GMPV9.4

The Askja volcanic system, located in the North Volcanic Zone of Iceland, consists of a central volcano with three nested calderas (Kollur, Askja, and Öskjuvatn) and a 20 km wide and ~190 km long fissure swarm with a NNE-SSW trend. Kollur caldera is ~5 km wide and formed in the Pleistocene while the younger 8-km wide Askja caldera, the largest among the three, formed in the Holocene. The smaller (~4 km) and lake-filled Öskjuvatn caldera is located within the Askja caldera and formed following the 1875 Plinian eruption. This event was followed by several localized eruptions along the Öskjuvatn ring fault system (1921, 1922, and 1929) and the last eruption occurred in 1961 in correspondence with the Askja northern caldera border. After this eruption, the Askja caldera first underwent inflation for several years followed by slow (< 1 cm/yr) subsidence over decades. In early August 2021, the volcano entered a period of unrest with new earthquake activity located below the central volcano, and the GNSS station OLAC, located near the center of Askja caldera, started to uplift at a high rate (~3 cm/week). The uplift continued until the end of November 2021. Here we use SAR images acquired from four different orbits (two ascending and two descending) by the Sentinel-1 satellites to study the ground deformation during this unrest period. Only data from the first half of the unrest period could be used (until the end of September). Later, heavy snow resulted in the loss of interferometric coherence within the caldera, preventing retrieval of the deformation signal. The maximum ground displacement of ~10 cm (from the end of July to the end of September) was found at the center of the Askja caldera, near the western shore of Öskjuvatn Lake. Interestingly, the interferograms show an asymmetric deformation pattern that follows the ring faults in the northwestern part of Askja caldera. Analytical models suggest that a roughly 7 x 3 km² NW-SE elongated sill inflated at a shallow depth of ~2 km below the Askja caldera. However, simple sill models cannot explain the asymmetrical deformation pattern observed in the InSAR data. Therefore, using boundary element modeling, we find that while the magmatic intrusion accounts for the broad uplift, possible ring-fault activity would localize the deformation close to the caldera rim. Furthermore, an elongated sill, like the one obtained from the first source estimation, would probably activate only a part of the ring-fault system, leading to an asymmetric deformation pattern.

How to cite: Nobile, A., Vasyura-Bathke, H., Viltres, R., Trippanera, D., Gunnar Ófeigsson, B., Ruch, J., and Jónsson, S.: Likely ring-fault activation at Askja caldera (Iceland) during the 2021 unrest, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9059, https://doi.org/10.5194/egusphere-egu22-9059, 2022.

At the beginning of August 2021, inflation was detected at Askja volcano, on a continuous GNSS station located to the west of Öskjuvatn and on interferograms generated using data from four separate Sentinel-1 tracks. Ground deformation measurements at Askja commenced in 1966 with levelling observations and since this time additional ground monitoring techniques have been employed, including GNSS and Satellite interferometry (InSAR) to detect long-term changes. Ground levelling measurements undertaken between 1966-1972 revealed alternating periods of deflation and inflation. Measurements from 1983-2020 detailed persistent subsidence of the Askja caldera, initially at an inferred rate of 7 cm/yr, decaying in an exponential manner. Suggested explanations for the long-term subsidence include magma cooling and contraction, or withdrawal of magma – eventually facilitated by an extensive magma-rich plumbing system, with an open conduit between the uppermost and the deeper parts of the magmatic system. This presentation will focus on the recent period of uplift and provide an overview of the GNSS and InSAR observations to date and present the latest geodetic modelling results which describe the best-fit source for the observed deformation.

How to cite: Parks, M., Ófeigsson, B., Drouin, V., Sigmundsson, F., Hooper, A., Geirsson, H., Hreinsdóttir, S., Friðriksdóttir, H., Sturkell, E., Hjartadóttir, Á., Lanzi, C., Li, S., Barsotti, S., and Óladóttir, B.: Deformation observations and geodetic modelling during the recent unrest at Askja volcano, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9381, https://doi.org/10.5194/egusphere-egu22-9381, 2022.

Monitoring crustal movements is essential to volcanic hazard assessment in areas of active volcanism. These surface movements occur on a wide range of time scales and wavelengths. However, the origin of crustal movements is not always associated with volcanic activities, particularly in areas with rigorous human activities (i.e., ground water extraction). It is challenging yet critical to distinguish between the ongoing volcanic and anthropogenic activities. In this study, we focus on the East Eifel Volcanic Field, which consists of multiple active Quaternary volcanoes. We report areas of uplift and subsidence 2-3 km away from each other near the Laacher See volcanic crater (2-3 km distance), and investigate the mechanisms responsible for the reversed deformation in such close proximity.

PS-InSAR measurements by the BodenBewegungsdienst Deutschland (BBD) show notable ground displacements in this area for the period between 2014 and 2019. The deformation is clearly mapped by three different tracks of the Sentinel-1 satellite – two ascending and one descending, which confirms the robustness of the signal being detected by PS-InSAR. The main deformation is round in shape, and the rates peak up to 10 mm per year in line-of-sight (LOS) for the uplift area near the village Glees and reach down to -4 mm LOS for the subsidence zone in the vicinity of the village Wehr. To investigate the likely mechanism responsible for the ground displacements, we model the crustal movements with two spherical pressure point sources (i.e., the Mogi sources) simultaneously using a combined global and local optimization scheme. In the inversion, we search for the optimal combinations for a set of four parameters (latitude, longitude, depth and volume) for each Mogi source. The global optimization is achieved by Multi-Level Single-Linkage algorithm and we use the PRAXIS algorithm to find the local minimum. We include all three tracks of data, of which the different satellite viewing geometries help stabilize the inversion.

Our results show that the uplift trend in Glees can be explained by an additional volume of 13000 m³ per year at 530 m depth. The subsidence near Wehr can be best fitted by a decrease in volume of 1700 m³ per year at 340 m depth. The modelling results show a trade-off between depth and volume, however, the uncertainties are smaller for the subsidence source near Wehr. Residuals trending in SW-NE direction are observed at the Glees uplift area, and the relatively large parameter uncertainties for Glees uplift zone are likely due to sparse persistent scatters there. Given the shallow depth of the Mogi sources, we interpret the Glees uplift being predominantly associated with fluid refilling in the respective volume caused by former CO₂ extraction. The subsidence around Wehr is linked to ongoing industrial CO₂ extraction. Our study identifies anthropogenic factors that may cause ground deformation in an active volcanic region, and has implications for future volcanic hazard assessment.

How to cite: Frietsch, M., Bie, L., Ritter, J., Rietbrock, A., and Schmitt, B.: Current crustal movement in the East Eifel Volcanic Field – anthropogenic or volcanic?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9479, https://doi.org/10.5194/egusphere-egu22-9479, 2022.

Large silicic systems can produce devastating eruptions with emitted volumes greater than 100 km³ and worldwide impacts. Such eruptions suggest the presence of significant reservoirs of silicic magma at shallow depths. Understanding how these reservoirs form is crucial to understanding how they affect the surrounding rock. But the shape and the organization of magmatic storage are still debated, despite their crucial influence on the results of theoretical predictions. Based on physical considerations of silicic-magma properties and the continental-crust state of active systems; our hypothesis is that the rise of silicic magma is stopped by the Brittle Ductile Transition. As the relaxation time of the ductile part of the crust is very short compared to the lifetime of such systems, magma storage could be considered as a buoyant liquid stored beneath an elastic plate. We thus used a plate model to theoretically predict the stress above those large magma chambers. To test our hypothesis, we computed the general behaviours of large silicic systems and compared them to natural cases. We first calculated the stress field produced in the plate. Results show that stressed values can reach tens of MPa, which is enough to cause plate failure. Then, we compared reservoir dimensions and volumes predicted by our model when failure could occur with documented ones for past eruptions. We showed that the two are consistent with each other. In a broader perspective, we then showed that stresses produced in the plate by the magma chamber can produce circular faults above the storage zone. This result has direct implications for the understanding of caldera formation during large silicic eruptions.

How to cite: Morand, A., Tait, S., and Brandeis, G.: Contribution of the use of a plate model to calculate the stresses at large silicic systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-583, https://doi.org/10.5194/egusphere-egu22-583, 2022.

The location and volume change of pressurized magma chambers can be constrained by inverse modelling of the surface displacements they cause. Through a joint inversion of surface displacements and gravity changes the chamber mass change during the pressurization period can also be inferred. Such inversions often start with constraining the deformation source parameters using the deformation data alone (step 1). Using these parameters the gravity data are then corrected for the effect of mass redistribution in the host rocks and surface uplift/subsidence associated with the chamber expansion (step 2). Next, the corrected gravity changes together with the source location from the deformation inversion are used to infer the intrusion mass (step 3). Provided that the intrusion compressibility is known, the intrusion density can be estimated from the intrusion mass and source volume change from step 1 and step 3, respectively (step 4).

