GMPV8.6 | Volcanic processes: tectonics, deformation, geodesy, unrest
EDI
Volcanic processes: tectonics, deformation, geodesy, unrest
Convener: Michael Heap | Co-conveners: Valerio Acocella, Virginie Pinel, Sigurjon Jonsson, Thorbjorg AgustsdottirECSECS, Kyriaki DrymoniECSECS, Tim DavisECSECS
Orals
| Fri, 19 Apr, 10:45–12:30 (CEST), 14:00–15:45 (CEST), 16:15–18:00 (CEST)
 
Room D2
Posters on site
| Attendance Thu, 18 Apr, 16:15–18:00 (CEST) | Display Thu, 18 Apr, 14:00–18:00
 
Hall X1
Posters virtual
| Attendance Thu, 18 Apr, 14:00–15:45 (CEST) | Display Thu, 18 Apr, 08:30–18:00
 
vHall X1
Orals |
Fri, 10:45
Thu, 16:15
Thu, 14:00
The session deals with the documentation and modelling of the tectonic, deformation and geodetic features of any type of volcanic area, on Earth and in the Solar System. The focus is on advancing our understanding on any type of deformation of active and non-active volcanoes, on the associated behaviours, and the implications for hazards. We welcome contributions based on results from fieldwork, remote-sensing studies, geodetic and geophysical measurements, analytical, analogue and numerical simulations, and laboratory studies of volcanic rocks.
Studies may be focused at the regional scale, investigating the tectonic setting responsible for and controlling volcanic activity, both along divergent and convergent plate boundaries, as well in intraplate settings. At a more local scale, all types of surface deformation in volcanic areas are of interest, such as elastic inflation and deflation, or anelastic processes, including caldera and flank collapses. Deeper, sub-volcanic deformation studies, concerning the emplacement of intrusions, as sills, dikes and laccoliths, are most welcome.
We also particularly welcome geophysical data aimed at understanding magmatic processes during volcano unrest. These include geodetic studies obtained mainly through GPS and InSAR, as well as at their modelling to imagine sources.

The session includes, but is not restricted to, the following topics:
• volcanism and regional tectonics;
• formation of magma chambers, laccoliths, and other intrusions;
• dyke and sill propagation, emplacement, and arrest;
• earthquakes and eruptions;
• caldera collapse, resurgence, and unrest;
• flank collapse;
• volcano deformation monitoring;
• volcano deformation and hazard mitigation;
• volcano unrest;
• mechanical properties of rocks in volcanic areas.

Orals: Fri, 19 Apr | Room D2

Chairpersons: Michael Heap, Valerio Acocella, Virginie Pinel
10:45–10:50
Volcano uplift, subsidence, and collapse
10:50–11:00
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EGU24-13606
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ECS
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On-site presentation
Matias Villarroel, John Browning, Martin Schöpfer, Carlos Marquardt, and Pamela Jara

Collapse calderas form when the roof of the magma chamber collapses downwards as a consequence of magma withdrawal due to either over- or underpressure within the chamber during large eruptions. Caldera morphology, orientation, and internal architecture can be influenced by the tectonic conditions within the crust. Various theoretical, field, and modeling studies have suggested that collapse calderas are shaped by a combination of outward-dipping reverse faults and inward-dipping normal faults. However, the role of the regional stress field and pre-existing crustal faults in shaping a caldera or modifying the conditions of fault nucleation is less clear. This is important since many calderas form in areas that are subjected to regional stresses and of intense crustal faulting. This study utilizes two-dimensional Distinct Element Method (DEM) models to explore the influence of regional stresses and pre-existing structures on collapse caldera evolution and resulting geometric style. To do so we model a crustal segment comprised of a shallow magma chamber that gradually decreases in volume, mimicking the process of magma withdrawal. To address the interplay between the stress regime and the dynamics of caldera collapse we applied the Rankine Stress Limit to Coulomb's friction law, which relates the shear stress (τ) to the effective normal stress (σ’n). This provides both active (ka) and passive (kp) limit stress states for a cohesionless material, by assuming a critically stressed crust with a friction angle 𝜙, thus it is defined the earth pressure coefficient (𝑘) being the horizontal (σh) to vertical (σv) effective stress ratio: k = σh /σv. For a cohesionless rock mass with friction angle 𝜙 the coefficients are: ka = 1–sin𝜙/1+sin𝜙 = 1/kp. Therefore, k is 1 for the isotropic case, k < 1 for extension (ka) and k > 1 for compression (kp). The effective vertical stress is, for a normally pressurized rock mass, given by: σv = ρ’gh, where ρ’ = ρbulk–ρfluid is the buoyant density, g is gravity and ℎ the depth. Pre-existing faults are represented by cutting the rigid blocks and assigning contact properties to the resulting facets. Our findings demonstrate that both the critical underpressure for collapse onset and the internal architecture of calderas are significantly influenced by the regional stress field of the crustal segment in which they are embedded. Moreover, the pre-existing faults do change both the geometry and style of collapse indicating an important role during caldera formation. By testing various fault spacings and properties, we identified parametric ranges within which pre-existing faults either contribute to or refrain from influencing the overall collapse geometry. These findings hold significance in reconstructing the underlying processes from well-preserved collapse calderas and in comprehending the conditions required for future collapses at potential caldera volcanoes.

How to cite: Villarroel, M., Browning, J., Schöpfer, M., Marquardt, C., and Jara, P.: The role of regional stress and pre-existing faults on collapse caldera onset and architecture, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13606, https://doi.org/10.5194/egusphere-egu24-13606, 2024.

11:00–11:10
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EGU24-17868
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ECS
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On-site presentation
Mehdi Nikkhoo and Vladimir Lyakhovsky

The eruption style and structural stability of lava domes are determined by the mechanical strength (rigidity), porosity and temperature of their constituent magmas and the stress (pressure) and strain rates acting on them. Both rigidity and porosity of dome materials evolve with time as a result of (1) formation of new micro-fractures (damage) due to cooling and/or increasing strain rates (causing rigidity decrease and porosity increase) and (2) large effective pressures (causing porosity decrease and compaction) in lava domes. The interaction between damage and porosity may lead to different deformation modes including transition between brittle or ductile behavior in the same material even at constant temperature, pressure and strain rate. We use a visco-poroelastic damage model to quantify the evolution of damage and porosity and their interactions in lava domes. The model is based on thermodynamic principles and uses a non-linear continuum mechanics formulation which predicts different effective elastic moduli for a solid when the loading changes from tension to compression. The model accounts for the temporal evolution of damage and porosity, damage-porosity interaction and gradual accumulation of irreversible deformation due to damage-related viscosity. Thus, the model can simulate a wide range of deformation mechanisms including local damage increase and strain localization leading to brittle failure, and cataclastic flow characterized by homogeneous damage increase and porosity decrease (inelastic compaction). We apply this continuum damage-porosity model to lab experiments on lava samples form Volcán de Colima (Mexico) and Galeras volcano (Colombia). We show that the model allows us to distinguish the contributions of different deformation mechanisms in the course of each experiment. For each volcano, we compare the model parameters constrained by the lab experiments and discuss the implications of the results for up-scaling the model and performing natural-scale simulations of lava dome deformations. 

How to cite: Nikkhoo, M. and Lyakhovsky, V.: A mechanical model for lava dome deformations using the visco-poroelastic damage rheology , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17868, https://doi.org/10.5194/egusphere-egu24-17868, 2024.

11:10–11:20
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EGU24-5131
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On-site presentation
Daniele Carbone, Flavio Cannavò, Chiara Montagna, and Filippo Greco

Decrease of the local gravity field and ground deflation were observed at Mt. Etna through continuous measurements, during a 2-month period when more than 20 short-lasting explosive eruptions took place. Results from the joint inversion of the gravity and ground deformation data are cross-checked against the output of a numerical code providing independent geochemical insight on how the density of the magmatic liquid/gas mixture in the source reservoir varies as a function of the pressure. This cross-analysis provides a framework to explain why (i) the bulk volume reduction sensed by the ground deformation data is much lower than the volume of the erupted products and (ii) the observed gravity changes point to a strong mass decrease, that is incompatible with a pure mechanism of magma withdrawal. Contraction of the source reservoir was mostly buffered by pressure-driven exsolution and expansion of H2O and CO2, which compensated the withdrawal of magma and led to the inferred mass decrease.

How to cite: Carbone, D., Cannavò, F., Montagna, C., and Greco, F.: Gas buffering of magma chamber contraction during persistent explosive activity at Mt. Etna volcano, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5131, https://doi.org/10.5194/egusphere-egu24-5131, 2024.

11:20–11:30
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EGU24-10865
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On-site presentation
Gregor Weber, Juliet Biggs, and Catherine Annen

Volcanoes often change shape over timescales of months to decades, and such signals are likely influenced by the long-term physical evolution of magmatic systems over hundreds of thousands to millions of years. The link between these different timescales is often overlooked. In this presentation, I will show how volcanic surface deformation in response to a sudden overpressure at depth evolves over the long-term history of magmatic systems. To do this, I integrate thermal models of large-scale magma system evolution with thermo-mechanical simulations of surface deformation. We examined how changes in magma flux, magmatism duration over hundreds of thousands of years, and the depth of an overpressure source impact post-injection viscoelastic surface movement over a 10-year period. Our findings show that the duration of the long-term magmatic activity and magma supply rate significantly affect surface deformation over timescales of years. The results show that due to thermal heterogeneity in the crust, asymmetrical patterns of surface deformation can emerge in time due to viscoelastic processes, potentially similar to temporal patterns of magma movement. When uplift originates from deep sources (around 10 or 15 km below the surface), deformation follows a consistent uplift trend, dissipating within a few years with little dependence on past magma flux or system lifespan. Conversely, shallow sources (around 5 km below) display a strong dependence on long-term magma supply rate and system lifespan, resulting in distinct patterns of post-intrusive subsidence and subsequent uplift for colder magma systems, or exclusive uplift for hotter and longer-lived systems. These findings align exceptionally well with the deformation behaviour and geophysical tomography at Tullu Moye and Aluto volcanoes in the East Africa Rift. In conclusion, understanding how long-term magmatic processes interact with short-term volcano deformation is crucial for interpreting signals of volcanic unrest.

How to cite: Weber, G., Biggs, J., and Annen, C.: Linking long-term magma evolution and short-term volcano deformation , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10865, https://doi.org/10.5194/egusphere-egu24-10865, 2024.

11:30–11:40
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EGU24-6041
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ECS
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On-site presentation
Lun Ai, Thomas Walter, and Felipe Aguilera

Lava emplacement in a summit crater is often associated with unpredictable explosions and volcanic hazards, especially for volcanoes that are popular with tourists. The Lascar volcano, Chile, experienced a sudden eruption in December 2022, followed by the extrusion of lava. We acquired a series of Pleiades tri-stereo satellite images covering this new eruptive episode. Using a photogrammetric approach, we generated high resolution point clouds and orthomosaics from the satellite images. By directly comparing distances between point clouds, we are able to quantify morphological and structural details and changes. We find initial uplift of the crater floor due to lava extrusion and rockfall deposits, and evidence for subsidence and the formation of a funnel centered on the crater floor. To understand the mechanical factors controlling the uplift and subsidence of the crater floor, we designed a novel set of analogue experiments to simulate lava extrusion and subsidence inside a scaled 3D printed mould of the Lascar crater. We account for geometric and topographic effects by running these extrusion and subsidence models. Sand and sand-plaster mixtures extrude and subside from a vertical conduit at a constant rate, simultaneously recorded by a digital camera at 10-second intervals. We use particle image velocimetry (PIV) method to track and visualize displacements on the crater floor. The results show that extrusion and subsidence occurs along distinct shear faults, which are constrained by the diameter of the underlying conduit. The shear faults are represented as concentric fractures and are consistent with the ring features observed at Lascar. By comparing satellite observations with analogue models, we develop a conceptual model in which a lava extrusion is affected by withdrawal from the conduit, forming a funnel-shaped surface depression associated with inward-dipping radial erosion gullies. Thus, our observations and analogue models also help to define the position and dimensions of the volcanic conduit, which is essential for understanding future episodes of the ups and downs of the Lascar crater floor.

How to cite: Ai, L., Walter, T., and Aguilera, F.: The ups and downs of the Lascar crater floor, and the resulting fracture pattern analyzed by satellite stereo photogrammetry and 3D printed mould analog experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6041, https://doi.org/10.5194/egusphere-egu24-6041, 2024.

11:40–11:50
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EGU24-11
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ECS
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On-site presentation
Emily Mick, Cyril Muller, and John Stix

Studies of deformation in volcanic settings are typically focused on active magmatic systems where inflation due to the injection of magma is an important indicator of potential eruptive activity. Phreatic eruptions are the result of the sudden flashing of trapped water to steam without the eruption of magma, and the resulting deformation is at a much smaller scale that is more difficult to detect. Rincon de la Vieja volcano is highly active system in northern Costa Rica that experiences frequent, predominantly phreatic and phreatomagmatic, eruptive activity. Multiple GNSS stations are set up and maintained by OVSICORI as part of their nationwide network including stations located 1 km south-west (summit station) and 5 km northwest (flank station) of the active vent. The summit station shows repeated movement towards the vent (northeast) 1-2 months prior to significant eruptions (infrasound magnitude > 4.5) on January 30th, 2020, April 15th, 2020, May 25th, 2020 and January 6th, 2022. Using a 30-day moving average, the north-south component appears to be the most reactive with repeated deformation of approximately 5 mm compared to ~2 mm for the east-west component. The vertical component does not show a similar signal prior to single events, however it does show significant uplift (up to 20 mm) during periods of high eruptive activity. This signal is most prominent in 2020 and 2022 when Rincon experienced hundreds of eruptive events per year resulting in a saw-tooth pattern of deformation. Similar signals are not visible on the flank station, potentially indicative of a shallow pressure source close to the vent itself and consistent with pressurization within the shallow hydrothermal system. To date, a phreatic eruption has not been successfully forecast owing to a lack of reliable precursory signals. Improved eruption forecasting likely requires a combination of measurements to document changes in gas flux, seismic signals, thermal signatures, and deformation.

How to cite: Mick, E., Muller, C., and Stix, J.: Ground Deformation Prior to Phreatic Eruptions at Rincón de la Vieja Volcano, Costa Rica Detected Using GNSS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11, https://doi.org/10.5194/egusphere-egu24-11, 2024.

11:50–12:00
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EGU24-18593
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ECS
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On-site presentation
Andrea Barone, Maurizio Fedi, Antonio Pepe, Pietro Mastro, Pietro Tizzani, and Raffaele Castaldo

Nowadays, modeling ground deformation field is a widely used strategy for monitoring volcanic areas since Differential Synthetic Aperture Radar Interferometry (DInSAR) technique provides maps and time-series with satisfactory spatial and temporal resolutions. In particular, in the case of SAR images acquisitions along both satellites orbits, the estimated information is the East-West and vertical components of the related three-components ground deformation field. The deformation along the North-South direction (i.e., along track) is therefore usually not available; while different techniques have been proposed to solve this task, the resolutions and accuracies of these retrieved measurements are not always satisfactory.

