The Hawaii-Emperor seamount chain stretches westward from the “Big Island” of Hawaii for over 6000 km until the oldest part of the Emperor chain is subducted at the Kuril and Aleutian trenches. Still regarded as the iconic hotspot-generated seamount chain it has been sampled, mapped, and studied to give insights into numerous oceanic phenomena, such as seamount and volcano formation and associated intraplate magma budgets, the past absolute motions of the Pacific plate and the drift of the Hawaiian plume, and the thermal and mechanical properties of oceanic lithosphere. Much early work on determining the flexural rigidity and equivalent elastic plate thickness that supports the large volcano loads that comprise the chain was focussed on the Hawaiian Ridge, with a major multichannel seismic expedition to the Hawaiian Islands in 1982 providing clear and direct evidence of plate flexure, as well as the indirect effect this deformation has on Earth’s gravity field. Numerous studies have since followed. However, the older part of the chain, beyond the ~50 Ma “bend”, has been much less well studied due to its remoteness, but recent expeditions have provided new marine seismic data to allow an estimation of elastic thickness along the Emperor chain and how they compare to the information we have along the Hawaiian Ridge. Here, we present preliminary work on determining the elastic thickness beneath the Emperor Seamounts. Unlike the Hawaiian Ridge, where the age of the lithosphere at the time of loading (i.e., the difference in age between the underlying seafloor and the formation age of a seamount or oceanic island) is remarkably constant, along the Emperor chain there are major variations in the age of loading, compounded by higher uncertainty due to limited seamount age sampling and the chain’s location within the Cretaceous Quiet Zone. Thus, models with variable elastic thickness as a function of location along the Emperor chain are required. In this presentation, we discuss several models that seek to account for the new seismic imaging of the top and base of flexed oceanic crust (i.e. Moho) at Jimmu guyot while at the same time honouring the characteristic gravimetric signature of the Emperor seamount edifices and their flanking moats. The Optimal Regional Separation (ORS) method is used to isolate the flexural loads, while seismic tomography and different velocity/density relations are explored for assigning suitable load and infill densities that vary spatially, and we search for optimal density and elastic parameters which minimize the misfit to both the residual gravity as well as the seismically observed flexure in the vicinity of Jimmu guyot. The first-order result is a clear thinning of the elastic thickness as we move from south to north: the implications of which we examine here for the tectonic evolution of the northwest Pacific Ocean and the long-term (>10⁶ a) mechanical properties of oceanic lithosphere.

How to cite: Wessel, P., Watts, T., Xu, C., Boston, B., Cilli, P., Dunn, R., and Shilington, D.: Variation in Elastic Thickness along the Emperor Seamount Chain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6118, https://doi.org/10.5194/egusphere-egu23-6118, 2023.

Correct estimation of the timing of velocity changes (break points) and associated uncertainties in ground deformation observed with Global Navigation Satellite System (GNSS) coordinate time series is crucial for understanding various Earth processes and how they may couple with each other. To simultaneously estimate break points, velocity changes and their uncertainties, we implement Bayesian modeling with Markov Chain Monte Carlo algorithm for GNSS time series. As the presence of white noise (WN) and time-correlated flicker noise (FLN) in GNSS time series was found to affect velocity estimation, synthetic data experiments are first conducted to investigate their effect on break point estimation. The results indicate that reliable estimates are obtained only when the value of velocity change is larger than FLN amplitude. With the presence of WN and FLN, whose amplitudes are one twentieth and one fourth of the velocity-change value, the estimation bias and uncertainty are <0.5 mm/yr and ~5 mm/yr for velocity change, and <30 d and ~100 d for break point, respectively. In this case the uncertainty is one magnitude larger than that with only the presence of WN. Then the proposed method is applied to model two velocity changes detected manually during 2014-2015 at the Krafla volcanic system, North Volcanic Zone (NVZ), Iceland. Similar accuracy and precision as the synthetic data experiments can be expected in east component of the real data as the velocity-change values are 6.9-16.5 times of the WN amplitudes and 2.5-4.0 times of the FLN amplitudes from preliminary analysis. Considering the uncertainty estimated with 95% confidence interval, the first break point at the three continuous GNSS stations in the Krafla area suggests a change in extension pattern across the NVZ prior to the beginning of a major rifting episode that started on 16 August 2014 at the Bárðarbunga volcanic system, which is ~130 km south of Krafla. The first break point at KRAC station in the Krafla caldera occurs on 2-4 July 2014, with 95% confidence interval being 4 May to 13 August 2014. The first velocity change is about 7.6 to 9.8 mm/yr to the west with its uncertainty ranging from 4.5 to 14.4 mm/yr. The velocities approximately resume to the original level after the second change at the end of 2014 or early 2015, whose chronological relationship with the end of Bárðarbunga-Holuhraun episode cannot be asserted because of uncertainties. The results may indicate coupling of activities between the volcanic systems in the NVZ via processes not well understood. Further work is needed to confirm these results and their significance.