We show that the original gravity data (only corrected for ambient effects) are directly related to the deformation source parameters through the deformation-induced gravity changes and the free-air effect. Thus, both of these effects, which have been mostly considered as nuisance, in fact can be harvested to provide better constraints on the deformation source parameters and the mass changes. We propose a Bayesian framework for the joint inversion of deformation and gravity data by which all the deformation source parameters and chamber mass change are constrained simultaneously. This way, steps 1 to 3 of the previous approach are carried out at once. The advantages of the suggested approach are: (a) this way the gravity data help constrain deformation source parameters with smaller uncertainties, (b) it leads to a smaller uncertainty for the inferred mass change, (c) the optimal relative weights of various deformation and gravity datasets can be estimated as hyper-parameters within the Bayesian inference, thus, they are estimated directly and in an objective way, (c) the gravity and deformation stations need not be co-located, (d) errors associated with interpolation of vertical displacements at gravity benchmarks are avoided, (e) the uncertainty of vertical displacements is no longer propagated into the reduced gravity changes, and thus, mass changes are estimated more accurately.  

We apply this approach to the deformation and gravity data associated with the 1982-1999 inflation period at Long Valley caldera. The results agree with those from earlier efforts; however, show a clear improvement in the constrained source parameters and the intrusion mass. We discuss the implications and benefits of this approach depending on the relative quality of the deformation and gravity data.

How to cite: Nikkhoo, M. and Rivalta, E.: A new framework for simultaneous inversions of deformation and gravity data applied to the 1982-1999 inflation at the Long Valley caldera, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9620, https://doi.org/10.5194/egusphere-egu22-9620, 2022.

Igneous sheet-complexes transport magma through the crust, but most studies have focused on single segments of the magma-transport-system or have low resolution. In the Jameson Land Basin in East Greenland, reflection-seismic data and extensive outcrops give unparalleled constraints on mafic intrusions down to 15 km. This dataset shows how sill-complexes develop and how magma is transported from the mantle through sedimentary basins. The feeder zone of the sill-complex is a narrow zone below basin, where a magmatic underplate body impinges on thinned crust. Magma was transported through the crystalline crust through dykes. Seismic data and published geochemistry indicate magma was supplied from a magmatic underplate, without perceptible storage in crustal magma-chambers and crustal assimilation. As magma entered the sedimentary basin, it formed distributed, bowl-shaped sill-complexes throughout the basin. Large magma volumes in sills (4-20 times larger than the Skaergaard Intrusion), and few dykes highlight the importance of sills in crustal magma-transport. On scales smaller than 0.2 km, host-rock lithology, and particularly mudstone tensile strength-anisotropy, controls sill-architecture in the upper 10km of the basin, whereas sills are bowl-shaped below the brittle-ductile transition zone. On scales of kilometres and towards basin margins, tectonic stresses and lateral lithological changes dominate architecture of sills.

How to cite: Eide, C. H., Schofield, N., Howell, J., and Jerram, D.: Transport of mafic magma through the crust and  sedimentary basins: Jameson Land, East Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7207, https://doi.org/10.5194/egusphere-egu22-7207, 2022.

Understanding the processes that govern the inter-eruptive dynamics of volcanic calderas (e.g., Campi Flegrei, Yellowstone) is crucial to detect unrest and better forecast their activity. This is an important concern to monitoring agencies because calderas may represent major hazards to modern societies, both at local and global scale. One of the most intriguing caldera-related phenomena is the so-called breathing, i.e., continuous inflation-deflation cycles on the order of up to 10s of centimeters per year and with characteristic periodicities ranging from a few years to decades. In this study, we explore the breathing activity of Domuyo volcano (Argentina), a dacitic-rhyolitic caldera in the Southern Andes whose most recent eruption occurred >10,000 years ago (Lundgren et al., 2020); and the recent breathing phase leading to the moderate (volcano explosivity index 3) eruption in January 2020 at Taal volcano (Philippines). In particular, we integrate geodetic data (retrieved from the synthetic aperture radar -SAR- sensors onboard ALOS, ALOS-2, Radarsat-2, and Sentinel-1 satellites) with a recently discovered observable found to emerge on active volcanoes during unrest (Girona et al., 2021): low-temperature (~1 K over ambient temperature), large-scale (up to 10s of km²), long-term ( 6 months/1 year) thermal anomalies (retrieved from the moderate resolution imaging spectroradiometers -MODIS- onboard NASA’s Terra and Aqua satellites). Our analysis shows that geodetic and thermal unrest are significantly correlated, although the time series are phase shifted. To interpret these phase shifts and their implications, we develop a first-order, 1D numerical model based on mass, momentum, and energy conservation that couples the permeable flow of gases through the shallow crust, the viscoelastic deformation of the crust, the condensation of magmatic water vapor in the subsurface, and the diffusive transport of heat to the surface. Our preliminary results show that: (i) phase shifts between thermal and geodetic time series are controlled by detection limits, and by the coupling between magma reservoir processes and the transport of gas and heat through the crust; (ii) the pressure inside magma reservoirs can oscillate spontaneously during quiescent outgassing at the typical breathing timescales, thus suggesting that some geodetic and thermal unrest episodes are not necessarily associated to new magma inputs, but to the intrinsic dynamics of active magma reservoirs. This study has important implications for assessing volcanic hazards through improved eruption forecasting methods.

Girona, T., Realmuto, V. & Lundgren, P. Large-scale thermal unrest of volcanoes for years prior to eruption. Nat. Geosci. 14, 238–241 (2021). https://doi.org/10.1038/s41561-021-00705-4.

Lundgren, P., Girona, T., Bato, M.G. et al. The dynamics of large silicic systems from satellite remote sensing observations: the intriguing case of Domuyo volcano, Argentina. Sci Rep 10, 11642 (2020). https://doi.org/10.1038/s41598-020-67982-8.

How to cite: Girona, T., Lundgren, P., Bato, G., and Puleio, C.: Low-temperature thermal unrest and deformation at active volcanoes: The intriguing case of Domuyo and Taal calderas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6194, https://doi.org/10.5194/egusphere-egu22-6194, 2022.

In September 2017, volcanic unrest in the vicinity of Mount Agung, Bali, Indonesia, increased drastically as a dike intruded between Agung and Batur volcanoes. This intrusion was followed by 5 weeks of declining activity before the eventual explosive eruption from Agung’s summit starting on November 21, 2017. We use high-resolution satellite SAR imagery to detect pre-eruptive intra-crater uplift at Agung volcano. We show that deformation of the crater floor occurred together with the dike intrusion to the northwest of the volcano. We attribute the deformation to a hydrothermal system less than 300 m below the surface that was activated by the injection of magmatic gasses. This finding indicates that Agung’s shallow magmatic system was active from the start of the increased unrest. Additionally, we observe a pulse of intra-crater uplift within 3-0.5 days prior to the onset of the eruption. The second pulse of uplift was one of the only precursors to the eruption and was probably caused by interaction between the hydrothermal system and the ascending magma. The detection of localized deformation during a volcanic crisis has important implications for eruption and unrest forecasting at Mount Agung and similar volcanoes and argues for monitoring with high-resolution SAR, which is capable of achieving both outstanding spatial resolution and, if sufficient satellites are used, excellent temporal coverage.

How to cite: Bemelmans, M., Biggs, J., Wookey, J., Poland, M., Ebmeier, S., and Syahbana, D.: High-resolution InSAR reveals deformation inside the crater of Agung, Indonesia, prior to the 2017 eruption., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3883, https://doi.org/10.5194/egusphere-egu22-3883, 2022.

The present research is aimed at evaluating the wide surficial deformation associated with the destructive 1928 fissure eruption on Mt. Etna, Italy: with its high effusion rates and the low elevation of the main eruptive vents, this eruption caused the destruction of the Mascali town. The main aim of our work is to reconstruct the geometry, kinematics and origin of the system of faults and fissures formed during the 1928 event. Our study has been performed through a multidisciplinary approach consisting of field observations, aerial photo interpretation and Finite Element Method (FEM) modeling through COMSOL Multiphysics® (v5.6). Field data consist of 438 quantitative measurements: azimuth values, opening direction and aperture of dry/eruptive fissures, as well as attitude and offsets of faults. Our detailed structural analysis allowed us to detect four different tectonic settings related to dike propagation scenarios, which, from west to east, are: 1) a sequence of 8 eruptive vents surrounded by a 385-m wide graben, 2) a 2.5-km long single eruptive fissure, 3) a half-graben up to 74-m-wide and a symmetric 39-m-wide graben without evidence of eruption, 4) alignment of lower vents along the pre-existing Ripe della Naca faults. 

