magma ascent conduits (e.g., dykes and inclined sheets), which facilitate magma evacuation and may feed volcanic eruptions, remains poorly documented in natural examples.

The excellently exposed silicic, sub-volcanic Miocene Reyðarártindur Laccolith in SE Iceland offers an opportunity to investigate how magma ascent within inclined sheets, which emanated from the laccolith, related to intrusion construction and deformation in the surrounding host rock. We combine detailed structural mapping with anisotropy of magnetic susceptibility (AMS) analyses, which allow us to map magnetic rock fabrics that reflect magma flow patterns, to show that the laccolith comprises of several distinct magma lobes that intruded laterally towards the south-west. Each lobe intruded, inflated, and coalesced along a NE-SW primary axis facilitated by doming (i.e., forced folding) of the host rock. We also shown that pre-existing NNE-striking, left-stepping, en-echelon fault/fractures, as well as those generated during intrusion-induced host rock uplift, host moderately to steeply inclined rhyolitic/granophyric sheets that emanate from the lateral terminations of some flow lobes.

Based on the observed geometrical relationships between AMS fabrics and the sheet margins where magnetic foliations subparallel sheet contacts, or characterize an imbrication fabric, we suggest that magma evacuated moderately to steeply upward via these fault/fracture-controlled sheets. As these inclined sheets dip towards the laccolith, any eruptions they may have fed would have been laterally offset from the laccolith and any overlying surface deformation driven by forced folding. Our study shows that magma evacuation and ascent from laccoliths can be facilitated by inclined sheets that form at the lateral terminations of magma lobes that are spatially controlled by laccolith construction (e.g., flow direction and doming of the host rock) and the presence of pre-existing structures.

How to cite: Twomey, V., McCarthy, W., and Magee, C.: Structural controls on the emplacement and evacuation of magma from a sub-volcanic laccolith: Reyðarártindur Laccolith, SE Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14930, https://doi.org/10.5194/egusphere-egu21-14930, 2021.

The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. The island was built by both explosive, phreatomagmatic phases and by effusive activity forming lava shields covering parts of the explosively formed tuff cones.  Constraints on the subsurface structure of Surtsey achieved mainly based on the documented evolution during eruption and from drill cores in 1979 and in the ICDP-supported SUSTAIN drilling expedition in 2017(an inclined hole, directed 35° from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019). 

We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme.  Detailed gravity data were obtained on Surtsey in July 2014 with a gravity station spacing of ~100 m. Density measurements for the seafloor sedimentary and tephra samples of the surface were carried out using the ASTM1 protocol. By comparing the results with specific gravity measurements of cores from drillhole in 2017, a density contrast of about 200 kg m^-3 was found between the lapilli tuffs of the diatreme and the seafloor sediments.  Our approach is to divide the island into four main units of distinct density: (1) tuffs above sea level, (2) tuffs below sea level, (3) lavas above sea level, and (4) a lava delta below sea level, composed of breccias over which the lava advanced during the effusive eruption.  The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores. 

A complete Bouguer anomaly map is obtained by calculating a total terrain correction by applying the Nagy formula to dense DEMs (5 m spacing out to 1.2 km from station, 200 m spacing between 1.2 km and 50 km) of both island topography and ocean bathymetry.  Through the application of both forward and inverse modeling, using the GM-SYS 3D software, the results provide a 3-D model of the island itself, as well as constraints on diatreme shape and depth.

How to cite: sayyadi, S., T. Gudmundsson, M., Högnadóttir, T., White, J., M.C. Belart, J., and D. Jackson, M.: 3D Gravity modeling of the volcanic island of Surtsey, Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15769, https://doi.org/10.5194/egusphere-egu21-15769, 2021.

For magma chambers to form or volcanic eruptions to occur magma must propagate through the crust as dikes, inclined sheets and sills. The vast majority of models that investigate magma paths assume the crust to be either homogeneous or horizontally layered, often composed of rocks of contrasting mechanical properties. In subduction regions that have experienced orogenesis, like the Andes, the crust has been deformed over several million years, resulting in rock layers that are commonly folded and steeply dipping. The assumption of homogeneous properties or horizontal layering then does not capture all of the potential magma path crustal interactions. Here we tackle this problem by determining the effect of a crust made of steeply inclined layers in which sills and inclined sheets are emplaced. We combine field observations from a sill emplaced in the core of an anticlinal fold at El Juncal in the Chilean Central Andes, such as lithologies, sill and fold limbs attitude, sill length and layers and sill thickness, with a suite of finite element method models to explore the mechanical interactions between inclined layers and magma paths. Our results demonstrate that the properties of the host rock layers as well as the contacts between the layers and the crustal geometry all play an important role on magma propagation and emplacement at shallow levels. Sill propagation and emplacement through heterogeneous and anisotropic crustal segments changes the crustal stress field promoting sill arrest, deflection or propagation. Specifically, sills are more likely to be deflected when encountering shallow dipping layers rather than steeply dipping layers of a fold. Mechanically weak contacts encourage sill deflection due to the related rotation of the maximum principal compressive stress and this effect is attenuated when the fold layers are more steeply dipping. This processes may change the amount and style of surface deformation recorded, with significant implications for monitoring of active volcanoes.

How to cite: Clunes, M., Browning, J., Cembrano, J., Marquardt, C., and Gudmundsson, A.: Crustal folds alter local stress fields as demonstrated by magma sheet – fold interactions in the Central Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13845, https://doi.org/10.5194/egusphere-egu21-13845, 2021.

The 2011-2012 Cordon-Caulle eruption was the largest subaerial eruption of the 21th century. An inflation captured from InSAR between 2007 and 2009 was related to a volume of magma injection too small to have triggered this eruption. Here, we benefit from SAR imagery acquired by ALOS-1, ENVISAT and SENTINEL-1 data, to analyze the temporal and spatial behavior of ground displacements before, during and after the eruption. We find that a similar prolate spheroidal source explains the data for the pre-eruptive and post-eruptive periods. Then we explore two tectonically-related hypotheses to explain the observed displacements during the explosive phase of the eruption. Therefore, first we model InSAR data using standard inversion models to evaluate how slip motion along specific structures explain surface observations. Our results show that the explosive phase's ground displacements could have been produced either by the collapse of the caldera and the graben overriding the reservoir, or by slip motion along a dextral-strike slip fault zone related to the North-South trending Liquiñe-Ofqui fault zone. Second, we use 3D numerical models and elasto-plasticity to assess the failure conditions along both structures resulting from an overpressure applied at the wall of the prolate-spheroidal reservoir. Our results show that a magma injection consistent with the 2007-2009  inflation signal rather promotes constriction at the roof of the reservoir, which tends to impede fluid flow towards the surface. The presence of a relatively weak graben-caldera structure in our models show that this constrictional area is enhanced. On the other hand, the elasto-plastic pattern resulting from the application of a dextral-slip motion along the LOFZ branch-fault generates a dilatational plastic zone that connects the reservoir wall to the surface, where it coincides with the location of the 2011 eruption. Hence we propose that the LOFZ branch-fault, weakened during the pre-eruptive inflation phase, destabilized and slipped two years later in a way that it served as open channels for fluid migration from the magma reservoir up to the surface.

How to cite: Novoa Lizama, C., Gerbault, M., Rémy, D., Cembrano, J., Lara, L., Tassara, A., Hassani, R., Baez, J. C., and Ruz, J.: Could the Liquiñe-Ofqui fault zone promote the 2011 Cordon Caulle eruption ?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9519, https://doi.org/10.5194/egusphere-egu21-9519, 2021.

Volcanoes commonly subside during eruptions as magma flows out of a chamber, but continued subsidence during non-eruptive episodes is not easy to explain. In this work, we use InSAR and source modelling to understand the causes of the continued subsidence of Dallol, a nascent volcano along the spreading Erta Ale ridge of Afar (Ethiopia). The Dallol volcano never erupted and no volcanic deposits originating from the volcano exists at the surface. Recent seismicity, diking and continuous deformation of a crustal magma chamber indicate the Dallol is a nascent central volcano with its own rift segment. An active magma plumbing exists and the injection of a dike beneath the volcano was imaged in 2004 from InSAR data. This unrest episode was followed by complete quiescence until subsidence started in 2008. We analysed InSAR data from 2004-2010 to create time-series of line-of-sight (LOS) surface deformation. Average velocity maps show that subsidence centred at Dallol initiated in October 2008 and continued as far as February 2010 at an approximately regular rate of up to 10 cm/yr. The inversion of InSAR average velocities found that a sill-like source, located a depth between 1.2 and 1.5 km under Dallol with a mean volume change of  -0.62 to -0.53 10⁶ km³/yr and a radius of approximately 1.6 km, best fits the InSAR observations. The observed volume change could be explained by changes in pore fluid pressure in a confined hydrothermal aquifer or by thermoelastic deformation caused by changes in temperature in a volume of rock. Simple models of poro-elastic and thermo-elastic contraction indicates that the observed deformation would require either a decrease in pore fluid pressure of the order of 10^-2G, where G is the rock shear modulus, or a decrease in temperature between 60 °C and 80 °C.  

How to cite: Battaglia, M., Pagli, C., and Meuti, S.: The continued 2008-2010 subsidence of Dallol on the spreading Erta Ale ridge: InSAR observations and source models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9211, https://doi.org/10.5194/egusphere-egu21-9211, 2021.