How to cite: Yang, Y., Sigmundsson, F., Geirsson, H., Lanzi, C., Hreinsdóttir, S., Drouin, V., Zhou, X., and Ma, Y.: Bayesian modeling of velocity break points in GNSS time series and the effect of noise on their estimation: Did velocity anomalies in the Krafla volcanic system, north Iceland, precede the Bárðarbunga-Holuhraun 2014-2015 rifting episode?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7374, https://doi.org/10.5194/egusphere-egu23-7374, 2023.

Localized ground deformation at volcanoes in extensional setting may occur because of strain localization. The magmatic system of a volcano with its liquid magma, magma mush, and hot crust will cause a rheological anomaly, where material properties may be very different from surrounding crust and mantle. Numerical models based on the Finite Element Method (FEM) are used to explore ground deformation at volcanoes in extensional environments, considering realistic volcano models with heterogeneous multi-layered structure, with both elastic and viscoelastic rheology. The effects of localized lateral and vertical variations in terms of geometry and material properties of the crust are explored, in a model domain undergoing stretching applied perpendicular to the lateral domain boundaries of one and two-layers model (at a rate of 17.4 mm/yr applied in our models). A one-layer model displays the same elastic feature throughout the whole domain except for a localized upper volume with lower elastic properties, compared to the surrounding crust, to simulate the shallow magmatic system. In a two-layer model, the top elastic layer overlies a viscoelastic layer that locally reaches shallower levels to symbolize the deep magmatic system beneath the shallow low-rigidity volume previously introduced. A localized surface subsidence signal is a characteristic feature of magmatic system with a large body of localized viscoelastic rheology at shallow depth. The subsidence signal is strongly dependent on the viscosity and volume of the up-doming viscoelastic material. A model with viscosity of 5 × 10¹⁹ Pa s in the up-doming material, and a 7 – 15 km-thick elastic layer, show a small subsidence rate, ~0.1 – 0.4 mm/yr. Our models show an increase of the localized subsidence rate, from 1.9 to 5.5 mm/yr, as the viscosity decreases from 10¹⁸ Pa s to 10¹⁶ Pa s in the up-doming material. Lower viscosities (<10¹⁶ Pa s) show no further change in subsidence rate when compared to the 10¹⁶ Pa s solution. We apply three-dimensional FEM models to improve understanding of the subsidence at the Krafla and Askja volcanic systems (1989-2018 and 1983-2018, respectively) in the Northern Volcanic Zone of Iceland. The two subsiding areas (roughly 9 × 10 km each) lie in about 50 km-wide zone which marks the North America-Eurasia divergent plate boundary. The rate of subsidence at Krafla was ~1.3 cm/yr in 1993-2000 and slowed down to 3-5 mm/yr in 2006-2015. The rate of subsidence at Askja decayed more slowly than Krafla. During the 1983-1998 the subsidence rate was ~5 cm/yr; in 2000-2009, geodetic monitoring showed that the subsidence slowed down to ~2.5 cm/yr. Comparison of FEM models to geodetic data in North Iceland suggests that plate divergence processes may account for part of the observed subsidence, dependent on how extensive rheological anomalies in relation to magma are beneath the volcanoes.

How to cite: Lanzi, C., Sigmundsson, F., Geirsson, H., Maree Parks, M., and Drouin, V.: Strain Localization at Volcanoes Undergoing Extension: Investigating Long-term Subsidence at Krafla and Askja in North Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8378, https://doi.org/10.5194/egusphere-egu23-8378, 2023.

Dykes (Mode I extension fractures) supply magma from deep reservoirs to the surface and subject to their propagation paths, they can sometimes reach the surface and feed volcanic eruptions. Most of the times they mechanically stall in the heterogeneous crust or deflect through pre-existing fractures forming sills. Although several studies have explored dyking in heterogeneous regimes, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear.