We propose a novel methodology for the imaging of the North-South deformation related to volcanic environments and, therefore, the retrieval of the three-component ground deformation field. In particular, we employ the theory of the potential functions on deformation in order to use the integral transforms of potential fields and recover the North-South component.

The proposed workflow is here tested on simulated deformation datasets by considering the commonly used analytic volcanic deformation sources, such that Mogi’s, Okada’s and Yang’s models. The outcomes of the simulations prove that the use of the potential functions theory allows the imaging of the North-South component of deformation with negligible errors with respect to the expected one.

We finally use this new methodology for studying the Sierra Negra volcano (Galapagos Islands, Ecuador) and retrieving the three-component of ground deformation field occurred during the 2017 – 2018.5 unrest, which has preceded the eruption. Specifically, we perform a comparison with GNSS data by showing that the proposed technique is able to image the pre-eruptive North-South component of deformation with a mean error of about 5% for this case-study, which is a surprising result for this kind of application.

We conclude by specifying the next step of this study, which will be based on the modeling of volcanic deformation sources through the use of the inferred three-component ground deformation field.

How to cite: Barone, A., Fedi, M., Pepe, A., Mastro, P., Tizzani, P., and Castaldo, R.: Evaluating the North-South deformation component from DInSAR data in volcanic framework., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18593, https://doi.org/10.5194/egusphere-egu24-18593, 2024.

12:00–12:10
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EGU24-3516
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solicited
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Highlight
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On-site presentation
Susanna Ebmeier, Eoin Reddin, Eleanora Rivalta, Marco Bagnardi, Scott Baker, Andrew Bell, Patrica Mothes, and Santiago Aguaiza

The Western Galápagos volcanoes of Alcedo, Cerro Azul, Darwin, Fernandina, Sierra Negra, and Wolf have exceptionally high rates of eruption and unrest.  Deformation rates measured using Interferometric Synthetic Aperture Radar are high magnitude during eruptions and episodes of magmatic intrusion, but also significant during inter-eruptive periods.  There are characteristic differences in deformation and unrest styles between the volcanoes that have persisted for at least three decades, indicative of the impact of topography, magmatic zone maturity and magmatic flux.   

Here, we focus on analysing the trends in displacements at these six volcanoes over the past three decades. These show correlations not only in long-term uplift and subsidence, but also in short term fluctuations in displacement rate.  Correlation is especially high during episodes of high melt flux into the shallow crust, indicating some degree of connectivity in the subsurface. We are able to rule out static stress changes, shallow hydraulic connections and radar processing artefacts, and suggest that the mechanism for connectivity lies in pore pressure diffusion at the base of the crust, as inferred at Hawai’i.

Volcanic deformation is generally interpreted in the context of shallow magmatic reservoirs treated as discrete independent systems.  However, in the Western Galápagos, and potentially many other places around the world, they are actually the most accessible expression of vertically extensive, heterogeneous magmatic systems.

How to cite: Ebmeier, S., Reddin, E., Rivalta, E., Bagnardi, M., Baker, S., Bell, A., Mothes, P., and Aguaiza, S.: Patterns of deformation and connectivity at Western Galápagos Volcanoes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3516, https://doi.org/10.5194/egusphere-egu24-3516, 2024.

Volcanic unrest and failure 1
12:10–12:20
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EGU24-11005
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ECS
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On-site presentation
Lilian Lucas, Peter C. La Femina, Patricia M. Gregg, Matthew S. Head, Machel Higgins, and Andrew F. Bell

Studying the interactions between magmatic and volcano-tectonic processes is critical to understanding the behavior of volcanic systems and the triggering of eruptions. Sierra Negra Volcano, Galápagos is one of the largest basaltic calderas on Earth, and its latest eruption in 2018 marked the first time an eruption in the Galápagos was recorded by both GNSS and seismic networks. These unprecedented data sets provide a unique opportunity to investigate the dynamics of eruption triggering and test hypotheses for dike initiation and migration. Observational and modeling studies of Sierra Negra’s previous eruption in 2005 hypothesize that tensile opening induced by a Mw5.3 earthquake on the southern intra-caldera trapdoor fault system resulted in magmatic dike initiation and eruption along the northern rim of the caldera (Gregg et al., GRL, 2018). In the ~13 years following the 2005 eruption, the caldera of Sierra Negra uplifted ~6.5 m (Bell et al., Nat. Comm., 2021). Sierra Negra’s inflation coincided with an increase in Mw > 4 earthquakes located along the intra-caldera fault system from late 2017 to June 2018 and a Mw5.4 earthquake occurred ~9 hours prior to the first eruptive fissure opening on 26 June 2018 (Bell et al., JGR, 2021). The similarities between the 2005 and 2018 pre-eruption sequences provide important clues about the dynamics of eruption triggering at Sierra Negra. In this study, we build upon previous numerical analyses of the 2005 and 2018 eruption (Gregg et al., GRL, 2018; Gregg et al., Sci. Adv., 2020; Bell et al., Nat. Comm., 2021) to model stress changes associated with the 2018 pre-eruptive Mw5.4 earthquake and begin to investigate dike initiation and magma migration leading to the first fissure opening. Specifically, thermomechanical finite element models are implemented in COMSOL Multiphysics to test the hypothesis that the Mw5.4 thrust fault earthquake promoted tensile failure and dike rupture in the northern region of the magma system. Future numerical models will test the hypothesis that the resulting stress field of the Mw5.4 earthquake controlled the pathway of dike migration. Previous numerical deformation models which exclude fault rupture (e.g., Gregg et al., Sci. Adv., 2018) do not result in system failure leading to eruption (i.e., tensile failure in the model space between the magma chamber and surface). Our new numerical model includes a segment of the intra-caldera Trapdoor Fault, and we solve for fault rupture parameters of the 26 June 2018 Mw5.4 earthquake, such as fault geometry and slip, and calculate the resulting stress and strain. The best-fit earthquake parameters are estimated by comparing the observed (cGPS-derived) and modeled co-seismic deformation. The stress field induced by both magma system inflation and fault rupture is evaluated to investigate failure of the volcanic edifice and optimal dike propagation pathways. Preliminary results demonstrate the importance of including fault displacements in model calculations of Sierra Negra’s stress evolution. In future numerical models, we aim to model and constrain magmatic intrusion geometries using pre- and syn-eruptive cGPS data to better understand the impact of static stress transfer in eruption triggering.

How to cite: Lucas, L., La Femina, P. C., Gregg, P. M., Head, M. S., Higgins, M., and Bell, A. F.: Numerical modelling of earthquake induced stress changes and dike migration preceding the 2018 eruption of Sierra Negra Volcano, Galápagos, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11005, https://doi.org/10.5194/egusphere-egu24-11005, 2024.

12:20–12:30
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EGU24-8016
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ECS
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On-site presentation
Clement de Sagazan, Lise Retailleau, Muriel Gerbault, Aline Peltier, Nathalie Feuillet, Fabrice J. Fontaine, and Wayne C. Crawford

Mayotte island experienced a large volcanic eruption 50 km offshore in 2018-2021, creating the submarine volcano “Fani Maoré”. The eruption was accompanied by intense seismicity at mantle depths (20-45 km), divided into a “proximal” and a “distal” cluster centered 10 and 30 km east from the island, respectively. Previous studies suggest that two separate magma reservoirs may lie at the top and bottom of the proximal cluster. Here, we assess whether two reservoirs are a mechanically viable explanation for the proximal cluster’s truncated conical shape.

We developed finite-element models of pressurized magma reservoirs in a 2D axisymmetric domain, modeling the reservoirs as compliant elastic ellipsoids embedded in an elastoplastic host rock. We find that, at these depths, extremely low friction is required to generate failure at realistically low reservoir pressures. This implies in turn that mechanical weakening must occur at these depths. The weakening could be induced by fractures or pore fluid overpressure in the volcanic system. We find that two superimposed reservoirs can generate a plastic domain between them, if they are spatially close enough. Several reservoir geometries (from spherical to sill-like) are plausible.

A conical fracture domain is more likely to appear for reservoirs with opposite pressure loads (i.e. one inflating, one deflating). Given the geometrical match with the proximal seismicity cluster at Mayotte, we suggest that the shallower (Moho-depth) reservoir is inflating, creating a potential hazard for Mayotte island. 

How to cite: de Sagazan, C., Retailleau, L., Gerbault, M., Peltier, A., Feuillet, N., Fontaine, F. J., and Crawford, W. C.: Seismicity near Mayotte explained by interacting magma bodies: Insights from numerical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8016, https://doi.org/10.5194/egusphere-egu24-8016, 2024.

Lunch break
Chairpersons: Kyriaki Drymoni, Tim Davis, Sigurjon Jonsson
14:00–14:05
Volcanic unrest and failure 2
14:05–14:15
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EGU24-4510
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ECS
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On-site presentation
Yan Zhan and Yiwen Huang

Dikes feed volcanic eruptions, causing devastating hazards and global impacts. Monitoring magma ascent through dike propagation can significantly enhance hazard assessment and mitigation. However, direct observation of dike propagation remains elusive. Among the available data, dike-induced earthquakes offer the best tracing of subsurface dike movement. These earthquakes may facilitate dike propagation by damaging the rock or slowing down the dike by releasing accumulated stresses. Yet, the relationship between these earthquakes and rock damage remains unclear. To clarify this relationship, we have developed a new dike propagation model that couples damage mechanics with porous flow to explore the local stress field's influence on fluid mobility within the dike. Our model's results show that the energy released during the rock-damaging process aligns with the seismicity induced by the dike. Furthermore, the model-calculated local stresses near the dike can explain the observed fault plane solutions associated with dike propagation. The new model also reveals the controls on magma ascent velocity, intrusion geometry, and surface deformation, with implications for other volcanic systems such as Bardarbunga, La Palma, and Piton de la Fournaise volcanoes.

How to cite: Zhan, Y. and Huang, Y.: A New Dike Propagation Model Linking Seismicity and Rock Damage Mechanics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4510, https://doi.org/10.5194/egusphere-egu24-4510, 2024.

14:15–14:25
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EGU24-9979
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ECS
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On-site presentation
Peter Makus, Marine Denolle, Christoph Sens-Schönfelder, Manuela Köpfli, and Frederik Tilmann

Mt. St. Helens is an explosively erupting volcano located in close vicinity to major metropolitan centres on the US West Coast. In recent history, Mt. St. Helens (MSH) erupted twice, in 2004 and 1980, causing more than 50 fatalities and over one billion USD of damage. Here, we present a seismic velocity change time series (dv/v) of an unprecedented length covering the years 1998-2023 recovered from seismic ambient noise. We discuss challenges arising from the very heterogeneous nature of the dataset recorded on a variety of seismic stations and discuss methods to address them. To reconcile measurements from different periods, we rely on an approach that simultaneously normalises our measurements and allows us to locate our dv/v estimates in space. Finally, we compare our obtained results to a multitude of auxiliary measurements, including GPS, earthquake, and meteorological data.  By employing models that link dv/v to these mechanisms, we attempt to unravel the contribution of each mechanism to our velocity change estimate. At volcanoes like MSH, our ultimate goal is to reliably isolate the volcanic contribution to dv/v, thereby aiding the identification of potential volcanic precursors.

How to cite: Makus, P., Denolle, M., Sens-Schönfelder, C., Köpfli, M., and Tilmann, F.: Understanding the long-term 4D Dynamics of the Seismic Velocity at Mount St Helens, WA, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9979, https://doi.org/10.5194/egusphere-egu24-9979, 2024.

14:25–14:35
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EGU24-19088
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On-site presentation
Eleonora Rivalta, Lorenzo Mantiloni, Geoff Kilgour, Sigrún Hreinsdóttir, Jennifer Eccles, Ian Hamling, and Michael Rowe

The Auckland Volcanic Field (AVF) consists of ~53 volcanoes, distributed over an area of ~ 360 km2. Located within the AVF is Auckland City, New Zealand’s largest population centre (~1.7M people), highlighting the need to adequately model future pre-eruption scenarios for enhanced preparedness. Geological evidence shows that past eruptions were variably explosive and formed maars, lava shields, and tuff rings, largely controlled by the extent of magma-water interaction. Any future eruption from a new vent location within the AVF would cause significant socio-economic impacts, extensive evacuations, and national-scale impacts. Our work aims to constrain the next probable vent location using novel physics-based approaches.

Current approaches to identifying the next AVF vent location use statistical analysis to define probability maps. Here we use a novel approach based on physical understanding of dyke propagation and newly developed 3D numerical codes that consider crustal stresses as the main controls on the orientation of dyke pathways. We estimate regional stresses based on GNSS data and consider surface mass redistributions at the Hauraki Rift and other volcano-tectonic structures in the wider area to constrain the overall elastic stress field. We backtrack magma pathways from known vent locations downward through the crust. Pathways are oblique and reach below the Hauraki Gulf or Firth of Thames (~30 km E of Auckland City) at the inferred depth of magma dyke release (35-50 km). We infer a common magma source is physically plausible in that location.

Further work will improve the robustness of the model, constrain the spatial spread of vents over time, dyke propagation velocity, and implications for early identification of future volcanic unrest.

 

How to cite: Rivalta, E., Mantiloni, L., Kilgour, G., Hreinsdóttir, S., Eccles, J., Hamling, I., and Rowe, M.: Locating the Auckland Volcanic Field's magma reservoir through magma pathway retrogression, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19088, https://doi.org/10.5194/egusphere-egu24-19088, 2024.

14:35–14:45
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EGU24-19530
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On-site presentation
Maria Charco, Pablo J. González, José L.G. Pallero, Laura García-Cañada, and Carmen Del Fresno

After 50 years of quiescence, the most voluminous eruption since historical records started at La Palma took place (September 19 – December 13, 2021, 85 days and 9 hours of duration). The observed deformation field during the eruption was consistent with a deflating reservoir located at Moho depth beneath Cumbre Vieja volcano. This reservoir has been previously studied and determined that magmas can stagnant and reside there over a wide range of time-scales varying from days-weeks to a few centuries. 

During the eruption, applying some basic principles we made a forecast of the eruption duration. Under the assumption of mass conservation in a close-system, the pressure drop, responsible for the observed deflation signal, controls eruption duration. On day 38th of the eruption and despite its simplicity, one of our models with a pressure drop equal to 1% of the initial reservoir overpressure provided an estimated duration of 86 ± 7 days. Therefore, less than halfway along the actual duration of the La Palma eruption, the proposed model was able to estimate a possible tight duration. This duration was consistent with historical records of eruption durations in La Palma ranging from 24 to 84 days. The lack of a priori bounds on the pressure drop necessary to cease the eruption made the forecast too uncertain to have operational impact. In hindsight, we empirically show that the pressure drop in the reservoir was actually limited by mass conservation. We conclude that the magma dynamics of the Moho reservoir was the dominant control on the eruptive volume evolution. This study demonstrates that near real-time forecasts of eruption durations will be possible in future similar eruptions at La Palma. Our study opens the possibility to explore the applicability of this method to other volcanoes.