We present a study of the deformation pattern along the Canary archipelago through the analysis of continuous GNSS data. We use data spanning 2011–2017 period to retrieve precise horizontal displacements and a broad calculation of the strain. Geodetic data are interpreted in light of the regional tectonics, which is proven to play a key role in the volcanic eruptions that take place in the archipelago. The common-mode component filtering technique is applied to improve the signal-to-noise ratio of the time series of the GNSS daily solutions before retrieving the geodetic velocities. Through a triangular segmentation approach, we retrieve the 2D infinitesimal strain from the velocities along the Canaries and map deformation patterns in various sectors of the volcanic archipelago. We found areas of maximum deformation west of Tenerife, Gran Canaria and Fuerteventura Islands. A sharp change in shear strain between Tenerife and Gran Canaria is recognized, delineating a sector of intense seismicity, which is mostly associated with a well-known major submarine fault that separates the two insular edifices. On this submarine tectonic structure, we have performed a tentative simulation of the horizontal deformation and strain caused by one of the strongest (mbLg 5.2) earthquakes of the region. Our strain analysis supports the possibility that the main tectonic lineaments are being influenced by the regional stress field. Furthermore, the seismic areas between islands seem mainly influenced by the regional tectonic stress, rather than by the local volcanic activity. This is in accordance with the extensional and compressional tectonic regimes, already identified by other authors, which might favour episodes of volcanism in this volcanic archipelago.

How to cite: Riccardi, U., Arnoso, J., Benavent, M., Tammaro, U., Montesinos, F. G., Blanco-Montenegro, I., and Vélez, E.: Deformation patterns in Canary Islands volcanic area from GNSS data analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8464, https://doi.org/10.5194/egusphere-egu21-8464, 2021.

The largest continental igneous province, the Siberian Traps, was formed within the Siberian platform at the Paleozoic-Mesozoic boundary, ca. 252 million years ago. Despite the continuous and extensive investigation of the duration and rate of trap magmatism on the Siberian platform, these questions are still debated. Moreover, the post-Paleozoic thermal history of the Siberian platform is almost unknown. This study aims to reconstruct the thermal history of the Siberian platform during the last 250 Myr using the low-temperature thermochronometry. We have studied intrusive complexes from different parts of the Siberian platform, such as the Kotuy dike, the Odikhincha, Magan and Essey ultrabasic alkaline massifs, the Norilsk-1 and Kontayskaya intrusions, and the Padunsky sill. We use apatite fission-track (AFT) thermochronology to assess the time since the rocks were cooled below 110℃. Obtained AFT ages (207-173 Ma) are much younger than available U-Pb and Ar/Ar ages of the traps. This pattern might be interpreted as a long cooling of the studied rocks after their emplacement ca. 250 Ma, but this looks quite unlikely because contradicts to the geological observations. Most likely, the rocks were buried under a thick volcanic-sedimentary cover and then exhumed and cooled below 110℃ ca. 207-173 Ma. Considering the increased geothermal gradient up to 50℃/km at that times, we can estimate the thickness of the removed overlying volcanic-sedimentary cover up to 207-173 Ma as about 2-3 km.

The research was carried out with the support of RFBR (grants 20-35-90066, 18-35-20058, 18-05-00590 and 18-05-70094) and the Program of development of Lomonosov Moscow State University.

How to cite: Bagdasaryan, T., Veselovskiy, R., Zaitsev, V., and Latyshev, A.: Thermal history of the Siberian platform: Apatite Fission-Track data from the Permian-Triassic magmatic complexes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9702, https://doi.org/10.5194/egusphere-egu21-9702, 2021.

As volcanic systems undergo unrest, understanding the conditions required for reservoir failure, the associated timescales, and the links to geophysical observations are critical when evaluating the potential for eruption. The characteristics and dynamics of a pressurised magmatic system can be inferred from episodes of surface deformation, but this process is heavily reliant on the assumed crustal rheology. In volcanic regions, shallow or long-lived magmatic systems can significantly perturb the regional geothermal gradient, altering the rheology of the surrounding crustal rock. Viscoelasticity incorporates a time-dependent viscous deformation response, accounting for the increased ductility and thermomechanical heterogeneity induced by the modelled reservoir.

Here, we investigate the influence of an imposed thermal regime on the critical reservoir overpressure (OPc) required to facilitate failure in elastic and viscoelastic models, alongside the predicted critical surface uplift (Uc). By evaluating tensile and Mohr-Coulomb failure criteria on the reservoir walls, we can determine the mechanical stability of the magma reservoir and identify the conditions that are susceptible to failure. We explore a range of reservoir temperatures (representing felsic, intermediate, and mafic magma compositions) and background geothermal gradients, to simulate varied volcanic regions, and use the Standard Linear Solid viscoelastic rheology together with a temperature-dependent viscosity structure, calculated from the thermal constraints. The models incorporate mechanical heterogeneity in the form of a temperature-dependent Young’s modulus, accounting for the thermal weakening of the surrounding crustal rock. We use an overpressure rate of 10 MPa yr^-1, in excess of lithostatic pressure, that produces an average elastic volumetric strain rate of ~3-7x10^-12 s^-1, depending on the imposed thermal regime.

We show that reservoir failure is systematically inhibited by incorporating viscoelasticity, with OPc for Mohr-Coulomb failure increasing by up to 65% with respect to the corresponding elastic model. The greatest increases in OPc, and Uc, are observed when pairing cool reservoir temperatures (i.e., felsic composition) with low background geothermal gradients. In contrast, stress partitioning due to the viscoelastic crustal rheology promotes failure at the ground surface, decreasing the required OPc for tensile failure by up to 32%. The greatest reductions in OPc are produced in models that couple a hot reservoir temperature (i.e., mafic composition) with low background geothermal gradients. By resisting mechanical failure on the reservoir wall, temperature-dependent viscoelasticity impacts the conditions required for dyke nucleation and propagation. Further to this, a viscoelastic crustal rheology dramatically reduces the timescales for throughgoing failure; complete brittle failure connecting the reservoir to the ground surface. This occurs much earlier than suggested by elastic models, which could have implications for interpreting the conditions, and onset, of a potential eruption.

How to cite: Head, M., Hickey, J., Thompson, J., Gottsmann, J., and Fournier, N.: Thermomechanical Controls on the Timing of Magma Reservoir Failure in a Viscoelastic Crust, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11191, https://doi.org/10.5194/egusphere-egu21-11191, 2021.

Mature volcanic systems (e.g., Yellowstone, USA; Campi Flegrei, Italy) are fed by stratified magma reservoirs – small bodies of eruptible, crystal-poor silicic magma are suspended within a larger volume of non-eruptible, crystal-rich mush. Lavas erupted from these systems record geochemical evidence for long-term (10³ to 10⁵ years) deep storage followed by short (<1 to 10³ years) residences in shallow chambers prior to eruption. Evidence for protracted magma ascent is frequently absent, suggesting deep-seated magmas rise quickly in reservoirs despite the high viscosity and low permeability of crystal-rich mushes. We hypothesize that deformation of a reservoir (by intrusion of new magma, passing seismic waves, tectonic stresses, etc.) allows low viscosity magmas to intrude high viscosity mush, creating mechanical instabilities that focus magma migration and facilitate rapid magma ascent through the reservoir.

To test this hypothesis, we are conducting high-temperature and high-pressure deformation experiments in a gas-medium, Paterson apparatus. Samples consist of a disk of soda lime glass (“magma”) stacked in series with a disk of a composite (“mush”) composed of borosilicate glass and fine quartz sand (44-106 μm). The mush has a crystal fraction of 80%. The stacked magma and mush disks are overlain by permeable ceramics. Sample assemblies are heated to 900°C (above the glass transition temperatures for soda lime and borosilicate glasses) and pressurized to 200 MPa confining pressure. At 900°C the magma viscosity is 10⁴ Pa s and the mush viscosity is ~10¹²-10¹⁴ Pa s. Following heating and pressurization, samples either dwell at high P-T conditions for extended time or are subjected to axial compression (strain rates of 10^-5-10^-3 s^-1; shortening up to 50% of the length of the mush disk) or pore pressure gradients (a pressure difference across the sample of 10-150 MPa, equivalent to 2-30 MPa/mm over the length of the mush disk). After dwelling or deformation, samples are rapidly quenched and decompressed, cut in longitudinal sections and polished. Polished samples are analyzed in an SEM to collect back-scatter electron images and compositional maps. BSE images can be used to look for melt structures (e.g., viscous channels, dikes) that form in the mush during deformation. The compositions of magma (soda lime) and mush (borosilicate) melts are different, therefore compositional maps can be used to look for their respective spatial distributions. In static experiments, no magma intrudes the mush. We expect deformation to facilitate magma intrusion and that the volume of intruding magma will increase with increasing strain rate, strain and pore pressure gradient. These experiments will shed light on the role deformation plays in instigating magma ascent in stratified magma reservoirs.

How to cite: Ryan, A., Zimmerman, M., and Hansen, L.: Deformation driven magma ascent in stratified magma reservoirs: an experimental study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1397, https://doi.org/10.5194/egusphere-egu21-1397, 2021.