Here, we coupled field observations with FEM numerical modelling using the software COMSOL Multiphysics (v5.6) to explore the mechanical and geometrical conditions that promote (or not), dyke-sill propagation in glacial-tectonic conditions. We used as a field example the Stardalur cone sheet-laccolith system, located in the Esja peninsula proximal to the western rift zone. The laccolith is composed of several vertical dykes that bend into sills and form a unique stacked sill ‘flower structure’. We modelled a heterogeneous crustal segment composed of lavas (top) and hyaloclastites (bottom). We then studied the emplacement of a dyke with varied overpressure values (P_o = 1-10 MPa) and regional extension (Fe = 0.5-3 MPa) loading conditions at the lava/hyaloclastite contact. In the second stage, we added an ice cap as a body load to explore dyking subject to unloading due to glacier thickness variations (0-1 km).

Our results have shown that the presence of the ice cap can affect the dyke-sill propagation and the spatial accumulation of tensile and shear stresses below the cap. The observed field structure in non-glacial regimes has been formed either due to the mechanical contrast (Young’s modulus) of the studied contact, a compressional regime due to pre-existing dyking or faulting, or finally, high overpressure values (P_o  ≥ 5 MPa). Instead, in a glacial regime, the local extensional stress field below the ice cap encourages the formation of the laccolith when the ice cap becomes thinner (lower vertical loads). Our models can be applied to universal volcanoes related to glacier thickness variation and sill emplacement.

How to cite: Drymoni, K., Tibaldi, A., Pasquaré Mariotto, F., and Bonali, F. L.: Dyke-sill propagation in glacial-volcanotectonic regimes: The case study of Stardalur laccolith, SW Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6230, https://doi.org/10.5194/egusphere-egu23-6230, 2023.

The propagation mechanics and fluid dynamics of magma-filled fractures, such as dykes and sills, are fundamental to the generation of sub-surface signals which indicate magma is on the move. Dykes play a major role transporting magma from depth to the surface, and modelling the dynamics of dyke growth remains a primary objective to improve the interpretation of a wide range of geophysical, petrological and geochemical evidence of magma ascent. We present results from scaled analogue experiments using Liverpool’s new Medusa Laser Imaging Facility to quantify the fluid flow dynamics and solid deformation during magma ascent in dykes. Our results detail the characteristics of dyke ascent from inception to eruption, with magma flow regimes and host-rock deformation mode dependent on dyke geometry, host-rock properties, density contrasts and magma rheology. Our results pose new conceptual models upon which the signals of magma movement in nature should be interpreted.

How to cite: Kavanagh, J. and Chalk, C.: Using analogue experiments to explore fundamental processes during magma ascent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13854, https://doi.org/10.5194/egusphere-egu23-13854, 2023.

One of the best-known examples worldwide of monogenetic volcanism is the Parícutin volcano. The eruption began its formation in the middle of a cornfield in February 1943 and lasted until March 1952. Parícutin is the youngest edifice of the Michoacán-Guanajuato Volcanic Field, which was witness initially by local inhabitants, and later by scientists and other observers. Observations of the eruption documented the remobilization of primary ashfall by rainfall and wind. Despite these observations, the resulting reworked deposits have not yet been described in the stratigraphic sequence. The distinction between primary pyroclastic and reworked deposits is critical for the geological understanding of eruptive processes and related hazards because of their different origins, frequencies, and environmental impacts. This categorization is not always obvious and needs a detailed study to characterize the complex interbedding of both types of deposits that coexist in the volcanic sequence. Referenced to these, we conducted new field reconnaissance, coupled with laboratory analyses of the ejecta ash fraction. The detailed composite stratigraphy obtained consists of six widely dispersed fallout deposits interbedded with seven reworked units. These reworked deposits display sedimentary structures produced by tephra remobilization due to lahars and stream flows. In addition, some layers show dunes and ripples generated by duststorms. By using GIS tools, we integrated the existing data with our new composite stratigraphic column and the distribution map of the syn-eruptive reworked deposits. This analysis reveals that more than 70% of the total thicknesses correspond to syn-eruptive reworked deposits. Therefore, previous studies had overestimated the distribution of primary tephra from the Parícutin explosive phases. The lowest and flattest areas with wide rill networks, which are located 4 to 6 km north of the volcano, are composed of up to 90% reworked deposits. In contrast, proximal locations with gentler slopes located at medium altitudes better preserve pyroclastic deposits. To that end, we constructed a new isopach map of the pyroclastic deposits based on the distribution of the reworked deposits. This study brings new light to understanding the sedimentary processes that occur during volcanic eruptions and highlights the importance of recognizing pyroclastic and reworked deposits during monogenetic eruptions.

