Displays

For the past decades, several numerical studies have successfully reproduced the concentric uplift pattern observed above the Altiplano-Puna Magma Body (APMB) in the central Andes. However, the temperature- and strain rate-dependent viscoelastoplastic rheology of rocks, the buoyancy of magma, the effects of modelling in 3D as well as the shape of the magma body have often been simplified or neglected.

Here, we use a joint interpretation of seismic imaging and gravity anomalies to constrain location, 3D shape and density of the magma body. With the help of the thermo-mechanical finite difference code LaMEM, we then model the surface deformation and test our results against observations made by Interferometric Synthetic-Aperture Radar (InSAR) missions. This way, we gain insights into the dynamics and rheology of the present-day magmatic system and can test how a change to the current conditions (e.g., magma influx) could impact it.

We find that only an APMB with a maximum thickness of 14 to 18 km and a corresponding density contrast to the surrounding host rock of 100 to 175 kg/m³ satisfies both tomography and Bouguer data. Based on that and the chemistry of eruption products, we estimate the melt content of the APMB to be on the order of 20 - 25%. We also find that the observed uplift can be reproduced by magma-induced buoyancy forces without the need for an additional pressure source or magma injection within the mush, and that the geometry of the top of the magma body exerts a major control on the deformation pattern at the surface.

How to cite: Spang, A., Baumann, T., and Kaus, B.: 3D Geodynamic Models of the Present-Day Altiplano-Puna Magmatic System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5388, https://doi.org/10.5194/egusphere-egu2020-5388, 2020.

Volcanic eruptions are foundational events shaping the Earth’s surface and providing a window into deep Earth processes. We document here an ongoing magmatic event offshore Mayotte island (Western Indian Ocean) unprecedented in terms of emitted volume of lava and duration of the seismic crisis.This event gave birth to a deep-sea volcanic edifice 820m tall and ~ 5 km³ in volume, located 50 km from Mayotte. A plume with distinct chemical signatures compared to open-ocean seawater emanated from the edifice, generating an exceptional 1900m-high vertical acoustic anomaly in the water column. Noble gas analyses in the vesicles from a popping rock dredged on the flank of the edifice, indicate rapid magma transfer from the asthenosphere. The edifice is located at the tip of a WNW-ESE–striking volcanic ridge composed of many other edifices, cones and lava flows constructed by past eruptions. Starting in May 2018 thousand of earthquakes were triggered by the magmatic event. The space-time distribution of the seismicity suggests that magma below the center of the ridge was transported to the new edifice over a few weeks in dikes that penetrated the brittle mantle a result of a lithosphere-scale extensional episode accommodating motion along a transfer zone between the East-African rifts and Madagascar. Since the eruption’s onset, the seismicity is mostly concentrated closer to the island, in an exceptionally deep zone (25-50 km) overlain by a zone of enigmatic, very low frequency, tremors.

How to cite: Feuillet, N., Jorry, S., Crawford, W., Deplus, C., Thinon, I., Jacques, E., saurel, J.-M., Lemoine, A., Paquet, F., Satriano, C., Aiken, C., Laurent, A., Cathalot, C., Rinnert, E., Gaillot, A., Scalabrin, C., Moreira, M., Peltier, A., Beauducel, F., and Ballu, V. and the Tellus SISMAYOTTE and MAYOBS Team: Birth of a large volcanic edifice offshore Mayotte (Comoros Island, Western Indian Ocean), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11307, https://doi.org/10.5194/egusphere-egu2020-11307, 2020.

Western Galápagos calderas experienced repeated eruptive and non-eruptive unrest in the last decades, only partially studied. Here we investigated, using the Synthetic Aperture Radar Interferometry (InSAR) and geodetic modelling, the eruptive and the non-eruptive unrest episodes occurred in two of the less studied calderas of the western Galápagos: Alcedo and Cerro Azul. Alcedo underwent repeated non-eruptive unrest from 2007 to 2011, while Cerro Azul experienced an unrest, from 2007 to 2008, culminated in two eruptive phases from May 29th to June 11th 2008. Results highlight how Alcedo experienced two episodes of uplift due to new magma injections in its shallow magma reservoir, separated by an episode with a limited lateral propagation of magma, probably interrupted for the lack of new magma supply in the magma reservoir. Results also hint to a possible relationship between these short-term unrest episodes and the longer-term process of resurgence at Alcedo. As for Cerro Azul, we overcame unwrapping errors affecting some of the InSAR data of Cerro Azul by proposing a new method, based on the wrapped phase differences among nearby pixels, to invert the wrapped phase directly. Our results highlight how the eruption was preceded by long-term pre-eruptive inflation (October 2007 – April 2008). During the first eruptive phase, most of the magma responsible for the inflation fed the lateral propagation of a radial dike, which caused a first deflation of the magmatic reservoir. During the second eruptive phase, the further lateral propagation of the dike fed a radial eruptive fissure at the base of the edifice, causing further deflation of the magmatic reservoir. From the first to the second eruptive phase, the radial dike changed its strike propagating towards a topographic low between Cerro Azul and Sierra Negra. An increase in magma supply from the reservoir to the dike promoted the further lateral propagation of the dike, confirming the importance of a continuous supply of magma in the propagation of a dike. 

How to cite: Galetto, F., Hooper, A., and Bagnardi, M.: Unrest episodes at Alcedo and Cerro Azul (Galapagos) revealed by InSAR data and geodetic modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7188, https://doi.org/10.5194/egusphere-egu2020-7188, 2020.

Current approaches to vent opening forecast produce probabilistic maps on the base of the spatial density of past eruptive vents, as well as the surface distribution of structural features such as faults and fractures. One of the main challenges in forecasting future vent locations in the case of distributed volcanism is that we usually deal with scarce, spatially scattered data to support these approaches. As sophisticated as our statistical analysis can be, such data are difficult to interpolate between and extrapolate from, resulting in spatially coarse forecasts and large uncertainties. More recently, Rivalta et al. (2019) proposed a forecasting strategy to predict future vent locations, combining the physics of magma transport at depth (where magma trajectories are assumed to be driven entirely by stress) with a Monte Carlo inversion technique for key stress parameters. This method has been first tested on the Campi Flegrei caldera; however, further validations and development are needed. Here we validate the strategy of Rivalta et al. with data from analog models (air injection in gelatine). We stress a gelatine block in controlled conditions (extension/compression, surface loading/unloading, layering) and observe air-filled crack trajectories. With these data, we test a flavour of the strategy that combines boundary element magma trajectory calculations with a  Monte Carlo Markov chain approach. We find the scheme is able to retrieve the parameters of the stress imposed on the gelatine and forecast subsequent vents in the same experimental setups. We also discuss how it may be applicable to natural cases, and what data are necessary for the approach to be feasible.

How to cite: Mantiloni, L., Davis, T., Gaete Rojas, A. B., and Rivalta, E.: A Monte Carlo Markov Chain Approach to Stress Inversion and Forecasting of Eruptive Vent Locations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9580, https://doi.org/10.5194/egusphere-egu2020-9580, 2020.

Magmatic dikes are a naturally occurring type of fluid-driven fractures [1] propagating in the lithosphere driven by buoyancy (more precisely by the difference between the in-situ minimum horizontal stress gradient and the magma weight). Fully-coupled modelling of these 3D fractures is very challenging and most contributions until today have been restricted to 2D plane-strain. These 2D investigations have highlighted the importance of the head-tail structure, notably the fact that lubrication flow in the tail is driving the growth of the hydrostatic head [2, 3]. We investigate the 3D development of a buoyant dike from a point source, focusing on the case of a finite volume release under homogeneous conditions (homogeneous material properties and buoyancy contrast). We use the fully coupled planar 3D hydraulic fracture growth solver PyFrac based on the implicit level set algorithm [4].

This configuration shows an early time behaviour heavily dominated by the effects of the pulse release. The initially radial hydraulic fracture transitions toward a large time buoyant dike solution. At large time our simulations tends to the finger-like/constant breadth solution [5] albeit extremely slowly. Our results confirm the 3D toughness dominated head structure and the importance of the viscous tail as the driving mechanism for the dynamics of such a 3D Weertman’s pulse (form of the head). Depending on the initial phase of the pulse release, we observe an overshoot of the dike breadth when it is initially strongly dominated by viscous dissipation. Using a scaling analysis, we characterize the transition from the early time radial finite pulse fracture to the late dike constant breadth solution. Our simulations show, that the time when the buoyant force takes its full dominance is crucial and governs the existence (or not) of an overshoot. Mainly we show that the overshoot depends on a transitional time/lengthscale. A detailed understanding of the fracture propagation after the end of the finite volume release (yet without buoyancy) is key to quantify this lengthscale. We thus present scalings and semi-analytical solutions for this case and discuss its relevance for the transition toward a buoyancy driven dike propagation.

[1]  E. Rivalta, B. Taisne, A.P. Bunger, and R.F. Katz. Tectonophysics, 638:1–42, 2015.

[2]  J. R. Lister and R. C. Kerr. J. Geohpys. Res. Solid Earth, 96(B6):10049–10077, 1991.

[3]  S. M. Roper and J. R. Lister. J. Fluid Mech., 536:79–98, 2005.

[4]  A. P. Peirce and E. Detournay. Comput. Methods in Appl. Mech. Eng., 197(33-40):2858–2885, 2008.

[5]  L.N. Germanovich, D. I. Garagash, Murdoch, L., and Robinowitz M. AGU Fall meeting, 2014.

How to cite: Möri, A., Lecampion, B., and Zia, H.: Fully-coupled 3D modelling of magmatic dike propagation - finite pulse release from a point source , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21351, https://doi.org/10.5194/egusphere-egu2020-21351, 2020.

Volcano eruption forecasting relies on models of sub-volcanic magmatic plumbing systems that link ground deformation to sub-surface magma movement. However, many of these models typically assume that eruption sites occur directly above laccolithic reservoirs. Furthermore, many of these models assume deformation of the host rock is exclusively elastic with few studies highlighting the role inelastic deformation (e.g., faulting/fracturing). Whilst the dynamics of magma flow have previously been well constrained in ancient in sub-volcanic systems, its geometrical and kinematic relationship with the corresponding host rock deformation remains poorly understood which, is critical to volcanic hazard assessment.

Here, we examine the structure of the shallow-level (i.e. intruded <1 km below the palaeosurface), silicic Reyðarártindur laccolith in SE Iceland, and demonstrate how the underlying mechanisms of lateral magma flow coupled with pre-existing host rock structures influenced the localisation of volcanic activity. In particular, we use anisotropy of magnetic susceptibility (AMS) fabric analysis and show that the intrusion contains several laterally emplaced magma lobes, with magma flowing along a SW-NE axis, parallel to the strike of pre-existing, steeply dipping fault arrays in the host basalt lavas. Lateral magma flow and inflation of the lobes promoted upward intrusion along these pre-existing faults, which we posit acted as preferential pathways for magma to reach eruption sites that were laterally offset by tens to hundreds of metres from the underlying main intrusion.

Our interpretation provides field evidence for the reactivation of pre-existing structures as inclined magma conduits to eruptive vent sites on the outer margins of subjacent lateral magma bodies. This supports seismic observations where (i) Volcanoes overlie the lateral tips of subjacent intrusions in subvolcanic systems; (ii) ground, and host rock deformation preceding eruptions can be most prominent in areas adjacent to the volcano site; and (iii) volcanoes overlie and are aligned along fault traces suggesting that pre-existing normal faults influence the localisation of volcanic activity.

How to cite: Twomey, V., McCarthy, W., Magee, C., and Petronis, M.: Pre-existing fault-controlled eruptions from the lateral tips of a laccolith in SE Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17969, https://doi.org/10.5194/egusphere-egu2020-17969, 2020.

Long-term volcano deformation cannot be well understood without considering crustal viscoelasticity because the presence of magma is expected to significantly lower the crustal viscosity beneath volcanoes. In this study, we examine viscoelastic crustal response to continuous magma supply into the upper crust and its sudden discharge. We use a three-dimensional (3-D) finite element model composed of an elastic layer underlain by a linear Maxwell viscoelastic layer with spatially uniform viscosity, in which a sill emplaced at the bottom of the elastic layer inflates with constant rate, during which the deflation due to an eruption suddenly occurs. Our numerical experiment finds that viscoelastic response to the sill deflation causes post-eruption surface uplift, depending on how much viscoelastic relaxation progresses in response to sill inflation due to pre-eruption magma supply and how much the sill deflates during the eruption. However, the recovery of the post-eruption surface is always later than that of the sill volume, because the viscoelastic response to the sill inflation reduces the surface uplift. Magma recharge is required to bring the surface to the elevation that was at immediately before the eruption. We adopt our viscoelastic model to geodetic data in and around the Aira caldera, southern Kyushu, Japan. It is found that the observed exponential-like surface recovery after the 1914 eruption can be explained if: (1) The effective crustal viscosity is ∼5×10¹⁸ Pa s, (2) the sill emplacement, whose equatorial radius is ∼2 km, occurs at a depth of ∼11 km, (3) a constant inflation rate of the sill is ∼0.009 km³/yr, which has continued since ∼50 yr before the 1914 eruption, and (4) the sill deflates by ∼0.4 km³ during the 1914 eruption, ∼4 times less than the eruptive volume. The sill inflation during the first ∼50 yr after the eruption is lower than that predicted by an elastic model, but larger thereafter. Fit to geodetic data after ∼1975 can be improved by introducing temporal variation of the inflation rate, which is a topic of investigation for a future study.