All active polygenetic volcanoes erupt magma sourced from a shallow crustal reservoir.  Those chambers are complex entities that act as a collector of magma originating from deeper crustal sources. The geometry of those active storage systems depends on the rheology of the magma and on the rock properties of the host. Studying how the geometry influences the eruptive behaviour of a magma chamber has implications for our understanding of volcanic hazard.
We introduced a simple model where a magma reservoir is cooled by an overlying geothermal system and recharged by a deeper magma source. The geometry of the chamber is defined by its volume and aspect ratio. The model tracked changes in pressure, mixture enthalpy and composition, and implemented parameterisations of eruption, hydrothermal cooling, viscoelastic relaxation, and volatile leakage. The thermodynamic properties of the melt, crystals and water were computed using rhyolite-MELTS.
A large number of simulations sweeping our parameter space gave us insight into how the different magmatic processes trade off with respect to the geometry of the inclusion. An example of the complex control of geometry on the eruptive behaviour can be made regarding cooling and the effective compressibility of an ellipsoidal inclusion. On the one hand, a larger aspect ratio will favor eruptibility by offering a larger area for cooling therefore increasing the exsolution of water and pressure build up. On the other hand, a larger aspect ratio will work against eruptibility by decreasing the compressibility making it harder to build overpressures within the chamber. We found that a specific geometry is required in order for a chamber to erupt without any external stimuli (such as a large recharge event).
A limiting factor of our model is the assumption of a perfect mixing. Whereas, in reality, we would expect recharge, cooling and leakage to occur within specific regions of the chamber. In a model where mixing is not considered perfect, those processes would be a source of heterogeneity. We could conjecture that under the right conditions, eruptible regions would appear within the chamber. A model focusing more on the flows within the chamber might be able to give additional insights on the eruptive behaviour of magma chambers.

How to cite: Letourneur, M., O'Sullivan, J., Gravley, D., Gualda, G., and Dempsey, D.: Influence of geometry on eruptive behaviour of magma reservoirs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-976, https://doi.org/10.5194/egusphere-egu21-976, 2021.

Understanding the physical properties of magma reservoirs and their fluid/mechanical behaviour is crucial for improving geophysical models. New evidence suggests that large bodies of magma are difficult to maintain for an extended time period and that melts may instead reside within crystal-mush reservoirs which consist of variably packed frameworks of crystals and interstitial melt. Most existing volcano deformation models assume a pressurized cavity embedded in a homogeneous or heterogenous elastic half-space and therefore ignore the presence of crystals and the possible poroelastic mechanical response to melt intrusion or withdrawal. Here, we consider the magma reservoir to be entirely porous, comprising melt distributed between solid crystals. We investigate the influence of poroelastic mechanical behaviour on reservoir pressure development and resultant spatio-temporal surface deformation. We examine the post-intrusion and post-eruption time-dependent pressure evolution in the magma reservoir due to melt diffusion in the porous domain. Unlike the classic (cavity) models for volcanic surface deformation, an observable post-eruptive or post-intrusion time-dependent inflation can occur without an additional mass change if the reservoir is sufficiently permeable. Post-intrusion and post-eruption timescales vary depending on the porosity of the mush (melt fraction), permeability and magma viscosity. Our study confirms that reservoir inflation and surface deformation can occur without an intrusion or withdrawal of melt but are instead controlled by the mush's poroelastic behaviour. 

How to cite: Alshembari, R., Hickey, J., Williamson, B., and Cashman, K.: Insights into the poroelastic mechanical behaviour of a crystalline magma reservoir and its influence on modelling volcano surface deformation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9258, https://doi.org/10.5194/egusphere-egu21-9258, 2021.

The tortuous travel of magma through the crust may sometimes result in volcanic eruptions at the surface. In the brittle crust, magma propagation usually occurs by fracturing the rock and opening its own way through them. This process of diking is controlled by the interaction of many complex physical processes including rock fracture, flow of compressible fluids, phase transitions, heat exchange. Current models of dikes consider either a fracturing-dominated approach, that neglects the viscous flow and allow to estimate the trajectory of dike propagation, or a viscous-dominated approach that neglects the fracturing at the dike tip allowing to infer the propagation velocity of the dike. Here we propose a new numerical approach aiming at modeling both the magma path and velocity. We start from a two-dimensional Boundary Element model solving for the trajectory of a quasi-static crack in an elastic medium subjected to external stress (Maccaferri et al, 2011), and implement the effects of the viscous fluid flow assuming a Poiseuille flow. We build on the previous work by Dahm (2000) but relaxing the assumption of stationarity, and thus allowing to take into account heterogeneous crustal stresses, complex dike paths, and dike velocity variations. The fluid flow results in a viscous pressure drop applied to the crack wall, which modifies the crack shape and contributes to the energy balance of the propagating dike. In fact, the energy dissipated by viscous flow is linearly dependant on the viscosity of the fluid and the crack velocity. It follows that the velocity can be inferred from the total energy budget by imposing that the viscous energy dissipation and the energy spent to fracture the rocks equals the strain-plus-gravitational energy release. However, the viscous dissipation strongly depends on the opening of each dislocation element, causing numerical instabilities in the calculation of the dike velocity due to the fracture closure at the dike tail. We will present first results of velocities derived with this approach considering only a static crack shape (that is to say neglecting the modification of the crack shape induced by the flow). We will discuss the influence of various parameters (crack size, Young’s modulus value...), and will compare the numerical velocities obtained with observations, first considering velocities measured in analogue experiments when injecting fluids of various viscosity (air and oils) in gelatin tanks, and secondly using diking events documented at basaltic volcanoes (such as Piton de la Fournaise (Réunion) and Mount Etna (Sicily)).

How to cite: Furst, S., Pinel, V., and Maccaferri, F.: Propagation velocity of magma intrusions, a new 2D numerical approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8628, https://doi.org/10.5194/egusphere-egu21-8628, 2021.

The uprise of  magma dikes that split in branches  are regularly outcropping as en echelon structures, segmented dikes, or finger like intrusions are documented examples. Dike segmentation and finger formation at different scales have been attributed commonly to effects of the host rock: 1) crustal heterogeneities that interact with the magma such as faults, fractures, and joints; 2) local rotation of the principal stress axes orientations during emplacement;  3) changes in the host rock elastic properties due to chemical corrosion, unconsolidation and weathering. Less attention has been devoted to the effect of the magma flow in leading to segmentation and formation of fingers, but the effect of fluid flow might be relevant due to the complex flow dynamics of magmas.  In past experiments presented by  Chavez-Alvarez et al.  (2020a) and Chavez-Alvarez and Cerca (2020b), he relevance of viscous forces in hydrofracturing was analyzed by quantitatively comparing the evolution of experimental dikes of contrasting rheology (Newtonian and shear thinning), where segmentation was documented for the case of shear thinning fluids. Here we provide an analysis of the hydrofracturing conditions that prevail before the segmentation of hydrofractures that transport shear thinning fluids. We evaluated parameters of toughness and viscous regimes in conditions of the hydrocrack inception, early development and propagation before segmentation. Furthermore some aspects of the flow such as Reynolds number and flow trajectories inside the experimental dikes are presented. 

References

Chàvez-Alvarez, M. J., Cerca-Martìnez, M. Bustos-Cervantes N. 2020a. Contrasting emplacement modes of water (Newtonian) and Carbopol suspension (shear thinning) injected in gelatin: insights for magma dikes.   (In revision).

Chàvez-Alvarez, M. J. and Cerca-Martìnez, M. 2020b: Dyke segmentation: an experimental approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13768, https://doi.org/10.5194/egusphere-egu2020-13768, 2020

How to cite: Chavez, J. and Cerca, M.: Flow and fracturing conditions before the segmentation of experimental dikes , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9810, https://doi.org/10.5194/egusphere-egu21-9810, 2021.

By modelling the magnitude and spatial distribution of surface displacement induced by different representations of magma conduits, more informed decisions can be made for the deployment of real-time monitoring devices, such as tiltmeters, and aid interpretations of stress changes within the subsurface. The existence of varying forms of magma conduit is widely known, despite this, the effect of laterally elongated conduits on magma flow processes and resulting surface deformation at volcanoes has not been systematically explored.

By varying the ellipticity of the volcanic conduit cross-section we assess the relative importance of laterally elongated conduits when considering flow processes and surface deformation. The scenario of magma ascent through a dyke that changes into a cylindrical conduit closer to the surface is also considered, herein referred to as a complex conduit. Both shear stress on the conduit walls due to viscous magma flow resistance and the pressurisation of conduits are used as source mechanisms.

When considering the pressurisation of different conduit geometries, the displacement field induced by an elongated conduit (where semi-axes a and b of the elliptical cross-section equal a=10b) is an order of magnitude larger than that of a cylindrical conduit. Moreover, for the case of the complex conduit, the displacement field is dominated by the dyke form of the deeper conduit, with little influence from the transition region between elongated and cylindrical conduit. When considering shear stress as a source mechanism, the displacement field induced is primarily vertical and radially symmetric even at the smallest spatial scales ($<1$ km), independent of ellipticity of conduit origin. The ellipticity of conduits with equal cross-sectional area has a significant control on the flow rate, and therefore, the magnitude of shear stress achieved under equal pressure gradients. The deformation resulting from shear stress on the conduit walls is also influenced by the depth of rheological changes within the magma and the inter-dependency with conduit geometry.

How to cite: Eaton, E., Neuberg, J., and Marsden, L.: Elliptical Versus Cylindrical Magma Conduits, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8749, https://doi.org/10.5194/egusphere-egu21-8749, 2021.