How to cite: Charco, M., González, P. J., Pallero, J. L. G., García-Cañada, L., and Del Fresno, C.: La Palma (Canary Islands) eruption 2021: Forecast and hindcast of eruption duration, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19530, https://doi.org/10.5194/egusphere-egu24-19530, 2024.

14:45–14:55
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EGU24-2645
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ECS
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On-site presentation
David Sanz-Mangas, Inés Galindo, Raúl Pérez-López, Miguel Ángel Rodríguez-Pascua, María Ángeles Perucha, Carlos Camuñas, Julio López-Gutierrez, Juan Carlos García López-Davalillo, Carlos Lorenzo, Gonzalo Lozano, Juana Vegas, Rayco Marrero, Mario Hernández, José Francisco Mediato, and Nieves Sánchez

Multi-vent opening in monogenetic eruptions in the Canary Islands poses a threat considering the fast population increase over the last years. On the 19th of September of 2021 the last volcanic eruption of La Palma Island took place in the Cumbre Vieja volcanic ridge. The lava issued during the eruption affected more than 3000 buildings. The eruption was mainly concentrated along a main fissure that formed a cinder cone of approximately 200 m-high topped by several craters trending NW-SE. Although the geophysical data did not suggest the possibility of new vents opening far from the main fissure, more than 80 low effusion rate vents were opened following NW-SE, N-S and E-W directions. Effusive vents were opened as far as 3 km from the main fissure. Hawaiian style dominated in distal vents, and fast-flow pahoehoe lavas inundated new urban areas apparently out of danger to the south of the lava field. Previous historic eruptions show a similar pattern of several fissure-type vents extending over more than 4 km like Martín in 1642, El Charco in 1712 or San Juan in 1949.

In the 2021 eruption some possible precursors were observed previous to the distal vents opening such as CO2 diffuse gas anomalies, the opening of small fractures, local deformation, fumarolic activity and related small landslides before the feeder dike reached the surface. Since distal vents opening was unnoticed by the geophysical monitoring, we propose a detailed monitoring of diffuse gas emission and local fragile and ductile deformation in a radio of several kilometres from the main fissure. The previous knowledge of the detailed volcano-tectonic structure is also essential.

How to cite: Sanz-Mangas, D., Galindo, I., Pérez-López, R., Rodríguez-Pascua, M. Á., Perucha, M. Á., Camuñas, C., López-Gutierrez, J., García López-Davalillo, J. C., Lorenzo, C., Lozano, G., Vegas, J., Marrero, R., Hernández, M., Mediato, J. F., and Sánchez, N.: Fissure-type vents at 2021 Cumbre Vieja volcanic eruption , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2645, https://doi.org/10.5194/egusphere-egu24-2645, 2024.

14:55–15:05
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EGU24-3407
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On-site presentation
Luca De Siena, Antonella Amoruso, Simona Petrosino, and Luca Crescentini

Campi Flegrei caldera, one of the most dangerous volcanoes in the world, is experiencing the strongest seismic and deformation unrest of the last 40 years. Geophysical, environmental, and geochemical responses during volcanic unrest at any volcano are difficult to couple: this is especially true at a caldera where deformation signals and earthquakes are attributed to magma and fluid/rock interactions at depths as well as tidal and meteoric forcing at the surface. Here, we applied Empirical Orthogonal Functions analysis, a technique developed within climatic and environmental Sciences, to GPS data. The technique allows the spatiotemporal separation of the dominant deep-sourced inflation from environmentally controlled signals associated with extension at Campi Flegrei caldera. This separation bridges the gap between deformation, seismic and geochemical responses, clarifying the processes that started the ongoing volcanic unrest. Persistent meteoric forcing during the 2017-18 hydrological year, located in the middle of a five-year drought, changed the decadal trend of seismic energy and secondary deformation components, pairing their spatial patterns. The result was a block in the carbon dioxide released in 2018 at Solfatara, the primary stress-release valve at the caldera. The subsequent overpressure weakened the fractured eastern caldera, opening pathways for hot materials produced by the dominant deep deformation source to reach the surface. Our results show how environmental forcing can favour volcanic unrest in pressurised calderas.

How to cite: De Siena, L., Amoruso, A., Petrosino, S., and Crescentini, L.: Geophysical responses to an environmentally-boosted volcanic unrest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3407, https://doi.org/10.5194/egusphere-egu24-3407, 2024.

Special focus: recent activity at Campi Flegrei
15:05–15:15
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EGU24-6693
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solicited
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Highlight
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On-site presentation
Christopher Kilburn, Eric Newland, Nicola Alessandro Pino, Stefano Carlino, and Stefania Danesi

Large volcanic calderas can take decades or more to return to activity after centuries in repose. Their reawakening frequently triggers several, intermittent episodes of unrest before magma finally erupts. The non-eruptive episodes can divide scientific opinion about the cause of unrest and its outcome. The Campi Flegrei caldera is a remarkable example. Fifteen kilometres across, it is Europe’s largest active caldera and supports a population of more than 360,000 people to the west of Naples in southern Italy. It has been episodically restless since 1950, for the first time in four centuries. Uplifts in 1950-52, 1969-72, 1982-84 and since 2004 have created a caldera-wide bulge that, close to its centre, has raised the coastal town of Pozzuoli by more than 4 m, while tens of thousands of small earthquakes have shaken the volcano to depths of 4 km.

The behaviour is consistent with repeated rupture of the crust. The most recent rupture developed between 2013 and 2023. The rate of local volcano-seismic earthquakes evolved from an exponential increase, through a constant rate to a hyperbolic increase with time. This is the classic pre-rupture sequence for elastic-brittle rock being extended under an approximately constant rate of supplied stress.

We used changes in the sequence to forecast the approach to rupture in real-time. Observations followed the forecast trend through the first nine months of 2023, by which time the increase in seismicity was expected to continue until early 2024. Instead, the rupture sequence culminated in October 2023, since when the rates of seismicity have decayed. The end of rupturing was brought forward by an increase in the number of larger magnitude earthquakes, which accelerated rates of stress loss compared with previous months. Uplift had also slowed by December 2024.  Each rupture sequence increases the amount of damage in the crust. Other factors being equal, therefore, if any new magma can reach the shallow crust in the near future, it is likely to meet a lower resistance to eruption than has been the case since unrest began in 1950.

How to cite: Kilburn, C., Newland, E., Pino, N. A., Carlino, S., and Danesi, S.: Real-time forecasts of unrest at Campi Flegrei, Southern Italy, 2013-2023., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6693, https://doi.org/10.5194/egusphere-egu24-6693, 2024.

15:15–15:25
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EGU24-7847
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On-site presentation
Elisa Trasatti, Ana Astort, Marco Polcari, Luca Caricchi, and Mauro A. Di Vito

Campi Flegrei Caldera (Italy) is affected by a still ongoing unrest characterized by increasing seismicity rates, gas emissions and ground deformations. Multi-technique geodetic data (satellite, inland and seafloor GNSS measurements) are collected to understand the evolution of the unrest from its beginning in 2007 to the end of 2023, to get insights on the plumbing system. The data show increasing rates of deformation in the last 16 years, focusing in the caldera center. 3D finite element models are employed in a Bayesian inversion framework, including the elastic heterogeneous structure of the underlying medium based on the newest seismic tomography of the area. The analysis divides the whole period into seven distinct time intervals, based on the changes in ground displacement time series. The modeling approach implements a double-source plumbing system: a shallower source with its depth and geometry determined by the inversion framework, and a second deeper tabular source at 8 km depth, consistent with the petrological and geochemical evidence of melt and massive degassing from the deeper portion of the magmatic system. The results reveal that the shallower source beneath Pozzuoli exhibits a gradual decrease in depth, from 5.9 km during 2007-2010 to 3.9 km during 2015-2023. The shallower seismicity, above 3 km depth, is influenced by the long-term straining of the local crust due to the continuous inflation of the shallower source. Concurrently, the deeper tabular source at 8 km depth experiences a limited but constant deflation over time. The depicted plumbing system evidences a sequential growth of horizontal opening and volumetric expansion of the shallower source, likely fed by the deeper source for 16 years at least, for a total volume variation of about 60 million cubic meters. To determine whether the shallower source is fed by fluids and/or magma, we performed calculations of volatiles and/or magma transfer from 8 km upwards, considering different settings. The most plausible scenario accounts for magma ascent associated with degassing and outgassing. Indeed, the volumetric variation calculated from geodetic data for the shallower source reflects the injection of an equivalent volume of magma and a deep source that is continuously refilled by a flux of magma comparable to the ascending one.

How to cite: Trasatti, E., Astort, A., Polcari, M., Caricchi, L., and Di Vito, M. A.: Evolution of the plumbing system at Campi Flegrei caldera (Italy) during the 2007-2023 unrest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7847, https://doi.org/10.5194/egusphere-egu24-7847, 2024.

15:25–15:35
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EGU24-11227
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On-site presentation
Luca Crescentini, Antonella Amoruso, and Adriano Gualandi

Geodetic data measure deformation of various origins (e.g., tectonic, volcanic, hydrological, human-induced). To attempt separating the different signals underlying the observations, data can be analysed as in a blind source separation (BSS) problem. A common technique to tackle BSS problems is the Independent Component Analysis (ICA), which decomposes the dataset into a set of independent components (ICs) under the assumption of a linear mix of the non-moving sources.

We use a variant of ICA (vbICA, variational Bayesian ICA; Choudrey and Roberts, 2003) to analyze ground displacement time series from ERS-ENVISAT SAR images in a large area including Campi Flegrei and Vesuvio volcanoes (Italy) between 1993 – 2010. The time series, which have gaps, were obtained through the SBAS technique and provided to us by IREA-CNR.

Our analyses evidence two significant ICs. Their spatial and temporal features indicate that one of the ICs (IC1 in what follows) is related to Campi Flegrei only and describes the subsidence occurred before 2000, the mini-uplifts started in 2000 and 2005, and a post-2005 uplift. The other significant IC (IC2 in what follows) is related to the subsidence occurred at Vesuvio after 2001 (Amoruso & Crescentini, 2023) and an additional (with respect to IC1) post-2001 Campi Flegrei dynamics.

The IC1 spatial pattern confirms the results in Amoruso et al. (2014): it is satisfied by the joint effects of two pressurized sources embedded in an elastic layered half-space, i. e. a sill at a depth of about 3.5 km and a small spheroid at a depth of about 2 km; the two sources satisfy large-scale and local (Solfatara fumarolic field) deformation, respectively.

The IC2 spatial pattern is consistent with Amoruso & Crescentini (2023) as regards Vesuvio. As for the Campi Flegrei area, it is quite complex and difficult to ascribe to a single source, even as general as a moment tensor. If the whole IC2 spatial pattern is inverted for small (with respect to depth) pressurized spheroids (point sources), two deep sources (depths larger than about 8 km) acting in the Campi Flegrei area are needed in addition to the deflating source beneath Vesuvio. The three sources appear inactive before 2000; afterwards the two deep sources beneath Campi Flegrei show opposite behaviour.

We show that the scenario outlined by our results is consistent with geophysical (e.g., gravity) and petrological data. It is also consistent with subsequent pressurization of a sill-like source at about 8 km depth, inflating at least since 2015 (Amoruso & Crescentini, 2022).

References

Amoruso et al. (2014), J. Geophys. Res: SE, 119, 858–879.

Amoruso, A., and Crescentini, L. (2022). Remote Sens., 14, 5698.

Amoruso, A., and Crescentini, L. (2023). Remote Sens., 15, 3038.

Choudrey, R., and Roberts, S. (2003). Neural Computation, 15(1), 213-252. 

How to cite: Crescentini, L., Amoruso, A., and Gualandi, A.: From subsidence to uplift at Campi Flegrei, with an eye to Vesuvio, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11227, https://doi.org/10.5194/egusphere-egu24-11227, 2024.

15:35–15:45
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EGU24-19589
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On-site presentation
Flora Giudicepietro, Manuela Bonano, Claudio De Luca, Prospero De Martino, Federico Di Traglia, Mauro Antonio Di Vito, Riccardo Lanari, Giovanni Macedonio, Michele Manunta, Fernando Monterroso, Pasquale Striano, and Francesco Casu

The Campi Flegrei caldera (southern Italy) is an active volcano whose last eruption occurred in 1538. This caldera is characterized by ground displacements (subsidence or uplift), often referred to with the term "bradyseism". Over the last two decades the Campi Flegrei caldera was affected by a phase of uplift which became progressively more intense over time and was accompanied by increasing seismicity and geochemical anomalies. The Campi Flegrei deformation pattern generally shows a bell-like shape, with the zone of maximum uplift in the central area corresponding to Rione Terra, that is the historic district of Pozzuoli. In the 2021-2023 period the OV-INGV seismic network detected significant seismicity and the GNSS and DInSAR measurements highlighted a high uplift rate of the central area of the Caldera. In this period, seismicity was distinctly felt by the population several times (maximum magnitude Md = 4.2) and the uplift of the central sector of the caldera reached a level that made it difficult to enter the ancient fishermen's port of Pozzuoli (about 120 cm compared to the ground level in 2005). We have carried out a detailed analysis of the ground deformations relevant to the 2021-2023 time interval. Our study has highlighted a local anomaly of the caldera deformation pattern in the Solfatara-Pisciarelli-Olibano hydrothermal area. This anomaly became well recognizable in 2022 and it further developed during 2023. Moreover, it affects the area in which the earthquakes with greater magnitude occurred in the Campi Flegrei. We interpret this zone as a possible weakness area in the crustal structure of the Caldera and, therefore, we believe that a detailed monitoring of this zone is foreseen because it may provide some relevant insights on the caldera dynamics and the related hazard.

How to cite: Giudicepietro, F., Bonano, M., De Luca, C., De Martino, P., Di Traglia, F., Di Vito, M. A., Lanari, R., Macedonio, G., Manunta, M., Monterroso, F., Striano, P., and Casu, F.: Anomaly detection within the 2021-2023 deformation pattern of the Campi Flegrei (Italy) caldera through the analysis of DInSAR and GNSS data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19589, https://doi.org/10.5194/egusphere-egu24-19589, 2024.

Coffee break
Chairpersons: Sigurjon Jonsson, Valerio Acocella, Virginie Pinel
16:15–16:20
Volcanic unrest and failure 3
16:20–16:30
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EGU24-8401
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On-site presentation
Gilda Currenti, Luigi Carleo, and Alessandro Bonaccorso

Lava fountains at Etna volcano are spectacular explosive eruptions consisting of powerful jets of gas and solid particles that cause a huge impact both to air traffic and urban areas due to ash dispersal and fall-out.