As a next step, several numerical models have been developed to investigate the relationship between diking and surficial deformation. We performed sensitivity analyses, by modifying crucial parameters, such as a range of dike overpressure values (1-20 MPa), host rock properties (Young modulus ranging from 1 to 30 GPa), stratigraphic sequence, and layer thickness. Furthermore, the distribution of tensile and shear stresses above the dike tip has been evaluated. Results revealed the presence of temporary stress barriers, which consist of soft (e.g. tuff) layers, that control the surficial deformation above a dike propagating to the surface by suppressing the distribution of shear stresses.

How to cite: Russo, E., Tibaldi, A., Bonali, F. L., Corti, N., Drymoni, K., De Beni, E., Branca, S., Neri, M., Cantarero, M., and Pasquarè Mariotto, F.: The destructive 1928 fissure eruption of Mt Etna (Italy): surficial deformation revealed by field data and FEM numerical modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11437, https://doi.org/10.5194/egusphere-egu22-11437, 2022.

Coastal and ocean island volcanoes are renowned for having unstable flanks, which expresses as slow seawards flank sliding observable by geodetic techniques and/or catastrophic sector collapses. A large section of these unstable flanks is often below sea level, where information on the volcanotectonic structure and, in particular, ground deformation are limited. Consequently, kinematic models that attempt to explain measured onshore ground deformation associated to flank instability are poorly constrained in the offshore area. This is also the case for Mount Etna’s unstable south-eastern flank that slides seawards at rates of 2-3 cm/yr. Displacements associated to flank movement, observed onshore by geodetic and remote sensing techniques, show maximum values at the coast and kinematic models consistently predict even larger movements seawards of the coast. Our seafloor geodetic measurements between 2016 and 2018 confirmed that offshore flank slip is equal or slightly larger compared to onshore slip. The main displacement was released during one slow slip event. Here, we present new data from a second deployment of the seafloor geodetic network in the same location with the same direct-path acoustic ranging technique and a modified network design. The measurements allow reconstructing relative seafloor displacement within the network at sub-centimetre precision, from September 2020 until November 2021. The preliminary results indicate a possible eastward sliding of the flank, although the overall slip of <1 cm is close to the limit of resolution. Flank slip is continuous over the observation period. With our seafloor geodetic network, we are able to record different styles of fault slip and deformation rates. Ongoing long-term monitoring will show how these styles of deformation interact, and which type of flank movement is dominant in the offshore sector.

How to cite: Urlaub, M., Petersen, F., Bonforte, A., Gross, F., and Kopp, H.: Flank instability at Mount Etna: new insights from seafloor deformation monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3623, https://doi.org/10.5194/egusphere-egu22-3623, 2022.

The monitoring and characterization of volcanic systems are performed through measurements of different nature; among these, the development of the remote sensing technologies has supported the analysis and interpretation of the ground deformation field, for which the Differential SAR Interferometry (DInSAR) technique provides a large amount of densely sampled measurements over space and time (Dzurisin, 2007). The modeling of these datasets leads to understand the changes of physical and geometrical parameters of deep and/or shallow volcanic reservoirs by using different strategies, such as the forward (Lu et al., 1998), the parametric (Battaglia et al., 2013) and tomographic (Camacho et al., 2020) inverse modeling. Unfortunately, these methods could bring to ambiguous interpretation of deformation measurements because of ambiguities of inherent, theoretical, algebraic, instrumental/experimental nature.

Here, we model the deformation field in volcanic framework through a different approach, which is mainly based on harmonic elastic fields satisfying the homogeneity laws; in particular, we use multi-scale procedures, such as the Multiridge (Fedi et al., 2009) and ScalFun (Fedi et al., 2007) methods, and boundary analysis technique, such as the Total Horizontal Derivative (THD) (Blakely, 1996), for unambiguous estimate of the geometrical parameters of the deformation sources, which are the depth, the horizontal position, the shape and the horizontal extent.

Starting from the harmonic solutions of the Navier’s equation, Castaldo et al. (2018) and Barone et al. (2019) have shown that multi-scale methods are valid tools to study simple field sources as the Mogi one, according to the homogeneity law and the Euler’s equation. To generalize this approach, we show the use of multi-scale methods to model sources with any geometry, also irregular. We test our methodology, which is an integration of multi-scale techniques, on Finite Element synthetic deformation field generated through Comsol Multiphysics software package; we consider both regular and irregular geometry cases by analysing different deformation component estimating the source geometry without any reference model.

Finally, we use the proposed approach to investigate the ground deformation pattern of the 2004 – 2010 uplift episode occurred at Yellowstone caldera resurgent domes area and the 2013 unrest event at Fernandina volcano (Galapagos Archipelago, Ecuador); in the first case, we use the vertical component and the integrated multi-scale approach to highlight the geometrical irregularities of the retrieved sill-like intrusion; in the second case, we analyse the E-W component retrieving a ≈ 1.5 km b.s.l. deep pipe-like source.

We conclude that our approach is crucial for retrieving an unconstrained geometrical model of the deformation source.

How to cite: Barone, A., Fedi, M., Pepe, A., Pepe, S., Solaro, G., Tizzani, P., and Castaldo, R.: Integrated Multi-scale approach for constraining source parameters responsible of deformation field in volcanic framework., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-607, https://doi.org/10.5194/egusphere-egu22-607, 2022.

Starting from July 2021, a gradual unrest of Vulcano volcano was recorded by monitoring system managed by INGV, marked by a progressive change of many parameters from the multi-disciplinary networks.

The fumaroles located on the crater rim and along the flank of the cone shown temperature increase ( up to 350 degree Celsius) and  an increase of the flux of carbon dioxide and sulfur dioxide in gas emissions. Furthermore, the increase of the occurrence of with very-long-period (VLP) events was recorded by seismic network, and a rapid uplift of about 1 cm/month was recorded at VCRA GNSS permanent station located on the North slope of the “La Fossa” cone.

In order to image the ground deformation accompanying the unrest phase, we analyzed the 2020-2021 ascending and descending ESA-Copernicus Sentinel-1A and 1B C-band SAR (Synthetic Aperture Radar) acquired in TopSAR (Terrain Observation with Progressive Scans SAR) Interferometric Wide mode with A-DINSAR techniques. On October 2021 a new GNSS survey was performed on the ”Lipari-Vulcano” network. We integrated the SAR data and the GNSS data applying the SISTEM method, and the preliminary results are consistent with the Vulcano hydrothermal system dynamics, with a deformation pattern limited to the cone area.

In order to monitoring continuously and more in detail the change in ground deformation, on December 2021 we installed 4 additional GNSS mobile stations and a permanent GB-RAR (ground-based real aperture radar) on the island. The GB-RAR system was installed at the Lipari Observatory, at a distance of about 5 km from Vulcano, and it is able to image the whole Vulcano north area, with a rectangular pixel resolution of 3x30 m and a precision of the displacement along the line of sight of about 1 mm.

At time of this abstract no ground deformation have been recorded in the last month, the microseismic activity reduced but the fumarole temperatures at the crater and gas emissions of carbon and sulphur dioxide remained at high level.

How to cite: Francesco, G., Bonforte, A., and Puglisi, G.: The 2021 unrest phase of Vulcano volcano (Aeolian islands) detected by SAR,GNSS and GB-RAR, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12183, https://doi.org/10.5194/egusphere-egu22-12183, 2022.