Geodetic modelling has become an established procedure to interpret the dynamics of active volcanic plumbing systems. Most established geodetic models implemented for inverting geodetic data share similar physical assumptions: (1) the Earth's crust is modelled as an infinite, homogeneous elastic half-space with a flat surface, (2) there is no anisotropic horizontal stress to simulate tectonic stresses, (3) the source boundary conditions are kinematic, i.e., they account for an instantaneous inflation or deflation of the source. Field and geophysical observations, however, provide evidence that significant inelastic shear deformation of the host rock can accommodate the propagation of dykes and sills. We show that inelastic processes accommodating the emplacement of dykes in the brittle crust have large implications for dyke-induced surface deformation patterns.

We present two quantitative laboratory experiments that simulate two distinct dyke emplacement mechanisms, in agreement with geological and geophysical observations: (1) dyke propagation as a tensile fracture through a dominantly elastic host in gelatin, and (2) dyke propagation in the silica flour as viscous indenter, which pushes its ahead plastic host that dominantly fails in shear. The syn-emplacement surface deformation is monitored during each experiment. Each dyke emplacement mechanism triggers drastically distinct surface deformation patterns: two uplifting bulges separated by a trough in the gelatin experiment, in good agreement with the expected dyke-induced deformation predicted by the rectangular dislocation model, versus a single uplifting elongated bulge above the apex of the dyke in the silica flour experiment. This first-order difference shows that (1) the rheology of the host and the emplacement mechanisms of dykes are key factors for interpreting dyke-induced geodetic data at active volcanoes, and (2) static, kinematic geodetic models, such as the rectangular dislocation model, have limitations for revealing the physics and dynamics of volcanic plumbing systems.

There is no geodetic model associated with dyke emplacement able to reproduce the single uplifting bulge measured in our silica flour experiment. Instead, such surface deformation pattern is usually fitted with geodetic models of inflating spherical, ellipsoidal or horizontal planar sources. Our silica flour experiment thus shows that (1) a successful data fit is not sufficient and does not imply a physically relevant interpretation, and (2) dykes emplaced as viscous indenters should be considered as an alternative interpretation of single uplifting bulges measured at active volcanoes. This implies that novel geodetic models accounting for dykes emplaced as viscous indenters should be designed to interpret dyke-induced surface deformation patterns in favorable geological settings, e.g. felsic volcanoes.

In summary, our study motivates the design of new geodetic models that move beyond elasticity, i.e. that account for the realistic elasto-plastic mechanical behavior we know occurs in the Earth's brittle crust. In addition, it highlights the added value of our laboratory volcano geodesy approach, which can be the foundation for designing novel geodetic models that accounts for processes that cannot be implemented in numerical models.

How to cite: Bertelsen, H. S., Guldstrand, F., Freysteinn, S., Pedersen, R., Mair, K., and Galland, O.: Beyond elasticity: Are Coulomb properties of the Earth’s crust important for volcano geodesy?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13325, https://doi.org/10.5194/egusphere-egu21-13325, 2021.

The Thermo-Poro-Elastic (TPE) inclusions contribute to deformation and stress in volcanic and hydrothermal areas. Differently from other deformation source models (e.g. magma chambers), the TPE sources effects are due to pore-pressure and temperature changes of the fluid within the inclusion. So that the TPE inclusions can allow large deformations even in those volcanic environments in which there is no evidence of a shallow magmatic body. This kind of sources also provides large deviatoric stresses, promoting different types of focal mechanisms both inside and around them. With respect to a previous work, we propose a numerical model that allows for a more realistic representation of TPE sources: we can represent inclusions with an arbitrary geometry and we take into account the elastic stratification of the crust, thanks to a modified version of the EDGRN/EDCMP code. We can also represent the case of a depth dependent distribution of pore pressure and temperature changes within inclusions, as expected during the transient stage of fluid propagation and temperature diffusion. We found that elastic layering and transient changes of the TPE source can promote both normal and thrust earthquakes in its interior. For the 1982-84 unrest episode at Campi Flegrei the inversion of geodetic data leads to a lower misfit between modeled and measured deformation data, with respect to a homogeneous medium and the retrieved geometry and location of the thermo-poro-elastic are in good agreement with the observed distribution of seismicity.

How to cite: Nespoli, M., Belardinelli, M. E., and Bonafede, M.: A numerical approach for modeling thermo-poro-elastic deformation sources in volcanic and hydrothermal regions., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8282, https://doi.org/10.5194/egusphere-egu21-8282, 2021.

Gravity change observations at volcanoes provide information on the location and mass change of intruded magma bodies. Gravity change and surface displacement observations are often combined in order to infer the density of the intruded materials. Previous studies have highlighted that it is crucial to account for magma compressibility and the shape of the gravity change and deformation source to avoid large biases in the density estimate. Currently, an analytical model for the deformation field and gravity change due to a source of arbitrary shape is lacking, affecting our ability to perform rapid inversions and assess the nature of volcanic unrest.  

Here, we propose an efficient approach for rapid joint-inversions of surface displacement and gravity change observations associated with underground pressurized reservoirs. We derive analytical solutions for deformations and gravity changes due to the volume changes of triaxial point-sources in an isotropic elastic half-space. The method can be applied to  volcanic reservoirs that are deep compared to their size (far field approximation). We show that the gravity changes not only allow inferring mass changes within the reservoirs, but also help better constrain location, shape and the volume change of the source. We discuss how the inherent uncertainties in the realistic shape of volcanic reservoirs are reflected in large uncertainties on the density estimates. We apply our approach to the surface displacements and gravity changes at Long Valley caldera over the 1985-1999 time period. We show that gravity changes together with only vertical displacements are sufficient to constrain the mass change and all the other source parameters. We also show that while mass change is well constrained by gravity change observations the density estimate is more uncertain even if the magma compressibility is accounted for in the model.

How to cite: Nikkhoo, M. and Rivalta, E.: Analytical modelling and joint inversion of surface displacements and gravity changes at volcanoes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4887, https://doi.org/10.5194/egusphere-egu21-4887, 2021.

There is mounting evidence that rainfall can be instrumental in triggering or otherwise modulating primary volcanic activity. Individual case studies have revealed a link between rainfall and volcanism at Piton de la Fournaise (La Réunion), Mount St. Helens, Kīlauea (both USA), Las Pilas volcano (Nicaragua), and Soufrière Hills volcano (Montserrat), among others. Additionally, there exists a wealth of anecdotal evidence of rainfall-induced volcanism around the world. Do these discrete examples reflect a prevalent underlying link between rainfall and volcanic activity?

We extract and analyse multi-decadal rainfall timeseries from satellite data to assess whether the duration and timing of annual rainfall plays a role in modulating eruption frequency at different volcanoes. By comparing observed eruption distributions over time with the theoretical probability of those distributions, we identify around three dozen volcanic systems—~15 % of the volcanoes in our pre-filtered catalogue—where the eruption record appears to be strongly correlated with the wettest parts of the year. Our analyses reconfirm previous observations at several volcanoes and suggests that they are indeed symptomatic of a broader link between volcanism and the hydrological cycle.

Shallow-seated physical explanations often involve either the thermal contraction of recently-emplaced lava, fluid-induced pressurisation of the interior of a dome, or a combination of both. Deeper-seated mechanisms  include rainfall perturbing the regional stress within or applied by the volcanic edifice in one of two primary different ways: (a) by changing the load overlying the magma chamber, or (b) by changing the threshold for mechanical failure (either prompting opportunistic dyke propagation or directly facilitating magma chamber rupture).These mechanisms are underpinned by a single common process: the infiltration of meteoric water into the edifice.

We demonstrate that pressure transfer models yield pressure fluctuations at magma-relevant depths in line with previously theorised trigger stresses. Infiltration-induced quasistatic stresses can bring about a long-lived increase of pore pressure above hydrostatic, in contrast to the short-lived dynamic stress pulses observed at shallow depths. Assuming realistic fluid transport properties, we model pressure perturbations of order 10 kPa in the immediate subsurface, attenuating rapidly in the uppermost couple of kilometers. These pressure changes are a non-negligible fraction of the tensile strength of material thought to be important in dyke propagation, highlighting that the potential for time-variant fluid pressure within the edifice is an important consideration.

We anticipate that satellite-derived precipitation data will prove invaluable in integrating rainfall into future quantitative studies, volcano monitoring programs, and probabilistic hazard assessment. Aside from the possibility for initiation of primary volcanic activity, rainfall is a demonstrable driver of many secondary hazards, such as lahars, debris flows, mass movement, acid rain.  As ongoing climate change is projected to result in increasingly extreme rainfall patterns over the coming century, the potential for rainfall-triggered volcanic activity may be set to increase in the future. Rainfall is both measurable and, to a degree, forecastable: the inclusion of continuous ground- and satellite-based meteorological monitoring—in tandem with simple models of pressure transfer—could prove invaluable in providing some advance warning of these hazards.

How to cite: Farquharson, J. and Amelung, F.: Pore fluid pressure evolution in volcanic environments: the role of rainfall, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-503, https://doi.org/10.5194/egusphere-egu21-503, 2021.