The evolution of a lava fountain at Etna is usually a gradual process that progresses from a weak strombolian activity, passes to a typical lava jet and ends with the formation of a sustained eruptive column. Typically, lava fountain events last from tens of minutes to few hours. The interaction of the magma with the surrounding rock during such eruptive episodes induces tremor (0.5 - 5 Hz) and ultra-small deformation (10-9 to 10-7) of the superficial crust and generates geophysical signals at a wide ranges of amplitudes and time scales. Seismometers can capture only the higher frequency content of such signals by measuring volcanic tremor. Due to the small amount of related deformation, the traditional geodetic methods, such as GPS and InSAR, are not able to reveal significant variations because of the low precision (GPS resolution > 1 cm) or very low sampling frequency (InSAR temporal resolution limited by satellite passages). This limit is overcome by using Sacks-Evertson strainmeter that measures the volumetric deformation of the surrounding rock with the highest achievable resolution (10-10 to 10-11) and in a very wide frequency range (10-7 to > 20 Hz). Thanks to its characteristics, the strainmeter is perfectly suitable to explore the full spectrum and the very small amplitudes of the strain signal exerted by the lava fountain episodes at Etna, covering the frequency gap between the seismic and the common geodetic techniques.

In this work, we analyzed the co-eruptive strain changes recorded by the borehole strainmeter network concurrently with more than 60 lava fountain events that occurred at Etna volcano between 2020-2022. We investigated all the lava fountain events, highlighting the main characteristics of the eruptive phases and their transition that characterize such eruptions, both in the high and in the low frequency band. These characteristics furnish fundamental constraints to improve the characterization of eruptive processes that lead to lava fountain events.

How to cite: Currenti, G., Carleo, L., and Bonaccorso, A.: Linking the gap between seismic and geodetic observations during the 2020-2022 lava fountains at Etna volcano, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8401, https://doi.org/10.5194/egusphere-egu24-8401, 2024.

16:30–16:40
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EGU24-8240
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ECS
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On-site presentation
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Noemi Corti, Alessandro Tibaldi, and Fabio Luca Bonali

During eruptions, magma arrives at the surface through vertical dikes. However, dikes often arrest in the crust, not feeding an eruption. Moreover, their emplacement causes a concentration of tensile and shear stresses in the host rock, that can lead to fracturing and/or faulting at the topographic surface. The relation between magma intrusion and dike-induced surface deformation has been analysed in the last decades through analytical, analogue and numerical models, but mostly considering an elastic and homogeneous half-space. Realistic data should therefore be considered to overcome this limitation.

For this reason, in this work, field structural data are used as inputs for numerical modelling. Three case studies, all affected by shallow dike emplacement, are considered: the 1928 and 1971 eruptive fissures on Mt. Etna (Italy), and the Younger Stampar eruptive fissure in SW Iceland. On Mt. Etna, dike-induced brittle deformation is visible at the surface, in plan view for both cases, and in section view for the 1971 case study. In Iceland, two dikes (one feeder and one arrested) are exposed along a cliff; the tip of the arrested dike is only 5 m below the surface, but no brittle deformation is observed. These case studies allow us to investigate the parameters that i) favour/inhibit dike-induced brittle deformation at the surface, ii) affect the geometry of dike-induced graben faults, and iii) promote dike arrest at shallow depths.

We collected structural data integrating classical fieldwork and remote sensing analyses, using high-resolution 2D and 3D models, reconstructed through Structure from Motion photogrammetry from drone images and historical aerial photos. We used all these structural data as inputs for 2D Finite Element Method numerical models, using the software COMSOL Multiphysics. In the models, sensitivity analyses were run to analyse the parameters that affect dike propagation and the induced surface deformation.

This work underlines the role of layering on the formation of stress barriers and on the distribution of dike-induced stresses, that concentrate in stiffer materials and are suppressed in softer layers. Furthermore, it confirms the effects of dike overpressure and inclination on its propagation and on dike-induced stresses. Topography also affects the dike propagation path and the geometry of dike-induced graben faults. Finally, the role of lateral compression induced by nearby previous intrusions is investigated, showing how this can promote dike arrest and the lack of brittle deformation.

How to cite: Corti, N., Tibaldi, A., and Bonali, F. L.: Analysis of dike-induced stresses and deformation: new insights from Mt. Etna and SW Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8240, https://doi.org/10.5194/egusphere-egu24-8240, 2024.

Special focus: recent volcanic activity in Iceland
16:40–16:50
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EGU24-11770
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On-site presentation
Adriano Nobile, Hannes Vasyura‐Bathke, Daniele Trippanera, Jöel Ruch, and Sigurjón Jónsson

Unrest episodes at volcanic systems are often associated with ground displacements produced by the pressure changes inside magma chambers at depth. The interactions with preexisting faults can complicate the deformation pattern observed at the surface. Calderas are volcanic systems characterized by a surface depression formed when the roof block collapses along ring faults, triggered by the rapid depressurization of an underlying magma chamber. As caldera ring faults are zones of weakness in the subsurface, we can expect stress interactions between the magma source and the ring faults during unrest episodes or eruptions. An example of such interaction likely occurred at Askja volcano during the 2021-2023 unrest episode. 

The Askja volcanic system is located in the North Volcanic Zone of Iceland. It consists of a central volcano with three nested calderas in the middle of a fissure swarm. Geodetic data have shown that the Askja caldera floor continuously subsided from 1983 until August 2021, when the volcano entered a period of unrest with rapid uplift and increased seismic activity. The seismicity decreased after three months, while the uplift continued for two years until it substantially slowed down in September 2023.

We use Sentinel-1 SAR images to study the ground deformation at Askja volcano between 2016 and 2023. Only Summer acquisitions can be used since the area is covered by snow during the rest of the year, preventing retrieval of the deformation signal due to lack of coherence. The InSAR time series shows steady subsidence of the Askja caldera floor between July 2016 and July 2021, and then, in early August 2021, the displacement changed to uplift. In only one month, the uplift matched the subsidence of the previous five years. By September 2023, the maximum uplift reached ~70 cm in the center of Askja caldera. Deformation maps show an asymmetric pattern that follows the ring faults in the northwestern part of Askja caldera. The pattern is similar for both the subsidence and uplift periods, suggesting the same magma body deflated before the unrest and then inflated when the pressure increased in August 2021. 

Using boundary element models, we assessed the ground deformation resulting from the interaction between an inflating sill and the caldera ring faults. Then, we estimated the source parameters using Bayesian inference. While a magmatic sill source can account for the broad uplift, triggered ring fault movement localizes the deformation close to the caldera rim, yielding an asymmetric deformation pattern that better fits the observed data. 

Even if this unrest didn’t culminate in an eruption, it highlights the importance of closely monitoring this volcanic system with InSAR technique. Indeed, this provides spatial data, enabling us to observe the peculiar deformation pattern. In synergy with the mapped faults and fractures, this allowed us to better understand the volcano's behavior and interactions with the rift and obtain an accurate image of its magmatic system.

How to cite: Nobile, A., Vasyura‐Bathke, H., Trippanera, D., Ruch, J., and Jónsson, S.: Interactions between an inflating magma chamber and caldera ring faults at Askja volcano, Iceland, during the 2021-2023 unrest episode, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11770, https://doi.org/10.5194/egusphere-egu24-11770, 2024.

16:50–17:00
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EGU24-19913
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On-site presentation
Egill Árni Gudnason, Vincent Drouin, Yilin Yang, Freysteinn Sigmundsson, Thorbjörg Ágústsdóttir, and Anette K. Mortensen

Theistareykir is one of five active volcanic systems of the Northern Volcanic Zone, NE Iceland, along with Krafla, Fremrinámar, Askja and Kverkfjöll, from north to south, respectively. The Theistareykir volcanic system includes a N-S trending rifting fissure swarm, approximately 70-80 km long and 7-8 km wide, extending through it. There are neither postglacial eruptive fissures nor a clear caldera formation at Theistareykir, with the latest eruption occurring ~2,400 years ago.

Theistareykir comprises a high-temperature geothermal system which has been systematically explored over the past 50 years, with around 20 exploration and production wells drilled to date. Since 2017, geothermal energy has been utilised at Theistareykir with a 90 MWe power station currently operated by Landsvirkjun, the National Power Company of Iceland. Extensive monitoring of the geothermal field is carried out through e.g., various geophysical measurements.

An inflation was observed to start at Theistareykir at the beginning of 2023, with the centre of uplift approximately 2.5 km west of the Theistareykir power plant. Earthquake activity in Theistareykir occurs in more or less three separated clusters, and coinciding with the start of inflation, an increase in seismicity rate was observed within the northernmost cluster, with the largest earthquake reaching ML 2.2 at 5.2 km depth. Earthquake depths within this cluster range between ~5-7 km, deepening towards north. No significant change is observed in faulting mechanisms within this cluster, despite the inflation, with oblique strike-slip events most common.

The vertical component of the continuous Global Navigation Satellite System (GNSS) station in Theistareykir (THRC), located ~0.5 km northeast of the uplift centre, indicates a best-fit onset time of the inflation around 9 February 2023, and an initial uplift of 21.5 mm/yr.

Synthetic Aperture Radar Interferometry (InSAR) of Sentinel-1 images was used to measure the inflation. The anomaly is ~10 km wide and the uplift in its centre is ~12-15 mm between the summers of 2022 and 2023. Knowing that the uplift started around the beginning of 2023, the actual uplift rate is therefore ~20-25 mm/yr at the uplift centre. This is similar to the two previous inflation episodes observed in the area in 1995-1996 and 2006-2009.

Geodetic modelling, using the InSAR data, indicates that a model with a point source pressure within a uniform elastic halfspace can explain the observations. The inferred source has a centre depth in the range of 4.4-6.2 km (95% confidence interval), and a volume change of (1.1-2.5) x 106 m3 (95% confidence interval) until the end of summer 2023.

Our aim is to understand better the activity and identify the driving processes, and their implications for the geothermal field. Results will be presented in the context of past earthquake and deformation data.

How to cite: Gudnason, E. Á., Drouin, V., Yang, Y., Sigmundsson, F., Ágústsdóttir, T., and Mortensen, A. K.: Changes in seismicity and observed deformation related to inflation at the Theistareykir high-temperature geothermal field, NE Iceland, in 2023-2024, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19913, https://doi.org/10.5194/egusphere-egu24-19913, 2024.

17:00–17:10
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EGU24-18083
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solicited
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Highlight
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On-site presentation
Kristín Jónsdóttir, Halldór Geirsson, Benedikt Halldórsson, Kristín Vogfjörð, Michelle Parks, Sigurlaug Hjaltadóttir, Vincent Drouin, Ragnar Heiðar Þrastarson, Benedikt G. Ófeigsson, Magnús Tumi Guðmundsson, Lilja Magnúsdóttir, Sara Barsotti, Freysteinn Sigmundsson, and Matthew Roberts

The Reykjanes Peninsula in SW Iceland is transacted by a divergent plate boundary with oblique spreading. Volcanic unrest periods, marked by fissure eruptions widely across the peninsula, seem to occur with regular intervals, approximately every 800-1000 years. These volcanic unrest periods have durations of 100 up to 400 years. In 2020, it became clear that magma was on the move again after 800 years of quiescence, as repeated uplift was measured in the vicinity of the Svartsengi geothermal area. Minor subsidence was recorded between uplift periods and seismicity increased again, only after the previous state of uplift had been surpassed, in line with the so-called Kaiser effect. A year later, a dike intrusion in Fagradalsfjall triggered earthquake activity tens of km away as stored tectonic stresses along the peninsula were released. After a clear decline in earthquake activity, an eruption took place in Geldingdalir, Fagradalsfjall, on 19 March 2021, the first one in over 6000 years in that region. At the time of writing, 4 volcanic eruptions have occurred since 2021 and in total roughly 20 magmatic intrusive events have taken place on the Reykjanes Peninsula.

Recently an escalation in volcanic activity has been observed. In late October 2023, the 5th period of uplift started in Svartsengi signifying faster magma inflow rates than previously inferred. Seismicity increased and was widespread in line with increased stresses above an inflating sill at about 5 km depth.  On 10-11 November, during nearly 12 hours of intense seismic activity, the magma found its way from the magma storage beneath Svartsengi some 2 km laterally  towards the center of an old crater row and creating a 15 km long shallow dike. Subsidence was observed above Svartsengi as the magma was drained from beneath and a graben formed beneath the coastal town of Grindavík where extensive faulting caused considerable damage. On 18 December, a similar but smaller magma intrusive event originating in Svartsengi occurred, causing an eruption approximately at the center of the original dike. This time, earthquakes only occurred about 90 minutes before the eruption onset and no clear trend of earthquakes migrating from Svartsengi towards the laterally offset dike were detected. At the time of writing (10 January, 2024), a similar amount of magma volume is inferred to have accumulated beneath Svartsengi since shortly before the last eruption, however, seismicity is still at normal background levels. 

The volcano monitoring team at the Icelandic Meteorological Office in close collaboration with geoscientists at the Insitute of Earth Science at the University of Iceland and HS Orka, have been under immense pressure to interpret the ongoing activity. A vital part has been to interpret seismicity rates and earthquake locations and any changes thereof, along with modeling dike and sill inflow rates from geodetic measurements. We show that meaningful interpretation of earthquake activity can only be done when jointly interpreted together with deformation and stress models as stress changes heavily influence earthquake locations and the temporal onset of earthquake activity.

How to cite: Jónsdóttir, K., Geirsson, H., Halldórsson, B., Vogfjörð, K., Parks, M., Hjaltadóttir, S., Drouin, V., Þrastarson, R. H., Ófeigsson, B. G., Guðmundsson, M. T., Magnúsdóttir, L., Barsotti, S., Sigmundsson, F., and Roberts, M.: Interpreting seismicity and earthquake locations during the recent unrest on the Reykjanes Peninsula in SW-Iceland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18083, https://doi.org/10.5194/egusphere-egu24-18083, 2024.

17:10–17:20
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EGU24-14543
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On-site presentation
Xingjun Luo, Nicolas Oestreicher, Wenbin Xu, and Joël Ruch

Oblique rift zones and bookshelf structures in the Reykjanes Peninsula are part of the intricate boundary that separates the North American from the Eurasian plates. Studying their evolution over several years provides a deeper understanding of plate tectonic processes and also aim to better understand the tectonic conditions that precede volcanic eruptions. After a period of dormancy lasting 800 years, the Reykjanes Peninsula has experienced strong episodic plate boundary motions since at least 2017 and four eruptions in 2021, 2022, and 2023 (twice). These events have been accompanied by significant seismic activity and ground displacement related to strain release at the plate boundary and around dike intrusions.

Here we employed D-InSAR, stacking-InSAR, and PSI time series to investigate the deformation occurring in the Reykjanes Peninsula from June 2016 to December 2023, covering the period before and during the onset of the eruption phases. Due to the fast deformation during large earthquakes and eruptions, we separately analyze dike intrusions before the four eruptions, five earthquake swarms, and seven time series between the above-mentioned events. The discretization of the observation period allows us to improve the InSAR process for different events and to avoid confusing the deformations originating from different events. Using InSAR and seismicity, we identifiund displacement and earthquake swarms in the Fagradalsfjall area in July 2017, July 2020, August 2020 and October 2020, highlighting an activation of localized portions of the plate boundary at least four years before the first eruption. The overall earthquake distribution aligns with the plate boundary (N070), but suggests a bookshelf structure composed of north-south fault ruptures.