How to cite: Yamasaki, T., Sigmundsson, F., and Iguchi, M.: Viscoelastic crustal deformation in the Aira caldera before and after the 1914 eruption of the Sakurajima volcano, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2236, https://doi.org/10.5194/egusphere-egu2020-2236, 2020.

The ca. 182 Ma Jurassic dolerite sills of Tasmania, SE Australia, overlap in age with dolerite sills and basaltic lavas in the Ferrar province, Antarctica, and the Karoo, South Africa. Hence, the Tasmanian dolerites have long been considered to be part of a major Large Igneous Province that extended parallel to the Jurassic margin of Gondwana from what is now southern Africa, the Transantarctic Mountains, to Tasmania and South Australia. Two hypotheses have been proposed for the Ferrar and Tasmanian dolerites. 1) They are related to a mantle plume emplaced in the present-day Wedell Sea region, implying long-range, shallow-crustal transport of magmas in sills and dykes over distances of up to 4,000 km. 2) They are sourced from the mantle below Tasmania and Antarctica, implying only short-range lateral transport at the level of emplacement. We report results from a combined structural and anisotropy of magnetic susceptibility (AMS) study of the Tasmanian dolerites conducted to evaluate these hypotheses by differentiating between flow patterns and structural architectures in sills that are indicative of local versus distal sources.

Detailed structural mapping and 3D modelling indicate that no more than a few individual large sub-horizontal dolerite sheets were emplaced parallel to bedding in Permian sedimentary host rocks. They are offset by map and outcrop scale steps that we interpret to be NW-SE-trending, steeply dipping broken bridges.

The AMS of dolerite was measured in oriented samples collected from 126 sites across Tasmania. Their mean bulk magnetic susceptibility is ~0.01 SI units, which together with high-temperature susceptibility measurements indicate that the AMS is carried by magnetite, which occurs as skeletal grains with morphologies controlled by the petrofabric of plagioclase and pyroxene. These observations, and scant microstructural evidence for solid-state deformation, indicate that the AMS records a magmatic fabric that formed during emplacement and crystallization of the dolerite sheets. Magnetic lineations are dominantly subhorizontal, trending mostly NW-SE. Steeply-moderately inclined magnetic lineations are rare and mostly plunge SE. Subsets of shallow N-S and NE-SW lineations are associated with sites with subvertical E-W and NW-SE striking magnetic foliations. Magnetic foliations are dominantly subhorizontal, parallel to bedding in the surrounding sedimentary rocks, and the upper and lower contacts of subhorizontal dolerite sheets. Anomalous subvertical E-W and NW-SE striking magnetic foliations are associated with steps or broken bridges observed in the field and cross sections.

The AMS results are consistent with dominantly NW-SE magma flow within subhorizontal sheets, which is supported by the NW-SE orientation of steps and broken bridges. The architecture of segmented sheet fronts indicates that the polarity of sill propagation was from SE to NW. This finding is inconsistent with a magma source immediately below Tasmania and implies lateral transport from another location. However, the magma flow vector does not point back to the Ferrar dolerites in Antarctica, and therefore does not support the long-range Ferrar-Tasmania LIP hypothesis. Rather fabrics in the Tasmania dolerite are consistent with lateral flow from the present SE, perpendicular to the Gondwana margin with a source in the back-arc of the associated subduction zone

How to cite: Cruden, A., Gordon, A., and Barter, J.: Emplacement of Jurassic dolerite sills in Tasmania: Implications for Australia-Antarctica connections and Gondwana breakup, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3281, https://doi.org/10.5194/egusphere-egu2020-3281, 2020.

We investigated the major episodes of dome growth in the Campi Flegrei caldera occurred during the last period of large eruptive activity (Epoch 3, between 5.5 and 3.5 ka), and in the historical time. The first doming event occurred at the start of Epoch 3  where the caldera floor raised for at least 100 m. Following the Plinian eruption of Agnano-Monte Spina (AMS, 4.55 ka), a new uplift phase occurred with the set up of several lava domes (e.g., Olibano, Accademia and Solfatara cryptodome), the Averno-Solfatara  (AVS, 4.3 ka) and Astroni (AST, 4.2 ka) eruptions. This unrest episode was accompanied by severe and widespread faulting and fracturing well recorded in the stratigraphic record (Vitale et al., 2019). Finally, the last episodes of doming occurred before the eruption of Monte Nuovo volcano (MN, 1538 CE) and in the last century (1950-1985 CE). The 1538 CE uplift reached a maximum vertical displacement of ca. 15 m, whereas the 1950-1985 events reached a total dislocation of ca. 4 m. In order to study the former ground deformation pattern, we reconstructed the top surface of the La Starza succession, the latter formed by marine-transitional sediments deposited between 15 and 5.5 ka deposited in large part of the caldera floor. We used information from onland well-logs and seismic profiles in the Gulf of Pozzuoli. The same approach was used for the top surface of the younger marine succession, called Pozzuoli Unit (PU) (Isaia et al., 2019), emplaced following the AMS eruption and predating the AVS eruption. Subtracting the historical deformation pattern and considering the sea-level change in that time frame, we observe that the center of vertical deformation was located, for both Top Starza and Top PU surfaces, close to the Cigliano vent, and therefore not coinciding with the 1538 CE and recent deformation center, both defined by the same deformation center located close to the town of Pozzuoli. The resulting surfaces well mark local deformations related to the activity of major faults and the minor caldera formed following the AMS Plinian eruption. The restoring of the deformation of major faults with the Okada’s fault model has furnished useful information about the amount of displacement and rates of the faults' activity in the last ca. 6 ka.

Isaia, R., Vitale, S., Marturano, A., Aiello, G., Barra, D., Ciarcia, S., Iannuzzi, E., Tramparulo, F.D.A., 2019. High-resolution geological investigations to reconstruct the long-term ground movements in the last 15 kyr at Campi Flegrei caldera (southern Italy). Journal of Volcanology and Geothermal Research, 385, 143-158. doi: 10.1016/j.jvolgeores.2019.07.012

Vitale, S., Isaia, R., Ciarcia, S., Di Giuseppe, M. G., Iannuzzi, E., Prinzi, E. P., Tramparulo, F.D’A., Troiano, A. 2019. Seismically induced soft‐sediment deformation phenomena during the volcano‐tectonic activity of Campi Flegrei caldera (southern Italy) in the last 15 kyr. Tectonics, 38(6), 1999-2018.

How to cite: Vitale, S., Isaia, R., Natale, J., and Tramparulo, F. D.: Doming and faulting processes driving ground deformation at Campi Flegrei caldera (southern Italy): a modeling for the last 6 ka, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7000, https://doi.org/10.5194/egusphere-egu2020-7000, 2020.

Caldera unrest is often attributed to magma intrusion into a sill. In several cases, like Fernandina and Sierra Negra, Kilauea south caldera, and Campi Flegrei, the sill is km-sized and km-deep. A few questions related to sill emplacement at calderas seem still unanswered: how do sills form and spread, why can magma propagate for kilometers without solidifying, and why do ground deformation data rarely, if ever, detect sill propagation.
When considering isoviscous incompressible magma intruding at a constant rate into a homogeneous half-space under non-isothermal conditions and forming a circular sill, mathematical modeling includes: a fluid-dynamic equation (relying on lubrication theory), a fracture propagation criterion, an elasticity equation (link between fluid overpressure and sill opening), and a heat-transfer magma-solidification equation. As already known, a small lag must exist between the fluid (magma) and fracture fronts, because of the large pressure gradients required to drive a viscous liquid into a narrow opening.
We show that the free-surface effects on the elasticity equation are negligible, provided that depth-to-radius is smaller than one, as at the above-mentioned calderas; thus, spreading occurs like in an infinite medium. Taking advantage of published studies on hydraulic fracture propagation, first we consider isothermal spreading, as governing equations admit approximate analytical solutions for sill radius, sill opening, fluid overpressure and lag size.  Next we consider non-isothermal spreading of an isoviscous incompressible single-component magma, which is initially at its solidification temperature.
We show that if the sill is at least a couple of kilometers deep and the product of viscosity and injection rate is sufficiently small, then the lag between the magma and fracture fronts is much smaller than the sill radius during most of the propagation process; as a consequence, propagation velocity is practically unaffected by the lag, except for the initial phase. Because of the way solidified magma thickness and sill opening grow with distance from the tip in the near-tip region, zero-lag non-isothermal spreading would stop after travelling unrealistically short distances, unless magma intrudes rocks that are as hot as the solidification temperature or has unrealistic overpressures. Thus, we consider how the lag might affect the sill maximum size, by preventing solidification at the tip. We compute non-isothermal propagation velocity and the solidified magma thickness by adapting the approach originally developed by Dontsov (2016) for the zero-lag propagation of penny-shaped hydraulic fractures with leak-off; then we relate the lag size to the propagation velocity using the isothermal solutions.
We find that the lag plays a fundamental role in postponing the sill arrest by magma solidification, because heat exchange between the magma and the hosting rock is effective only behind the lag, where the magma has some finite thickness and sill opening grows with distance from the tip faster than thickness of solidified magma.
As for ground deformation, we show that its pattern does not change appreciably over time if the final sill radius is smaller than 2 to 3 km: this explains why it is usually attributed to the inflation of a stationary source.

How to cite: Crescentini, L. and Amoruso, A.: Non-isothermal propagation and arrest of km-sized km-deep sills at calderas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10323, https://doi.org/10.5194/egusphere-egu2020-10323, 2020.

Soufrière Hills volcano on Montserrat in the West Indies showed five episodes of magma extrusion and as many pauses in its 25years of volcanic activity. This eruptive behaviour exhibited cyclic deformation pattern where extrusive “phases” showed island-wide deflation and all “pauses” have been linked to inflation, the last of which remains ongoing. Several models have been developed over the years; all based on magma intrusion and extrusion, into, or from one or several reservoirs, respectively. Using the entire eruptive history, we demonstrate that both, pauses and phases can be linked to a single magma body. Through extensive numerical modelling, we explore in this presentation some alternative routes to magma intrusion, considering several magmatic processes. These range from crystallisation of magma (second boiling) to pressurisation through a free gas phase, to the extreme case where intrusion of fresh magma has ceased years ago, while the inflation is continuing. 

How to cite: Neuberg, J. and Pascal, K.: The continuing inflation of Montserrat – and the end of the intrusion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19745, https://doi.org/10.5194/egusphere-egu2020-19745, 2020.

In volcanology, as in other branches of geosciences, uncertainties exist around how well rock properties constrained on the laboratory scale represent those at the field scale. For volcano deformation, scale-related uncertainties are compounded by changes in geomechanical properties as progressive deformation evolves to large strains. Furthermore, such large strain deformation is often localised along large-scale discontinuities. It is therefore difficult to investigate this deformation by using traditional continuum modelling approaches. Here we provide an overview of recent Discrete Element Method (DEM) modelling results as applied to large strain, edifice-scale deformation phenomena, such as lava dome instability and caldera collapse. The DEM is a particle-based numerical modelling approach that enables simulation of strain localisation and highly discontinuous deformation.

Upscaling the geomechanical properties of volcanic rocks from the laboratory to the field can be achieved in DEM models through a calibration process that simulates both the laboratory rock testing and field-scale examples. For lava dome collapse, through comparison of observed and modelled attributes (e.g., displacement, dome growth), we infer that field-scale bulk rock properties (i.e., strength, elastic moduli) are approximately 30% of typical laboratory-scale properties. For caldera collapse, varying the same geomechanical properties produces a range of observed styles of caldera collapse, but the properties required at the edifice scale are approximately a factor of 10 lower than typical laboratory-scale properties. Both the calibration of geomechanical properties and the structural outcomes of DEM simulations, and hence the accuracy of upscaling, are fundamentally dependent on the model resolution, which is a function of both the particle size and distribution. The chosen resolution particularly affects rock strength, fracture toughness, and crack development and propagation. Nonetheless, previously reported discrepancies between seismic and geodetic moments for certain volcano-tectonic events are consistent with the upscaled geomechanical properties in edifice-scale DEM simulations, in that such discrepancies can be explained by a similar-sized reduction in the properties derived from laboratory-scale rock tests.  