Useful minerals containing rare Earth elements (REE) and metals are sourced from magma bodies, but exactly how these elements initially leave the magma is not well known. Here we present textural and chemical analyses of mineral-filled fracture bands within the rhyolitic Sandfell laccolith exposed in eastern Iceland. The fracture fillings showcase dynamic and complex textures and imply multiple energy levels during precipitation. The dominant mineral phases are Fe- and Mg-oxides, Mn carbonate, and La/Ce oxide. The textures they present are comb, laminate, radial, and a rounded reworked clastic texture filling the tips. Microtomography images of hand-samples show the fractures are stretched-penny shaped, and contain 80 vol% fillings and 20 vol% void space. The connectivity of fractures within one band is limited to 1-3 neighbours, via small oblique fractures joining two main fractures together. µXRF measurements revealed distinct halos of 0.8 wt% Fe depletion surrounding each facture, and within the fracture-fill a strong enrichment in an unusual suite of elements including Fe, Mn, Cl, Zn, Cr, Y, Ce, and La. This assemblage is puzzling, as many of these elements are typically carried by fluids which have strong alteration effects on the surrounding rock, and there is a lack of this kind of alteration at Sandfell. Our working hypothesis is that the formation of the fractures provided a degassing pathway through the impermeable magma. However, the nature and the composition of the magmatic volatiles are as yet unknown. The minimal connectivity between fractures (at hand-sample scale) suggests fluid would have travelled through the length of one to three fractures until intersecting with another fracture band system, and minerals precipitated along the way. Given the ubiquitous occurrence of the fracture bands within the laccolith, this small-scale process compounds into large amounts of mass transfer overall. The fractures at Sandfell may be a snapshot of the initial process of removing incompatible elements from silicic magma.

How to cite: Witcher, T., Burchardt, S., Heap, M., Kushnir, A., Pluymakers, A., Schmiedel, T., Pitcairn, I., Mattsson, T., Kaskes, P., Claeys, P., Barker, S., and Lissenberg, J.: Enrichment of immobile elements in synmagmatic fractures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9161, https://doi.org/10.5194/egusphere-egu22-9161, 2022.

The crustal structure is one of the fundamental factors that affects the type, composition, and spatial distribution of monogenetic volcanoes. The formation of maars, the second-most common type of monogenetic volcanoes, is mainly influenced by crustal lithologies, depth of explosions, and water-magma interactions together with magma rheology and tectonic structures. The Acıgöl caldera, located in the extensional setting of the central Anatolian plateau, contains both felsic and mafic maars. This rare compositional juxtaposition makes it a suitable location to better understand the relationship between magma chemistry and maar architecture. It includes closely spaced yet compositionally different monogenetic complexes (i.e., maars with either lava dome or scoria cone) and provides a fabulous opportunity to elucidate the role of crustal processes in the eruptional dynamics of maars.

Here we present an integrative study with detailed morphological (drone mapping), depositional (componentry, ash morphology), and petrological (whole-rock, glass, and mineral geochemistry) characteristics of rhyolitic (whole-rock; ~76.7 wt.% SiO₂, glass; ~77.2 wt.% SiO₂) İnallı, Kalecitepe, Acıgöl, and Korudağ maars, and mugearitic (~52.7 wt.% SiO₂) İcik maar. Our observations show a wide range of morphological features with spectacular examples of nested and compound craters. Field observations, together with the detailed stratigraphical analysis and literature-based geochronological data, reveal that the formations of maars and the subsequent lava domes or scoria cones are spatially migrating events within the same magmatic episode. We hence relate this to the rejuvenation of conduits, along with the pre-existing structures of the Acıgöl caldera that are almost perpendicular to the local extensional direction (NE-SW).

Non-modal batch melting models reveal that all investigated maars have a similar parental magma source (i.e., the most primitive basalt in central Anatolia with the Mg# of 72.4). This is formed by partial melting of a metasomatized lithospheric mantle with contribution from an OIB-like asthenospheric melt. The uprising magma that also produced the entire Quaternary volcanics in central Anatolia was possibly trapped at different crustal depths beneath the Acıgöl caldera and formed the maars with various degrees of magmatic differentiation processes. We conclude that İcik maar emanated from a relatively deep (lower crustal?) mantle-derived magma source evolved by assimilation and fractional crystallization processes. In contrast, the felsic maars were presumably formed by the short-lived ponding of the same magma source at shallower depths, which was partially assimilated by the basement intrusive rocks and dominantly shaped by the feldspar-driven fractional crystallization. Finally, the well-exposed examples of felsic maars in the study area and their comparison with the mafic counterparts could be a good contribution to the ever-growing literature on maar volcanism.

How to cite: Uslular, G., Gençalioğlu-Kuşcu, G., Ruch, J., Lupi, M., Higgins, O., Bégué, F., and Caricchi, L.: Bimodal maar volcanism in a post-collisional extensional regime: A case study of Acıgöl (Nevşehir) volcanic field (central Anatolia, Turkey), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10225, https://doi.org/10.5194/egusphere-egu22-10225, 2022.

A common method of characterising dikes is to plot their measured maximum thickness (T) against their horizontal length (L). This method has been applied widely to fault systems to determine critical mechanical controls on intraplate fault evolution, in which the maximum displacement D_max  is related to L by Dmax=γLⁿ, where typically n=1. This power law D_max-L relationship (with scatter) is inferred to represent scaling under constant driving stress. For dikes and other opening mode fractures (e.g., joints, veins, and sills) T-L scaling is typically shown as n=0.5 (i.e. T=αL^0.5 ) albeit with significant scatter in aspect ratio at all data-rich length scales. In contrast to the frictional control for shear faults, this square root scaling is consistent with growth under conditions of constant rock properties, including material fracture toughness K_IC (i.e., the ability of a material containing a crack to resist fracture). Understanding scaling relationships therefore has significant implications for the mechanics of intrusions and other opening mode fractures.

                Thickness versus length (T-L) data for dikes (and veins, sills, etc., but here we focus on dikes) are universally interpreted using a linear elastic 2D pressurised crack model. The model assumes mechanical equilibrium, such that the stress intensity, K , at the tip of the dike is equal to the mode I fracture toughness of the country rock, K_IC . Measured thickness to length ratios are generally consistent with reasonable magma excess pressure estimates, in the range of 1–10 MPa, but the large areas over which that pressure operates in a constant pressure model results in extremely large stress intensity at the tip, which then requires excessively large fracture toughness to stabilise the crack: for most dike sets, K_IC=300-3000 MPa.m^0.5, which is about 100–1000 times that of measured K_IC values for rocks at upper crustal depths.

Here we propose that solidified intrusions variably preserve internal pressure gradients (required for magma flow), representing cracks controlled by kinetics; they are non-equilibrated structures and cannot be treated in continuum with toughness-controlled, uniform pressure (equilibrium) structures such as veins, or many types of scaled analogue model. Early stages of dike growth (inflation) result in increasing length and thickness, but magma pressure gradients within the dike may serve to drive late-stage lengthening at the expense of maximum thickness (relaxation). For cracks in 2D, we find that inflation is controlled by the magma injection rate, viscosity, and host rock stiffness. Pressure relaxation in the dike is controlled by magma viscosity and host rock stiffness, with the timescale of operation controlled by host rock thermal diffusivity (i.e., cooling toward eventual solidification). This combination of parameters imposes conditions that are unique to individual dikes and dike systems of variable volume, magma type, host rocks, and depth of emplacement, hence we suggest there is no unique scaling law for solidified intrusions. Host rock fracture toughness has no impact on kinetics-controlled dike growth in the upper crust, with the key controls being the host rock compliance relative to the magma flow, which will change during dike emplacement

How to cite: Gill, S., Walker, R., McCaffrey, K., and Greenfield, C.: Dike geometry and scaling controlled by kinetics rather than host rock toughness, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3732, https://doi.org/10.5194/egusphere-egu22-3732, 2022.

The physics describing fluid-filled fracture growth is simple to describe, but extremely challenging to implement in an analytical, and even in a numerical modelling scheme. The fracturing process is governed by the equations for a brittle-elastic medium, while the internal flow is described by fluid dynamics equations. The pressure profile within the fluid-filled crack, the crack shape, and the velocity of crack growth, results from the solution of the coupled elastic and fluid-dynamic problem, that is far from been trivial. Magmatic dykes can be seen as a sub-set of the larger family of fluid-filled fractures. So far, two main schools have been established for modelling magmatic dykes: they have been named “fracture dominated” and “viscous dominated”, according to the fracture propagation regime that they target. Fracture dominated models are used when the fluid viscosity contributes with a negligible forcing to the total budget of the problem. They can describe complex crack shapes, account for heterogeneous stress fields and crustal heterogeneity, and compute the direction of crack growth. However they give no information about the crack propagation velocity. On the other hand, the viscous dominated school, drastically simplifies the crack geometry and the crustal structures, but can account for the interaction between elastic and viscous forces, hence it can compute the crack propagation velocity along a prescribed trajectory.