We use the vbmethod to decompose the InSAR time-series into independent components of deformation such as intrusions, earthquakes, and tectonic plate motion. From the InSAR time series analysis, we observed that before each dike intrusion, the Southern Fagradalsfjall-Krysuvik () area exhibits an overall southeastward movement. The results of vbICA also suggest that this area has been accelerating since 2020.  

The comprehensive observations of tectonic and volcanic activity in the Reykjanes Peninsula, using both InSAR time series and seismicity over seven and a half years provide valuable insights to better understand the onset of oblique rifting events at divergent plate boundaries.

How to cite: Luo, X., Oestreicher, N., Xu, W., and Ruch, J.: Episodic events of oblique rifting using InSAR time series and seismicity (2016 – 2023), Reykjanes Peninsula (Iceland) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14543, https://doi.org/10.5194/egusphere-egu24-14543, 2024.

17:20–17:30
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EGU24-18235
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On-site presentation
Halldór Geirsson, Michelle M Parks, Freysteinn Sigmundsson, Vincent Drouin, Benedikt G Ófeigsson, Chiara Lanzi, Áslaug G Birgisdóttir, Cécile Ducrocq, Andrew Hooper, Páll Einarsson, Kristín Jónsdóttir, Sigrún Hreinsdóttir, and Sonja H M Greiner

Neighboring volcanic systems sometimes show evidence of some form of interconnection, for example by inflating or deflating either in phase or in anti-phase. We review here the course of events on the Reykjanes Peninsula (RP) in the ongoing unrest since approximately 2020, using volcano geodesy.

There are several volcanic systems on the RP, from west to east: Reykjanes, Svartsengi, Fagradalsfjall, Krýsuvík, Brennisteinsfjöll, and Hengill, with Fagradalsfjall being the least developed. All these volcanic systems, except Brennisteinsfjöll, have shown signs of unrest in the past years and decades: Three uplift episodes occurred at Svartsengi during 2020; one or two subtle deformation events further west on Reykjanes in 2020, and further uplift episodes at Svartsengi in May 2022, October 2023, November 2023, and December 2023 - January 2024. Inflation was observed at Krýsuvík during the summer of 2020; and a M5.6 earthquake occurred in Krýsuvík in October 2020.

As of beginning of 2024, three eruptions have occurred at Fagradalsfjall (in 2021, 2022, and 2023) and one eruption at Svartsengi in December 2023. Each eruption has been preceded by a dike intrusion, often intertwined with complex patterns of faulting, near-surface fracturing over wide areas, and creep along segments of the plate boundary. Additional dike intrusions in December 2021 in Fagradalsfjall and in Svartsengi in November 2023 did not breach the surface. The dike growth has spanned timescales of just over an hour to several weeks; furthermore, small dikelets accompanied new vent openings during the 2021 eruption. The dikes were emplaced in the brittle crust, above ~8 km depth, spanned several decimeters to meters in thickness, and released locally a great amount of plate-tectonic stresses. Re-inflation following each eruption or dike intrusion is usually observed, however, the temporal style of uplift rates varies considerably from time to time. Co-eruptive deflation was observed during the 2021 Fagradalsfjall eruption and the 2023 Svartsengi eruption.

The detailed deformation observations and modeling for the unrest periods reveal complex interactions of tectonics and magmatism across several volcanic systems on the RP. During 2020-2024, localized deformation and seismicity have alternated between different volcanic systems on the RP, such that only one system is inflating or erupting at a time. This observation may be interpreted in terms of deep pressure coupling between the systems. Furthermore, the deformation events cause significant stress changes at neighboring volcanic systems, affecting the probability of dike propagation and seismicity as well as conditions for magma accumulation. 

How to cite: Geirsson, H., Parks, M. M., Sigmundsson, F., Drouin, V., Ófeigsson, B. G., Lanzi, C., Birgisdóttir, Á. G., Ducrocq, C., Hooper, A., Einarsson, P., Jónsdóttir, K., Hreinsdóttir, S., and Greiner, S. H. M.: Deformation patterns of the Reykjanes Peninsula unrest 2020-2024, Iceland: evidence for interconnected neighboring volcanic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18235, https://doi.org/10.5194/egusphere-egu24-18235, 2024.

17:30–17:40
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EGU24-20338
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On-site presentation
Joël Ruch, Simon Bufferal, Elisabetta Panza, Stefano Mannini, Adriano Nobile, Birgir Óskarsson, Nils Gies, and Ásta Rut Hjartardóttir

The Reykjanes Peninsula is located at the boundary between the North American and the Eurasian plates. The Peninsula is experiencing an oblique rifting episode that started with a strong earthquake swarm the 24 February 2021, preceded by sparse swarm occurrences in the decade before. This activity has been followed by a volcanic eruption the 19 March 2021 and by three other eruptions in 2022 and 2023 after ~800 years of quiescence in this region. These series of events offer a unique opportunity to explore the relation between tectonic, faulting and volcanic activity in a highly oblique rift zone.

 

Here we focus on faulting activity during the onset period of the ongoing rifting episode, from February to March 2021. We use an extensive dataset of field observations and high resolution drone orthomosaics and DEMs over a ~30 km2 area to map, quantify and characterize the widespread ground fracturing associated with the oblique rifting activity. We mapped ~20’000 ground cracks of metric to decametric length, centimetric extensional offset, and clear dextral shear component, well-correlated to major earthquakes. Most fractures show en-échelons structures globally aligned along NS-striking fault zones up to 3-4 km long. By analyzing the timing of the ground fracturing thanks to our repeated field observations, seismic data and InSAR images, we relate most ground fractures to earthquakes of Mw ≥ 5.0 that occurred in the month preceding the March 2021 Fagradalsfjall eruption. Using optical image correlation from drone data and air photos, we further characterize in unprecedented details several NS fault zones that were reactivated up to three times during the event and were already existing before.

 

Our results show dominant strike-slip features, atypical in rift zones, that highlight the geometry of a bookshelf-mode activity along a diffuse and highly oblique plate boundary. These findings further question the relation between tectonic and magmatic activity at mid-oceanic ridges. Thanks to our immediate on-site response in early March 2021, we witnessed extensive ground fractures that have been quickly lost within a year due to erosion or recovered by lava flows, pointing out a potential under-representation of diffuse fracturing when studying oblique volcanic systems.

How to cite: Ruch, J., Bufferal, S., Panza, E., Mannini, S., Nobile, A., Óskarsson, B., Gies, N., and Hjartardóttir, Á. R.: Faulting activity during the 2021 oblique rifting event in the Reykjanes Peninsula (SW Iceland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20338, https://doi.org/10.5194/egusphere-egu24-20338, 2024.

17:40–17:50
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EGU24-16352
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ECS
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On-site presentation
Chiara Lanzi, Halldór Geirsson, Freysteinn Sigmundsson, Michelle Maree Parks, and Vincent Drouin

Ground deformation during an eruption may help to interpret physical processes related to the plumbing system. Here, we report the co-eruptive deformation of the Fagradalsfjall (SW-Iceland) eruption in 2021, that occurred in an oblique rift zone. The eruption lasted six months, 19 March - 21 September, following several weeks of intense seismic activity. The spatial and temporal analysis of Global Navigation Satellite System, GNSS, and Interferometric Synthetic Aperture Radar, InSAR, (by Sentinel-1) observations of ground displacements locate changes in the deformation pattern during the eruptive period. Three temporal changes in the subsidence rates and horizontal motion towards the eruptive area are identified: the first period, T1, 19 March–12 May; the second period, T2, 12 May–30 July, and the third period, T3, 30 July–21 September. The maximum deformation rate (20 mm/yr in line-of-sight) is observed in T2 and coincides with the average effusive rate increase (from 8 m3/s in March–April to 9–13 m3/s in May, Pedersen et al., 2022). We jointly inverted the GNSS and InSAR data to place constraints on the size and location of the source of subsidence during the six-month eruption. Initial modelling result (InSAR and GNSS) indicates a point-source at mid-crust level, 9.5-10.5 km depth and a volume decrease of 18-21 × 106 m3. The deflation volume estimated is significantly lower than that of the lava flow field, with a bulk volume of 150 ± 3 × 106 m3of lava (Pedersen et al., 2022). A residual signal is observed in our model, centered above the source location and around the eruptive center. Both the residual signal and the lower-than-expected volume change suggest additional inflow from a deeper source in agreement with evidence of physical mixing of magma from a mantle supply after the start of the eruption (Halldórsson et al., 2022). A link to a deeper source influences the influx rate of the magma and, consequently, the magma available. Both local seismicity rate and seismic moment release gradually decreases between the onset of the eruption and late April. Afterwards, both show a relatively constant rate, until the end of the eruption.

 

 

 

 

Pedersen, G., Belart, Joaquín M.C., Óskarsson, B., Gudmundsson, M. et al (2022). Volume, Effusion Rate, and Lava Transport During the 2021 Fagradalsfjall Eruption: Results From Near Real‐Time Photogrammetric Monitoring. Geophys. Res. Lett., 49. 10.1029/2021GL097125.

 

Halldórsson, S.A., Marshall, E.W., Caracciolo, A. et al. (2022). Rapid shifting of a deep magmatic source at Fagradalsfjall volcano, Iceland. Nature 609, 529–534 https://doi.org/10.1038/s41586-022-04981-x

How to cite: Lanzi, C., Geirsson, H., Sigmundsson, F., Parks, M. M., and Drouin, V.: Co-eruptive crustal deformation changes associated with the 2021 Fagradalsfjall eruption (SW-Iceland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16352, https://doi.org/10.5194/egusphere-egu24-16352, 2024.

17:50–18:00
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EGU24-19525
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On-site presentation
Michelle Parks and the ISVOLC Team

ISVOLC is a 12 partner research project funded by the Icelandic Research Fund, addressing the effects of climate change-induced ice retreat on seismic and volcanic activity. The project started 1 April 2023, and has a duration of 3 years. It is led by the Icelandic Meteorological Office, in collaboration with the University of Iceland.

Glaciers in Iceland have been retreating since 1890 and climate change simulations predict that the majority may disappear within a few hundred years. Retreating ice caps cause glacial isostatic adjustment (GIA) as well as changes to the subsurface stress field. Glacier covered volcanic systems are most affected, but also crustal conditions outside glaciers as well as magma generation at depth. Eruption likelihood may be modified, as occurred during the Pleistocene deglaciation, as more melt accumulates under Iceland because of ice retreat. However, there are several uncertainties: i) if, how and when this new magma reaches the surface; ii) if stability of existing magma bodies is modified; iii) if deglaciation is already resulting in accumulation of larger volumes of melt within crustal reservoirs; iv) how induced variations in the stress field may affect future volcanic activity. ISVOLC is focussing on four active volcanoes in Iceland (Katla, Askja, Grímsvötn and Bárðarbunga), to address these research questions.

Katla volcano lies beneath Mýrdalsjökull ice cap in S-Iceland. It is capable of generating large explosive eruptions within its caldera, with ash plume heights between 14-20 km accompanied by major jökulhlaups. GNSS observations from stations on nunataks of the glacier, and the surrounding region, combined with seismicity and changes to ice-cauldrons suggests a combination of processes are occurring, including GIA and magma inflow.

At Askja volcano, inflation commenced at end of July 2021 after decades of subsidence. This was detected on both GNSS observations and Sentinel-1 interferograms. Geodetic modelling indicates the onset of unrest was triggered by migration of magma within the uppermost part of the volcano plumbing system, followed by influx of new melt from depth. At the time of writing (January 2024) inflation continues but at a lower rate.

In the Bárðarbunga volcanic system, the six-month long 2014-2015 Holuhraun eruption was accompanied by gradual caldera collapse of up to 65 m and preceded by a two-week period of 48 km long lateral dyke propagation with extensive seismicity and deformation. Geodetic observations show that re-inflation started in July 2015, immediately after the end of the eruption. This may be explained by a combination of renewed magma inflow and viscoelastic readjustment of the volcano. GNSS and seismic observations show an increase in rate of inflation and seismicity since early 2023.

Grímsvötn subglacial volcano is the most frequently erupting volcano in Iceland, with eruptions in 1998, 2004 and 2011. A GNSS station shows a prominent inflation cycle between eruptions. Deformation at this volcano has surpassed that observed prior to recent eruptions and its aviation color code was elevated to yellow in January 2024 due to a short-lived intense seismic swarm.

How to cite: Parks, M. and the ISVOLC Team: An update of recent geodetic observations and modelling results at key Icelandic volcanoes within the ISVOLC project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19525, https://doi.org/10.5194/egusphere-egu24-19525, 2024.

Closing remarks

Posters on site: Thu, 18 Apr, 16:15–18:00 | Hall X1

Display time: Thu, 18 Apr 14:00–Thu, 18 Apr 18:00
Chairpersons: Michael Heap, Tim Davis, Kyriaki Drymoni
X1.151
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EGU24-100
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ECS
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Kendra Ní Nualláin and Claire Harnett

Volcanic domes are inherently unstable structures as they grow incrementally, with varied extrusion rates, material properties, and directions of flow. These instabilities can bring about volcanic dome collapse, leading to turbulent and hot avalanches of material that can devastate communities surrounding a volcano, as well as affecting the volcano’s eruptive dynamics.

The objective of this research is to investigate the effect of hydrothermal alteration on dome stability, where hydrothermal alteration typically results in mechanical weakening of volcanic rock. To achieve this goal, it is important to understand the spatial distribution of alteration within a dome. The internal structure of the La Soufrière de Guadeloupe dome was mapped by Heap et al. (2021), whereby electrical conductivity surveys were carried out to obtain the rock porosity and therefore the density variation within the dome. The density contrasts were correlated with mechanical parameters (i.e., uniaxial compressive strength of volcanic rock) to obtain a 3D internal strength map of the volcano. We designed a novel methodology to input this geophysical data into a new 3D particle-based Discrete Element Method model. This involves creating a digital elevation model from satellite data and interpolating the geophysical data to assign strengths to each modelled particle.

We show here the results of alteration scenario testing. This involves varying the degree of alteration-induced weakening, the spatial extent, and the size of alteration zones. This allows us to make predictions on potential for collapse and direction of material flow, quantify collapse volumes, and explore small-scale to large-scale failures. In particular, we investigate the effect of ongoing alteration of the La Soufrière de Guadeloupe dome. Observations show pervasive hydrothermal alteration, particularly in an area in the south of the dome known as the “bulge”. This represents a potential detachment plane and thus is a focus for our collapse models.

Thus far, key findings from our investigations suggest that even near-surface alteration can cause deep-seated deformation. We also show varied weakening scenarios for a bulk rock strength of 10% and 50% of the original strength, with a focus on the southern flank of the dome. To date, no 3D dynamic models of stability exist and therefore these models are key to forecasting volcanic hazards as a result of hydrothermal alteration.

How to cite: Ní Nualláin, K. and Harnett, C.:  Deconstructing the role of hydrothermal alteration in 3D volcanic dome collapse in La Soufrière de Guadeloupe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-100, https://doi.org/10.5194/egusphere-egu24-100, 2024.