How to cite: Bolós, X., Macias, J. L., Ocampo-Díaz, Y. Z., and Tinoco, C.: Reworking processes during monogenetic eruptions. The case of the Parícutin volcano, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5994, https://doi.org/10.5194/egusphere-egu23-5994, 2023.

Eruptions at long-inactive volcanoes are usually preceded by days to months of unrest as magma migrates gradually to shallower depths. This is built into plans by civil protection agencies for societal response. Here we show that at São Jorge, Azores, after 60 years of repose, magma reached almost the surface in a vertical dike intrusion within a few hours of the seismicity onset with no previous precursory signals. São Jorge lies in a rift zone where extensional stress is expected to be built over time to accommodate magma at depth. Recent eruptions at São Jorge have produced pyroclastic density currents, and the potential for an eruption to occur with little warning poses a significant risk. Deformation associated with the event reached other neighboring islands over a distance of at least 45 km away from São Jorge. Deformation was high on the first day of activity (>50 mm within March 19-20) and significantly decreased afterward. The combined analysis of GNSS and InSAR data allows using a model of segmented rectangular dislocations with multiple patches for data inversion. A maximum opening of 1.7 m at 4-6 km depth is inferred from the modeling. We interpret the cause of the initial vertical shallow injection to be due to host rock failure conditions triggered by deviatoric stresses. We investigate why lateral spreading of the dike occurred soon after the initial injection. Using a FEM simulation, we show how the tension at the tip of a vertical propagating dike is high at the start and decreases with shallower depths, reaching similar levels of tension found at the lateral parts of the dike and increasing the probability of lateral propagation.

How to cite: D'Araújo, J., Hooper, A., Lazecky, M., Sigmundsson, F., Ferreira, T., Silva, R., Gaspar, J., and Marques, R.: Sudden shallow dyke intrusion at São Jorge Island (Azores) after 60 years of repose, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9104, https://doi.org/10.5194/egusphere-egu23-9104, 2023.

Volcanic eruptions are often preceded by episodes of inflation and emplacement of magma along tensile fractures. Here we study the 2021 Cumbre Vieja eruption on La Palma, Canary Islands, and present evidence for tensile fractures dissecting the new cone during the terminal stage of the eruption. We use synthetic aperture radar (SAR) observations, together with drone images and time-lapse camera data, to determine the timing, scale and complexities associated with the fracturing event, which is diverging at a topographic ridge. By comparing the field dataset with analogue models, we further explore the details of lens-shaped fractures that are characteristic for faults diverging at topographic highs and converging at topographic lows. The observations made at Cumbre Vieja and in our models are transferrable to other volcanoes and add further evidence that topography is substantially affecting the geometry and complexity of fractures and magma pathways, and the locations of eruptions.

How to cite: Walter, T. R., Zorn, E., Gonzalez, P., Sansosti, E., Munoz, V., Shevchenko, A., Plank, S., Reale, D., and Richter, N.: Late complex tensile fracturing interacts with topography at Cumbre Vieja, La Palma, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3344, https://doi.org/10.5194/egusphere-egu23-3344, 2023.