A few years ago, we teamed up, coming from these two different modelling schools, with the aim of merging our approaches in a single modelling scheme. Here we present a new modelling scheme, which computes the dynamic shape of a moving fluid-filled crack, built with the BE technique, in plane strain approximation (2D). Our model account for heterogeneous crustal stress and complex fracture propagation paths, and compute the crack shape considering the fluid viscosity and the crack propagation velocity. The crack velocity can be given as input to our model, or computed as output in the assumption that the main sources of energy dissipation are the brittle fracturing and the laminar viscous flow. We compare our model results with previous numerical models from the fracture dominated and viscous dominated schools, and present the implications of our findings with regards to some of the most important parameters characterising a magmatic intrusion, such as its volume, buoyancy and viscosity of magma, and rock fracture toughness. Eventually we show an application of the model to the rising of the dyke that fed the 1998 Piton de la Fournaise eruption (La Réunion Island).

How to cite: Maccaferri, F., Furst, S., and Pinel, V.: Modelling the shape of a growing fluid-filled crack and computing its propagation velocity: application to magmatic dykes., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4214, https://doi.org/10.5194/egusphere-egu22-4214, 2022.

There are few analytical models of 3D dyke ascent due in part to the algebraic complexity of deriving such solutions but also due to a lack of numerical schemes that can be used to test the validity of their simplifying assumptions. Recent developments in hydro-fracture codes allow for numerical simulation of constant inflow/finite batches of fluid rising towards the ground surface (Zia and Lecampion, 2020). Such schemes allow us to formulate and test some analytical approximations of this process.

Recently, analytical formulations have reproduced in three dimensions the self-sustaining ascent of a batch of fluid, where a fracture ascends upwards once a given “critical" volume of fluid is injected (Davis et al., 2020; Salimzadeh et al., 2020; Smittarello et al., 2021). The critical volume is dependent on: the rock stiffness, the density contrast between the fluid and rock and the rock toughness. Such formulations have been verified numerically, showing that relatively small batches of fluid are required before these begin to ascend towards the ground surface. In particular, these estimated critical volumes are below observed eruptive volumes and far below typical industrial fluid injection volumes. We investigate how accounting for fluid flow in the model can lead to better estimates of the critical volumes, ascent timescales and the fracture size.

We first detail an approximation of the ascent speed for a given volume of fluid, deriving an approximate maximum ascent speed of a fracture. We show this speed is linearly proportional to the injected volume and inversely proportional to the material stiffness and fluid viscosity. Secondly, we adapt the 2D similarity solution of Spence and Turcotte (1990), showing how to scale this in 3D. This solution describes how the ascent speed decelerates from its initial velocity. We note that in particular the decay in the front velocity is dependent on volume (V) and time (t) with the following scaling V^(1/2)/t^(2/3). Our resulting analytical solution matches well to decay speeds from 3D numerical experiments with a finite fluid batch. We discuss the implications this scaling has on the ascent speed of magmatic intrusions and the stability of industrial operations.

Lastly, we briefly discuss formulations describing how density, stress and stiffness interfaces can trap ascending fractures.

Davis, T., Rivalta, E. and Dahm, T., 2020. Critical fluid injection volumes for uncontrolled fracture ascent. Geophysical Research Letters, 47(14), p.e2020GL087774.

Salimzadeh, S., Zimmerman, R.W. and Khalili, N., 2020. Gravity Hydraulic Fracturing: A Method to Create Self‐Driven Fractures. Geophysical Research Letters, 47(20), p.e2020GL087563.

Smittarello, D., Pinel, V., Maccaferri, F., Furst, S., Rivalta, E. and Cayol, V., 2021. Characterizing the physical properties of gelatin, a classic analog for the brittle elastic crust, insight from numerical modeling. Tectonophysics, 812, p.228901.

Spence, D.A. and Turcotte, D.L., 1990. Buoyancy‐driven magma fracture: A mechanism for ascent through the lithosphere and the emplacement of diamonds. Journal of Geophysical Research: Solid Earth, 95(B4), pp.5133-5139.

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

How to cite: Davis, T. and Rivalta, E.: An analytical model for the ascent speed of a viscous fluid batch in three dimensions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1431, https://doi.org/10.5194/egusphere-egu22-1431, 2022.

We study the thermal erosion and mechanical fragmentation of dyke host rocks using a thermodynamical and fluid-mechanical approach. It is inferred that the latent heat of magma mainly causes the thermal damage of dyke host rocks and encourages thermal erosion. The application of fluid-dynamical shear stress on the dyke walls induced by turbulence magma flow results in mechanical fragmentation., We calculated the Reynolds number to confirm these findings to decipher the nature of magma flow through the dykes. The estimated Reynolds number for 30 dykes is in excess of 2000 suggesting that magma ascends turbulently through the dykes. The turbulence of magma flow provides additional energy to derive thermal erosion and mechanical fragmentation.  In order to better understand the thermo-mechanical effect of dyke host rocks, we used the mass conservation principle. Equations for mass conservations are derived to better explain the complex interactions between magma and host rock. Heat transfer, magma flow rate, magma flow velocity, and host rock melting are calculated. The presence of xenoliths in the dykes is primary evidence that the dykes have been mechanically fragmented. We present an integrodifferential equation to understand the kinematic of mechanical fragmentation and size of xenoliths varies due to secondary Collison within a dyke. Presented results are useful to understand the nature of magma, dyke host rock melting, and magma evolution.

Key words: Thermal erosion, mechanical fragmentation, turbulent magma flow, dykes

How to cite: Patel, R., Sarma, D. S., and Panda, A.: Thermo-mechanical effects of dyke host rocks in response to turbulent magma flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9033, https://doi.org/10.5194/egusphere-egu22-9033, 2022.

After January 1977 and January 2002, the third historically known flank eruption of Nyiragongo volcano and the first ever to be recorded by dense measurements both on the ground and from space started on the 22^nd of May 2021, although no alarming precursory unrest had been reported. Nyiragongo lava flows threatened about 1 million of inhabitants living in the cities of Goma (Democratic Republic of Congo) and Giseny (Rwanda).

In the following days, seismic and geodetic data as well as fracture mapping revealed the gradual southward propagation of a shallow dike from the Nyiragongo edifice underlying below Goma airport on May 23-24, then Goma and Gisenyi city centers on May 25-26 and finally below the northern part of Lake Kivu on May 27. Southward migration of the associated seismic swarm slowed down between May 27 and June 02. Micro seismicity became more diffuse, progressively activating transverse tectonic structures previously identified in the whole Lake Kivu basin.

Here we exploit ground based and remote sensing data as well as inversion and physics-based models to fully characterize the dike size, the dynamics of dike propagation and its arrest against a structural lineament known as the Nyabihu Fault. This work highlights the shallow origin of the dike, the segmented dike propagation controlled by the interaction with pre-existing fracture networks and the incremental crater collapse associated with drainage which led to the disappearance of the world’s largest long-living lava lake on top of Nyiragongo.

How to cite: Smittarello, D., Barrière, J., d'Oreye, N., Smets, B., Oth, A., Michellier, C., Shreve, T., Grandin, R., Cayol, V., Wauthier, C., Derauw, D., Geirsson, H., Theys, N., Brenot, H., Froger, J.-L., Muhindo, A., and Kervyn, F.: Structural failure and shallow dike intrusion at Nyiragongo volcano (D.R Congo), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2704, https://doi.org/10.5194/egusphere-egu22-2704, 2022.

The Piton de la Fournaise volcano is located on the southeastern part of La Réunion Island and is inserted in the tectonic framework of the Indian Ocean. It is one of the most active worldwide volcanoes and it can be classified as a hot-spot basaltic one.

In this work, we focus on the eruption occurred from 11 to 15 August 2019 on the southern-southeastern flank of this volcano, inside the Enclos Fouqué caldera. In particular, this distal event was characterized by the opening of two eruptive fissures and accompanied by shallow volcano-tectonic earthquakes.

Firstly, we investigate the surface deformations induced by the occurred eruptive activity, by exploiting Differential Synthetic Aperture Radar Interferometry (DInSAR) measurements; they are obtained by processing the data collected by the Sentinel-1 satellite of the Copernicus European Program along ascending and descending orbits. Due to the position of the island in the southern hemisphere, the processed S1 interferograms are characterized by a 12-days temporal baseline; for this reason, they measure the ground deformations generated during both the pre- and co-eruptive phases. Then, we analyze the distribution of the relocated hypocenters to recognize the activated structures and to furnish further constraints to our model. Finally, we perform an analytical modelling to the computed coseismic DInSAR displacements, with the aim of investigating the volcanic source/s responsible for the measured surface deformation field.

The retrieved results reveal that several volcanic sources (one sill and four dikes, in particular) have been active during the pre- and the co-eruptive phases, allowing the magma transport towards the surface; their action can justify the complexity of the observed deformation pattern. Our findings are in good agreement with the seismicity recorded by the Observatoire Volcanologique du Piton de la Fournaise network and with several geophysical evidences, such as the comparison between the volume of the retrieved sources and the erupted magma volumes, and the fissures location.