How to cite: Harnett, C., Holohan, E., Thomas, M., and Schöpfer, M.: Upscaling of geomechanical properties in Discrete Element Method (DEM) models of volcano-tectonics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3379, https://doi.org/10.5194/egusphere-egu2020-3379, 2020.

In this paper, we present the activities relevant to the microwave monitoring of the Stromboli volcano ground deformation, performed by IREA-CNR (Institute for the Electromagnetic Sensing of the Environment) and UNIFI (University of Florence) as Centres of Competence for the Italian Civil Protection Department.

The availability of Synthetic Aperture Radar (SAR) system provides, among several techniques, accurate information on the volcano morphology and deformation, thus allowing us to understand the on-going volcanic changes. In this work, we present the results of a back-analysis (from 2015) of the volcano behaviour in terms of ground deformation and an insight on the volcano crisis occurred from July 3 2019, by using Differential Interferometry SAR (DInSAR) measurements.

The generated DInSAR results are both satellite and ground based. In particular, we show the displacement time series obtained with Sentinel-1 data acquired from March 2015 to October 2019 over the whole island and from ascending and descending orbits, and the displacement estimated with a Ground-Based SAR placed for the Sciara del Fuoco and summit craters sensing.

Moreover, the combination of the deformation measurements retrieved with both monitoring systems, which are characterized by independent acquisition geometries, allowed us to partially reconstruct a 3D deformation field of Sciara del Fuoco area.

Finally, we show the preliminary result of a test about an operational monitoring service based on new methodologies for the processing of airborne SAR data, aimed at evaluating its relevance for Civil Protection purposes in volcanic risk context.

This work is supported by the 2019-2021 IREA-CNR and Italian Civil Protection Department agreement, and by the 2019-2021 UNIFI and Italian Civil Protection Department agreement.

How to cite: De Luca, C., Di Traglia, F., De Novellis, V., Esposito, C., Nolesini, T., Manzo, M., Tizzani, P., Natale, A., Berardino, P., Perna, S., Casagli, N., Lanari, R., and Casu, F.: A microwave monitoring service for the study of the Stromboli volcano deformation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9443, https://doi.org/10.5194/egusphere-egu2020-9443, 2020.

We focus on the eruption of Mt. Etna which took place on 24 December, 2018. The eruption occurred after a month of unrest and was accompanied by a seismic swarm that culminated in the M4.9 earthquake on the 26th, with epicentre on the eastern flank of the volcano. We jointly analyse ground deformation and gravity data to estimate the geometrical and kinematic parameters of the source structure, together with the density of the intruding material. The data used in this study were recorded by stations in the INGV-OE monitoring network (21 GPS stations and 2 gravity stations equipped with superconducting gravimeters), during the interval of 23 to 28 December (pre to post eruption). We assume a dike-type source for the forward calculation in the defined objective function. A pattern search algorithm (PSA) is used for the iterative minimization of the misfit error. In order to estimate the posterior probability density function (PDFs) of the model parameters, we also use a Markov Chain Monte Carlo (MCMC) approach. Indeed, the calculated PDFs provide more information about the uncertainties of the model parameters, which helps to understand overall tendencies of the solutions. We first test the constrained inversion of the gravity data, to calculate the density of eruptive magmatic body, by fixing the geometrical parameters of the dike, previously retrieved through inversion of the deformation data only. Using this approach, it is possible to suitable explain the deformation data and the gravity change observed at the station in the near field (MNT), while the gravity change at the other station (SLN) remain unexplained. We then invert jointly both deformation and gravity datasets, in order to adequately fit all the observations. The final model gives a density value of ~1.8-2.0 g/cm3. This value is significantly lower than the density of bubble-free magma and indicates either the involvement of gas in the intrusive process, or the formation of dry fissures during the emplacement of the dyke.

How to cite: Chauhan, M. S., Cannavò, F., Carbone, D., and Greco, F.: New insight into the December 2018 Etna eruption through the joint inversion of ground deformation and gravity data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-564, https://doi.org/10.5194/egusphere-egu2020-564, 2020.

The 1.85 Ga Sudbury Igneous Complex, Canada, is the remnant of a ~3 km thick impact-generated crustal melt sheet, caused by a 10-15 km large chondritic asteroid or comet that had left behind an impact structure of ~200 km prior to tectonic deformation und subsequent erosion. However, less is known about how deep the impactor penetrated the continental crust and where the source of the impact melt was. Mixing models including radioisotopes and trace elements on locally exposed country rocks have been used to evaluate their relative contribution to the impact melt. Based on this, Darling et al. (2010) have argued for shallow melting of the upper crust (UCC) only, either due to an oblique impact and/or a low-density bolide (comet). In contrast, the abundance of siderophile elements in impact melt-rocks was taken as evidence of a lower crustal source (Mungall et al. 2004), i.e. overlying rocks of the middle and upper crust must have been removed during the crater excavation stage. U-Pb age data on zircon xenocrysts also point to the involvement of rock types not exposed on surface (Petrus et al. 2016) in agreement with theoretical simulations, which have predicted a >20 km deep but unstable transient cavity (Ivanov & Deutsch 1999).

Large-scale (10s of km) and well-exposed impact melt dykes are a unique feature of Sudbury. The dykes are of granodioritic/quartz dioritic composition and are interpreted as clast-laden melt injections into the basement instantaneously after the impact (Pilles et al. 2018). Their vitric margins and distal extremities should therefore approximate the undifferentiated bulk composition of the Sudbury Igneous Complex prior to sulfide saturation. A compilation of published and new geochemical data of these dykes reveal a remarkably strong affinity (r² >0.989) to the average middle continental crust (MCC) as given by Rudnick & Gao (2014), especially in terms of major elements and fluid-immobile transition metals (Th, Zr, Hf, Nb, Ta, Ti, Sc, REE). The dykes are, however, significantly enriched in Ni, Cu and Cr, and to a lesser extent in V, Co and P relative to the typical UCC and MCC. A systematic loss of volatiles (Tl, Cd, Sn, Zn, Pb, Ag, Cs, Rb, Na, K, Ga, As) compared to either crustal model is not evident. These new observations favour a scenario in which the impactor and supracrustal rocks in the target area became vaporized and ejected. Shock melting affected predominantly the middle crust of the Canadian Shield. We also propose that the rocks that contributed to the impact melt were, on average, more mafic than the typical UCC and MCC. This is consistent with the report of exotic mafic-ultramafic xenoliths within the Sudbury Igneous Complex (Wang et al. 2018) and its anomalously high PGE concentrations (Mungall et al. 2004). (Ultra-)mafic rocks hidden at mid-crustal depth were a likely source of Ni-Cu-PGE-Co and gave rise to world class ore deposits presently mined at Sudbury. Such (ultra-)mafic intrabasement body might also explain the 1200 km² Temagami magnetic anomaly in the eastern vicinity of the Sudbury Complex.

How to cite: Kawohl, A., Frimmel, H. E., Whymark, W. E., and Bite, A.: On the depth of crater excavation and melting during the Sudbury impact: geochemical evidence from chilled impact melt dykes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11, https://doi.org/10.5194/egusphere-egu2020-11, 2020.

Within the scope of our project “Modelling melt ascent through the asthenosphere-lithosphere-continental crust system: Linking melt-matrix-two-phase flow with dyke propagation” it is necessary to implement mechanisms with appropriate conditions to generate dykes which are propagating independently.

Conditions for self-propagating depend on the density contrast of melt and rock and the geometry of the fracture. Certain limits for the fluid-filled volume and dyke width must be reached. The height must be longer than the Bouguer length. To satisfy these conditions enough melt under overpressure must be available in the source region to supply the growing dyke.

A known and accepted mechanism for dyke generation is a tension fracture whichs opening space immediately is filled by fluid melt. The normal stress due to expansion of the magma on the wallrock causes tension therein parallel to the melt front. In brittle material the yield stress for extension is very low and the confining cold rock easily cracks.

With depth pressure, temperature and ductility of crustal rock and consequently the yield stress for the tensile cracking increases. Furthermore, the background permeability or connectivity, and finally the height of fluid columns decrease and the fluid overpressure is not high enough to exert matrix extension. Another dyke initiation mechnism must be found for the deeper parts of the crust.

A not smooth melt front - and pillows are often seen on top of magma chambers – provides shear stresses and stress concentrations. Above a certain yield stress for shear failure shear bands start to evolve. In such a network of fracture zones permeability should increase. Melt may intrude, coalesce bands and develop a growing dyke. Such a local scenario will be modelled and results presented. A further aim is the parametrisation of these mechanisms.

How to cite: Wallner, H. and Schmeling, H.: Exploring Mechanisms and Conditions for the Generation of Self-propagating Dykes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12479, https://doi.org/10.5194/egusphere-egu2020-12479, 2020.

Dike propagation in the earth crust, often a precursor of major volcanic eruptions, usually generates a seismic response by activating small fractures (micro-seismicity) and larger existing faults (greater magnitude events). The conceptual interpretation is essentially viewed as a fluid-driven fracture advancing in the rock mass and altering the existing state of stress in its surroundings. Because dikes are filled with high-temperature magma, which can exceed 1000 °C, it is likely that they will alter the initial temperature while propagating. The temperature increase can generate pore water pressurization as a function of its rate of change. Pore pressure in turns diffuses through the porous and fractured rock, altering the initial effective stress state. Additionally, hot dikes also generate thermally-induced stresses. The stress changes in the rock are therefore affected by temperature and pore pressure as much as they are by mechanically induced fracturing. In this contribution, we have studied the coupled processes of temperature, pore pressure and deformation induced by diking. We have employed finite element analyses to solve the boundary value problem of a progressing dike. The main goal is to highlight the effects generated by temperature increase in the rock surrounding the dike. Thermal pressurization depends on heat loading rate, hence on diking advancement speed, and on surrounding rock permeability. Rock permeability also controls the diffusion of pore pressure, the size of the area affected by pressurization and the magnitude of pressurization. Results from numerical models show that positive Coulomb stress changes (instabilities) can be triggered by thermal effects at several hundred meters away from the dike, implying that even non-advancing dikes could generate a seismic response. We prove the importance of accounting for thermo-poromechanical effects in studying the seismic response during diking, a widely unexplored field which could have major implications for the assessment of volcanic eruptions’ precursory signals.

How to cite: Nagel, T., Parisio, F., Rivalta, E., and Vinciguerra, S.: Thermo-poromechanical induced seismic effects during diking, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13142, https://doi.org/10.5194/egusphere-egu2020-13142, 2020.

Hydrofractures induced by a pressurized fluid inside a solid host material occur in nature as joints, veins, and dykes. Due to the heterogeneity of the material properties, rock structure, fluid rheology, and in-situ stress state, the process of hydrofracturing in nature is highly complex. As a result, it is difficult to measure and predict the behavior of natural hydrofractures in field conditions. Fracture segmentation is observed in most materials at every scale from microns to kilometres and dykes are not the exception.  In particular, dykes not always emplace as individual, symmetric and planar structures in the host rock. In many cases even in homogeneous rocks, dykes exhibit segmentation of the type of en chelon-like structures and fingering. The causes of dyke segmentation have been associated with: (1) rock heterogeneity (i.e. pre-existing structures); (2) mixed-mode I+III loading; and (3) instabilities of dike growth process. However, there are still many open questions related to the origin of dyke segmentation, including at which level each of the mentioned processes influences its propagation. In order to have a first approach of study to this phenomenon, a series of laboratory experiments in transparent materials of dyke propagation have been performed. We present the results of experiments of analogue dykes that transport Newtonian and shear thinning fluids that lead to segmentation, in absence of rotational stresses and heterogeneity of the host media. We use these experiments as the most direct source of observations of dike geometry. These experiments allowed the visualization in real time of the developing geometry of the analog dykes and the direction of their propagation.

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

Magmatic intrusions often produce ground deformation that can be studied by geodetic techniques. In the past two decades, many volcanic dike and sill emplacements (sometimes associated to eruptions) in different tectonic settings have been analyzed through InSAR. However, in only a few cases, the post-intrusive behavior has been studied. Here we analyze the post-diking deformation in Harrat Lunayyir, which is a mononogenetic volcanic field located in western Saudi Arabia on the eastern margin of the Red Sea Rift.