Caldera collapses and flank failures, eventually associated with violent explosive eruptions, punctuate the history of volcanoes worldwide and represent major highly hazardous events in their evolution. Nevertheless, their link to magma transfer and storage in the plumbing system, together with the nature of weakness zones responsible for volcano collapses still need to be fully elucidated. We performed rapid decompression experiments on a set of basaltic rocks (lavas, dolerite dikes, gabbros) from Piton de la Fournaise, La Réunion, spanning a very large range of petrophysical properties. Samples derived from the most recent  caldera-related explosive breccias of this volcano. Petrophysical measurements revealed a corresponding variability in density, porosity, P-wave velocity (dry and wet), and uniaxial compressive strength. The large variation in P-wave velocity and strength is interpreted to be the result of the wide ranges in texture (porosity/vesicularity) and lithology. Notably, some of the dense gabbroic units that have remained intact despite likely having experienced several natural cycles of heating and cooling are comparatively weak. We infer that volcano instability should not be interpreted solely in terms of altered rock units. On one side, the interface between shallow intrusive bodies and the vesicular lava pile represents a potential interface for repeated sill emplacement, which favour flank sliding. On the other side, weak shallow seated granular intrusive rocks with variable amounts of interstitial melt respond in a brittle fashion to rapid decompression during caldera and flank collapse events. The large petrophysical heterogeneity of crustal rocks together with the occurrence of shallow intrusive bodies must be considered when interpreting monitoring data and assessing potential hazards related to the stability of basaltic volcanoes.

How to cite: Di Muro, A., Kueppers, U., Heap, M., Scharzlmueller, F., and Dingwell, D.: From permanent flank sliding to catastrophic collapse and explosive eruptions at basaltic volcanoes: the role of shallow intrusive magma bodies., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3204, https://doi.org/10.5194/egusphere-egu21-3204, 2021.

Volcanic flank collapse has caused over 20,000 casualties in the past 400 years, and is one of the most dangerous hazards affecting communities and infrastructure near volcanoes. Flank instability has mostly been investigated at ocean volcanoes, due to their ability to trigger deadly tsunamis, however, these collapses are prevalent across volcanic settings, with all but one volcano in Guatemala with elevation over 2000m having experienced flank collapse, like Pacaya Volcano. At Pacaya, there is evidence for at least one past collapse, and transient SW flank motion has been identified accompanying vigorous eruptions in 2010 and 2014. We use InSAR time-series analysis to reveal, for the first time, long-term displacement of the SW flank of Pacaya during a period of volcanic quiescence from 2011-2013. This motion extended into 2014, with increased displacement rate attributed to dike intrusion during a major eruption. Subsequent static stress change analyses investigated the interactions between the modeled dike intrusion and detachment slip. Our research highlights that long-term flank motion might be more prevalent than currently recognized and that an awareness of existing structural weaknesses such as detachment faults and of possible magma-faulting interactions is vital when assessing the likelihood and style of volcanic flank collapse.

How to cite: Gonzalez Santana, J. and Wauthier, C.: Flank motion detected between 2010 and 2014 through InSAR time-series analysis at Pacaya Volcano, Guatemala, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3475, https://doi.org/10.5194/egusphere-egu21-3475, 2021.

Volcanic domes form when lava is too viscous to flow away from an active volcanic vent; instead, the lava accumulates into a mound consisting of a hotter, ductile core and a colder, brittle outer layer. An existing lava dome grows when new material is injected into the core of the dome, causing the  outer layer to stretch and develop tensile fractures. With continued dome growth, these weaknesses can propagate to form an extensive fracture network and the dome may fail. Collapse events often generate rock falls and debris avalanches, lahars, and high-speed pyroclastic flows, endangering populations residing at the base of a volcano. Since such fractures represent potential failure planes, in this project we aim to understand the role they have in destabilising lava domes.

This project will build on the work published by Harnett et al. (2018), which demonstrates the suitability of a discrete element modelling approach to simulate dome emplacement and evolution. Specifically, this project is designed to:

1. Use high-resolution photogrammetry to characterise the possible fracture states of a dome;

2. Establish up-scaled rock-mass properties by performing geomechanical experiments on both fractured and non-fractured samples of dome rock from prior collapses;

3. Develop a numerical model to investigate how the presence and properties of fracture networks influence dome stability.

The model, developed using PFC, will be used to identify critical fracture states that can signify a dome collapse is likely to occur. Under the current model, parallel bonds simulate the fluid magma core and flat joints simulate the solid talus material. This project will build on this original model by incorporating discrete fracture networks into the smooth-joint model to implement dome fracturing. The new model will look to investigate the effect  of a fracture network on a static dome that, when in its unfractured state, is stable under gravity. Additionally, the model will be designed such that inputs can include experimentally derived rock-mass properties. It is hoped that, by incorporating observational and experimental data into a more  complex model, the dynamic evolution of fractures in a growing lava dome can be investigated and the ongoing likelihood of a dome collapse event can be assessed.

Harnett, C. E. et al., 2018. J. Volcanol. Geoth. Res., 359: 68-77.

How to cite: Myers, A., Harnett, C., Heap, M., Holohan, E., and Walter, T.: Characterising fracture patterns at growing lava domes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13573, https://doi.org/10.5194/egusphere-egu21-13573, 2021.

Over the years, various satellites like ERS-1, ERS-2 and Envisat has been in use for the interferometric capability for a wide range of geophysical and environmental applications. With the launches of Sentinel-1A and 1B satellites in 2014 and 2016 respectively, the availability of SAR data from every part of the world has been increased many folds. With short revisit times of 1-6 days, the Sentinel-1 and the planned Tandem-Land NISAR missions provide an unprecedented wealth of topography and surface change data using InSAR technique. Utilizing these Synthetic Aperture Radar (SAR) acquisitions, repeated approximately from the same point in space at different times, it is possible to produce measurements of ground deformations at some of the world’s active volcanoes and can be used to detect signs of volcanic unrest. Most of the existing traditional algorithms like Permanent Scatterer (PS) analysis and Small Baseline Subset (SBAS) technique are computationally extensive and cannot be applied in near real time to detect  precursory deformation and transient deformations. To overcome this problem, we have adapted a minimum spanning tree (MST) based spatial independent component analysis (ICA) method to automatically detect deformation signals of volcanic unrest. We utilize the algorithm’s capability to isolate signals of geophysical interest from atmospheric artifacts, topography and other noise signals, before monitoring the evolution of these signals through time in order to detect the onset of a period of volcanic unrest, in near real time. We demonstrate our approach on synthetic datasets having different signal strengths, varying temporally. We also present the results of our approach on the volcanic unrest of Mt. Thorbjörn in Iceland on 2020 and also the volcanic unrest of a volcano in Mexico from 2017 to 2019.

How to cite: Ghosh, B., Motagh, M., Haghshenas Haghshenas, M., and Walter, T.: Using minimal spanning tree based ICA optimization for volcanic unrest determination, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3200, https://doi.org/10.5194/egusphere-egu21-3200, 2021.

The Long Valley Caldera, California (USA), has been restless over the past few decades, experiencing seismic swarms and ground deformation episodes. The last inflation began in late 2011, when a radially symmetric tumescence was detected coinciding with a large resurgent dome within the caldera. Since then, a continuous inflation with quasi-steady rate of ~1.5 cm/yr has been observed.  Earthquakes mostly occur within the caldera along the South Moat Seismic Zone, to the south of the maximum deformation area. Although the area is tectonically active, increased seismic activity has been documented during periods of renewed inflation since the onset of this tumescence in 1978. In this study, we aim to investigate the nature and dynamics of the long-term unrest at Long Valley Caldera, as well as to provide new insights into the interaction between magmatic and tectonic processes. For this purpose, we consider a variety of datasets including geodetic and seismic records over the period spanning from late 2011 to the end of 2020. A complete seismic catalog supports our study, with more than 200 M2.5-4.5 earthquakes recorded since 2011, most with epicenters located within the caldera. Measurements from a dense network of continuous GPS stations collected in the last 10 years are analyzed in combination with high resolution Interferometric Synthetic Aperture Radar (InSAR) data. For full temporal coverage, we integrate InSAR velocities obtained from the acquisition of different satellite missions. We use, in particular, data from SAR systems operating with X and C-bands such as TerraSAR-X, COSMO-SkyMed and Sentinel-1. The multi-sensor dataset (i.e., GPS and multi-mission InSAR data) compensate the limitations of each technique, with reliable mapping of the deformation pattern evolving over several years. Data analysis highlights uplift velocities with peaks of ~2 cm/yr within the caldera and beyond its southern rim. Moreover, compared to the first half of the period of analysis (2011-2014), the area affected by high deformation rates is broader in the last several years (2017-2020). Models based on the geodetic data are developed to constrain the deformation source and to better interpret the observed signals. This study is motivated as a contribution to the understanding of this long-lived caldera unrest, for a more reliable hazard assessment.

How to cite: De Paolo, E., Trasatti, E., Tolomei, C., and Montgomery-Brown, E. K.: The 2011-2020 long-term sustained inflation at Long Valley Caldera:  investigation of the interaction of magmatic and tectonic processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5394, https://doi.org/10.5194/egusphere-egu21-5394, 2021.