X1.152
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EGU24-16777
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ECS
Jens Niclaes, Pierre Delmelle, and Hadrien Rattez

Volcanoes are inherently unstable, causing tremendous catastrophes, such as cities destruction or large tsunamis creation. These large flank collapses are not one-time events, it happens cyclically over the life of a volcano. One of the potential causes of such phenomena is hydrothermal alteration: Reactive fluids coexisting with a heat source interact with the host rocks and modify their mechanical properties. In most volcanoes, these hydrothermal alterations have a negative impact on the brittle-ductile transition of volcanic rocks, promoting a ductile failure behavior instead of a brittle one. However, the mechanisms behind large volcanic flank collapse are still obscure, especially when hydrothermal alteration is involved. The influence of the transition of mechanical behavior is rarely considered when the stability of the volcano is assessed. We performed Finite Element Method simulations, in dry and wet conditions, on 2D and 3D geometries of the Tutupaca volcano before its collapse at the end of the 18th century. To assess the stability, the strength reduction method was applied for each configuration allowing the obtention of the factor of safety and the most critical failure mechanism. The collapse is best reproduced when the volcanic rocks are modeled as a Mohr-Coulomb material with a compressive cap. The cap offers the consideration of the low brittle-ductile transition observed in previous experimental studies of altered volcanic rocks. Our results demonstrate that hydrothermal alteration influences the stability of a volcano through the brittle-ductile transition variation. These results are an entry point into assessing the instabilities of volcanoes because of hydrothermal alteration. They consider silicic and argillic alterations, but many others exist, and they might alter the rocks in a different way than reducing the brittle-ductile transition. These preliminary results are a basis to start adding complexity with, for example, external events such as earthquakes or meteorologic changes. 

How to cite: Niclaes, J., Delmelle, P., and Rattez, H.: Hydrothermal alteration shifting brittle-ductile transition promotes volcanic flank collapses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16777, https://doi.org/10.5194/egusphere-egu24-16777, 2024.

X1.153
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EGU24-10901
Alessandro Bonforte, Stefano Branca, Cubellis Elena, Salvatore Gambino, Francesco Guglielmino, Francesco Obrizzo, Laura Privitera, Giuseppe Puglisi, and Umberto Tammaro

Mt. Etna volcano is located along the eastern coast of Sicily. In this region, the general N-S compressive regime related to the Africa – Eurasia collision interacts with the WNW-ESE extensional regime associated to the Malta Escarpment dynamics, observable along the eastern coast of Sicily.

A general eastward motion of the eastern flank of the volcano has been measured with always increasing detail and its relationship with the eruptive and magmatic activity is being investigated. The complex interaction between regional stress, gravity forces and dike-induced rifting of Mount Etna, seems to have a role in the eastward movement of the Mt. Etna eastern flank. In this context the Pernicana Fault system identifies the northern boundary of the mobile sector.

It is formed by discrete segments, arranged in a right stepping en-échelon configuration, of a left-lateral shear zone that dissects the north-eastern flank of Etna. Its kinematics is related to shallow seismic crises (M ≈ 4.0) occurring along the western segment, with dip-slip displacement and left-lateral components. The eastern segment, ESE trending, shows only aseismic creep with purely left-lateral displacement.

The dynamics of the fault has been analyzed by a multi-disciplinary approach: levelling, tiltmeters, InSAR and GNSS.

The fault system shows clear traces on SAR interferograms and time series. InSAR data allows tracking the path of the Pernicana fault from the NE rift to the coastline; the eastwards motion abruptly disappears north of the fault, producing a left-lateral transcurrent kinematics at a rate of about 30 mm/y. Episodic accelerations are visible on GNSS and InSAR data from different sensors, related to seismic crises and eruptive activity. The dense GNSS network is measured periodically and has more than seventy benchmarks. The time series of this network began in 1988 and from then on its configuration has been continuously improved. Two GNSS networks lie across the eastern segment of the Pernicana fault. The first one, located in the “Rocca Campana” area, was installed in April 1997; the second one, located a few kilometers westward, in the “Rocca Pignatello” area, was measured for the first time in July 2002 upgrading an EDM network. The aim of these networks is to detail the structural framework and displacements along the aseismic sector of the Pernicana fault. Finally, the levelling route on Mt Etna, installed in 1980, is 150 km long and consists of 200 benchmarks. Part of the levelling route crosses the Pernicana fault, at an altitude of 1500 and 700 m asl. Measures on this network started on eighties and provide a high detail on the vertical kinematics allowing strong constraints in modelling the sources of slip episodes.

Integration of this wide spectrum of geodetic data allows strongly constrained ground deformation pattern to be defined and modeled. Furthermore, the very long time series available for the different datasets on the Pernicana fault, allows its behavior to be investigated in time and its role and relationships in the framework of flank instability and eruptive activity to better understood.

How to cite: Bonforte, A., Branca, S., Elena, C., Gambino, S., Guglielmino, F., Obrizzo, F., Privitera, L., Puglisi, G., and Tammaro, U.: The dynamics of the Pernicana Fault System (Mt. Etna, Sicily) investigated by 4 decades of multiparametric ground deformation data: inferences on the interaction between flank and magma dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10901, https://doi.org/10.5194/egusphere-egu24-10901, 2024.

X1.154
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EGU24-11296
Craig Magee and Susanna Ebmeier

Space for magma intrusion in the subsurface is often created by uplifting and bending of overlying rock, producing a forced fold. This intrusion-induced forced folding can deform the free surface, driving ground movement at active volcanoes. Monitoring such ground movement using satellite- and ground-based instrumentation plays a key role in volcanic eruption forecasting. Specifically, modelling ground movement allows us to assess eruption threats, by estimating intrusion properties (e.g., geometry, depth, volume, and pressure), and understand of volcanic system evolution and behaviour. Yet building accurate ground movement models to reliably estimate intrusion properties requires knowledge of a volcano’s subsurface composition and structure; information which is often limited or unavailable. Many ground movement models therefore tend to use analytical or numerical approaches that embed simple intrusion geometries within a homogeneous, isotropic, and linearly elastic medium (i.e., a material of uniform composition and structure). To assess the reliability and validity of such ground movement models, it would thus be beneficial to identify scenarios where known and modelled intrusion properties can be confidently compared.

Seismic reflection data image Earths subsurface in 3D at metre- to decametre-scale resolutions and can thus capture the detailed geometry of ancient intrusions and overlying forced folds. Where such intrusion-fold pairs have been seismically imaged, these data show: (1) intrusion geometries are typically complex; (2) host stratigraphic sequences comprise multiple lithologies; and (3) forced fold amplitudes are often less than intrusion thicknesses, implying space for magma was generated by both uplift and internal fold deformation (e.g., compaction). Importantly, seismic reflection data uniquely allow us to measure and model syn-emplacement ground movement driven by forced folding, whilst independently determining the geometry, size, and depth of underlying intrusions. Here, we examine an Early Cretaceous laccolith and forced fold pair imaged in 3D seismic reflection data from the Exmouth Plateau, offshore NW Australia. We consider how post-emplacement, burial-related compaction has reduced the fold amplitude by using local borehole data, which describe the lithology and seismic velocity of the folded strata, to decompact the succession and recover estimates of the original fold geometry. From these estimates of the original fold geometry, we calculate possible vertical and horizontal displacement components of deformation; this displacement data can be considered akin to that acquired during monitoring of ground movement at active volcanoes. By applying standard analytical methods to estimate intrusion properties from this pseudo-ground movement data, we compare model outputs to the true location, geometry, and size of the seismically imaged intrusion.

How to cite: Magee, C. and Ebmeier, S.: Magma Accommodation and Ground Movement Analysis: testing the reliability of analytical volcano deformation models , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11296, https://doi.org/10.5194/egusphere-egu24-11296, 2024.

X1.155
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EGU24-11682
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ECS
Alejandra Vásquez Castillo, Francesco Guglielmino, Flavio Cannavò, Alessandro Bonforte, and Giuseppe Puglisi

In the final months of 2020, the summit craters of Mount Etna displayed intense Strombolian-type activity as well as an increase in seismicity. In December 2020, a period of paroxysms with powerful, brief bursts of lava fountaining began, which intensified in February 2021 and lasted until April.

We used both ascending and descending Sentinel-1 SAR images along with daily GNSS solutions at 21 stations to evaluate the surface deformation at Mount Etna in order to understand the dynamics of the shallow plumbing system, which is probably related with the feeding of the observed paroxysmal activity. According to the InSAR and GNSS time series, the volcano edifice entered a period of intense and continuous deflation for almost three months, matching the prolonged paroxysmal activity characterized by the occurrence of 17 lava fountain episodes. To integrate the two data sets, we have applied the 3D SISTEM algorithm, which allows to estimate 3D ground displacements by combining GNSS measurements of deformation and differential Interferometric Synthetic Aperture Radar (DInSAR) maps of surface displacement. We have used analytical models to constrain the sources of the paroxysmal activity and to evaluate the deflating source parameters by inverting the displacement obtained with the 3D SISTEM algorithm. Preliminary results reveal a centripetal deformation pattern that might be linked to a shallow source below the summit craters area. However, a detailed analysis of the deformation pattern indicates the presence of contributions that are not related to the magmatic source, but are probably attributable to tectonic or geomorphologic processes.

The aim of this work is therefore twofold. First, to infer the shape and dynamics of the magmatic feeding system of Mount Etna and its magma discharging regime. Second, given the complexity of the deformation signals at Mount Etna, to analyze how to deal with their different contributions including volcanic‐, tectonic-, geomorphological processes, and atmospheric noise.

How to cite: Vásquez Castillo, A., Guglielmino, F., Cannavò, F., Bonforte, A., and Puglisi, G.: Etna's paroxysmal activity in 2021: A deflation episode revealed by joint DInSAR and GNSS ground deformation analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11682, https://doi.org/10.5194/egusphere-egu24-11682, 2024.

X1.156
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EGU24-11747
Owen McCluskey, Paolo Papale, Chiara Montagna, and Deepak Garg

We adopt a forward model approach to ground deformation through the use of GALES (GAlerkin LEast Squares) to simulate the mixing of magmas of variable compositions and temperatures, coupled with the elastodynamic response of the surrounding medium. GALES is a finite element parallel C++ code which solves for both the fluid and elasto-dynamic equations. Firstly, the mass, momentum and energy conservation equations are solved through GALES to simulate magma transfers across reservoirs connected through dykes. This allows the computation of the space-time stress distributions along the geometrically complex magma-rock boundary.

Such stress distributions are then employed by GALES as a set boundary conditions in elasto-dynamic simulations to compute the space-time distribution of rock displacement within the heterogeneous rock system and on the free surface. The computed synthetic time series for surface ground deformation at places corresponding to the position of actual receiver stations are finally analysed and compared to the real observational data at Mount Etna. 

The geometry of the plumbing system, the temperature and major oxide composition of the involved magmas, and their water and carbon dioxide contents, are constrained from the bulk knowledge at the highly investigated, highly monitored, well-known Etna volcano. The space-time dependent physical properties of the multiphase magmas are computed on the basis of the local composition and volatile partition between the gas and melt phases.

The results highlight the relationships between observations from surface monitoring networks and deep magma dynamics. In particular, they allow an in-depth investigation of ground oscillations with periods from seconds to hours, covering the intermediate range between seismic and geodetic observations which is being increasingly accessed to direct measurements. Such an intermediate frequency range emerges as being rich with new information on underground magma dynamics, potentially opening new perspectives and possibilities to magma monitoring and volcanic forecasts.

 

How to cite: McCluskey, O., Papale, P., Montagna, C., and Garg, D.: Relating magma dynamics and ground deformation patterns at Mount Etna, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11747, https://doi.org/10.5194/egusphere-egu24-11747, 2024.

X1.157
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EGU24-20339
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ECS
Nicolas Oestreicher, Joël Ruch, Þorsteinn Sæmundsson, Jón Kristinn Helgason, Nicolas Serrano Vega, Xingjun Luo, Patricia Leva, Jasmin Maissen, Michael Hohl, Jordan Aaron, Andrea Manconi, Halldór Geirsson, Daniel Mc Ginnis, Elisabetta Panza, Yohann Chatelain, and Frédéric Arlaud

In the summer of 2021, Askja caldera entered a renewed period of unrest, which was marked by a significant uplift of the caldera floor (over 70 cm in 2.5 y) and a slight increase in background seismicity. These indicators suggest the presence of magma rising from depth, potentially heralding an eruption in the months or years ahead. The renewed activity has increased the risk of landslides, particularly along the already unstable slopes of the eastern Öskjuvatn caldera. A major landslide in 2014 triggered a tsunami in the adjacent lake that inundated the lakeshore, reaching several tens of meters above its pre-event surface. To gain a deeper understanding of the unresting phase and its associated hazards that may lead to an eruption, the installation of a comprehensive monitoring system is key.

In the summer of 2023, a dense monitoring network was established to address these shortcomings. Three time-lapse cameras were installed to track ground movement along the unstable eastern caldera rim. Three corner reflectors were deployed to capture InSAR data, even during the snow-covered winters. A continuous GNSS instrument was also installed to monitor ground displacement continuously. We also covered the entire Öskjuvatn caldera rim with several drone surveys, in 2020, 2021 and 2023, obtaining high-resolution DEMs and orthomosaics to study ground deformation in the past few years.

However, arctic conditions prevail during winter months at Askja caldera. Extensive wind-sculpted ice structures have formed on the stations and prevent using the corner reflectors and time-lapse cameras at their full capacity. Storm- to hurricane-force winds have damaged highly exposed stations on the shoulders of the caldera ring faults. We propose technical improvements for extreme conditions and show preliminary results of our monitoring system. In particular, we show a detailed structural map based on our drone data and extensive field observations, thousands of fractures and other geological features providing a kinematic analysis for different parts of the caldera ring faults cliffs.

This collaborative effort between Swiss and Icelandic institutions has established an unprecedented monitoring system for an unresting volcano susceptible to eruptions and landslides. The multi-tools approach offers valuable insights into the behaviour of such calderas and could serve as a model for similar monitoring efforts worldwide.

How to cite: Oestreicher, N., Ruch, J., Sæmundsson, Þ., Helgason, J. K., Serrano Vega, N., Luo, X., Leva, P., Maissen, J., Hohl, M., Aaron, J., Manconi, A., Geirsson, H., Mc Ginnis, D., Panza, E., Chatelain, Y., and Arlaud, F.: Monitoring the surface deformation of an active volcano during a new unrest phase (Askja caldera, central Iceland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20339, https://doi.org/10.5194/egusphere-egu24-20339, 2024.

X1.158
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EGU24-13052
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ECS
Martina Pedicini, Noemi Corti, Alessandro Tibaldi, Federico Pasquaré Mariotto, and Fabio Luca Bonali

The Northern Volcanic Zone (NVZ) of Iceland identifies the northernmost portion of the emerging Mid-Atlantic plate boundary. Its peculiar location enables us to observe the main features that characterise slow-spreading ridges directly on the field. Here we present the first outcomes on the characterisation of the structure of the NVZ, focusing on two out of the seven volcanic rifts that constitute the area, namely the Theistareykir and the Fremrinamar.