Between April and July 2009, an intensive seismic swarm occurred in the area with many earthquakes above magnitude 4 and the largest earthquake of M_w 5.7. InSAR data showed that the earthquake swarm was triggered by the emplacement of a dike intrusion that stopped only ~1 km below the surface. Dike length was estimated to be ~7 km and with a maximum opening 4 m. Above the intrusion, a ~10 km long and ~5 km wide graben formed during the activity with up to 1 m of fault slip on the border faults. In the post diking phase up to present, micro-sesmicity (0<Ml<3.5) has been continuously registered in the graben region gradually fading out either in terms of earthquake rate and energy release.

In February 2017, a new seismic swarm occurred ~60 km north of Harrat Lunayyir and another swarm started in October 2018, about 30 km southwest of the volcanic field. Both swarms are still ongoing with a few events per week and M_l<3.5. By using Sentinel-1 images, acquired during the period 2015-2019, we derived deformation rate maps for the entire Harrat Lunayyir volcanic field. No ground deformation was detected at the locations of the recent seismic swarms, and a thorough analysis of seismic signals excludes the swarms were caused by new magmatic intrusions. However, within the Harrat Lunayyir graben region, we noticed a steady and long-lasting subsidence of ~1 mm/yr. During the 2015-2019 period, the total seismic moment release would only be able to accommodate less than 0.1 mm of the observed subsidence and thus the current post-diking deformation is mainly aseismic.

In order to reconstruct the entire post-diking deformation history in Harrat Lunayyir we also analyze older available SAR images (Envisat, ALOS, TerraSAR-X, TanDEM-X). Our preliminary results show that the subsidence rate in the graben area was faster just after the intrusion (few cm in two months) but then rapidly decayed as well as the seismicity. We are now investigating different processes that can cause post-diking deformation, such as residual opening of the dike, post-diking settlement of faults and fractures, release of gases into fractures, cooling of the dike, and post-diking viscoelastic relaxation. Modelling of the deformation source will contribute to the understanding on which of these post-diking processes might be the dominant one in Harrat Lunayyir.

How to cite: Nobile, A., Cao, Y., Youssof, M., Trippanera, D., Passarelli, L., and Jónsson, S.: Post-diking deformation in Harrat Lunayyir (Saudi Arabia) from InSAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8272, https://doi.org/10.5194/egusphere-egu2020-8272, 2020.

In many ancient and active volcanic provinces dyke systems represent radial and concentric patterns. In İstanbul, NW Turkey, late Cretaceous dykes, which are emplaced in pre-Cretaceous basement rocks consisting of sedimentary rocks of Palaeozoic and Triassic ages, have both patterns. In the region, late Cretaceous volcanism is represented by three elements, (1) The Çavuşbaşı granitoid, (2) volcano-sedimentary units and (3) dykes.

Age of the Çavuşbaşı granitoid is given as 67.91±0.63 to 67.59±0.5 Ma. It is emplaced in shallow depth and has an indistinct contact aureole. Volcano sedimentary units were deposited in an intra-arc basin. Three types of dykes are reported in the region: lamprophyre, diabase and intermediate to felsic dykes (72.49±0.79 to 65.44±0.93 Ma). Different petrology and the crystallization depths of the crystals in the dykes and the Çavuşbaşı granitoid suggest two different magma chambers emplaced at two different depths, the Çavuşbaşı granitoid representing the shallower one.

Upper Cretaceous dykes are concentrated around the Çavuşbaşı granitoid and extend almost as far as 30 km away from the pluton. The intrusion of the plutonic body of the Çavuşbaşı granitoid caused a dome structure in the basement rocks. The formation of this dome structure may have controlled the stress field and the orientation of the dyke system. Similar patterns are observed in the British Tertiary igneous province, Galapagos volcanoes, Boa Vista (Cape Verde), Summer Coon volcano, Spanish Peak Mountain and Dike Mountain (Colorado), Vesuvio, Etna and Stromboli (Italy).

We suggest that Upper Cretaceous volcanic edifice in the İstanbul region is related to an arc volcano similar to the andesitic volcanoes in the Sumatra Island; we name it the Bosphorus Volcano.  

How to cite: Ülgen, S. C., Şengör, A. M. C., Keskin, M., and Aysal, N.: Bosphorus Volcano; Signs of an Ancient Volcano on an Ancient City, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13226, https://doi.org/10.5194/egusphere-egu2020-13226, 2020.

The magmatism activities exert significant impact in sedimentary basins as the Zhongjiannan Basin (ZJNB), western South China Sea (SCS). We have evaluated multibeam bathymetric and multichannel seismic reflection data acquired by the Guangzhou Marine Geological Survey in recent years, in order to investigate the distribution, the characteristics and the subsurface structures related to the seafloor domes found in the northeastern ZJNB. Data reveal that there are forty two domes occurring in water depths between 2312 m and 2870 m, clustered around volcanic mounds and seamounts in the study area. These domes generally show circular to elongated or irregular plan views, can reach up to 26080 m in perimeters, and the vertical reliefs are tens to hundreds of meters. They have gentler flanks with average slope values of 1.46°~7.73° and basal areas between 0.85 km² and 42.06 km². The seismic reflection sections reveal that domes’ formation and development are attributed to igneous intrusion events in the strata. The igneous intrusions heat surrounding organic-rich sediments and release hydrocarbons and fluids, which accumulate and uplift the overlying strata immediately above the sills and form forced folds, manifesting as domes on the seafloor. These sill-folds-dome structures provide possibility for hydrocarbon generation, migration and accumulation and have important implications for petroleum prospectivity in the ZJNB.

How to cite: Geng, M., Zhang, R., Song, H., and Guan, Y.: Sill-related seafloor domes in the Zhongjiannan Basin, western South China Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13041, https://doi.org/10.5194/egusphere-egu2020-13041, 2020.

Calderas often inflate up to a few metres for weeks to years, which is evidence of short-term unrest. Some calderas also show larger uplift (up to a thousand metres), achieved over the long-term (hundreds to thousands of years), manifest by a resurgent dome or block. How the short-term inflation relates to long-term resurgence is still poorly understood, even though established views consider the two processes distinct. This study exploits the longer deformation time series now available for several calderas, as well as the better understanding of magmatic processes and their evolution, to try to bridge the gap between these two scales of uplift. Available data challenge established views, suggesting that resurgence, rather than being produced by constant or continuous uplift, is the net cumulated result of tens to thousands distinct episodes of inflation, even interrupted by deflation episodes, as observed on short-term unrest. These inflation episodes are ascribed to distinct pulses of shallow magma emplacement, with most of the magma remaining intruded, especially in felsic calderas. This supports an incremental growth of magmatic systems, consistently with that observed below resurgent calderas and what is inferred for plutons. Comparing the uplift (as expression of the intrusive record) and eruptive histories or resurgent calderas opens new exciting research paths to understand the causal relationships between intruded and erupted magma at a given caldera, thus enhancing its long-term eruptive forecast.

How to cite: Acocella, V.: Bridging the gap from caldera unrest to resurgence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11047, https://doi.org/10.5194/egusphere-egu2020-11047, 2020.

Large silicic magma reservoirs preferentially form in the upper crust of 

extensional continental environments. However, our quantitative understanding of the link between mantle magmatism, silicic reservoirs and surface deformation during rifting is very limited. Here, we focus on Corbetti, a peralkaline caldera in the densely-populated Main Ethiopian Rift, which lies above a focused zone of upper mantle partial melt and has been steadily uplifting at ≤6.6±1.2 cm yr−1 for more than ten years. We show that a concomitant residual gravity increase of ≤9±3 μGal yr−1 by the intrusion of mafic magma at ∼7 km depth into a compressible and inelastic crystal mush best explains the uplift. The derived magma mass flux of ∼10^11 kg yr−1 is anomalously high

and at least one order of magnitude greater than the mean long-term mass

eruption rate. We demonstrate that periodic and high-rate magmatic rejuvenation of upper-crustal mush is a significant and rapid contributor to mature continental rifting.

How to cite: Gottsmann, J., Biggs, J., Lloyd, R., Biranhu, Y., and Lewi, E.: High magma flux beneath Corbetti caldera (Ethiopia) accommodated by a ductile and compressible reservoir, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5032, https://doi.org/10.5194/egusphere-egu2020-5032, 2020.

The largest volcanic eruptions in the geological record are typical of Large Igneous Provinces (LIPs) or of calderas. Known factors facilitating large eruptions include a large size of the feeding magma reservoir, massive vesiculation and gradual collapse of the magma reservoir roof to sustain pressure. Based on analytical models considering rock (visco)elasticity and magma compressibility, here we identify further controlling factors: the aspect ratio of the magma reservoir (equi-dimensional vs. elongated or crack-like), its orientation (vertical vs. horizontal) and its depth. We find that thin (crack-like) horizontally elongated reservoirs filled with gas-rich magma can best sustain pressure during eruptions and can thus evacuate a larger fraction of the magma they contain. In order for these melt lenses to accumulate magma without solidifying they should be located either in the lower crust or, if shallow, within large crystal mushes, where temperatures are high. All these factors are relevant for LIPs and caldera reservoirs and not for other settings. Our model predicts that eruptive volumes scale with the square of the horizontal dimension of the magma reservoir, and not with its third power, as it would be expected if reservoir volume was the main controlling factor. This scaling is supported by observations from calderas worldwide.

How to cite: Rivalta, E. and Nikkhoo, M.: Main controlling factors of enormous eruptions at calderas and Large Igneous Provinces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19843, https://doi.org/10.5194/egusphere-egu2020-19843, 2020.

Los Humeros Volcanic Field (LHVF) represents one of the key volcanic calderas in Mexico. Nowadays, LHVF is the third largest geothermal field in Mexico in terms of energy output, with an installed capacity of 94 MWe. The caldera is about 21 by 15 km wide and is located in the Serdán Oriental basin, east of the Trans- Mexican Volcanic Belt in the central-eastern part of the country, roughly 440 km away from the Middle American Trench. In this study we show results of numerical simulations of magma intrusion in order to better understand the deep origin of the caldera. For this purpose, we used high-resolution two-dimensional coupled petrological-thermomechanical numerical simulations of magma intrusion where an initial thermal anomaly was placed in the asthenosphere just below the lithospheric mantle. We performed a parametric study where we investigated the influence of several parameters such as the diameter of the thermal anomaly, the excess temperature and the regional tectonic regime. These 2D simulations were carried out using the finite difference method coupled with the cell marker technique and employing the multigrid method. The physical parameters used for the Earth’s layers (asthenosphere, lithospheric mantle, lower crust and upper crust) and for the composition of the magmatic intrusion were taken from literature and previously established models. In addition, we considered a viscoelastoplastic rheology and the simulations included erosion and surface sediment transport. Modeling results showed that only under certain conditions of temperature excess, initial diameter of the deep thermal anomalies that come in a specific chain-type sequence, it is possible to form a volcanic caldera similar with the dimensions of the LHVF. The temperature excess (ΔT = ~150K) suggested a deep origin for the thermal anomaly with an approximate depth of ~380 km, where currently the surface of the Cocos slab is located below the North American Plate. Additionally, we found that several magmatic pulses can reach the surface only if we consider in our models a small horizontal extension rate consistent with the extensional tectonic regime in the region.

How to cite: Bayona Ordóñez, A. D. and Manea, V. C.: Numerical simulations to study the geodynamic origin of Los Humeros Volcanic Field in Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2461, https://doi.org/10.5194/egusphere-egu2020-2461, 2020.

Deception Island is one of the most active volcanoes in Antarctica, with more than 20 monogenetic eruptions during the Holocene. The latest episodes of 1967, 1969 and 1970 have shown that volcanic activity on Deception Island can become a concern for tourists, scientists, and military personnel working on or near the island.

The objective of this work is, therefore to identify eruptive processes and the evolution of post-caldera volcanic edifices at Deception Island by morphometric analysis, supported by field observations. This methodology has been used since the 1970s to analyse mafic monogenetic volcanoes but it has not been fully developed until recently.

Tuff cones and rings, as a result of magma-water interaction, represent the most common eruptive events occurring during Deception Island's recent geological past and are therefore the most likely to occur in the near future. This work provides an opportunity to incorporate for the first time at Deception Island geomorphological observations for a better comprehension of the potential evolution of a future eruption and for a broader understanding of volcanic hazards on this island.

This research was supported by the MICINN grant CTM2011- 13578-E and was partially funded by the POSVOLDEC project (CTM2016-79617-P) (AEI/FEDER-UE). A.G. is grateful for her Ramón y Cajal contract (RYC-2012-11024). D.P. is grateful for his Beatriu de Pinós (2016 BP 00086) and Juan de la Cierva (IJCI-2016-30482) contracts. This research is part of POLARCSIC and AntVolc activities

How to cite: Pedrazzi, D., Kereszturi, G., Schamuells, S., Lobo, A., and Calle, J.: Morphometric analysis of the post-caldera monogenetic volcanoes at Deception Island, Antarctica: implications for landform recognition and volcanic hazard assessment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1375, https://doi.org/10.5194/egusphere-egu2020-1375, 2020.