Axial Seamount is the most active submarine volcano in the NE Pacific Ocean, and is monitored by instruments connected to a cabled observatory (the US Ocean Observatories Initiative Cabled Array), supplemented by autonomous battery-powered instruments on the seafloor at ~1500 m depth.  Axial Seamount is a basaltic hot spot volcano superimposed on the Juan de Fuca spreading ridge, giving it a robust and apparently continuous magma supply.  It has had three effusive eruptions in the last 23 years in 1998, 2011, and 2015.  Deformation measurements have been conducted at Axial Seamount since the late 1980’s with bottom pressure recorders (BPRs) that can detect vertical movements of the seafloor with a resolution of ~1 cm.  This monitoring has produced a long-term time-series including co-eruption rapid deflation events of 2.5-3.2 meters, separated by continuous gradual inter-eruption inflation at rates that have varied between 15-80 cm/yr.  The overall pattern appears to be inflation-predictable, with eruptions repeatedly triggered at or near a critical level of inflation.  Using this pattern, the 2015 eruption was successfully forecast within a one-year time window, 7 months in advance.  As of January 2021, Axial Seamount has re-inflated ~2.1 m (~83%) of the 2.54 m it deflated during the 2015 eruption, but the rate of inflation has been decreasing since then.  Our current eruption forecast window is between 2022-2026, based on the latest rate of inflation.  Modeling of the seafloor deformation data along with other recent results from ocean bottom seismometers and multichannel seismic surveys inform our interpretation of the subsurface structure of the volcano and the geometry and depth of the shallow magma storage system.

How to cite: Chadwick, W. W., Nooner, S. L., Wilcock, W. S. D., Tolstoy, M., Waldhauser, F., Kelley, D. S., Arnulf, A. F., Carbotte, S. M., and Beeson, J. W.: Axial Seamount: A Wired Submarine Volcano Observatory in the NE Pacific, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-988, https://doi.org/10.5194/egusphere-egu21-988, 2021.

Resurgence uplift is the rising of the caldera floor, mainly due to pressure or volume changes in the magma reservoir. Identifying resurgence structures and understanding their relationship to the magmatic reservoir is challenging. We investigate the resurgence structures of the Neapolitan Yellow Tuff (NYT) caldera (Italy) by integrating bathymetric data, high-resolution seismic profiles and Differential Synthetic-Aperture Radar Interferometry data. Our results show that the resurgent area is manifested as 1) a central dome constituted by two main blocks bounded by NNE-SSW trending faults, 2) an apical graben developed on top of the most uplifted block, 3) a peripheral zone including several uplifted and tilted blocks, bounded by inward-dipping faults. The onset of the uplift of the central dome occurred through re-activation, in reverse motion, of normal faults formed during the caldera collapse, and located in the peripheral zone. During periods of unrests, the blocks of the central dome move independently at different velocities, and the peripheral zone accommodates the deformation. The restless behaviour of the NYT caldera is the result of a shallow magmatic reservoir located at 3.5 ± 0.7 km, and characterised by a width that roughly corresponds to the extension of the overlaying resurgent area. Defining the caldera-forming fault system and identifying the area involved by the resurgence is crucial for estimating depth and width of the magma reservoir, and predicting the caldera behaviour during periods of unrest by localising possible vents and sectors that will deform. This knowledge contributes to the evaluation of the volcanic hazard.

How to cite: Corradino, M., Pepe, F., Sacchi, M., Solaro, G., Duarte, H., Ferranti, L., and Zinno, I.: Resurgent uplift at large calderas and relationship to caldera-forming faults and the magma reservoir: new insights from the Neapolitan Yellow Tuff caldera (Italy) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12301, https://doi.org/10.5194/egusphere-egu21-12301, 2021.

Appraisal of morphodepositional markers tied to ancient sea-levels in high-resolution seismic profiles together with geo-archaeological markers along the coast of the Pozzuoli Bay provided insights into the vertical deformation of the submerged part of the Campi Flegrei caldera (Southern Italy).

The collapse of the central part of the Campi Flegrei caldera is associated with the eruption of the Neapolitan Yellow Tuff (NYT) at ~15 ka. The NYT caldera collapse was followed by central dome resurgence associated with alternations of fast uplift and subsidence displacements that accompanied with discrete phases of intra-caldera volcanic activity. Previously, the evolution of ground movement in the Campi Flegrei caldera has been reconstructed using marine deposits uplifted onland or archaeological evidence and historical accounts and thus offers a mainly 2D appraisal of the deformation pattern. However, a complete reconstruction of post-collapse deformation suffers of the limitation that nearly two-thirds of the caldera are submerged beneath the Pozzuoli Bay.

We contribute to fill this gap by providing a reconstruction of offshore and coastal deformation through estimation of the vertical displacement of morphodepositional markers in high-resolution seismic reflection profiles and geoarchaeological markers directly surveyed at shallow depths. Our interpretation reveals the occurrence of different sediment stacking pattern whose provides evidence of rapid and oscillating ground movements. Whereas the offshore morphodepositional markers provide displacement information for the last ~12 ka, for the last ~2 ka our interpretation is supported by ancient Roman sea-level indicators. The multi-dataset analysis has allowed disentangling the signal related to the post-caldera dynamics from a broader deformation signal that affects this part of the extensional margin of the Apennines.

The integration of offshore data in the study of past episodes of ground deformation, by yielding a more complete picture of the ground motions associated to the post-collapse evolution of the Campi Flegrei caldera, bears a significant contribution for a 3D reconstruction of this high-risk resurgence caldera. Besides, the multidisciplinary approach presented here can be relevant for investigations of other calderas spanning the sea-land transition.

How to cite: Marino, C., Ferranti, L., Natale, J., Sacchi, M., and Anzidei, M.: Offshore ground movements in the Campi Flegrei caldera during the last ~12 ka, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15220, https://doi.org/10.5194/egusphere-egu21-15220, 2021.

Sakurajima, located on the southern rim of Aira caldera, is one of the most active volcanoes in Japan. From long term deformation trends, the volcano is showing an increased risk of large-scale eruption, emphasizing the need to better understand the magmatic system.

Deformation modelling, primarily using the Mogi method, has dominated the geodetic assessment history of Sakurajima. These methods, however, contain limitations, such as the assumption of a homogeneous crust, and have therefore not accurately depicted the magmatic system. Numerical modelling techniques have reduced this limitation by accounting for subsurface heterogeneity.

Analytical modelling studies have suggested multiple magmatic sources beneath Aira caldera and Sakurajima volcano, whilst the only numerical study undertaken so far indicated a single source. Here, we test the multiple deformation source hypothesis, whilst also incorporating subsurface heterogeneity and topography, using Finite Element (FE) numerical modelling, and geodetic data from Sakurajima.

Using a full 3D model geometry for Sakurajima and Aira caldera, preliminary forward modelling suggests a second deformation source produces our best fit to the measured geodetic data. Optimum results indicate a shallow prolate source 7-10 km below sea level (bsl), in addition to a deeper oblate source at ~13 km bsl. These preliminary findings produce greater shallow storage depths than the previous analytical models (3-6 km) and ties in with the trans-crustal magmatic system hypothesis.

Increasing our understanding of the Sakurajima magmatic system will enable improved interpretations of geodetic data prior to eruptions and will inform models for a range of similar volcanoes world-wide.

How to cite: Backhurst, R., Hickey, J., and Williamson, B.: Assessing the Multiple Pressure Source Hypothesis for the Sakurajima Volcano and Aira Caldera Magmatic System, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14799, https://doi.org/10.5194/egusphere-egu21-14799, 2021.

Surface displacements recorded in volcanically active regions are often driven by magmatic, hydrothermal or tectonic processes. Measuring the deformation experienced by the ground as a result of these processes allows to constrain the changing volcanic conditions and to infer quantitative estimates of the subsurface magmatic storage, thus increasing the knowledge of volcanic hazards for the closest local population. Interferometric synthetic aperture radar (InSAR) has proven to be an useful tool to observe ground deformation in volcanically active areas like the Sakurajima volcano, southern Japan, one of the most active volcanoes worldwide. Its current activity is characterized by degassing and almost daily explosive eruptions. We performed an InSAR time series analysis to identify and characterize time-dependent ground deformation using Sentinel-1 data between 2015 and 2020. During this period several large explosions with plume heights of up to 6000 m occurred. We found evidence of ground deformation associated with precursory inflation connected to major explosions. In addition, we processed interferograms spanning a remarkable event that occurred on August 15 2015, in which we identified strong deformation around the Showa crater, in agreement with previous studies.

How to cite: Vásquez-Castillo, A. and Hort, M.: Volcanic deformation at Sakurajima between 2015 and 2020 revealed by Sentinel-1 InSAR time series, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13355, https://doi.org/10.5194/egusphere-egu21-13355, 2021.

Satellite-based UV spectrometers can constrain sulphur dioxide (SO₂) fluxes at passively degassing volcanoes over decadal time scales. From 2005 to 2015, more than 15 volcanoes had mean passive SO₂ fluxes greater than 1 kiloton per day. Although the processes responsible for such high emission rates are not clearly established, this study aims to investigate the impact of strong degassing on the pressurization state of volcanic systems and the resulting ground deformation. One possible result of high degassing rates is the depressurization of the region where the melt releasing gas is stored, which may result in subsidence at the Earth’s surface. Passive degassing may depressurize pathways between deep and shallow magma storage regions, resulting in magma ascent and possibly eruption.