One of the main goals of the modern volcanology is produce accurate eruption forecastings. Not only from a scientific point of view, but considering that approximately 30 million people live in the vicinity of active volcanic areas and tens of thousands of people have lost their lives as a result of the direct effects of historical eruptions. Thus, in 2017 "The US National Academies of Sciences, Engineering and Medicine" considered the forecast of eruptions as one of the great challenges of Volcanology. Generally, the focus is on forecasting the eruption onset, however, forecasting the style, size and duration becomes relevant and properly manage long-duration eruption, e.g., during the 2021 La Palma (Canary Islands) eruption, whose main hazards were air pollution, ash fall and lava flows. In particular, the 2021 eruption of La Palma lava flows caused extensive devastation to the surrounding community: more than 2800 buildings and almost 1000 hectares of banana plantations and farmland were destroyed. In this study, we use co-eruptive GNSS series of deformation data to estimate the eruption's end. The forecast was based on the relationship between displacements and pressure changes provided by a purely elastic model of the medium. We also estimated the location of a magma reservoir. A depth of 10-15 km is inferred. This reservoir is consistent with the main seismogenic volume during the eruption. We interpret that the reservoir pressure dropped due the progressive withdrawal of magma that fed the eruption. We assumed that the magmatic plumbing responsible for the eruption was a closed system and that the magma contributions in this zone do not cause detectable deformations. Thus, we used the pressure drop as an indicator of the end of an eruption. With the benefit of the hindsight, we extensively tested our model considering different deformation time series spams in order to evaluate the feasibility of making near-real time predictions of the duration of the eruption, and derive some constraints about the magma system.

How to cite: Charco, M., González, P. J., Garcia-Cañada, L., and del Fresno, C.: Pressure drop as a forecasting tool of eruption duration: 2021 La Palma eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12339, https://doi.org/10.5194/egusphere-egu23-12339, 2023.

Investigation of the dynamic magma movement beneath the volcanos could provide critical information about the mechanism of volcanic eruption and therefore enhance the accuracy of eruption forecast.  Axial Seamount is an active submarine volcano located at the intersection of the Juan de Fuca Ridge and the Cobb hotspot.  Through its submarine surveillance network of Ocean Observatories Initiative (OOI), we observed magmatic activities that occurred before and during its latest eruption on April 24, 2015, as well as the following unrest events from the temporal variations of shear-wave velocity beneath Axial Seamount.

In this study, we applied the Rayleigh-wave admittance method, which uses the frequency-domain transfer function between seismic displacement and water pressure, to invert for shear-wave velocity changes beneath the submarine seismic stations.  The results illustrated that a large magma upwelling event happened beneath the AXEC2 (southeastern caldera of Axial Seamount) several weeks prior to its 2015 eruption, implying the magma movement through a pathway near the southeastern caldera and possibly triggered the subsequent eruption.  However, another magma upwelling event beneath the AXID1 station (southern caldera) between December 2016 and June 2017 occurred without triggering any noticeable eruption event. These magmatic activities demonstrate that the eruption of Axial Seamount is controlled by a complicated magma plumbing system.  The eruption probably depends on not only the magma influx but also the status of the plumbing system and the overlying crustal layer.  With the Rayleigh-wave admittance method and the real-time data from the OOI network, we can continuously monitor the status of Axial Seamount and provide more information for the next eruption.

How to cite: Wang, L. and Ruan, Y.: Dynamic magma movements beneath the Axial Seamount revealed by Rayleigh-wave Admittance Method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5843, https://doi.org/10.5194/egusphere-egu23-5843, 2023.

Under polar and subpolar climatic conditions, volcano edifice growth and stability are affected by extreme erosion rates, mass wasting, glacier loading (and unloading), and permafrost soil conditions. Relatively small changes in temperature can lead to very different snow and ice conditions in relation to all of the above. Therefore active, shallow magmatic plumbing systems and magmatic pathways might react sensitively to even minor changes of their surrounding environmental conditions. Almost constant degassing from the summit crater of Mount Curry (Zavodovski Island) and the presence of an active lava lake within the summit crater of Mount Michael (Saunders Island) suggest the existence of shallow magmatic plumbing systems at both volcanoes. They therefore represent exceptional study sites for investigating volcano processes under subpolar climatic conditions. Because of their remoteness, none of these islands are equipped with permanently installed ground-based instruments. We observe and quantify surface displacements related to volcanic activity, fumarolic activity, tectonic activity in the Scotia arc, as well as glacier flow from high-resolution combined TerraSAR-X and PAZ interferometry and amplitude offsets. Multi-temporal topographic data are available through the TanDEM-X SAR satellite mission and photogrammetric surveys conducted in April-Mai 2019 at Saunders Island and in January-February 2023 on Zavodovski Island. Here we introduce the first results of combining and exploring UAV photogrammetry with SAR satellite data. We present a geomorphological and structural analysis of Zavodovski Island and the outer subaerial and shallower submarine flanks of Saunders Island. We also estimate the glacier volume and volume change over time on Saunders as well as surface dynamics at Zavodovski. With this study we highlight the unprecedented detail and the valuable information that can be retrieved from tasked and targeted TerraSAR-X, TanDEM-X, and PAZ satellite acquisitions coupled

How to cite: Richter, N., Massimetti, F., Hart, T., Cartus, O., Leinss, S., Derrien, A., Zorn, E., Shevchenko, A., Wintersteller, P., Meschede, M., and Walter, T.: Volcano processes at the remote South Sandwich Islands of Zavodovski and Saunders observed from air and space, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17100, https://doi.org/10.5194/egusphere-egu23-17100, 2023.