The Krafla volcanic area in Northern Volcanic Zone of Iceland was characterized by deflation starting in 1989, suggesting a general pressure decrease and/or volume contraction at depth, which then exponentially decayed until having no significant deformation since around 2000.  In summer 2018, the volcano behaviour changed to inflation as observed both by Global Navigation Satellite System (GNSS) geodesy  and Sentinel-1 satellite radar interferometry (InSAR). Inflation since 2018 occurs at a rate of 10-14 mm/yr, centered in the middle of the caldera. No significant change in seismicity has occurred in the area in 2018, but seismic moment release ocurrs at a higher rate since middle 2019. Gravity stations in the area were remeasured in November 2019 for allowing comparison with earlier observations, and for providing reference for later studies. Initial modelling of the geodetic data is carried out assuming that the deformation is caused by a spherical source of pressure in an uniform elastic half-space. The result suggests that the deformation can be broadly explained by a single source of magma inflow at depth around 3.9-7.5 km, with the best-fit value around 4-4.5 km. We also apply the Finite Element Method (FEM) to additionally consider modification of the deformation field caused by Earth’s elastic heterogeneities and the uncertain geometry and  depth of the magma source. A set of FEM models are built with the COMSOL Multiphysics software in a 50x50 km domain where we test three different geometries of the source: a spherical source (radius 1000 km), a prolate ellipsoid,  and an oblate ellipsoid (sill-like) source, at 2.5, 4.0 and 5.5 km of depth. We also build a model to test how the vertical and horizontal displacements may be influenced by different elastic properties (e.g. Young’s modulus; about an order of magnitude different within a caldera boundary) for these sources. The results show that lateral variations in material properites can have a significant influence on ground deformation. Low-value Young’s inside caldera boundaries compared to higher values outside caldera boundaries will in particular influence the vertical displacement: the vertical displacement is about half of of what it is the original modelling.  The ratio of vertical to horizontal displacements will thus also be modified. This can in turn influence the inferred magma source geometry as it depends on the displacement ratios. The outcome of our study will provide better constrain for the elastic properties in Krafla area, and help understand the magma intrusion rate in the area.

How to cite: Lanzi, C., Drouin, V., Li, S., Sigmundsson, F., Geirsson, H., Hersir, G. P., Agustsson, K., Hreinsdottir, S., and Gudmundsson, A.: Renewed Inflation of Krafla Caldera, Iceland, since 2018: Sensitivity of Ground Deformation to lateral variation in Earth structure and architecture of the magmatic system explored with the Finite Element Method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19915, https://doi.org/10.5194/egusphere-egu2020-19915, 2020.

The Campi Flegrei caldera (southern Italy) is characterized by over one-third of its extension lying below the sea. In the last 15 ka the caldera floor has suffered hundreds of meters of ground deformation alternating uplift and subsidence episodes in response to the activity of the volcanic system. The evidence of significant uplifts is witnessed by the occurrence of marine sequences exposed on land, both along a 30 m high La Starza cliff and in numerous well logs. However, most of these sediments are currently hidden below the sea. This work aims to reconstruct the marine counterpart of the infill by using large multiscale reflection seismic data (>100 profiles) and an accurate seismic facies analysis. The latter consisted in the study and
comparison of seismic attributes, scaled to the resolution of the different datasets, to their geological analogs on land. Furthermore, by observing the changes in the pattern of on-lap terminations, thickness, amplitude, and distribution of erosive features of different horizons, we tentatively ascribed these sequences to the well-known continental deposits. The study of the whole sequence above the Neapolitan Yellow Tuff (15 ka) allowed us to gather relevant information about the relationships between stratigraphic record, ground deformation and sea-level changes. In particular, the reconstruction of buried surfaces gave us hints on the evolution of the volcanic system including the role of faults in terms of estimation of displacement and relationships with the different epoch of major eruptive activity.

How to cite: Natale, J., Vitale, S., Isaia, R., Tramparulo, F. D., Ferranti, L., Marino, C., Steinmann, L., Spiess, V., and Sacchi, M.: Correlation between submerged and continental infill at Campi Flegrei caldera: insights on the volcano-tectonic events of the last 15 kyr, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7409, https://doi.org/10.5194/egusphere-egu2020-7409, 2020.

It is 135 years after the 1883 volcano-triggered tsunami disaster, when Krakatau volcano became once more the source of a deadly tsunami striking without warning. We use data recorded on the ground and by satellite, to show that the volcano was in an elevated stage of activity throughout the year 2018, producing thermal anomalies associated with volcanic deposits, an increase of the island area and ground movement of the southwestern sector of the island towards the sea, increasing in June 2018. Following further intense activity on 22 December 2018, seismic data reveal the timing and duration when this sector collapsed. The landslide removed 102 million m³ of material subaerially, which was followed by ~15 minutes of phreatic explosions. This study allows better understanding of the complex hazard cascades, including precursory thermal anomalies, island growth and deformation, followed by sector collapse, tsunami waves, and finally explosive volcanic eruptions, and has important implications for designing early warning systems.

How to cite: Walter, T. R. and the Rapid Response Team: Precursors and processes culminating in the Anak Krakatau December 2018 sector collapse and tsunami , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2602, https://doi.org/10.5194/egusphere-egu2020-2602, 2020.

Lava dome collapses pose a hazard to surrounding populations, but equally represent important processes for deciphering the eruptive history of a volcano. Models examining lava dome instability rely on accurate physical and mechanical properties of volcanic rocks. Here we focus on determining the physical and mechanical properties of a suite of temporally-constrained rocks from different phases of the 1995–2010 eruption at Soufrière Hills volcano in Montserrat. We determine the uniaxial compressive strength, tensile strength, density, porosity, permeability, and Young’s modulus using laboratory measurements, complemented by Schmidt hammer testing in the field.

By viewing a snapshot of each phase, we find the highest tensile and compressive strengths in the samples attributed to Phase 4, corresponding to a lower permeability and an increasing proportion of isolated porosity. Samples from Phase 5 show lower compressive and tensile strengths, corresponding to the highest permeability and porosity of the tested materials. Overall, this demonstrates a reliance of mechanical properties primarily on porosity, however, a shift toward increasing prevalence of pore connectivity in weaker samples identified by microtextural analysis demonstrates that here pore connectivity also contributes to the strength and Young’s Modulus, as well as controlling permeability. The range in UCS strengths are supported using Schmidt hammer field testing. We determine a narrow range in mineralogy across the sample suite, but identify a correlation between increasing crystallinity and increasing strength. We correlate these changes to residency-time in the growing lava dome during the eruption, where stronger rocks have undergone more crystallization. In addition, subsequent recrystallization of silica polymorphs from the glass phase may further strengthen the material.

We incorporate the variation in physical and mechanical rock properties shown within the Soufrière Hills eruptive into structural stability models of the remaining over-steepened dome on Montserrat, considering also the possible effect of upscaling on the edifice-scale rock properties, and the resultant dome stability.

How to cite: Harnett, C., Kendrick, J., Lamur, A., Thomas, M., Stinton, A., Wallace, P., and Lavallee, Y.: Evolution of mechanical properties of lava dome rocks across the Soufrière Hills eruption, and application in discrete element models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14016, https://doi.org/10.5194/egusphere-egu2020-14016, 2020.

This year marks the 40^th anniversary of the 1980 Mt. St. Helens eruption and sector collapse. In acknowledgement to the vast research dedicated to understanding volcano collapse and debris avalanche dynamics, we have collated in a book the topic’s current state of the art. Within 12 chapters, this book contains reviews of and new insights from the work done over the past four decades, and provides outlooks and recommendations for future research. It is part of the Springer Book Series ‘Advances in Volcanology’ and the chapters contributed by a team of experts cover the following topics:

1. Introduction 
2. A historical perspective on lateral collapse and debris avalanches
3. Terminology and strategy to describe volcanic landslides and debris avalanches 
4. Distribution and geometric parameters of volcanic debris avalanche deposits 
5. Destabilizing factors that promote volcano flank collapse
6. Volcanic debris avalanche transport kinematics and emplacement mechanisms
7. Sedimentology of volcanic debris avalanche deposits
8. Climatic and paleo-climatic implications 
9. Computer simulation of volcanic debris avalanches
10. Volcanic debris avalanche deposits in the context of volcaniclastic ringplain successions
11. Cyclicity in edifice destruction and regrowth 
12. Volcanic island lateral collapses and submarine volcanic debris avalanche deposits

Finally, the aim of the book is to reach the professional research community as well as students and a broader audience interested in hazard management in volcanic environments.

How to cite: Roverato, M., Dufresne, A., and Procter, J.: Volcanic debris avalanches - from collapse to hazards, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1530, https://doi.org/10.5194/egusphere-egu2020-1530, 2020.

The relationship between volcanic and tectonic activity is well known. The volcanic activity strongly depend on the geodynamic context. This relationship is well highlight for systems like monogenic, mostly basaltic, volcanic fields (Cebrià and al, 2011). However, for complex, polygenetic, volcanic systems, this relationship remains very poorly constrained. The Mont-Dore Plio-Quaternary volcanic complex (4.7 to 0.3 My) is one of such polygenetic volcanic fields. This alkaline volcanism is located in the French Central massif. We define three eruptive cycles: The Bourboule caldera (3.3 to 2.2 My); the Aiguiller complex in the north (2.5 to 1.5 My) and the Sancy stratovolcano with the Adventif massif in the south-east (1.5 to 0.3 My).

Analysis coupling Coulomb fractures and faults kinematics in the variscan basement and directions of volcanic centers alignments analysed by Hough transform method highlight a strong influence of the basement fracturing on volcanism distribution. The late-variscan N20 and N160 main fracture directions were reactivated as normal faults during the oligocene E-W rifting. This fault system continued to act from the Miocene to the present day uplift, associated with new N20, flat-lying, coulomb fractures relevant with a present-day NW-SE compressional regional stress field. During the La Bourboule caldera activity, new N60 and N130 fractures were activated, some acting as normal faults. The contemporaneous vertical dykes injected the volcanic deposits mainly along the N60 direction. This suggest that this local N60-N130 brittle network were formed during the successive collapses that formed the La Bourboule caldera. In the Aiguiller massif, the brittle network is mainly composed of N-S and E-W directions. The E-W direction include normal faults that structure the north flank of the Mont-Dore horst. N-S trending volcanic dykes and alignments of monogenic volcanic events along the E-W directions point out a strong control of the fracturation of the granitic horst on the volcanic activity in the Aiguiller massif. The Sancy volcano and the Massif Adventif are marked by dykes and alignment of volcanic events that mostly trend N20. Only few dykes measured in the central area of the Sancy stratovolcano exhibit dispersed, radial, directions suggesting a local contribution of the volcanic edifice on the superficial stress field.

This study point out the strong control by the regional tectonic stress field on the activity of the Mont-Dore Plio-Quaternary volcanic complex. Alignment of monogenic edifices and dykes along the associated N20/N160 regional brittle directions is also evidenced in the northern monogenic field of the Chaine des Puys (Boivin et al. 2017). In contrast, larger volcanic activity such as caldera collapses or the building of a strato-volcano perturb the regional stress field creating a specific superficial stress field with its own fracture and faults networks.

Boivin et al. 2017. Volcanologie de la Chaîne des Puys. 6^e édition. Carte 1/25.000, 120x90 ; notice 199 p.

Cebrià, J.M., Martin-Escorza, C., Lopez-Ruiz, J., Moran-Zenteno, D.J., and Martiny, B.M. Numerical recognition of alignments in monogenetic volcanic areas: Exemples from the Michoacan-Guanajuato Volcanic Field in Mexico and Calatrava in Spain. Journal of Volcanology and Geothermal Research. 2011,201, 73-82.

How to cite: Daffos, C., Arbaret, L., Bourdier, J.-L., and Gumiaux, C.: Regional structural control on the Mont-Dore plio-quaternary volcanism (France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5569, https://doi.org/10.5194/egusphere-egu2020-5569, 2020.

The study of the stability of volcano flanks has been an active topic of research for the last few decades. In 2018, two major events renewed attention in this hazardous processes. In May 2018, following the beginning of a flank eruption at Kilauea volcano in Hawai’i, a M6.9 earthquake occurred along the Southern flank of Kilauea marking a dramatic but transient acceleration from its secular deformation rate. Alternatively, in December 2018, an intense period of volcanic activity preceded a catastrophic sector collapse which triggered a devastating tsunami at Anak Krakatou volcano (Indonesia). The two contrasting behavior events reveal our poor understanding of the physical processes controlling volcano stability.