We linked field surveys and remote sensing analysis to identify and classify all the features constituting these areas (i.e. normal faults, extension fractures, and eruptive fissures) and to collect quantitative data. Information regarding structures’ azimuth, length and vertical offset (for the normal faults subset) were collected to obtain a comprehensive characterisation of the rifts’ surficial deformation. Moreover, fault-slip profiles have been realised, to evaluate the along-axis rift propagation within the studied fissure swarms.

For both rifts normal faults represent the most abundant subset, also characterised by the highest length values. The analysis of faults’ dip directions highlights a clear preponderance of E-dipping scarps within the Theistareykir rift against a predominance of W-dipping ones within the Fremrinamar rift, supporting the hypothesis that they represent rift shoulders. Within both rifts, we observed a decrease in the surficial deformation moving away from the rifts’ central volcanoes. Additionally, the interpretation of the fault-slip profile displayed the tendency of the along-axis rift deformation to move away from the central volcanoes. Within the Theistareykir, the rift intersects with the Husavik-Flatey transform Fault (HFF), generating structures showing right-lateral strike-slip components.  Within the Fremrinamar rift, however, the intersection of the rift within the Grimsey Oblique Lineament leads to a local re-orientation of structures’ strikes, without any strike-slip component. These data corroborate the hypothesis that the GRL represents the offshore propagation of the Fremrinamar rift towards the Kolbeinsey Ridge, thus having a different behavior than the HFF.

Our study could contribute to the general understanding of how slow-spreading ridges develop, with a particular focus on how volcanic and tectonic processes concur in defining rift structures.

How to cite: Pedicini, M., Corti, N., Tibaldi, A., Pasquaré Mariotto, F., and Bonali, F. L.: Characterisation of slow-spreading ridges: the Theistareykir and Fremrinamar rifts, Northern Volcanic Zone (Iceland), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13052, https://doi.org/10.5194/egusphere-egu24-13052, 2024.

X1.159
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EGU24-16539
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ECS
Edgar U. Zorn, Anthony Lamur, Jackie E. Kendrick, Ulrich Kueppers, and Yan Lavallée

Volcaniclastic deposits compact during accumulation and burial, causing prolonged ground deformation, and potentially affecting edifice stability. Here we present the results of laboratory compaction experiments in which volcaniclastic material (in a confining cup) was progressively loaded with 0.1 MPa/min up to 20 MPa. We tested two lithologies consisting of natural basanitic scoria and crushed hyaloclastite, each sieved to a set of two grain sizes in the ash (0.5-2 mm) and lapilli (2-4 mm) range. During experiments, axial deformation and acoustic emissions were monitored, enabling us to quantify the progressive volume reduction and material properties. Two types of experiments were performed: dynamic loading tests and static creep test. The dynamic tests show that most of the deformation takes place within the first few MPa, decreasing non-linearly with load. Ultimately, samples compacted by up to 50 vol.% at 20 MPa (here equivalent to ~1,400 m depth). We use this compaction data to build a model of compaction and material properties as function of burial depth.

In repeat experiments, static tests were undertaken at select target loads (2, 5, 10 and 20 MPa) to measure time-dependent creep deformation at these loads over 6 hours. We find that compaction continues under static load as creep occurs in stages, displaying (1) initially rapid decline in compaction strain rates, which (2) then diminish more slowly over time and (3) eventually reach stable creep strain rates in most of our tests. Moreover, both total creep strains and stable creep rates are dependent on the applied load. Stable strain rates were highest between 5 and 10 MPa for all samples. The data shows that the lithology also influences the deformation behavior as we found the hyaloclastites compacted more efficiently during initial loading compared to the scoria, but in-turn creep strain rates were nearly an order of magnitude lower due to the more efficient compaction during loading. Our results highlight the relevance of gravitational material compaction for investigations of ground deformation and volcano flank instability (e.g., measured with InSAR) and introduce new material constraints to improve the interpretation and analysis of such signals. Deposit-specific compaction data may be integrated with ground deformation monitoring to interpret flank instabilities and assess collapse hazards, particularly in eruptions where deposition of new materials rapidly shifts overburden stresses.

How to cite: Zorn, E. U., Lamur, A., Kendrick, J. E., Kueppers, U., and Lavallée, Y.: Compaction and creep deformation of volcaniclastic material during burial , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16539, https://doi.org/10.5194/egusphere-egu24-16539, 2024.

X1.160
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EGU24-10472
Virginie Pinel and Catherine Mériaux

The lateral magma propagation is a common feature of rift zones, with vertical dykes flowing parallel to the rift direction and opening against the minimum compressive stress. Depending on the competition between vertical and lateral magma migration, these dykes may either feed an eruption or not. In this context, the topography which includes the edifice load acts against the rise of the magma and favor lateral migration radially away from the edifice central area, thus feeding peripheral vents. Here, we use the case of Nyiragongo volcano, a volcanic edifice located in the western branch of the East African Rift and culminating at 3,470 meter above sea level to study such combined effect of rifting-induced extension and topographic loading on both the orientation of vertical dykes and on the balance between lateral versus vertical magma propagation within the propagation plane. Using analytical and numerical models taking into account the effect of topography and the local West-East extension stress field, we show that the path of a dike coming from the volcanic edifice is first influenced by the load of the volcano, leading to a radial propagation while beyond 5 km, the extensional stress field dominates leading to a North-South propagation towards Lake Kivu. These results are consistent with the path of the magma deduced from geophysical observations for the last two eruptive events of the Nyiragongo volcano (2002 and 2021). Furthermore, the downward slope toward Lake Kivu and, to a lesser extent, the slight increase in southward rift extension both favour lateral magma propagation, but reduced magma buoyancy at shallow depths is required to explain the lateral propagation over more than 20 km, where the magma remains trapped beneath the lake.

How to cite: Pinel, V. and Mériaux, C.: Interplay between rifting-induced extension and surface loading effects illustrated by lateral magma propagation at Nyiragongo volcano, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10472, https://doi.org/10.5194/egusphere-egu24-10472, 2024.

X1.161
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EGU24-3311
Kostas Konstantinou

Dikes represent magma filled fractures that may propagate from a magma chamber to the surface producing an eruption, or alternatively may stall at some depth resulting only in deformation and seismicity. A crucial parameter for the modeling of dike propagation is fracture toughness, which can be defined as the critical stress intensity factor that is necessary for a fracture to propagate. Despite the fact that fracture toughness is a well defined physical quantity adopted from material science, its meaning and possible variation in volcanic environments remains poorly understood. Dike volume can provide valuable information on the level of fracture toughness and on its balance with viscous flow that ultimately determines the dynamics of dike propagation. Recently it has been shown that intrusion volume can be derived from the cumulative seismic moment release of earthquakes that accompany dike propagation. Here it is shown that a similar methodology can be utilized in order to reconstruct the volume history of dikes using high-quality earthquake catalogs from 8 volcanoes (Augustine, Bardarbunga, Cumbre Vieja, Etna, Hierro, Kilauea, Okmok, Redoubt) spanning different volcanological and tectonic settings. The pre-eruption dike volume is compared to Monte Carlo simulations of critical volume performed for a range of fracture toughness and density difference using realistic values of elastic moduli and Poisson ratio. The volume history for each eruption is also utilized for estimating magma flux rate in the dike in order to infer whether fracture toughness or viscous flow dominates dike propagation. Results show that in all the volcanoes considered fracture toughness of 100 MPa m1/2 can explain pre-eruption volumes indepedently of volcano type and length scale of the dike. In 6 out of 8 eruptions studied dike propagation fluctuated between being dominated by fracture toughness and viscous flow, while only in two cases propagation was driven almost exclusively by viscous flow.

How to cite: Konstantinou, K.: When dikes go critical: Fracture toughness and propagation dynamics using earthquake catalogs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3311, https://doi.org/10.5194/egusphere-egu24-3311, 2024.

X1.162
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EGU24-19494
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ECS
Tim Davis, Richard Katz, Adina Pusok, and Yuan Li

Radial mega-dyke swarms, found on Earth, Mars and Venus, radiate away from a central source in an asterisk-like pattern. Individual mega-dykes can reach lengths of 100s of kms and up to 100 metres in width (Ernst and Baragar, 1992), yet this similarity in the characteristic length among dykes of an individual swarm over such long distances remains enigmatic. In this study, we present theory and numerical models of dyke length. Here we hypothesise that the level of neutral buoyancy is inclined, allowing dykes to flow downslope. We postulate that the source of this inclination is crustal doming above a rising hotspot swell.

Existing models of fractures perched at their level of neutral buoyancy show the final length of the fracture L is highly dependent on the initial chamber pressure p, L∝p7/2 (Bolchover and Lister, 1999). Changes in this pressure of 10’s of MPa can cause the final length of the fractures to extend between the metre scale to 1000’s of kilometres. This suggests that the chamber pressure would have to be very stable for the injection of all dykes in a given array. In our model we will show that when the dyke propagates downslope then the dyke length is less sensitive to this source pressure. In our model, the wall rock deforms elastically but breaks when the fracture toughness is exceeded. Lubrication theory is used to model the flow within the dyke and the magma is allowed to solidify on contact with the wall. We simulate the dykes using PyFrac (Zia and Lecampion, 2020) and a simplified scheme akin to a pseudo-3D hydro-fracture model (Adachi et al., 2010). We derive equations to describe the energy sources and sinks driving the dyke to propagate laterally.

We show how the dyke height and speed increases as the slope of the level of neutral buoyancy is increased. Using our energy analysis, we show that for a dyke propagating down a constant slope the dissipation is balanced by the gravitational potential energy, resulting in a near constant tip speed. Retrieving the dyke tip speed from the model we estimate the final length of the dyke. We show that for dykes driven laterally by a stress gradient the final length is less sensitive to the magma chamber pressure. Our results show quantitatively how radial mega-dyke arrays are related to ground deformation above a rising hotspot head.

Adachi, J.I., Detournay, E. and Peirce, A.P., 2010. Analysis of the classical pseudo-3D model for hydraulic fracture with equilibrium height growth across stress barriers. International Journal of Rock Mechanics and Mining Sciences, 47(4), pp.625-639.

Bolchover, P. and Lister, J.R., 1999. The effect of solidification on fluid–driven fracture, with application to bladed dykes. Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 455(1987), pp.2389-2409.

Ernst, R.E. and Baragar, W.R.A., 1992. Evidence from magnetic fabric for the flow pattern of magma in the Mackenzie giant radiating dyke swarm. Nature, 356(6369), pp.511-513.

Zia, H. and Lecampion, B., 2020. PyFrac: A planar 3D hydraulic fracture simulator. Computer Physics Communications, 255, p.107368.

How to cite: Davis, T., Katz, R., Pusok, A., and Li, Y.: The influence of hotspot topography on mega-dyke propagation: theory and models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19494, https://doi.org/10.5194/egusphere-egu24-19494, 2024.

X1.163
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EGU24-12398
Fabio Luca Bonali, Noemi Corti, Federico Pasquaré Mariotto, Emanuela De Beni, Sofia Bressan, Massimo Cantarero, Elena Russo, Marco Neri, and Alessandro Tibaldi

In the present study we integrated data collected using field and Immersive Virtual Reality surveys with numerical models, in order to characterise a unique dyke-induced graben system, exposed both in section and plan view, characterised by an unexpected asymmetric fault geometry. Such volcanotectonic feature was formed during the 1971 eruption and is located near the northern wall of the Valle del Bove, Mt. Etna, southern Italy.

We firstly created a new structural map obtained from the analysis of historical aerial stereophotos encompassing a time interval from before to after the 1971 eruption; afterwards, we collected quantitative data on high-resolution drone-derived 3D models and field surveys carried out in the summer of 2022. Data collection on the vertical cliff was entirely carried out thanks to Immersive Virtual Reality techniques.

In plan view, the graben is 2-km-long and its width ranges 27-143 m from the bottom to the upper part of the section view, with about 82 m of difference in elevation from top to bottom. Graben faults clearly show an asymmetric setting in terms of attitude, with one fault dipping 70° to the south, and the other one dipping 50° to the north. Vertical offset values are greater at higher elevations. We also ran a set of numerical models, aimed at investigating the distribution and orientation of stresses around the inferred dyke tip and within the host rock. Comparison between field data and numerical models suggests the key role played by the inclined topography, as shown in section view, in determining the orientation of dyke-induced σ1 and σ3 in the host rock. This, in turn, controls the geometry of the graben faults, resulting in the observed asymmetric setting. Additionally, dyke-induced stress concentrations and vertical offset values support the hypothesis of a downward propagation of the graben faults, from the surface down to the dyke tip.  

How to cite: Bonali, F. L., Corti, N., Pasquaré Mariotto, F., De Beni, E., Bressan, S., Cantarero, M., Russo, E., Neri, M., and Tibaldi, A.: Immersive Virtual Reality and numerical modelling application to study a dyke-induced asymmetric graben: the 1971 Mt. Etna (Italy) case, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12398, https://doi.org/10.5194/egusphere-egu24-12398, 2024.

X1.164
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EGU24-13429
Ya-Chuan Lai, Min-Hung Shih, Cheng-Horng Lin, and Hsiao-Fen Lee

The research findings indicate that the Dayoukeng area is the most active region in the Tatun Volcano Group, Taiwan. In early 2022, mud ejecta was discovered near the main fumarole, indicating heightened activity. Comparative geochemical analysis revealed an abnormal increase in the cation concentration of hot spring at the end of 2021. Real-time webcam further identified additional steam activity above the main vent between Dec 12, 2021 and Jan 2, 2022. It is speculated that during this period, Dayoukeng may have experienced intensified steaming. A nearby network with dense seismic Zland nodes offers a unique opportunity to detect the signals during this anomalous activity in Dayoukeng. By scrutinizing and comparing the characteristics of these signals, we try to decipher the temporal variations of the sequence.

The data from nearby stations indicate a gradual increase in Dayoukeng’s activity starting from Dec 8, 2021. Initially, there is a gradual increase in signals, predominantly microearthquake within Dayoukeng. Subsequently, a notable increase in signals, characterized by a combination of seismic and acoustic signals, is observed. On Dec 12, microtremors possibly associated with mud ejections are detected. Following this, there is a repetitive occurrence of the previous seismo-acoustic observations, each enduring for several hours, persisting until a few days later. Such seismic data of dense short-period seismic network provides a chronological sequence of the Dayoukeng event, thereby facilitating the subsequent model for the entire event.

How to cite: Lai, Y.-C., Shih, M.-H., Lin, C.-H., and Lee, H.-F.: Analyzing Seismic Signals of the 2021 Dayoukeng Mud Ejection in Northern Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13429, https://doi.org/10.5194/egusphere-egu24-13429, 2024.