How to cite: Valerio, E., De Luca, C., Manzo, M., Lanari, R., and Battaglia, M.: Geodetic modelling of a multi-source deformation pattern retrieved through Sentinel-1 DInSAR measurements: the 11-15 August 2019 Piton de la Fournaise (La Réunion Island) eruption case-study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11497, https://doi.org/10.5194/egusphere-egu22-11497, 2022.

50 km East of Mayotte Island (North Mozambique Channel; Comoros Archipelago), a submarine volcanic edifice formed during the first year of a seismo-volcanic crisis, between May 2018 and May 2019. Thanks to the French ANR Project COYOTES and the SISMAORE oceanographic cruise (2021), a multichannel seismic profile gives the first in-depth image of the new East-Mayotte volcano and its surrounding volcanic area. The seismic interpretation reveals that several distinct magmatic phases affected the area. The new volcano is built on a ~150 m thick sedimentary layer. Beneath this sedimentary layer, we found a major volcanic layer, ~2.5 km thick, which extends ~91 km to the south and ~33 km to the north of the newly formed submarine volcano. This volcanic unit is composed of multiple seismic facies that may indicate distinct successive volcanic phases. We interpret this major volcanic layer as part of the Mayotte volcanic edifice, with the presence of a complex magmatic feeder system underneath. We observe a ~2.2-2.5 km thick sedimentary cover between the main volcanic layer, below the new volcano, and the top of the crust. We tentatively identified the top-Oligocene seismic horizon (~23 Ma) well above the main volcanic layer, and assuming a constant sedimentation rate we estimate the onset of the volcanism at Mayotte Island at 28 Ma.

How to cite: Masquelet, C., Leroy, S., Delescluse, M., Chamot-Rooke, N., Thinon, I., Lemoine, A., Franke, D., Watremez, L., Werner, P., and Sauter, D. and the SISMAORE team: Structure of a new submarine volcano and magmatic phases to the East of Mayotte, in the Comoros Archipelago, Indian Ocean., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10766, https://doi.org/10.5194/egusphere-egu22-10766, 2022.

Dyke propagation is the most common way of magma transfer towards the surface. Their emplacement generates stresses at their tips and the surrounded host rock initiating surficial deformation, seismic activity, and graben formation. Although active deformation and seismicity are studied in monitored volcanoes, the difference between dyke-induced and tectonic-controlled grabens is still less understood.

Here, we explore the difference between dyke-induced vs tectonic-controlled graben formation in stratovolcanoes with heterogeneous crustal properties like Mt. Etna (Italy) and Santorini (Greece). The field observations are related to Mt. Etna's 1928 AD fissure eruption, which partly generated dyke-induced grabens along its expression, and to the Santorini volcano, where tectonic-controlled grabens become pathways for later dyke injections. Field campaigns have revealed the stratigraphic sequence of the shallow host rock successions that became the basis of several suites of numerical models. The latter investigated the boundary conditions (overpressure or external stress field) and the geometrical and mechanical parameters that i) could produce temporary stress barriers and hence stall the propagation of a dyke towards the surface, and ii) shall form a graben at the surface. The detailed analysis, results and interpretations propose that soft materials in the stratigraphy, such as pyroclastic rocks, suppress the stresses at the vicinity of a propagating dyke and do not promote the generation of a graben above a propagating dyke. Also, the study explores the conditions where inclined ascending dykes produce semi-grabens and the generation of wide or narrow graben structures. Finally, the results give valuable insights on the field-related parameters that can encourage dyke deflection in pre-existing grabens in the shallow crust. All the latter can be theoretically applied in similar case studies worldwide.

How to cite: Drymoni, K., Russo, E., Tibaldi, A., Bonali, F. L., and Corti, N.: Dyke-induced vs tectonic-controlled graben formation in a heterogeneous crust: Insights from field observations and numerical models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10486, https://doi.org/10.5194/egusphere-egu22-10486, 2022.

When magma ascends through the shallow parts of terrestrial planetary crust, it deforms the surrounding host rocks. The deformation patterns observed at the surface offer indirect means to characterize the position, geometry and volume of subsurface magmatic intrusions. To enable real-time eruption forecasting during volcano unrest, most volcano geodetic models assume that magma intrusion induces linearly elastic deformation of homogeneous shallow planetary crust. Other indirect geophysical volcano monitoring data (e.g., seismology, gravimetry) however offer only limited opportunity for validating geodetic model results. Moreover, recent geological observations at exhumed volcano plumbing systems and geophysical observations of recent intrusion events have shown that plastic behaviour can dominate in heavily fractured and heterogeneous volcanic edifices and tectonically active areas. The question remains how large the effect of unaccounted plastic deformation could be on estimated intrusion characteristics.

Scaled laboratory experiments can be an innovative tool to assess by how much modelled magma intrusion characteristics – volume, geometry, position – deviate from reality in circumstances where plastic deformation processes are important. We used a tensile rectangular dislocation in a homogeneous, linearly elastic half-space to invert the three components of near-surface displacements extracted from X-ray Computed Tomography imagery of laboratory experiments of analogue dyke injection in cohesive mixtures of quartz sand and gypsum powder. The model results favored by the inversions are then compared to the three-dimensional characteristics of the analogue magma intrusions observed in the X-ray CT imagery. To further investigate the effect of more complex model geometry, we also used a tensile distributed-opening dislocation geometry. Preliminary results show that inversion results can be improved by fixing values of parameters that control the position of the modelled dislocation, but significant discrepancies remain between the modelled and observed intrusion geometry, orientation and volume. This test study helps gaining insight on the limitations of commonly used volcano geodetic modelling and inversion methods, and provides a novel basis for interpreting geological, geodetic and geophysical data related to volcanic deformation. The experimental results pave the way for developing complex forward models of magma-induced deformation in the heterogeneous shallow crust of terrestrial planets.

How to cite: Poppe, S., Wauthier, C., and Fontijn, K.: Elastic vs. plastic: Inversion of analogue magma-induced surface displacements in granular materials in laboratory experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4902, https://doi.org/10.5194/egusphere-egu22-4902, 2022.

Dikes play a significant role in transporting magma from the Earth's depth to the surface. Likewise, dikes constitute a network of intrusions connected to storage bodies that form the volcanic plumbing system promoting magma transport beneath and inside active volcanic centers, channeling its ascent during volcanic eruptions.

Characterizing the dike properties is critical for determining whether a dike will reach the surface and estimating the time it needs to do so. Increasing our understanding of diking could contribute to assessing the volcanic hazard.

We implement laboratory models by means of viscous-oil injections in solidified gelatin to study the dynamic properties of magmatic dikes propagating in the upper crust. We prepare gelatin at 1.5 wt.% gel and 15 wt.% salt to produce a host medium with lower resistance to fracturing and higher density that facilitates the propagation of viscous fluids. Salty gelatin is carefully prepared following a protocol that ensures the elastic properties remain consistent over all our experiments. We inject oils 1000 and 10000 times more viscous than water from the bottom of the gelatin tank. Injection volumes range from 10 to 50 ml. Such experimental setting ensures a correct scaling of magma buoyancy and viscosity to study dike dynamics. A camera facing the models follows the vertical trajectory of the dike. The second camera positioned above the models records the opening and width of the crack just before the eruption.

From camera data recorded for a large set of experiments, we constrain the propagation velocity for different dike volumes. We implemented these experiments to study fluid-filled crack velocity and velocity variations as a function of fluid volume, buoyancy, viscosity, and gelatin fracture toughness. We simulate the laboratory experiments using a numerical model for dike propagation to address fundamental questions about the total energy budget involved in the fluid-filled fracture propagation process. Here we present preliminary results concerning the energy budget, in particular, comparing the energy needed to extend the brittle fracture with respect to the energy dissipated by the viscous fluid motion and better characterizing the propagation regime of the experiments versus magmatic dikes.

We foresee the application of these models to caldera settings, focusing on Campi Flegrei, Italy.

How to cite: Gaete, A., Maccaferri, F., Rivalta, E., and Pino, N. A.: Energy budget during magma ascent: using viscous fluid-filled crack in laboratory models to investigate magmatic dike intrusions in natural settings, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5634, https://doi.org/10.5194/egusphere-egu22-5634, 2022.