Ultimately, instability of volcano flanks is characterized by the development and evolution of failure surfaces (faults and/or basal shear zones). Once established, for example at a rheological interface, a decollement fault should be a key element in the control of the mechanical interplay between the volcano-tectonic and gravitational forces. In this communication, I review our ability to map surface displacements measured with geodetic techniques into frictionally distinct regions on the fault surface. I explore a range of inverse modeling methods to estimate bounds on the extend of geodetically constrained fault slip areas. I apply the methods to the Southern flank of Kilauea volcano. The range of different solutions for fault slip models allows to critically assess whether there are regions of stable or variable frictional conditions. Mapping accurately the frictional behavior and constraining its location region will allow to generate more realistic dynamic models of volcano flanks and improve our understanding the physical processes controlling volcano stability.

How to cite: Gonzalez, P.: Sharp geodetic fault slip models for an improved understanding of volcano flank dynamics, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5674, https://doi.org/10.5194/egusphere-egu2020-5674, 2020.

The Solfatara-Pisciarelli area, located in the active Campi Flegrei caldera (Italy) hosts an intense hydrothermal activity, whose shallower expression is controlled by a complex pattern of fractures and faults. Volcanological and structural studies may be the key to disclose the relationships between brittle structures and hydrothermal activity, as well as to understand the dynamic processes and possible eruption scenarios. For this purpose, we present the results of a volcanological and structural survey combined with Electrical Resistivity Tomography (ERT) and Self Potential data. Three ERT surveys has been performed in order to reconstruct the Pisciarelli structural setting and the relationships of the main fractures and faults with the underground fluid circulation. Two measured profiles crossing the main mud pool and fumaroles of Pisciarelli and has been repeated every three months to evaluate the possible influence of seasonal effects on the hydrothermal system. These profiles performed during the last year have been compared with a first ERT prospection carried on in correspondence of a 100 m long survey line, which crosses along the W-E direction the Pisciarelli permanent mud pool and its main fumarole. The comparison of the results with temperature, geochemical data and rainfall rates allowed to separate the areas dominated by seasonal effects from areas where deeper injected gasses cumulate in the subsoil. Further indication on the fluid circulation and structures derived by a mapping of the self-potential anomaly realized for the whole Solfatara-Pisciarelli area. The rocks exposed in the Pisciarelli area host a large number of faults and fractures, the latter often related to fault damage zones. Cross-cutting fault and fracture relationships and their relations with the volcanic sequences suggest that NW-SE and NE-SW trending faults are sealed by Solfatara deposits (4.28 ka); whereas E-W and N-S trending faults cross-cut the youngest volcanic succession (Astroni deposits, 4.25 ka). Several landslide deposits were recognized in the higher part of the Pisciarelli fumarole field, mainly due to intense rock fracturing, hydrothermal alteration, mud-pool activity and steep relieves surrounding the mud pool. Ancient landslide deposits overlying mud sediments, similar to those nowadays forming within the active mud pool, cropping out along the slope, at about 5 meters above the present mud pool level. New landslide phenomena could seal off the mud pool and fumaroles of Pisciarelli, with a possible consequence to trigger an hydrothermal explosions as described for other hydrothermal systems in the world.

How to cite: Isaia, R., Di Giuseppe, M. G., Natale, J., Tramparulo, F. D., Troiano, A., and Vitale, S.: New insights on the structural setting of the Pisciarelli fumarole field (Campi Flegrei caldera): implications for evolution and eruptive scenarios , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13178, https://doi.org/10.5194/egusphere-egu2020-13178, 2020.

On September 11, 1989, after four months of Strombolian activity at the summit craters, effusive activity began on Mt. Etna and lasted about a month.

The 1989 eruption of Mt. Etna was characterized by the formation of two fracture systems, striking NE-SW and NNW-SSE, and both starting from the SE Crater on September, 24.

The NE-SW system was followed by effusive activity while the NNW-SSE fractures opened for a length of 7 km without eruptive phenomena. Between September, 27 and October, 3 the fracture system propagated until it reached and cut the SP 92 provincial road (Zafferana - Rifugio Sapienza), near the 1792 effusive mouth, and continued southward for another 700 m.

We investigated the fracture southern branch dynamics through 30 years of ground deformation data collected by the discrete and continuous INGV monitoring networks. We considered levelling, GPS, EDM, and extensometers data. EDM and levelling measurements began in the 80s; on 2003 EDM measurements have been replaced by GPS.

During the 1989 eruption, EDM measurements showed variations of tens of centimeters on the lines close to the fracture.

Precise levelling discrete measurements revealed, in the period 4-16 October 1989 and during the 1991-1993 eruption a subsidence of some centimeters on benchmarks close to fracture.

A network of rod extensometers evidenced the fracture activation during the 2001 intrusion phases (12-17 July) measuring several centimeters of left lateral slip. Distance measurements and InSAR show signs of the fracture reactivation during the 2002 and 2018 eruptions.

Several authors show as the 1989 fracture zone connects the summit region of the volcano with the tectonic structures of the lower SE flank considering it as well part of the NNW-SSE oriented structure.

The dynamics of these last 30 years suggests that the 1989 fracture play an important role on the flank dynamics and strain distribution. It also represents a potential hazard to population because it represents a possible way of ascending magma also testified by cones aligned along the structure.

How to cite: Gambino, S., Aiesi, G., Bonforte, A., Brandi, G., Calvagna, F., Consoli, S., Distefano, G., Falzone, G., Ferro, A., Guglielmino, F., Laudani, G., Marsala, G., Obrizzo, F., Privitera, L., Puglisi, G., Russo, S., Saraceno, B., and Velardita, R.: Dynamics of the 1989 fracture system and relations with the Etna eruptive activity of the last 30 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19384, https://doi.org/10.5194/egusphere-egu2020-19384, 2020.

Unravelling the kinematics, development and origin of the structures along a volcano-tectonic rift is of paramount importance for understanding plate separation, seismicity, volcanic activity and the associated hazards. Here, we focus on an extremely detailed survey of the Holocene deformation field along the Northern Volcanic Zone of Iceland, the northernmost point of emergence of the Mid-Atlantic Ridge. The study of this extremely dynamic rift is also useful for a better comprehension of how mid-oceanic ridges work. The study is based on extensive field and unmanned aerial vehicle surveys performed over the last four years, completed by about 6000 measures collected at 1633 sites on fault strike, dip and offset, and fracture strike, dip, dilation direction and dilation amount. The rift, named Theistareykir Fissure Swarm, is composed of N-S to NNE-SSW-striking normal faults and extension fractures affecting an area 8 km-wide and 34 km-long. The computed overall spreading direction is N111° averaged during Holocene times, with values of N125° to the north and N106° to the south. The kinematics is characterised by the presence of complex components of right-lateral and left-lateral strike-slip motions, with a strong predominance of right-lateral components along structures parallel and coeval to the rift zone. The surveyed 33 Holocene faults (696 sites of measurement) along the central part of the rift show two opposite directions of fault/rift propagation, based on fault slip profile analyses. We discuss the possible causes of these characteristics and analyse in detail the interaction of both faults and extension fractures with the WNW-ESE transform Tjornes Fracture Zone, and in particular with the parallel right-lateral Husavik-Flatey Fault in the central part of the rift, and the Grimsey Lineament to the north. We also assess the role of: i) repeated dyke intrusions from the magma chamber outward along the plate margin, ii) regional tectonic stresses, iii) mechanical interaction of faults, and iv) changes in the rheological characteristics of rocks.

How to cite: Russo, E., Tibaldi, A., Bonali, F. L., Pasquarè Mariotto, F., Einarsson, P., and Hjartardóttir, Á. R.: Unravelling rift development: a key study from the Northern Volcanic Zone of Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-500, https://doi.org/10.5194/egusphere-egu2020-500, 2020.

To better understand the Late Triassic tectonic setting in the northern North China Craton (NCC), a multidisciplinary investigation, including structural geology, geochronology, anisotropy of magnetic susceptibility (AMS) and gravity modeling, has been carried out in the Dushan pluton. The Dushan pluton consists of monzogranite and biotite-rich facies along the pluton margin without sharp contact between them. The granite varies southwestwards from isotropic texture to arcuate gneissic structures, with locally mylonitic structures. The intensity of solid-state deformation increases southwestwards across the pluton, leaving preserved magmatic fabrics in the northeastern part. The compatible outward dipping magmatic and solid-state magnetic fabrics, together with mesoscopic fabrics, define an elliptic dome-like pattern with a NE-SW oriented long axis, despite the fabrics dip inwards in the southeastern margin of the pluton. Combining gravity modeling, the Dushan pluton presents an overall tabular or tongue-like shape with a northeastern root. The magnetic lineations nearly strike NE-SW, concordant with the stretching lineations observed in the mylonitic zones. We propose the emplacement mode that the Dushan pluton emplaced southwards through the feeder zone in its northeast, beginning probably with a sill. The later successive magma batches may laterally and upwardly inflate, deform and even recrystallize the former cool-down magma. This inflation forms an arcuate, gneissic to mylonitic foliation in the southwestern margin. The Dushan pluton is considered as typically post-tectonic in emplacement, recording a Late Triassic post-tectonic setting of the northern NCC.

How to cite: Qiu, H., Lin, W., Chen, Y., and Faure, M.: Emplacement mechanism of Late Triassic granitic Dushan pluton, North China and its tectonic implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5668, https://doi.org/10.5194/egusphere-egu2020-5668, 2020.

“Cirques” are funnel-shaped, seaward-narrowing valleys commonly observed on many volcanic islands worldwide, such as Tahiti (French Polynesia), La Palma or Gran Canaria (Canary), Anjouan (Comores), and Maui or Molokai (Hawai’i). Because they contradict the basics of regressive erosion by rivers, these geomorphic structures have been interpreted in many ways, including the erosion of volcano-tectonic depressions (crater, caldera, rift zone), the formation of leaf grabens caused by volcano spreading, or the subsidence of dense plutonic bodies within edifices. Piton des Neiges volcano (Réunion Island) is dissected by three cirques (Salazie, Mafate and Cilaos) and thus provides an excellent case to study the processes that lead to the formation of these funnel-shaped valleys. To do so, we performed a detailed field and photogrammetric mapping of the volcanic and volcaniclastic products outcropping in the cirques using an updated chrono-stratigraphy.

Our mapping reveals that the three cirques of Piton des Neiges are not delimited by faults, which excludes vertical movements as the primary cause of their formation. Rather, the cirques are built on former horseshoe-shaped depressions filled with volcaniclastic breccias (mostly related to debris avalanches and debris flows), and later covered by lava flow units. Importantly, the breccia are several hundred meters thick in the innermost parts of the cirques, but thin out until complete disappearance toward the outer flanks of the volcano.

In consequence, we interpret the basal volcaniclastic breccias as playing a major role in the formation of the cirques, by offering a weaker resistance than the lava flow units. This contrasted resistance leads to greater erosion rates on the inside of the volcano than on the outer flanks and, hence explaining the reverted funnel shape of the cirques. In our model, cirques are therefore erosional structures mostly guided by past dismantling episodes rather than by tectonic or volcano-tectonic structures.

How to cite: Paquez, C., Famin, V., Villeneuve, N., Michon, L., and Bénard, B.: How do cirques form in ocean island volcanoes: the case of Piton des Neiges (Réunion Island, Indian Ocean), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13517, https://doi.org/10.5194/egusphere-egu2020-13517, 2020.

Using numerical reconstructions of the morphology of the volcanoes in correlation with petrography, paleomagnetic and K-Ar age data we are showing the differences in eruptive activity between volcanoes in a post-collisional setting. North Harghita is a chain segment of the Călimani-Gurghiu-Harghita(Romania) volcanic range, composing by row of volcanic of partial overlapping edifices. It is formed from north to south by the following volcanic edifices: Răchițiș (small monogenetic aphanitic dacitic shield volcano) and the Ostoroș, Ivo-Cocoizaș, Vârghiș (including Harghita Băi) andesitic (dacitic) composite volcanoes.

The Miocene-Pliocene calc-alkaline volcanism developed in the North Harghita Mts. for ca. 2.4 Ma (6.3-3.9 Ma). The Răchițiș monogenetic volcano has been generated at ~ 5.8 Ma. The volcanic edifices of Ostoroș and Ivo-Cocoizaș were build up in the same time interval (6.3-5.0 Ma), lasting ~1.5 Ma each; Vârghiș main edifice indicate a <1 Ma-long activity (5.5-4.8 Ma), however dated debris avalanche suggest longer duration.

The Ostoroș and Ivo-Cocoizaș volcanic edifices after the build-up stage were followed by destructive east-oriented debris avalanches events (~ synchronous) and eruption activity stopped.

