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 (k_a) and passive (k_p) 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 (σ_h) to vertical (σ_v) effective stress ratio: k = σ_h /σ_v. For a cohesionless rock mass with friction angle 𝜙 the coefficients are: k_a = 1–sin𝜙/1+sin𝜙 = 1/k_p. Therefore, k is 1 for the isotropic case, k < 1 for extension (k_a) and k > 1 for compression (k_p). The effective vertical stress is, for a normally pressurized rock mass, given by: σ_v = ρ’gh, where ρ’ = ρ_bulk–ρ_fluid 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.

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.

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.

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.

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.

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 30^th, 2020, April 15^th, 2020, May 25^th, 2020 and January 6^th, 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.

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.

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.

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.

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.

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.

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.

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.

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.

Multi-vent opening in monogenetic eruptions in the Canary Islands poses a threat considering the fast population increase over the last years. On the 19^th 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.

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.

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.

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.

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.

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.

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.

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.

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.

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 M_L 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.

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.

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.

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.

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.

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.

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.