Lava dome collapse hazards are intimately linked with their morphology and internal structure. We present new lava dome emplacement models that use calibrated rock strengths and allow material behaviour to be simulated for three distinct units: (1) a ductile, fluid core; (2) a solid upper carapace; and (3) disaggregated talus slopes. We first show that relative proportions of solid and disaggregated rock depend on rock strength, and that disaggregated talus piles can act as an unstable substrate and cause collapse, even in domes with a high rock strength. We then simulate sequential dome emplacement, demonstrating that renewed growth can destabilise otherwise stable pre-existing domes. This destabilisation is exacerbated if the pre-existing dome has been weakened following emplacement, e.g., through processes of hydrothermal alteration. Finally, we simulate dome growth within a crater and show how weakening of crater walls can engender sector collapse. A better understanding of dome growth and collapse is an important component of hazard mitigation at dome-forming volcanoes worldwide.

How to cite: Harnett, C. and Heap, M.: Exploring lava dome mechanics & structure: how does stability change as a function of rock strength?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-691, https://doi.org/10.5194/egusphere-egu22-691, 2022.

The absence of precursory signals of recent eruptions at Mt. Ruapehu poses a problem for hazard assessment and risk mitigation at the popular Tongariro National Park. Ruapehu hosts an active hydrothermal system with volcanic unrest being driven by either migration of magma, hydrothermal fluids, or a combination of both. In our study, we develop a suite of 2D axisymmetric numerical models to study the detectability limit of precursory subsurface processes at Ruapehu to inform recommendations for monitoring protocols. In our models magmatic unrest (MU) results from pressurisation of a transcrustal elliptical mush zone due to the intrusion of juvenile magma which triggers a poroelastic response in the hydrothermal system. Hydrothermal unrest (HTU) is simulated by the injection of hot multicomponent and multiphase fluids (H₂O and CO₂) into Ruapehu’s hydrothermal system (HTS), where thermo-poroelastic responses are triggered. We simultaneously solve for ground displacement, self-potential (SP) anomalies and residual gravity changes resulting from the subsurface perturbations, with model parameterization adapted to Ruapehu. All models account for topography and subsurface mechanical and hydro-electric heterogeneities.

For a plausible reference parameter set, we find that geophysical observables are markedly distinct in their magnitude and wavelength in both magmatic and hydrothermal unrest scenarios. Most geophysical anomalies show their largest magnitudes directly above the hydrothermal system, with signals falling off rapidly with distance. At Ruapehu’s summit plateau (500 m from the HTS) vertical displacement amplitudes for MU simulations are 1.5 times smaller than maximum magnitudes of 1.2 cm for HTU simulations, with the latter being above conventical detection limits (1 cm in the vertical). Maximum residual gravity changes on the plateau are -4 μGal for HTU simulations and hence below detection levels of standard field observations, while for MU simulations with a source density change of 10 kg/m³ resulting signal magnitude is twice as high. Modelled SP anomalies are predicted to exceed conventional detection levels of 0.1 mV with typical SP signals for HTU simulations attaining maximal amplitudes of 1.3 mV, which are ~3 times larger than those resulting from MU simulations.

Parameter exploration shows that residual gravity changes for MU simulations are predominantly controlled by reservoir density changes, while SP polarity and magnitude strongly depends on the hydro-electric coupling coefficient for both unrest scenarios. Moreover, we find that the Biot-Willis coefficient (degree of poroelastic response) has the greatest influence on displacement amplitudes for HTU simulations, with negligible effect on displacement, SP and gravity changes resulting from MU simulations. Although gravity changes and displacements for reservoir strengths (volume/overpressure) > 7 km³/MPa are greater as for reference simulations, vertical displacement remains below detection levels. Magnitudes of all signals from HTU simulations correlate with fluid fluxes. Our interpretation of the findings is that magmatic unrest at Ruapehu should be identifiable by joint residual gravity and SP time series, whereas ground displacements >1 cm in the vertical and SP anomalies should be indicative of hydrothermal unrest.

How to cite: Arens, F., Gottsmann, J., Coco, A., Hickey, J., and Kilgour, G.: Numerical modelling of unrest signals at Mt. Ruapehu (New Zealand), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5637, https://doi.org/10.5194/egusphere-egu22-5637, 2022.

Recent studies have shown that large tectonic earthquakes are capable of triggering volcanic eruptions (i.e. increasing the number of eruptions within a defined time period) up to hundreds of kilometres away. However, the prevalence of eruption triggering is less clear, with findings ranging from little evidence for triggered eruptions, to a fourfold increase in the number of eruptions following nearby large earthquakes. Some of this variability is likely due to differences in definitions of what constitutes a triggered volcanic eruption, including a lack of consensus on the maximum distance and time lag between an earthquake and a triggered volcanic eruption, the minimum magnitude of earthquake considered, and how aftershocks are incorporated into the analysis. A further source of variability arises from the different datasets used, including regional versus global studies, and the inclusion of incomplete earthquake and eruption records from before the modern instrumental era. To help address these issues, we provide a comprehensive statistical study of how large earthquakes affect volcanic eruption rates, using complete and unbiased global datasets spanning 1960-2021. We take a systematic approach to investigating how parameters such as the maximum distance and time lag between earthquake-eruption pairs, the minimum earthquake magnitude considered, and the declustering of aftershocks affects the results. We also investigate how previously unstudied earthquake parameters such as source depth and mechanism affect the prevalence of eruption triggering. Our results are placed in statistical context through the use of Monte Carlo simulations using randomised earthquake and eruption catalogues. Preliminary results indicate that, contrary to a previous focus on large subduction megathrust earthquakes, deep normal faulting earthquakes have the greatest eruption triggering tendency. However, when compared with randomised earthquake and eruption catalogues, the overall statistical significance of observed eruption triggering is fairly low.

How to cite: Jenkins, A., Rust, A., and Biggs, J.: A global statistical study on the triggering of volcanic eruptions by large tectonic earthquakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8020, https://doi.org/10.5194/egusphere-egu22-8020, 2022.

Late Proterozoic to Early Palaeozoic metavolcano-sedimentary successions are important components of the Variscan massifs of Europe. Felsic and mafic metavolcanic rocks with Cambro-Ordovician protolith ages also occurs in the Staré Město Belt (SMB) in the Central Sudetes (Czech Republic, Poland) (e.g. Kröner et al. 2000). The SMB is the NNW-trending fold-and-thrust belt that forms the eastern margin of the Saxothuringian Zone of the Bohemian Massif. To constrain timing and geodynamic setting of the volcanism recorded in that part of the Saxothuringia, the whole rock geochemistry, zircon trace element geochemistry and U-Pb zircon geochronology of metabasalts, metagabbros and acid metavolcanites of the SMB were carried out.

Field and petrographic studies show that bimodal association in the SMB is mainly expressed by alternating layers of fine-grained amphibolites composed of Amp, Pl and Px and fine- and medium-grained acid metavolcanites composed of Qz, Pl, Kfs, Grt, Bt and Ms. Such close relationships between felsic and mafic meta-volcanic rocks suggest their common origin. Whole-rock geochemistry data suggest, however, a diversity both in the chemical composition and tectonic environments of formation of their igneous protoliths. Magmatic precursors of the amphibolites were tholeiitic and calc-alkaline basalts, andesitic basalts and andesites that were derived either from MORB, BABB, volcanic arc or within-plate magmas. The acid metavolcanites originated from rhyolites and dacites belonging to tholeiite, calc and calc-alkaline series. Geotectonic diagrams suggest that the felsic magmas were formed most likely in island arc or continental arc environments.

New LA-ICPMS zircon dating of two metadetrital rocks of the SMB revealed the predominance of Neoproterozoic-Cambrian and Palaeoproterozoic age clusters, characteristic for rocks of the Saxothuringian Zone. Zircon dating of four samples of acid metavolcanites, two samples of metabasalts and one sample of metagabbro confirmed that their igneous protoliths crystalized at the same time, at ca. 495-500 Ma. Trace elements in zircons were analyzed in all metavolcanic samples. Range of values of Nb/Yb = 0.001-0.1, U/Yb = 0.1-10 and Y = 25-6993 ppm are observed in both types of rocks and together indicate a contribution of continental crust in the SMB volcanites. Their values plotted on geotectonic classification diagrams of Grimes et al. (2015) suggest a continental arc setting for the whole Late Cambrian bimodal volcanism in the easternmost part of the Saxothuringian Zone.

The research was financed from the grant of the National Science Center, Poland No. 2018/29/B/ST10/01120.

References:

Grimes, C.B., Wooden, J.L., Cheadle, M.J., John, B.E., 2015.  “Fingerprinting” tectono-magmatic provenance using trace elements in igneous zircon. Contrib Mineral Petrol 170, 46.