Phreatic and hydrothermal eruptions remain among the most difficult to forecast. The frequent absence of clear precursor signals challenges volcanologists' ability to provide timely and accurate hazard advice. They remain poorly understood and have recently caused human fatalities. It is therefore paramount to better investigate such eruptions by integrating new methodologies to fully understand the preparatory processes at play and improve our ability to forecast them.

Among the different approaches to monitor volcanoes, seismology forms the basis, and most active volcanoes are nowadays equipped with at least one seismometer. Seismology is unique amongst the Earth Science disciplines involved in volcano studies, as it provides real-time information; as such, it is the backbone of every monitoring program worldwide. With data storage capabilities expanding over the last decades, new data processing tools have emerged taking advantage of continuous seismic records. Recent advances in volcano monitoring have taken advantage of seismic noise to better understand the time evolution of the subsurface. 

The well-established seismic interferometry has allowed us to detect precursory changes (dv/v or decorrelation) to phreatic eruptions at different volcanoes, thereby providing critical insights into the triggering processes. More recent approaches have provided insights into the genesis of gas-driven eruptions using seismic attenuation (DSAR: Displacement seismic amplitude ratio) and correlation with tidal stresses (LSC). Yet, puzzling observations have been made at different volcanoes requiring the use of numerical models and machine learning-based approaches, as well as complementary dataset to reach a more comprehensive understanding. This presentation will review recent insights gained into precursory processes to phreatic eruptions using seismic noise and how we could possibly forecast them. These tools are freely available to the community and have the potential to serve monitoring and aid decision-making in volcano observatories.

How to cite: Caudron, C., Girona, T., Lecocq, T., Ardid, A., Dempsey, D., and Yates, A.: Towards monitoring phreatic eruptions using seismic noise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7166, https://doi.org/10.5194/egusphere-egu23-7166, 2023.

Volcanic calderas are delimited by a ‘caldera wall’ which can be several hundred meters in height. This represents the degraded scarp of a fault that accommodates roof subsidence. Here, we assess the roles of friction and cohesion on caldera wall morphology by: (i) analysing the slope properties of several young natural calderas in the ALOS-3D global digital surface model (DSM), and (ii) comparing those observations to the results of a text-book analytical solution and of new Distinct Element Method (DEM) modelling.

Our analysis of the DSM suggest that caldera wall heights are not as closely linked to slope angle as previously suggested. Slope angles range from 20 – 65° and slope heights range from 99 m - 1085 m. We find that the smaller slope heights are not robustly tied to greater slope angle. When compared to analytical predictions, these slope-height data yield expected rock mass cohesion values of less than 0.25 MPa for all calderas, which is 2-3 orders of magnitude less than typical laboratory-scale values.

The DEM models explicitly simulated the process of progressive caldera collapse, wall formation and destabilisation, enabling exploration of the emergence of slope morphology as a function of increasing subsidence and of mechanical properties. Results confirm that low bulk cohesion values <0.5 MPa are required to reproduce the observed ranges of slope angles and slope heights, and they indicate that friction is the dominant control on slope evolution. Different failure mechanisms resulted as a function of cohesion and friction during early collapse: (1) granular flow with low friction and cohesion, and (2) block toppling at high friction and cohesion. During later collapse, shear failure dominates regardless of cohesion. At higher cohesion and/or friction values, the models resulted in non-linear concave-upward slope profiles that are seen at many natural calderas.

How to cite: Harnett, C., Watson, R., Holohan, E., and Schöpfer, M.: Mechanical controls on caldera slope morphology and failure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7530, https://doi.org/10.5194/egusphere-egu23-7530, 2023.