A lumped-parameter model developed by Girona et al., 2014 couples the mass loss by passive degassing with reservoir depressurization in an open volcanic system. However, this model has yet to be tested using real measurements of gas emissions and ground deformation. In our study, we focus on Ambrym volcano, the past decade’s top passive emitter of volcanic SO₂, which exhibits intriguing long-term subsidence patterns and no obvious pressurization preceding eruptive periods. We compare subsidence rates measured by InSAR to the system’s average daily SO₂ flux, focusing on a subsidence episode spanning 2015 to 2017 that is not clearly linked to magma removal from the system. Using realistic input parameters for Ambrym’s system constrained by petrology and gas geochemistry, a range of reservoir volumes and conduit radii are explored. Large reservoir volumes (greater than 30 km³) and large conduit radii (greater than 300 m) are consistent with depressurization rates obtained from geodetic modelling of InSAR measurements using the Boundary Element method. By comparing these values of reservoir volume and conduit radius with those estimated from geodesy, gas geochemistry, and seismology, we test the applicability and discuss uncertainties of the aforementioned lumped-parameter physical model to interpret the long-term subsidence at Ambrym volcano as a result of sustained passive degassing.

How to cite: Shreve, T., Grandin, R., and Boichu, M.: Can high rates of passive volcanic gas emissions induce reservoir depressurization at Ambrym volcano (Vanuatu)?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7998, https://doi.org/10.5194/egusphere-egu21-7998, 2021.

In May 2018, a submarine eruption started offshore Mayotte (Comoros archipelago, Indian Ocean), and was first detected as a series of earthquake swarms. Since then, at least 6.4 km³ of lava has erupted from a newly mapped volcanic edifice (MAYOBS campaigns), about 50 km east of Mayotte island. Since the onset of the eruption, GNSS stations on the island have recorded subsidence (up to 17 cm) and eastward displacement (up to 23 cm). We combine marine gravity data derived from satellite altimetry with finite element models to examine the magmatic system structure and its dynamics. First, we calculate the Mantle Bouguer Anomaly (MBA) by taking into account the gravitational effect of the bathymetry and the Moho interfaces, assuming a crust of constant thickness of 17.5 km and correction densities of 2.8 g/cm³ and 3.3 g/cm³ for the crust and mantle, respectively. We then invert the MBA to determine the anomalous density structures within the lithosphere, using the mixed Lp-norm inversion and Gauss-Newton optimization implemented in the SimPEG framework. The gravity inversion reveals two zones of low density, east of Mayotte island. The first is located NE of Petite Terre island between ~15 and 35 km depth, and the second is located further east, south of La Jumelle seamounts and extends from ~25 to 35 km depth. We interpret these low density regions as regions of partial melt stored in the lithosphere and estimate the volume of stored magma. Finally, we use the newly imaged low density bodies to constrain the magma reservoir geometry and simulate magma flow from this reservoir to the eruptive vent in a 3D, time-dependent, numerical model. The model parameters are adjusted by minimizing the misfit between the modeled surface displacement and that measured at the 6 GPS sites, between May 2018 and 2020. The deformation modeling reveals the temporal evolution of the magma flux during the eruption, and the resulting stress distribution in the crust explains the patterns of recorded seismicity. Together with the existing seismic and geodetic studies, the gravity data analysis and FEM models bring new constraints on the architecture of the magma plumbing system and the magmatic processes behind the largest submarine eruption ever documented.

How to cite: Le Mével, H., Miller, C. A., and Zhan, Y.: Architecture and dynamics of the magmatic system feeding the 2018 offshore Mayotte eruption from satellite gravity data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3623, https://doi.org/10.5194/egusphere-egu21-3623, 2021.

In the Atacama Desert, at the Precordillera of northern Chile, a series of Paleocene-Eocene caldera deposits and ring-faults are exceptionally well-preserved¹. Here we aim to build on previous mapping efforts to consider the location, timing and style of pre, syn and post caldera volcanism in the region. We focus on the partially nested caldera complexes of Lomas Bayas and El Durazno^2,3 where deposits record several stages of caldera evolution (pre-collapse, collapse/intra-caldera and extra-caldera, resurgence and post-collapse eruptive deposits). The pre-caldera basement is a thick sequence of early Paleocene mafic lavas^{4, 5}. The caldera complex formed between around 63 and 54 Ma^{4, 5}. Both calderas constitute subcircular structures approximately 13 km in diameter and are cut by several NNW to NNE-trending felsic dikes which are spatially related to felsic domes interpreted as resulting from post caldera formation unrest^1,4. These calderas have been interpreted as part of the Carrizalillo megacaldera complex² . We combine field observations, such as the attitude of dikes, as well as information on their dimension and composition, the size, location and composition of domes and lava flows, as well as the evidence of the regional stress field operating during the caldera evolution from measurements of fault kinematics. This data will be used as the input to finite element method models to investigate the effect of nested caldera geometry, ring-faults and crustal heterogeneities on the location of domes and eruptive centers generated during caldera unrest. The results will be potentially useful for constraining models of eruption forecasting during periods of unrest in calderas and ore deposition models which have been shown to be linked to caldera structure and magma emplacement.

References

¹ Rivera, O. and Falcón, M. (2000). Calderas tipo colapso-resurgentes del Terciario inferior en la Pre-Cordillera de la Región de Atacama: Emplazamiento de complejos volcano-plutónicos en las cuencas volcano-tectónicas extensionales Hornitos y Indio Muerto: IX Congreso Geológico Chileno, v. 2. Soc. Geol. de Chile, Puerto Varas.

² Rivera, O., and Mpodozis, C. (1994). La megacaldera Carrizalillo y sus calderas anidadas: Volcanismo sinextensional Cretácico Superior-Terciario inferior en la Precordillera de Copiapó, paper presented at VII Congreso Geológico Chileno. Acad. de Cienc. del Inst. Chilecol. de Geol. de Chile, Concepción.

³ Rivera, O. (1992). El complejo volcano-plutónico Paleoceno-Eoceno del Cerro Durazno Alto: las calderas El Durazno y Lomas Bayas, Región de Atacama, Chile. Tesis Departamento de Geología, Universidad de Chile, 242. (Unpublished).

⁴ Arévalo, C. (2005). Carta Los Loros, Región de Atacama. Servicio Nacional de Geología y Minería, Carta Geológica de Chile, 92, 1(100.000), 53 p.

⁵ Iriarte, S., Arévalo, C., Mpodozis, C. (1999). Mapa Geológico de la Hoja La Guardia, Región de Atacama. Servicio Nacional de Geología y Minería. Mapas Geológicos, 13, 1(100.000).

How to cite: Clunes, M., Browning, J., Marquardt, C., Cembrano, J., Villarroel, M., Rivera, O., and Mpodozis, C.: Reconciling the location of lava domes and eruption centers in Paleocene-Eocene calderas in northern Chile, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13865, https://doi.org/10.5194/egusphere-egu21-13865, 2021.

During the Tolbachik fissure eruption which took place from November 27, 2012 to September 15, 2013 a lava flow of area about 45.8 km² and total lava volume ~0.6 km³ was formed. We applied method of persistent scatterers to the satellite Sentinel-1A SAR images and estimated the rates of displacement of the lava field surface for 2017–2019. The surface mainly subsides along the satellite’s line-of-sight, with the exception of the periphery of the Toludski and Leningradski lava flows, where small uplifts are observed. Assuming that the displacements occur mainly along the vertical, the maximum average displacement rates for the snowless period of 2017–2019 were 285, 249, and 261 mm/year, respectively. On the Leningradski and Toludski lava flows the maximum subsidence was registered in areas with the maximum lava thickness.

To estimate the thermal subsidence of the lava surface we constructed a thermal model of lava cooling. It provides subsidence rate which are generally close to the real one over a significant part of the lava field, but in a number of areas of its central part, the real subsidence values are much higher than the thermal estimates. According to the thermal model when lava thickness exceeds 40 meters, even 5 years after eruption under the solidified surface there can be a hot, ductile layer, which temperature exceeds 2/3 of the melting one. Since on the Leningradski flow, the maximum subsidence is observed in the area of the fissure along which the eruption took place, one could assume that the retreat of lava down the fissure could contribute to the observed displacements of the flow surface. Subsidence can also be associated with compaction of rocks under the weight of the overlying strata. Migration of non-solidified lava under the solidified cover, also can contribute to the observed distribution of displacements - subsidence of the surface of the lava field in the upper part of the slope and a slight uplift at its periphery.

The work was supported partly by the mega-grant program of the Russian Federation Ministry of Science and Education under the project no. 14.W03.31.0033 and partly by the Interdisciplinary Scientific and Educational School of Moscow University «Fundamental and Applied Space Research».

How to cite: Mikhailov, V., Volkova, M., Timoshkina, E., Shapiro, N., Smirnov, V., Dmitriev, P., and Babayantz, I.: Subsidence of the lava flow formed during 2012-2013 Tolbachik fissure eruption: SAR data and thermal model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2939, https://doi.org/10.5194/egusphere-egu21-2939, 2021.