X1.165
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EGU24-13366
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ECS
Michelle Bensing, Sergio Vinciguerra, Giuseppe Puglisi, and Luca De Siena

Mt. Etna, located in the north-eastern area of Sicily (Italy), is one of the most active and hazardous strato-volcano in the world, both in terms of paroxysmal events and continuous effusive activity from the summit area and hazardous flank eruptions. Long-term processes of deep magma recharge and storage within the upper crust, passive magma ascent along pre-existing weaknesses, and forceful dyke intrusions allow magma to rise to the surface. Past studies provided evidence supporting the view that the interplay between magma dynamics and storage and the thermomechanical response of the host medium control magma rise and the brittle seismic response of the volcano basement and edifice.

To investigate this interplay, we created a 3D thermomechanical geodynamic model of Etna and the ground deformation response to different geological processes such as magma intrusion, gravitational spreading and main fault systems, especially with regard to the sliding of the southeastern flank. We used the Lithosphere and Mantle Evolution Model (LaMEM) code and achieved a higher model resolution by containerizing the code on the Open Computing Cluster for Advanced data Manipulation (OCCAM), an HPC cluster operated by the University of Turin and the Sezione di Torino of the Istituto Nazionale di Fisica Nucleare.

The model domain covers 41 x 39 x 14km in x, y and z direction and has two greater crustal layers with a horizontal boundary at z = 3.6km, which are inferred from laboratory results, with real topography implementation. The geometry of the flank and the position of the northern and southern fault boundary layers are based on geological evidences. Below the flank is a similar geometry that should function as a weakzone and control the sliding of the flank. Geometry and position of the high-velocity and fluid/gas pockets are based on Vp and Vp/Vs. The position of the two magma storages are inferred from geodetic outcomes. As LaMEM framework allows retrieving both deformation and gravity responses to the final model, we are currently achieving model results that ideally fit the actual GPS data recorded over 20 years in order to determine the rheological laws driving the long-term deformation.

How to cite: Bensing, M., Vinciguerra, S., Puglisi, G., and De Siena, L.: Seismic response to volcanic processes at Mount Etna: coupling thermomechanical simulations with seismic wave-equation modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13366, https://doi.org/10.5194/egusphere-egu24-13366, 2024.

X1.166
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EGU24-17383
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ECS
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Valentina Armeni, Lorenzo Mantiloni, Valerio Acocella, Eleonora Rivalta, Bodo Bookhagen, and Manfred R. Strecker

Volcanic activity in extensional geodynamic settings manifests itself in in-rift, off-rift, and inter-rift areas; the latter coinciding with structurally complex transfer zones between two rift segments. While in- and off-rift volcanism has been associated with the competition between tensional crustal stresses and gravitational unloading pressure, volcanism in inter-rift zones is still not adequately understood.

Here, we combine modelling and data from natural cases to test whether topographic highs in the inter-rift zone may control magma trajectories. We performed six analogue experiments tracking the propagation of air-filled cracks in gelatine by imposing three boundary conditions: differential tensile stresses, pre-existing anisotropies, and asymmetric and symmetric inter-rift topography. Next, we compared our results with Digital Elevation Model (DEM) analyses of young volcanic provinces such as the Virunga complex (Rwanda), the Adda’do magmatic segment (Ethiopia), and the Eifel (Germany).

Analogue results show different outcomes depending on the imposed boundary conditions. When only a differential tensile stress is applied, the air-filled crack trajectories tend to align perpendicular to the least principal stress (σ3) and focus on the centre of the gelatine box. In contrast, where inter-rift topography exists, the high sectors progressively attract the trajectories along the strike of the rift. Therefore, when injection occurs below the rift centre, magma is deflected across-rift, toward an off-rift location. Conversely, when magma injection occurs below the rift tip, magma is deflected along-rift, in the inter-rift zone. Finally, the spatial patterns of the air-filled cracks obtained by our modelling are consistent with the results of the DEM analysis of the three study areas, where volcanic activity focuses on the inter-rift segments and shifts away from the rift tips and axis as the rift widens and deepens.

How to cite: Armeni, V., Mantiloni, L., Acocella, V., Rivalta, E., Bookhagen, B., and Strecker, M. R.: What controls inter-rift volcanism?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17383, https://doi.org/10.5194/egusphere-egu24-17383, 2024.

X1.167
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EGU24-21930
High resolution monitoring of active faulting at the instable flank of Mt. Etna
(withdrawn)
Pia Victor, Silvia Crosetto, Raffaele Azzaro, Alessandro Bonforte, and Morelia Urlaub
X1.168
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EGU24-1203
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ECS
Lindsey Abdale, Lee Groat, J. Kelly Russell, and Leo Millonig

The Late Devonian Mount Grace carbonatites outcrop as thin, laterally discontinuous strata-bound lenses within the deformed and metamorphosed Monashee cover sequence of the Canadian Cordillera. The identified lithofacies range from carbonatite tuffs to tuff breccias, in line with a pyroclastic origin resulting from phreatomagmatic eruptions forming in a field of maar volcanoes. Carbonatitic eruptions occurred in a transgressive shallow marine platform setting along the western margin of paleo-North America. The timing and distribution of the Mount Grace carbonatites correlate with regional Late-Devonian back-arc extension and other rift-related sedimentary exhalative deposits, alkalic volcanism, and carbonatite and alkalic intrusions. Whole-rock geochemistry of the Mount Grace carbonatites shows a strong positive Nb anomaly, moderate REE contents with high LREE/HREE, and strongly negative Zr-Hf anomalies that overlap with global rift-related carbonatite compositions. A positive correlation exists between REE content and LREE/HREE, and Nb/Ta and Zr/Hf in Mount Grace samples that indicate primary carbonate and pyrochlore crystallization, increasing in the more evolved compositions. The evolved compositions correspond with higher proportions of phoscorite (apatite, biotite, ferrorichterite, and pyrochlore). We invoke an ascent model for the Mount Grace carbonatites, similar to other carbonatite/phoscorite complexes where an ascending parental carbonate-phosphate/Fe oxide-rich melt undergoes liquid immiscibility of phoscorite-enriched carbonatitic magma, allowing the lower density residual phoscorite-poor carbonatite magma to ascend rapidly through the crust. Zircon Hf and apatite and pyrochlore Nd and Sr isotopes from the Mount Grace carbonatites have relatively depleted mantle signatures at 360 Ma, very close to Focal Zone (FOZO) and high mu (238U/204Pb; HIMU)-like mantle reservoir endmembers similar to global ocean island basalts and indicates a mantle source for these melts, potentially of great depths. Apatite and pyrochlore Nd and Sr isotopes from the Mount Grace carbonatites fall within the range of values for a depleted mantle reservoir presumably developed at ~3 Ga that sits beneath the Canadian Cordillera based on data from carbonatites emplaced from 2700 to 110 Ma in the Cordillera and Canadian Shield. Zircon Hf from Mount Grace carbonatites overlap with this depleted FOZO-HIMU mantle endmember and extend towards more enriched Hf values, reflecting their metasomatic origins. We infer that reactivated crustal-scale rifts allowed the emplacement of small-degree partial melts of an underlying, moderately depleted mantle source.

How to cite: Abdale, L., Groat, L., Russell, J. K., and Millonig, L.: The enigmatic Mount Grace extrusive carbonatites, southeastern Canadian Cordillera: volcanic architecture, mantle source, and tectonomagmatic framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1203, https://doi.org/10.5194/egusphere-egu24-1203, 2024.

X1.169
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EGU24-4731
Antonella Amoruso and Luca Crescentini

Surface deformation in volcanic areas is often ascribed to inflation/deflation of pressurized cavities. Fast data inversion requires running many forward models based on the approximate computation of surface deformation due to selected expansive sources (sphere, spheroid, sill, and, more recently, scalene ellipsoid) embedded in a homogeneous elastic half-space. A simple very small spherical source (Mogi’s model; Mogi, 1958) often satisfy observations reasonably.

However, Earth is not homogeneous but characterized by vertical and horizontal heterogeneities; in many cases, vertical heterogeneities dominate and rigidity of the medium increases with depth. On the basis of these considerations, to highlight how the assumption of homogeneous elastic medium affects the inverted source parameters we (i) calculate the surface deformation due to point spheroids with vertical polar axis embedded in a layered half-space, and (ii) invert the computed surface deformations for the same source types (but with free geometry) embedded in a homogeneous half-space. In both forward and inverse modeling, the point source is schematized using an appropriate moment tensor (Davis, 1986); in forward modelling, we use Wang's Green functions (Wang et al., 2006) and, for comparison, also FEM. We consider two different examples of layering, which are approximately valid for Campi Flegrei (Amoruso et al., 2008) and Long Valley (velocity profiles from Biondi et al., 2023) respectively, and invert computed surface deformation (radial and vertical displacements) up to various distances from the source axis. We minimize both the mean square deviation (L2 norm) and the mean absolute deviation (L1 norm) of residuals.

The inversions show that:

1. as expected, the retrieved source appears shallower than the “real” source (i. e., focussing effect); the focussing effect depends on the source aspect ratio, generally increasing from prolate to oblate spheroids;

2. unless the “real” source is strongly vertically elongated (i. e. prolate), the retrieved source always appears very close to a spherical one (Mogi’s model); this effect depends on the source depth (less strong for shallow sources) and inversion norm (less strong for L1 norm).

Our results explain why a Mogi’s source so often satisfy deformation data, but also rise a big warning on the reliability of the inversions that provide it as a solution.

References

Amoruso, A., Crescentini, L., Berrino, G. (2008), Earth Planet. Sci. Lett., 272, 181-188.

Biondi, E. et al. (2023), Sci. Adv. 9, eadi9878.

Davis, P. M. (1986), J. Geophys. Res., 91, 7429-7438.

Mogi, K. (1958), Bull. Earthq. Res. Inst. 36, 99-134.

Wang, R., Lorenzo Martín, F., Roth, F. (2006), Comput. Geosci. 32, 527-541.

How to cite: Amoruso, A. and Crescentini, L.: Is it really a Mogi or a mirage caused by the assumption of medium homogeneity?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4731, https://doi.org/10.5194/egusphere-egu24-4731, 2024.

X1.170
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EGU24-13399
Magma storage and transport along volcanic rift zones constrained by geodetic data and dynamical models.
(withdrawn)
Alberto Roman and Paul Lundgren
X1.171
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EGU24-12793
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ECS
Poroelastic Deformation at Soufrière Hills: A New Perspective on Volcano Deformation Dynamics 
(withdrawn)
Rami Alshembari, James Hickey, Karen Pascal, Lorenzo Mantiloni, and Brendan T. McCormick Kilbride
X1.172
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EGU24-18471
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ECS
Deepak Garg, Paolo Papale, Antonella Longo, and Chiara Montagna

Ground deformation in volcanic settings can reflect pressurizing/depressurizing subsurface magma bodies, which could have geometries ranging from spheroid-like fluid-filled reservoirs to complex networks of dikes, sills, and crystal mush regions.  Having accurate forward models of deformation is important for resolving magma storage geometries and understanding stress states that influence the stability of volcanic areas and any potential eruption activity. In this regard, the finite element method (FEM) has enjoyed wide popularity due to its robustness and accuracy of results in handling of arbitrary geometries.  

We have developed an open-source hpc multiphysics finite element code Gales for solving a wide variety of PDEs. The code is parallelized using OpenMPI, aimed at multi-node (distributed memory architecture) machines. The software is written in modern C++ and can be used on a single desktop as well as on large clusters. The code offers to do static, quasistatic, and dynamic analysis for linear and non-linear elastic rock deformation in 2D/3D. The software can account for heterogeneous rock properties, real topography, and geometrical complexities associated with multiple magmatic reservoirs, connecting dykes, and volcanic conduits. 

The equations are solved using standard Galerkin FEM. For transient problems, temporal discretization is done using the second-order accurate generalized alpha method. The code has been verified on several test cases covering engineering benchmarking to problems with analytic solutions.

A recent validation exercise on "Drivers of Volcano Deformation", participated by an ample community worldwide, demonstrated Gales as one of the best open-source codes for providing accurate solutions for all exercises, with performance comparable with that of the commercial Comsol software in any individual application.

How to cite: Garg, D., Papale, P., Longo, A., and Montagna, C.: Gales: a multiphysics code for volcanic deformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18471, https://doi.org/10.5194/egusphere-egu24-18471, 2024.

X1.173
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EGU24-19503
Giovanni Florio, Maurizio Fedi, Mauro Di Vito, Federico Cella, and Valeria Paoletti

A comprehensive analysis of the gravity and magnetic fields of the Phlegrean Fields volcanic area reveals a complex structural setting. High resolution techniques, including multiscale boundary analysis and field transformations, highlight the position of density and magnetization boundaries of the Phlegrean Fields. The structural elements of the two datasets appear in a general agreement, but at the same time present differences, so yielding a complex and rich picture of the collapsed Phlegrean caldera and of the surrounding areas. Inside the caldera, a good consistence among some structural elements identified from our analysis and the seismicity can be established. Some hypotheses about the geological significance of the gravity and magnetic anomalies in the frame of the Phlegrean volcanological context are finally set up.

How to cite: Florio, G., Fedi, M., Di Vito, M., Cella, F., and Paoletti, V.: Structural elements from gravity and magnetic data in the Phlegrean Fields, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19503, https://doi.org/10.5194/egusphere-egu24-19503, 2024.

Posters virtual: Thu, 18 Apr, 14:00–15:45 | vHall X1

Display time: Thu, 18 Apr 08:30–Thu, 18 Apr 18:00
Chairpersons: Michael Heap, Valerio Acocella, Virginie Pinel
vX1.21
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EGU24-543
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Massimo Nespoli, Anna Tramelli, Maria Elina Belardinelli, and Maurizio Bonafede

Thermo-Poro-Elastic (TPE) inclusions are suitable to model the mechanical effects induced by hot and pressurized hydrothermal fluids pervading a closed volume of rocks. In fact, modeling of TPE deformation sources finds application in both geothermal and vulcanological fields. Some recent works showed that a cylindrical TPE inclusion located at about 2 km of depth contributed to the large and rapid soil uplift observed during the ‘82-’84 unrest phase in the Campi Flegrei caldera. In the present work, we demonstrate that such a source of deformation can be responsible for a significant contribution even in the current unrest phase, that started in 2005 and it is still in progress. We show that the time-series of soil uplift observed in the last years can be reproduced by assuming the rising of hot and pressurized fluids, possibly exsolved by a deep magmatic source, within the same deformation source responsible of the ‘82-’84 unrest. The existence of such a TPE inclusion at Campi Flegrei was supported by previous tomographic studies and it is reinforced by the new analysis of the b-values. In fact, we found a sharp variation of the b-value in correspondence of the depth of the modelled TPE inclusion. The decrease of the b-values is consistent with the fact that within the TPE inclusion the induced shear stress is maximum and the occurrence of larger earthquakes is favored. The results support the existence and the importance of the mechanical effects of fluids flow, during the unrest phases of the Campi Flegrei caldera.

How to cite: Nespoli, M., Tramelli, A., Belardinelli, M. E., and Bonafede, M.: Thermo-poro-elastic effects induced by fluid flow can explain the recent seismicity and deformation at Campi Flegrei (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-543, https://doi.org/10.5194/egusphere-egu24-543, 2024.