Assessing the history, dynamics and magnitude of pre-historic explosive volcanic eruptions relies heavily on the completeness of the stratigraphic records, the spatial distribution, and the sedimentological features of the pyroclastic deposits. Near-vent volcanic successions provide fundamental but often patchy information, both in terms of record completeness (e.g., scarce accessibility to the older deposits) and of the spatial variability of the sedimentological features. Hence, medial to distal sections increasingly represent essential integrative records.

Campi Flegrei (CF) is among the most productive volcanoes of the Mediterranean area, with a volcanic history comprised of well-known caldera-forming eruptions (e.g., Campanian Ignimbrite, CI, ~40 ka; Neapolitan Yellow Tuff, NYT, ~14 ka). Furthermore, recent studies correlated a well-known widespread distal ash layer, the so-called Y-3, with a poorly exposed proximal CF pyroclastic unit (Masseria del Monte Tuff, 29ka), allowing a re-assessment of the magnitude of this eruption, now recognized as a third large-magnitude (VEI 6) eruption at CF. The discovery of this large eruption reduces drastically the recurrence intervals of large-magnitude events at CF and has major implications for volcanic hazard assessment.

While the most powerful Late Pleistocene (e.g., post-NYT and partially post-CI) eruptions at CF have been the subject of extensive investigations, less is known about its earliest activity. Motivated by this knowledge gap, we have reviewed the research on Middle-Late Pleistocene eruptions from the CF (~160-90 ka) in light of new compositional (EMPA + LA-ICP-MS), grain-size distribution (dry/wet sieving and laser) and morphoscopy (SEM) data of tephra layers from proximal and distal settings, including inland and offshore records. Our study provides a long-term overview and cornerstone that will help provide future eruptive scenarios, essential for the quantification of recurrence times of explosive activity and in volcanic hazard assessment in the Neapolitan area. This overview sets the basis for modelling dispersion as well as eruptive dynamics parameters of pre-CI large-magnitude eruptions, needed to better understand the behavior of the CF caldera with a long-term perspective.

How to cite: Fernandez, G., Giaccio, B., Costa, A., Monaco, L., Albert, P., Nomade, S., Pereira, A., Leicher, N., Lucchi, F., Petrosino, P., Milia, A., Insinga, D., Wulf, S., Kearney, R., Veres, D., Jordanova, D., and Sottili, G.: New constraints on Middle-Late Pleistocene large-magnitude eruptions from Campi Flegrei, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6552, https://doi.org/10.5194/egusphere-egu23-6552, 2023.

Active calderas are typically characterized by shallow magmatic systems associated with marked geothermal anomalies and significant fluid releases. Ground deformation are generally associated with uplift or subsidence, induced by recharges or emptying/cooling of the magmatic storage system, by expansions or contractions of hydrothermal systems, or by combinations of these factors. The pressure variations in the hydrothermal systems can lead to an increase in the fumarolic and distributed soil degassing activity or in the sudden release of gas, leading to phreatic explosions, even to violent ones.

The Island of Vulcano (Italy), part of the Aeolian archipelago (southern Tyrrhenian Sea), contains an active caldera (La Fossa caldera) showing a widespread degassing and fumarolic activity, mainly localized in the main active volcano (La Fossa cone) and in other emissions zones within the caldera. The La Fossa caldera has shown signs of unrest since September 2021 and to date monitoring parameters have not returned to background levels.

Accordingly, the geophysical measurements obtained through the Vulcano Island monitoring infrastructures, which include geodetic and seismic data, were analysed. GNSS and DInSAR data, the former processed using the GAMIT-GLOBK software to calculate both time series and velocities of every remote station of the 7-stations network in Vulcano and Lipari islands, the latter processed through the P-SBAS technique, were used to identify the source of deformation. The seismic network data were exploited to discriminate the seismicity induced by regional tectonics from that induced by the magmatic or hydrothermal system (VT, VLP, tremor).

The inversion of the ground deformation measurements made possible to investigate the source within the hydrothermal system of the Fossa cone. Moreover. the seismic data analysis reveals the activation of regional crustal structures during the hydrothermal unrest, as well as the flow of hydrothermal fluids within the caldera structures linked to the presence of a pressurized hydrothermal system.

The presented results will provide a general overview of the main findings relevant to the Vulcano Island geodetic and seismic data inversion and analysis.