Soufrière Hills Volcano (SHV) is an andesitic dome-building volcano on the island of Montserrat (British West Indies). SHV began its current, and anomalously long, eruption in 1995, but eruptive activity has been intermittent with phases of lava extrusion separated by periods of relative quiescence. The current pause in eruption started in February 2010 and is the longest yet recorded, 10 years and 11 months at the time of writing (January 2021). Continuous GPS measurements show island-wide inflation from 2010 onwards, with the rate of inflation slowly decreasing with time. However, the length of the eruptive pause raises questions as to whether there have been significant changes to the magmatic system and/or the eruption at SHV might have ended. To assess the behaviour and evolution of the SHV magmatic system since 2010 and the relation to ongoing hazard assessment, we analyse the continuous GPS temporal deformation trends using a suite of geodetic numerical models. Our models incorporate a temperature-dependent viscoelastic rheology, topography derived from a Digital Elevation Model and three-dimensional variations in mechanical properties derived from seismic tomography. The models are driven using one of four possible time-dependent source functions, to simulate differences in the temporal evolution of the magmatic system. The results show that the observed deformation data requires a temporal source function whereby the magmatic system pressure is increasing with time. A viscoelastic crustal response cannot explain the long-term deformation trends alone. The nature of the source pressurisation is unclear, and could be due, for example, to one or a combination of, magma supply, degassing/volatile influx, or overturning within a transcrustal magmatic system. Continued pressurisation within the magmatic system highlights the need for sustained vigilance in the monitoring and management of the volcano and its surroundings.

How to cite: Hickey, J., Pascal, K., Head, M., Gottsmann, J., Fournier, N., Hreinsdottir, S., and Syers, R.: Magma system pressurisation and long-term surface deformation at Soufrière Hills Volcano, Montserrat, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14889, https://doi.org/10.5194/egusphere-egu21-14889, 2021.

Identifying driving mechanisms behind volcano deformation is one the key challenges of volcanology. Many geodetic models rely on simplified assumptions on source shape and the mechanical behaviour of surrounding rocks. However, geochemical, petrological and geophysical data illustrate complex architectures of sub-volcanic plumbing systems and crustal rocks. Mechanical heterogeneities fundamentally influence the stress vs. strain relationship and therefore require detailed analysis beyond the isotropic, homogenous, and elastic (IHE) half-space approximation embodied in traditional models.  
Here, we invert intra-eruptive ground displacements recorded between 2003-2005 on Montserrat to shed light on the magmatic plumbing system of Soufrière Hills Volcano.  Incorporating 3-dimensional crustal mechanical and topographic data in a finite-element model we show that the recorded displacements are best explained by a southeastward dipping (plunge angle of 9.3˚) vertically extended tri-axial ellipsoidal pressure source with semi-axis lengths of 1.9 and 2.0 km horizontally, and 5.0 km vertically.  The source is centred at 9.35 km depth below main sea level and embedded in independently imaged anomalously weak crustal rocks.  The source orientation appears to be controlled by the local stress field at the intersection of two major WNW-ESE and NW-SE striking tectonic lineaments. We derive an average volumetric strain rate of 8.4 x10^-12 s^-1 by transcrustal pressurisation which may have contributed to flank instability and mass wasting events in the southern and eastern sectors of the island.

How to cite: Gottsmann, J., Flynn, M., and Hickey, J.: 2003-2005 intra-eruptive  deformation at Soufrière Hills Volcano (Montserrat) modulated  by volcano-tectonics and weak crustal rocks  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10709, https://doi.org/10.5194/egusphere-egu21-10709, 2021.

Ground deformation offers vital insight into the activity of volcanoes, as well as the characteristics of the magmatic systems that feed them. The extended eruption of the Soufrière Hills Volcano (SHV) has allowed for the development of a comprehensive multi-disciplinary monitoring network, which has aided extensive research into the magmatic system underlying the volcano. The modern network comprises GPS, strainmeters, and cheaper Electronic Distance Measurement (EDM). However, the island’s EDM network has to date only being used for monitoring the SHV. Here, for the first time, we co-analyse the EDM dataset from 2010-19 with the GPS data from the same period. This study aims to delineate the modern magmatic system conditions by building 3D Finite Element Models, as well as assessing the best use of EDM data in modelling the SHV.

The island-wide deformation recorded over the past decade at the GPS network is broadly radial relative to the SHV dome, with a decreasing deformation rate. The EDM data shows line lengthening on the west and east flanks of the volcano, but minor line length shortening on the northern flank. We utilise Finite Element Modelling to model the SHV magmatic system as a single elongated prolate with 3D topography incorporated. We systematically test a wide range of parameters to explore how both EDM and GPS record perturbations to the magmatic system. Our preliminary results show that variations of certain parameters to the deeper magmatic system have an impact on both EDM and GPS timeseries, while some parameters (e.g., source pressure, source depth, and source location) have a more significant effect on EDM measurements than others (e.g., source shape).

How to cite: Johnson, A., Hickey, J., Pascal, K., Williamson, B., and Syers, R.: Modelling the Soufrière Hills Volcano; Investigating the Montserrat magmatic system with co-analysis of EDM and GPS data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7517, https://doi.org/10.5194/egusphere-egu21-7517, 2021.

Soufrière Hills volcano on Montserrat in the West Indies showed five episodes of magma extrusion and as many pauses in its 25 years of volcanic activity. This eruptive behaviour exhibited cyclic deformation pattern where extrusive “phases” showed island-wide deflation and all “pauses” have been linked to inflation, the last of which remains ongoing. Several models have been developed over the years; all based on magma intrusion and extrusion, into, or from one or several reservoirs, respectively. Addressing the entire eruptive history, we explore in this presentation several alternative models ranging from the continuous magma influx at depth to the extreme case where intrusion of fresh magma has ceased years ago, while the inflation is continuing. Both, purely elastic and visco-elastic rheologies are explored.

How to cite: Neuberg, J. and Taisne, B.: Explaining the continuing inflation of Montserrat, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14952, https://doi.org/10.5194/egusphere-egu21-14952, 2021.

Seamounts are isolated, underwater volcanoes with more than 100 m in relief. This kind of volcanism arises from the lithosphere or asthenosphere through fractional melt and is a direct manifestation of the tectonic-magmatic activity of the interior of the earth. While previous studies have quantified the global distribution of seamounts by their physical properties (e.g., height, semimajor axis, angle, etc.), these studies usually (1) assume an elliptical cone to model seamount shape, and (2) neglect the sediment coverage on the seamount, which results in significant uncertainties when comparing properties of seamounts near the continents covered with thick sediments to those in the open ocean covered with thin sediments.

We apply a large-scale Gaussian Process regression to recover the seamount topography covered by sediments for an accurate distribution of volcanism in the South China Sea basin (with an average thickness of 1.5 km sediments) and the entire Pacific Ocean (with < 300 m thick sediments). Specifically, we first use Tophat filtering to isolate short-spatial-wavelength seamount topography above long-wavelength seafloor. Subsequently, we apply Gaussian Process regression to learn the seamount structure above the seafloor in order to extrapolate the structure beneath the sediment. Lastly, we compute the seamount volume above the sedimentary basement (i.e., top boundary of the oceanic crust) and compare it to the volume above the seafloor. Our results show that for the South China Sea, there is a significant increase in estimated seamount volume above the basement as compared to above the seafloor. For the Pacific Ocean, due to the thin sediment coverage, we observe negligible differences between the two volume estimates. Thus, analysis of seamount properties in marginal basins in the West Pacific with thick sediment coverage can lead to significant underestimation of volcanism intensity if sub-seafloor topography is not accounted for. For these marginal basins, without massive hotspots or apparent evidence of mantle plumes, normal plate tectonic processes are likely responsible for the intensive oceanic volcanism.

How to cite: Zhao, Y. and Riel, B.: Accurate Quantification of Seamount Volcanism in Abyssal  Sediments Using Gaussian Process Regression, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4073, https://doi.org/10.5194/egusphere-egu21-4073, 2021.

Balıkesir Volcanites (BV) are included into the Balıkesir Volcanic Province and contain various products of Oligo-Miocene volcanic activity in NW Anatolia. BV are formed from trachyandesite, andesite and dacite lavas with associated pyroclastic rocks. In this study, we report the petrographical investigations, mineral chemistry results and geothermobarometry calculations of the Balıkesir Volcanites in order to deduce the magma chamber processes and crystallization conditions. Andesites present a mineral composition of plagioclase (An35–50) + amphibole (edenitic hornblende) +biotite ± quartz and opaque minerals. The major phenocryst phases in dacite lavas are plagioclase (An39–53), quartz, amphibole (magnesio-hornblende), biotite, sanidine and opaque minerals. The mineral composition of the trachyandesites, on the other hand, is represented by plagioclase (An38–57) + amphibole (pargasitic hornblende) + biotite + clinopyroxene (endiopside- augite) ± sanidine ± quartz ± opaque minerals. Balıkesir Volcanites present distinct textural properties such as rounded plagioclase phenocrysts with reaction rims, oscillatory zoning, honeycomb and sieve textures in plagioclase, reverse mantled biotite and hornblende crystals. The plagioclase- amphibole geothermobarometry calculations of Balıkesir volcanites indicate that, andesite and dacite lavas present similar crystallization temperature and pressures conditions of 798- 813°C and 1,98- 2.17 kbar. Oppositely, trachyandesites were crystallized under 857°C and 3,72 kbar temperature and pressure conditions. These results show that the andesite and dacite lavas were originated from the same magma chamber with the depth of 7km whereas trachyandesites were evolved in a deeper magma chamber with 13 km depth. Combined mineral chemistry, petrography and geothermobarometry studies indicate that the open system processes such as magma mixing/mingling and/or assimilation fractional crystallization (AFC) were responsible for the textural and compositional variations of the Balıkesir Volcanites.

How to cite: Ünal, A. and Altunkaynak, Ş.: Mineral chemistry and geothermobarometry of the Balıkesir Volcanites (NW Anatolia, Turkey) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12060, https://doi.org/10.5194/egusphere-egu21-12060, 2021.