The Vârghiș edifice complex (including Harghita Băi volcano), experienced an intense build up stage followed by a south-west-oriented debris avalanche failure event. The southernmost Rupea basaltic andesite mega-block is 6.8 Ma old and can be attributed to the Vârghiş volcano suggesting a much longer duration for the volcano lifespan; later at 3.9 Ma a small effusive event was generated in the failure crater.

DEM volume calculations include present exposed edifices and debris avalanches. Răchițiș is only of 0.8 km³; Ostoroș volcano edifice have 16 km³ and a debris avalanche deposits of 6.1 km³ suggesting a total volumes of 22.1 km³; Ivo-Cocoizaș volcano has 18.6 km³ and its debris avalanche deposits is of 12.6 km³, suggesting a total volume of 31.2 km³; Vârghiș volcano, the southernmost, has the largest volume of 84.9 km³ (111.7 km³ including Harghita Băi associated edifice) with a total debris avalanche deposits of 8.7 km³ with a total volume of 120.4 km³.

East-oriented debris avalanches of Ostoroș and Ivo-Cocoizaș travelled up to 20km where has been blocked by a higher morphology. South-west-oriented Vârghiș debris avalanche traveled up to 55km on a lower morphology, and it is much thinner.

The North-South-directed spatio-temporal evolution of North Harghita volcanic edifices reflect the southward propagation of strike-slip and normal faulting, following the post-collisional events in the East Carpathians.

Acknowledgements: This work was supported by a grant of the Ministry of Education and Scientific Research, CNCS-UEFISCDI, project number PN-II-IDPCE-2012-4-0137 and by grant of Ministry of Research and Innovation, CNCS–UEFISCDI, project number PN-III-P4-ID-PCCF-2016-4-0014, within PNCDI III.

How to cite: Mirea, V. and Seghedi, I.: Volcanoes morphology of the North Harghita (Romania) Volcanic chain segment : similarities and differences , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7584, https://doi.org/10.5194/egusphere-egu2020-7584, 2020.

The Hengill volcanic complex in SW-Iceland is located on a triple junction where two extensive and one conservative plate boundary meet. An uplift event, possibly caused by a magmatic intrusion, in the 1990ies caused a landrise of 8 cm over the period of 4 years and was accompanied by more than 90.000, mostly very small, earthquakes. We used cross-correlation to improve pick accuracy and applied a relative relocation algorithm to get high resolution earthquake locations of the earthquakes in the direct vicinity of the centre of the uplift. Relocated earthquake location reveal clustering and alignments of earthquakes that are mostly oriented in NNE and ENE direction. Then we recalculated focal mechanisms for the new locations and then use the Quakelook software to select the best fitting focal mechanism. Quakelook calculates a plane that best fits the locations of a cluster of earthquakes which then is compared to the database of possible focal mechanisms that all explain the polarity and amplitude data similar well. The projection of the slip vectors into the fault plane is then used to estimate the average movement along the fault. From the fault dynamics we learn about the stresses activating that fault.

The relocated earthquake distribution shows that the stresses induced by the uplift event must have been small in comparison to the regional stress since the activated faults do not respect the geometry of the uplift source but are rather in agreement to the regional stress field. The uplift did not cause any new breaks in the crust but rather reactivated existing faults which sub-optimally oriented in relation to the uplift.

How to cite: Blanck, H., Geirsson, H., Vogfjörd, K., and Hjörleifsdóttir, V.: Fault geometry and dynamics during the 1993-1998 uplift episode in Hengill, SW-Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6806, https://doi.org/10.5194/egusphere-egu2020-6806, 2020.

Episodes of ground deformation, relating to the unrest of a volcanic system, are often readily identifiable within geodetic timeseries (e.g. GPS, InSAR). However, the underlying processes facilitating this deformation are more enigmatic. By modelling the observed deformation signals, the ultimate aim is to infer characteristics of the deforming reservoir; namely the size and time-dependent evolution of the system and, potentially, the fluxes of magma involved. These parameters can be estimated using simple elastic models, but the presence of shallow or long-lived magmatic systems can significantly perturb the local geothermal gradient and invalidate the elastic approximation. Inelastic rheological effects are increasingly utilised to account for these elevated thermal regimes, where a component of viscous (time-dependent) behaviour is expected to characterise the observed deformation field.

Here, our investigations are concentrated on Taupō volcano, New Zealand, the site of several catastrophic caldera-forming eruptions. We use 3D thermomechanical models of the Lake Taupō region, featuring thermal constraints and heterogeneous crustal properties, to compare the commonly-used Maxwell and Standard Linear Solid (SLS) viscoelastic configurations under contrasting deformation mechanisms; a pressure condition (stress-based) and a volume-change (strain-based). By referring to models allocated a single viscosity value, we investigate the influence of a temperature-dependent viscosity distribution on the predicted spatiotemporal deformation patterns. Comparisons of the overpressure models highlights the influence of the crustal viscosity structure on deformation timescales, by enabling the SLS rheology to account for both abrupt and long-term deformation signals. For the Maxwell rheology, we show that the viscosity distribution results in unexpected deformation patterns, both spatially and temporally, and so query the suitability of this rheology in other model setups. Further to this, the deformation patterns in volume-change models are governed by the resulting stress response, and the effect of the viscosity structure on its propagation. Ultimately, we demonstrate that variations in crustal viscosity greatly influence spatiotemporal deformation patterns, more so than heterogeneous mechanical parameters alone, and consequently have a large impact on the inferences of the underlying processes and their time-dependent evolution. The inclusion of a crustal viscosity structure is therefore an important consideration when modelling volcanic deformation signals.

How to cite: Head, M., Hickey, J., Gottsmann, J., and Fournier, N.: Crustal viscosity and its control on volcanic ground deformation patterns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17915, https://doi.org/10.5194/egusphere-egu2020-17915, 2020.

Non-eruptive uplift and subsidence episodes at volcanic systems have been observed on volcanic systems around the world and understanding the complex source processes of the deformation is key to mitigate the hazard assessment or geothermal potential of the area. The Hengill area, an approximately 100 km² area in SW Iceland, located at the triple junction of the Eurasian plate, North-American plate and Hreppar Microplate, is one such example of a complex deforming volcanic system. The triple junction accommodates a total spreading and shear of 1.8 cm/yr through a systems of spreading ridges and “bookshelf-faulting” processes. The two active volcanoes of the area (Hrómundartindur and Hengill), last erupted ~2000 years ago. Beneath these adjacent volcanic systems, deep sources (5-7 km depth) caused successive episodes of broad-scale uplift (1993 – 1999; 2017 – 2018) and subsidence (2006 – 2017; 2018 – ongoing at the time of writing) in the area. These deep sources may be closely related as they have been located only 2-3 km from each other within the brittle-ductile transition zone of the area. More superficial sources (depth < 3 km) of deformation are also observed in the Hengill area, related to the extraction and injection of fluids in the Nesjavellir and Hellisheiði geothermal power plants.

Through the combination of GNSS, InSAR, analytical models and geophysical data sets from the area we investigate the spatial and temporal relation between these deep sources. The observed ground motions associated with these deep sources may be magmatic in nature (e.g. magma accumulation, degassing of older intrusions), however previous seismic tomography work (Tryggvason et al. 2002) in the area does not suggest a large partially melted magmatic body at those depths, hinting that other processes (e.g. hydrothermal) may be at the origin of some of these episodes. The correlation of geodetic measurements with geophysical and geothermal datasets may bring clues to constrain the nature of uplift and subsidence episodes in volcanic and high temperature geothermal areas such as the Hengill area.

How to cite: Ducrocq, C., Geirsson, H., Árnadóttir, T., Juncu, D., Kristjánsson, B. R., Gunnarsson, G., and Drouin, V.: Non-eruptive Uplift and Subsidence episodes beneath the Hengill Triple Junction, SW Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18000, https://doi.org/10.5194/egusphere-egu2020-18000, 2020.

Piton de la Fournaise volcano forms the southeastern part of La Réunion, an oceanic basaltic island in the southernmost part of Mascarene Basin (Indian Ocean). Five eruptions occurred at Piton in 2019, accompanied by seismic activity, lava flow, and lava fountaining. Here below, we focus on the fourth eruption occurred between August 11 and 15 on the southern-southeastern flank of the volcano, inside the Enclos Fouqué caldera. This eruption was characterized by the opening of two eruptive fissures. We retrieve the surface deformations induced by the eruptive activity through space-borne Differential Synthetic Aperture Radar Interferometry (DInSAR) measurements. First, we generated the coseismic deformation maps by applying the DInSAR technique to SAR data collected along ascending and descending orbits by the Sentinel-1 constellation of the European Copernicus Programme. The DInSAR technique allows us to analyze the deformation patterns caused by the 11 August 2019 eruption. We also retrieved the pre-eruptive deformation through the Small BAseline Subset (SBAS) DInSAR approach. Then, we modelled the DInSAR displacements to constrain the geometry and characteristics of the eruptive source. The modelling results suggest that the observed deformation can be attributed to the interaction between a shallow magma reservoir located at ~1.5-2 km depth below the summit, and the intrusion of a dike feeding the eruptive fissure inside the Enclos Fouqué caldera.

This work is supported by: the 2019-2021 IREA-CNR and Italian Civil Protection Department agreement; the EPOS-SP project (GA 871121); and the I-AMICA (PONa3_00363) project.

How to cite: De Novellis, V., Casu, F., De Luca, C., Manzo, M., Monterroso, F., Valerio, E., Lanari, R., and Battaglia, M.: Ground deformation associated with the August 2019 eruption of Piton de la Fournaise (La Réunion Island) inferred from DInSAR measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18664, https://doi.org/10.5194/egusphere-egu2020-18664, 2020.

Unrest at Bárðarbunga after a caldera collapse in 2014-2015 includes elevated seismicity beginning about six months after the eruption ended, including nine Mw>4.5 earthquakes. The earthquakes occurred mostly on the northern and southern parts of a caldera ring fault. Global Navigation Satellite System (GNSS, in particular, Global Positioning System; GPS) and Interferometric Synthetic Aperture Radar (InSAR) geodesy are applied to evaluate the spatial and temporal pattern of ground deformation around Bárðarbunga caldera outside the icecap, in 2015-2018, when deformation rates were relatively steady. The aim is to study the role of viscoelastic relaxation following major magma drainage versus renewed magma inflow as an explanation for the ongoing unrest.

The largest horizontal velocity is measured at GPS station KISA (3 km from caldera rim), 141 mm/yr in direction N47^oE relative to the Eurasian plate in 2015-2018. GPS and InSAR observations show that the velocities decay rapidly outward from the caldera. We correct our observations for Glacial Isostatic Adjustment and plate spreading to extract the deformation related to volcanic activity. After this correction, some GPS sites show subsidence.

We use a reference Earth model to initially evaluate the contribution of viscoelastic processes to the observed deformation field. We model the deformation within a half-space composed of a 7-km thick elastic layer on top of a viscoelastic layer with a viscosity of 5 x 10¹⁸ Pa s, considering two co-eruptive contributors to the viscoelastic relaxation: “non-piston” magma withdrawal at 10 km depth (modelled as pressure drop in a spherical source) and caldera collapse (modelled as surface unloading). The other model we test is the magma inflow in an elastic half-space. Both the viscoelastic relaxation and magma inflow create horizontal outward movements around the caldera, and uplift at the surface projection of the source center in 2015-2018. Viscoelastic response due to magma withdrawal results in subsidence in the area outside the icecap. Magma inflow creates rapid surface velocity decay as observed.

We explore further two parameters in the viscoelastic reference model: the viscosity and the "non-piston" magma withdrawal volume. Our comparison between the corrected InSAR velocities and viscoelastic models suggests a viscosity of 2.6×10¹⁸ Pa s and 0.36 km³ of “non-piston” magma withdrawal volume, given by the optimal reduced Chi-squared statistic. When the deformation is explained using only magma inflow into a single spherical source (and no viscoelastic response), the optimal model suggests an inflow rate at 1×10⁷ m³/yr at 700 m depth. A magma inflow model with more model parameters is also a possible explanation, including sill inflation at 10 km together with slip on caldera ring faults. Our reference Earth model and the two end-member models suggest that there is a trade-off between the viscoelastic relaxation and the magma inflow, since they produce similar deformation signals outside the icecap. However, to reproduce details of the observed deformation, both processes are required. A viscoelastic-only model cannot fully explain the fast velocity decay away from the caldera, whereas a magma inflow-only model cannot explain the subsidence observed at several locations.