Kröner, A., Štipská, P., Schulmann, K., Jaeckel, P., 2000. Chronological constraints on the pre-Variscan evolution of the northeastern margin of the Bohemian Massif, Czech Republic. In: Franke, W., Haak, V., Oncken, O., Tanner, D. (Eds.), Orogenic Processes: Quantification and Modelling in the Variscan Belt. Geological Society, London, Special Publications 179, pp. 175–197.

How to cite: Śliwiński, M., Jastrzębski, M., Machowiak, K., and Sláma, J.: Age and geotectonic setting of metavolcanic rocks in the eastern Saxothuringian margin: whole rock geochemistry, zircon trace element geochemistry and U-Pb geochronology of the Staré Město Belt (Czech Republic, Poland), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8363, https://doi.org/10.5194/egusphere-egu22-8363, 2022.

In Variscan Europe, bimodal magmatism related to Early Palaeozoic thermal event in the northern part of Gondwana has been widely documented in rock successions extending from Spain to Poland (e.g. Franke et al. 2017). The Kaczawa Complex, the SW Poland, contains Early Palaeozoic felsic, intermediate to basic volcanic rocks, and Cambrian to Early Carboniferous sediments all involved in complex processes of the Variscan collision(s). This contribution provides new LA-ICPMS UP zircon data that specify the age and provenance of some important rocks occupying the lower part of the stratigraphic column of the Kaczawa Complex: 1) Osełka metarhyodacytes, 2) Lubrza metatrachytes, 3) Radzimowice slates and 4) Gackowa metasandstones.

The U-Pb dating of zircons coming from the Osełka metarhyodacites yields a crystallization age of 500±5 Ma, while the zircon dating of the Lubrza metatrachytes yields the Concordia age of 495±3 Ma. These data confirm the early Palaeozoic age of the volcanism of the Kaczawa Complex (e.g. Muszyński, 1994; Kryza et al. 2007), but they strongly suggest a single event of the bimodal volcanic activity. An inherited age component of c. 630 Ma is present in the Lubrza metatrachytes. The zircon dating of the accompanied metasedimentary rocks i.e. two samples of Radzimowice slates and one sample of the Gackowa metasandstones yields comparable detrital age spectra. The maximum depositional ages of these rocks are ca. 535 Ma. The Radzimowice and Gackowa metasedimentary rocks show the predominance of Neoproterozoic age zircons clustering around 580-605 Ma, 630-640 Ma and 730-770 Ma, which indicates that the sedimentary basins were mainly supplied by erosion of crystalline rocks of Ediacaran up to Tonian age. Paleoproterozoic and Archean components (1.7 Ga, 2.0-2.1 Ga and 2.9-3.0 Ga) are less common.

All these data show that rocks from the lower part of the lithostratigraphic column of the Kaczawa Complex represent the Late Cambrian metavolcano-sedimentary successions. The detrital zircon age spectra indicate that the source areas for the Kaczawa Complex metapelites may have been in the West Africa Craton of Gondwana.

The research was financed from the grant of the National Science Center, Poland No. 2018/29/B/ST10/01120.

References:

Franke, W., Cocks, L. R. M., Torsvik, T. H. 2017. The Palaeozoic Variscan oceans revisited. Gondwana Research 48, 257–284.

Kryza R., J.A. Zalasiewicz, S. Mazur, P. Aleksandrowski, S. Sergeev, S. Presnyakov, 2007. Early Palaeozoic initial-rift volcanism in the Central European Variscides (the Kaczawa Mountains, Sudetes, SW Poland): evidence from SIMS dating of zircons. Journal of the Geological Society, London 164, 207-1215

Muszyński A., 1994. Kwaśne skały metawukanogeniczne w środkowej części Gór Kaczawskich: studium petrologiczne. Wyd. Nauk. UAM., seria geologia, Nr 15: 144 pp

How to cite: Jastrzębski, M., Machowiak, K., Śliwiński, M., and Sláma, J.: New age constraints for Early Palaeozoic volcanism and sedimentation of the Kaczawa Complex, the Sudetes (SW Poland), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8478, https://doi.org/10.5194/egusphere-egu22-8478, 2022.

The Campi Flegrei caldera (Italy) is one of the most dangerous volcanoes in Europe and is currently in a new phase (started in 2000 and still ongoing) of the unrest that has persisted intermittently for several decades (main crises occurred in 1950-52, 70-72 and 82-84). The current activity has prompted the Italian Civil Protection to move the Campi Flegrei volcano from the first (“base” or “green”) to the second (“warning” or “yellow”) level of alert since the end of 2012.

The geophysical and geochemical changes accompanying the unrest stimulated a number of scientific investigations that resulted in a remarkable production of articles over the last decade. However, large uncertainties still persist on the architecture of the caldera plumbing system as well as on the nature of the subsurface processes driving the current (and previous) unrest.

LOVE-CF is a 4-years project started in October 2020 and funded by INGV (Istituto Nazionale di Geofisica e Vulcanologia), with the aim of improving our ability to forecast the behaviour of the Campi Flegrei caldera, through a multi-disciplinary approach based on a combination of volcanological, petrological, geochemical, seismological and geodetic observations, as well as experiments and numerical models. 

We present the project objectives and methods, and show obtained preliminary results. Particularly our investigation includes: 

• a) the integration of structural, volcanological and petrological data from representative past eruptions with results of decompression experiments and numerical models of conduit dynamics and dyke propagation;
• b) innovative geochemical (new redox gas species and CH₄isotopes), minero- petrological (alteration products) and seismic (fumarolic tremor) measurements at the crucial “Solfatara-Pisciarelli” hydrothermal site as well as geochemical characterization of submarine emissions in the area of “Secca delle Fumose” in the Gulf of Pozzuoli which has been poorly-explored so far;
• c) novel multi-dimensional statistical analysis of seismic, geochemical and geophysical records collected (both on land and offshore) in the last decades and in the recent period of unrest, constrained by geological observations and advanced numerical modelling;
• d) comprehensive analysis of surface deformations from historical data (since 35 BC) to modern techniques (both in-situ and remote sensing), and related modelling to disclose the active plumbing system and the relationship among the different sources of deformation throughout the decades and centuries.

How to cite: Pappalardo, L., Caliro, S., Tramelli, A., and Trasatti, E. and the LOVE-CF team: Linking surface Observables to sub-Volcanic plumbing-system:a multidisciplinary approach for Eruption forecasting at Campi Flegrei caldera (Italy)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6487, https://doi.org/10.5194/egusphere-egu22-6487, 2022.

Faulting triggered by magma migration at depth is a not-rare phenomenon in volcanic areas, where they can be found at very different scales. By analogue and numerical models, it has been shown that these types of faults can display a complex structure that often comprises an array of fault segments with both normal and reverse senses of movement. In this work, we analyzed in detail, and for the first time using field data, a fault array associated with the collapse induced by underground magma migration. The fault array crops out in cross-section within a recent volcanic succession in the Campi Flegrei caldera (southern Italy). Analyses focused on defining the spatial and temporal relationships between the normal and reverse fault segments of the fault array to provide insights into the process of collapse development. Based on geometric and displacement data, we propose that normal and reverse faults likely acted simultaneously to accommodate the collapse after a rapid phase of fault propagation.

How to cite: Diamanti, R., Camanni, G., Natale, J., and Vitale, S.: Faulting induced by underground magma migration: new insights from detailed field analysis (Campi Flegrei, Italy), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7614, https://doi.org/10.5194/egusphere-egu22-7614, 2022.

We present a new stratigraphy, inferred from several drillings carried out in the framework of the ICDP Campi Flegrei Deep Drilling Project , for the largest volcanic eruption in Europe since at least the Late Pleistocene. The eruption produced the Campanian Ignimbrite of southern Italy. It is conventionally believed to have triggered collapse of the large Campi Flegrei caldera, which, in turn, has been identified as a source for future ignimbrite volcanism. New borehole and radioisotopic data challenge this interpretation. They indicate that the Campanian Ignimbrite was erupted through fissures in the Campanian Plain, north of Campi Flegrei, and was not responsible for caldera collapse. The results are consistent with ignimbrite volcanism being controlled by a common magmatic system beneath the Campanian Plain. Understanding the dynamics of the whole plain is thus essential for evaluating the likelihood of similar future events.

How to cite: De Natale, G., Kilburn, C. R. J., Rolandi, G., Troise, C., Somma, R., Fedele, A., Di Vincenzo, G., Rolandi, R., and Woo, J.: New data on Campanian Ignimbrite of southern Italy: changing paradigm for Campi Flegrei caldera and the Campanian volcanism, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12860, https://doi.org/10.5194/egusphere-egu22-12860, 2022.