How to cite: Di Traglia, F., Bruno, V., Casu, F., Cocina, O., De Luca, C., Giudicepietro, F., Lanari, R., Macedonio, G., Mattia, M., Monterroso, F., and Privitera, E.: Dealing with hydrothermal unrest in active calderas by jointly exploiting geodetic and seismic measurements: the 2021-22 Vulcano Island (Italy) crisis case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7174, https://doi.org/10.5194/egusphere-egu23-7174, 2023.

The geodynamic framework of Mount Etna volcano (Italy) is characterised by two superimposed tectonic domains: a compressional one, oriented N-S, and an extensional one, oriented approximately WNW-ESE. The combination of these two domains and the volcano activity, has generated a complex system of faults prevalently on the eastern flank of the volcano. The eastern flank is the most active area of the volcano in terms of deformation and seismicity. The velocities there are at least one order of magnitude greater than in the rest of the volcano flanks due to the eastward sliding of the eastern flank.

The monitoring and analysis of the acceleration occurring on the eastern flank of Mount Etna is the keystone to understand the volcano-tectonic dynamics that, apart from the tectonic and magmatic processes, involves the instability of this flank in a densely inhabited area.

In order to monitor the deformation, Istituto Nazionale Geofisica e Vulcanologia – Osservatorio Etneo (INGV-OE) and the GeoDynamic & GeoMatic Laboratory of the University of Catania integrate GNSS and InSAR products with twofold objective: to characterize the dynamics of the area and to analyse the deformation transients, this last in view of a possible use in the framework of an alert system.

Here, we analyse the ground deformation that occurred between 2016 and 2019 across the faults of the south-eastern flank of Mount Etna. On the south-eastern flank the deformation is accommodated by several faults which have different kinematics and behaviours. We discriminate the deformation transient and the activity of the Belpasso-Ognina lineament, Tremestieri, Trecastagni, San Gregorio-Acitrezza, Linera, Nizzeti and Fiandaca faults. The latter generated the 26 December 2018 earthquake, two days after the eruption of 24 December, which induced a clear post seismic deformation, detected by GNSS and InSAR data. In particular, we discriminate the deformation occurred along the San Gregorio-Acitrezza fault, which is accommodated by the Nizzeti fault, and we analyse the post seismic deformation along the Linera fault. We analyse the Slow Slip Events (SSE) that are observed in the GNSS and InSAR time series in the vicinity of the Acitrezza fault and we quantify and discuss the tectonic origin of the Belpasso-Ognina lineament that we interpreted as a tear fault.

How to cite: Carnemolla, F., Bonforte, A., Brighenti, F., Briole, P., De Guidi, G., Guglielmino, F., and Puglisi, G.: GNSS and InSAR study of the ground deformation of the eastern flank of Mount Etna from 2016 to 2019, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17466, https://doi.org/10.5194/egusphere-egu23-17466, 2023.

Measuring how the surface deforms in time and space plays a crucial role, not only for understanding volcanic mechanisms, but also for hazard assessment, risk mitigation and supporting crisis management. Mount Etna, one of the most active volcanoes in the world, with a growing population in its vicinity, has experienced an intense period of activity in recent years, mainly characterized by continuous degassing and recurring lava fountains. Due to this activity, continuous deformation can be observed at Mount Etna.

The summit craters showed brisk activity in the last months of 2020, accompanied by increasing seismicity. A period of paroxysms started in December 2020 and intensified in February 2021, with brief but violent eruptive lava-fountaining episodes, that continued throughout all the year. The focus of this study is to understand the dynamics of the near-surface feeding system by constraining the sources responsible for the observed paroxysms. To localize and describe the time-dependent ground deformation, we examine surface deformation at Mount Etna by means of an Interferometric Synthetic Aperture Radar time series analysis utilizing Sentinel-1 data between the second half of 2020 and the end of 2021. The onset of the paroxysms was preceded by an inflation period and deflation episodes were observed during the paroxysms period, which suggests a link between the volcano activity and the observed deformation. The findings may contribute to the discussion on the distribution and dynamics of magma reservoirs that form Mount Etna's conduit system and its interaction with the local tectonic regime.

How to cite: Vásquez Castillo, A., Guglielmino, F., and Puglisi, G.: On the 2021 Volcanic Paroxysmal Activity of Mount Etna: a Ground Deformation Analysis Using InSAR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10489, https://doi.org/10.5194/egusphere-egu23-10489, 2023.