How to cite: Li, S., Sigmundsson, F., Drouin, V., Parks, M. M., Jónsdóttir, K., Ofeigsson, B. G., Grapenthin, R., Geirsson, H., and Hooper, A.: Post-eruptive volcano inflation following major magma drainage: Interplay between models of viscoelastic response influence and models of magma inflow at Bárðarbunga caldera, Iceland, 2015-2018 , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19030, https://doi.org/10.5194/egusphere-egu2020-19030, 2020.

Underground pressure sources and rift zones may act jointly during phases of volcanic activity. Pressurization of magma bodies at shallow to intermediate depth, along with degradation of the mechanical properties of the host rock, can enhance tensile stress along zones of weakness, thus favoring magma intrusion. Such interactions were hypothesized at different volcanoes, including Mt. Etna, Piton de la Fournaise and Montserrat, from seismic, gravity and ground deformation data. Here we use a finite-element modeling approach to quantitatively understand possible mechanical interactions between a shallow pressure source beneath the summit caldera and the rift zones at Kīlauea Volcano (Hawai‘i). Past studies have demonstrated a strong connection between these structures, for example, with increases in seismic activity and extension across the rift, during phases of inflation of the summit. These observations suggest a coupling, which may modulate magma accumulation and transport processes along the rift.

How to cite: Pulvirenti, F., Aloisi, M., Carbone, D., Poland, M., and Vinciguerra, S.: Mechanical interactions between pressure sources and rift zones at Kilauea Volcano, Hawaii., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21540, https://doi.org/10.5194/egusphere-egu2020-21540, 2020.

Building on previous work aimed at identifying and characterizing the potential mechanical trigger controlling eruptions and destabilization at Piton de la Fournaise, we study the mechanical behavior of the volcanic edifice on a crustal scale. Do the recurrent earthquake pattern correspond to a destabilization structure, precursor of a large-scale flank sliding? Or instead to a reactivated area of magma storage (partially crystallized “sill”)? To answer these questions, we design numerical models which estimate the stress field associated with the volcanic complex. We use the ADELI finite element method in three dimensions, which handles elasto-visco-plastic rheologies. In these models, we take into account 1) the topographic load, 2) the major density and resistance heterogeneities within the volcano obtained from previous studies, and 3) the overpressure induced by the intrusion of a dike of arbitrary geometry.
The modeled dike injection generates deformation and stress fields such that their isocontours highlight an ellipsoidal cup structure extending from the central cone to a depth close to 0 and reaching the ends of the eastern flank. This zone could be assimilated to the zone of seismicity observed and described previously. Together with several systematic test cases, we will discuss the significance of these results, such as whether it reveals a rheological delimitation zone of the hydrothermalized bedrock, resulting from the combined influence of the topographic load and that of a magmatic injection.

How to cite: Gerbault, M., Fontaine, F., Peltier, A., Gailler, L., Hassani, R., Got, J.-L., and Ferrazzini, V.: Piton de la Fournaise, elasto-plastic models of stresses and deformation accounting for the topographic load and a magmatic injection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11571, https://doi.org/10.5194/egusphere-egu2020-11571, 2020.

Mt. Stromboli is an active volcano, located near the coasts of Sicily (Italy), in the Mediterranean Sea. Its volcanic activity is characterized by mild and frequent explosions, sometimes interrupted by occasional episodes of more vigorous activity, which can be accompanied by lava flows and more energetic eruptions, known as “major” or “paroxysmal” eruptions, according to the energy dissipated during the event.

Stromboli produced vulcanian eruptions in 2003, 2007 and July-August 2019, which were well recorded by the INGV monitoring network. In particular the last three events are studied through records from borehole strainmeters, which allow us to infer many details of source dynamics. These events are clearly preceded by a slow strain buildup, starting several minutes before the paroxysms, which can be used in future for civil protection purposes. The eruptions then consist of two or more pulses, with oscillations ranging from several seconds, as in 2007, to some minutes, such as in 2019 and lasting from several minutes to one hour after the explosions.

Mechanisms involved in the triggering process of the vulcanian explosions include an increase of magma flux ascending from sources located from 2 to 5-7 km depths and morphological complexity in the upper feeding system.

A preliminary early-warning algorithm, based on an evaluation of strain rate change, has been defined: it has shown itself capable of ascertain the occurring eruptions minutes before their summit onset.

Valuable information are embedded in the data used in the current work, which could be used not only for scientific purposes but also from civil protection for monitoring reasons. Such a variety of possible usage needs the setting of principles and legal arrangements to be implemented in order to ensure that data will be properly and ethically managed and in turn can be used and accessed from the scientific community.

Particular care is needed in order to harmonize the different rules regarding use of data/information, to identify any potential legal issues related to Intellectual Property (IP) and to set up clear and consistent principles related to IP Rights.

How to cite: Di Lieto, B., Romano, P., Scarpa, R., Linde, A. T., and Sangianantoni, A.: Early warning signals before paroxysmal activity at Stromboli volcano, Italy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20637, https://doi.org/10.5194/egusphere-egu2020-20637, 2020.

At 14:11 NZDT (01:11 UTC) on 9 December 2019, an explosive eruption (VEI=2) occurred on White/Whakaari Island in New Zealand’s northeast Bay of Plenty. The sudden eruption claimed 20 lives among the 47 tourists who were on the island at the time of the eruption. Several volcano-tectonic features overlap in the island such as a major caldera rim collapsing scarp to the west, a landslide, a crater lake and a large shallow hydrothermal system at the center, making complex the understanding of the eruption triggering factors. Here we use Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) data from 3 different tracks (1 ascending and 2 descending) spanning the period of 2014-2020 to investigate the spatio-temporal surface deformation evolution of White Island in the years before the eruption. By analyzing the InSAR time-series displacements between the two eruptions of April 2016 and December 2019, at least 4 separate stages can be identified that possibly relate to different parts of the volcanic eruptive cycle:  1) During April 2016 - February 2018, the crater lake edge and the western sub-crater wall rapidly moved downslope at a rate of ~6 cm/yr, while the central sub-crater area uplifted at a rate of ~3 cm/yr; 2) From February 2018 to January 2019, both the western and the central sub-craters uplifted at a rate of ~5 cm/yr; 3) During  the following six months, from January 2019 to June 2019, the western sub-crater started moving downslope again at a rate of ~3 cm/yr, while the central sub-cater kept moving up at a rate of ~4 cm/yr; 4) And finally, during June 2019 - December 2019 (until the eruption), uplift occurred around the western sub-crater again at a similar rate as in the central sub-crater area (~ 4 cm/yr). Seismic records before the eruption show that approximately 500 volcanic earthquakes located at a depth of ~ 5 km occurred at the southwestern part of White Island on June 2019, that may point to a shallow level intrusion of new magma. This upcoming magma might then have pressurized the shallow hydrothermal system during the fourth-stage uplift. Modeling of the uplift during June 2019 to December 2019 indicates a shallow source located at only ~200 m below the surface in the vicinity of the crater lake, likely coinciding with the shallow hydrothermal system responsible for the final 2019 phreatic eruption.

How to cite: Cao, Y., Trippanera, D., Li, X., Nobile, A., Yunjun, Z., Passarelli, L., Xu, W., and Jónsson, S.: InSAR Imaging of White Island from 2014 to 2020: Insights into the 2019 Phreatic Eruption, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10551, https://doi.org/10.5194/egusphere-egu2020-10551, 2020.

In summer 2019, two paroxysmal explosions occurred in Stromboli. The first one occurred on July 3, when the Strombolian ordinary eruptive activity did not show a significant intensification. The explosion formed an eruptive column more than 3 km high. A pyroclastic flow ran down the “Sciara del Fuoco” slope causing a victim and some injuries. Moreover, the pyroclastic flow spread over the sea surface for about one kilometer. On August 28, a second paroxysmal explosion occurred, similar to the previous one. Also in this case the eruption formed an eruptive column of more than 3 km and a pyroclastic flow that expanded along the “Sciara del Fuoco” slope and traveled about 1 km on the sea surface. In the period between the two paroxysms, effusive activity occurred from the summit crater area. The eruptive phase of summer 2019, which began with the paroxysm of 3 July, was not preceded by significant changes in the routinely monitored parameters, such as the hourly frequency (daily average) of the VLP events (typical of Stromboli) and the amplitude of the seismic signal (RSAM). For this reason, we have analyzed the seismic and dilatometric data, which were recorded by the INGV geophysical network in the period November 2018 - September 2019, focusing our attention on other parameters that can give indications on the activity state of the volcano. In particular, we analyzed the data of the broadband seismic stations, equipped with the Guralp CMG40T sensors, and the data of one Sacks-Evertson borehole strainmeter. We defined the "VLP size", which takes into account the waveform of the VLP events, in terms of both amplitude and duration. We also applied time varying Fractal Dimension (FD) analysis to the seismograms of a seismic station close to the crater area and we analyzed the polarization of the same signal. We carried out the polarization analysis both without applying a filter and by filtering the seismic signal in the typical frequency bands of the Stromboli volcanic tremor (1-3 Hz) and of the VLPs (0.5-0.05 Hz). We found that the "VLP size", the FD and the polarization parameters showed significant changes about one month before the paroxysm of July 3. In the short term, we applied an appropriately tuned STA/LTA algorithm to the data of the borehole strainmeter, which is installed on the island at about 2km from the craters, and we obtained an automatic detection of the paroxysmal events 10 and 7.5 minutes before the explosion of July 3 and August 28, respectively.

How to cite: Orazi, M., Giudicepietro, F., López, C., Macedonio, G., Alparone, S., Bianco, F., Calvari, S., De Cesare, W., Delle Donne, D., Di Lieto, B., Esposito, A., Peluso, R., Privitera, E., Romano, P., Scarpato, G., and Tramelli, A.: The 2019 eruptive phase of Stromboli volcano through multiparametric geophysical observations., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11260, https://doi.org/10.5194/egusphere-egu2020-11260, 2020.

Transient seismicity at active volcanoes poses a significant risk in addition to eruptive activity.
This risk is powered by the common belief that volcanic seismicity cannot be forecast, even on a long
term. Here we investigate the nature of volcanic seismicity to try to improve our forecasting capacity. To this
aim, we consider Ischia volcano (Italy), which suffered similar earthquakes along its uplifted resurgent
block. We show that this seismicity marks an acceleration of decades‐long subsidence of the resurgent block,
driven by degassing of magma that previously produced the uplift, a process not observed at other
volcanoes. Degassing will continue for hundreds to thousands of years, causing protracted seismicity and
will likely be accompanied by moderate and damaging earthquakes. The possibility to constrain the future
duration of seismicity at Ischia indicates that our capacity to forecast earthquakes might be enhanced when
seismic activity results from long‐term magmatic processes, such as degassing.

How to cite: Di Vito, M., Trasatti, E., Acocella, V., Del Gaudio, C., Weber, G., Aquino, I., Caliro, S., Chiodini, G., de Vita, S., Ricco, C., and Caricchi, L.: Magma Degassing as a Source of Long‐Term Seismicity at Volcanoes: The Ischia Island (Italy) Case, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22449, https://doi.org/10.5194/egusphere-egu2020-22449, 2020.

It has been shown that in the aftermath of megathrust earthquakes the forearc region moves trenchwards promoting crustal extension alterating the long term stress regime in place before the earthquake during the inter-seismic periods. In the far field such variations are less well-recognised and their influence on volcanic arc activity poorly constrained.

To tackle this problem we deployed a temporary seismic network in the volcanic arc of Southern Andes from November 2013 to April 2015 to investigate the tectonic deformation imposed by the M8.8 2010 Maule megathrust earthquake. The network is centred on the Nevados de Chillan Volcanic Complex is an Andean-transverse NW-oriented structure whose orientation is not well compatible with the current tectonic regime. The Nevados de Chillan faces one of the regions that slipped the most during the 2010 M8.8 Maule earthquake. The system was also reactivated after the earthquake and its activity is still ongoing at writing.

We compared the deformation of the geological records such as faults, fractures and dikes (assumed to be representative of inter-seismic periods) against the focal mechanisms inverted from shallow moderate-magnitude earthquakes occurred in the arc from 2010 to 2015. We found out that the geological record shows the imprinting of both long term inter-seismic and perturbed shorter term post-seismic deformation. In particular, the latter may create the conditions to re-activate NW pre-existing tectonic structures enhancing the magma upwelling sitting in the upper lithosphere.

Our work suggests that the kinematics driving the growth of NW-striking volcanic systems in the Southern Central Andes are affected by both magmatic and tectonic processes, with the latter experiencing short-lived perturbations.

How to cite: Lupi, M., Trippanera, D., Gonzalez-Vidal, D., Tassara, A., D'Amico, S., Catalina, C., and Marc Muelle, S.: Transient tectonic switch in volcanic arcs: observations from the Southern Andes ( 33S - 38S)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19326, https://doi.org/10.5194/egusphere-egu2020-19326, 2020.