GMPV9.1

The receiver function analysis (RF) is a commonly used and well-established method to investigate crustal and mantle structures, removing the source, ray-path and instrument signatures. RF gives the unique signature of sharp seismic discontinuities and information about P and S wave velocities beneath a seismic station. In particular, using the direct P wave as a reference arrival time, and the relative arrival time of P-to-S (Ps) conversions and multiple reflections allow constraining the principal crustal structures and studying the effects of dipping interfaces and crustal layering.

We have applied RF analysis to the active volcanic islands of Tenerife and La Palma (Canary Islands). In recent years, both islands have increased their seismic activity and showed variation in geochemical parameters attributed to a magmatic-hydrothermal activity. Previous studies evidenced in La Palma and Tenerife a seismic Moho depth at 14 km and 12 and 15 km, respectively, but it is not clear because there are some others discontinuities under the stations (Lodge et al., 2012). Other RF studies indicated a depth of seismic Moho discontinuity between 16 and 30 km beneath the eastern islands to 11-15 km under the western isles, observing a thinning of the crust towards the west (Martinez-Arévalo et al., 2013). 

We processed 313 teleseisms recorded by 17 stations for Tenerife and 252 teleseisms recorded by six stations for La Palma. Since the receiver functions display a significant complexity, as expected in oceanic volcanic islands, we applied a transdimensional inversion approach to image the 1D velocity structure beneath each station. We observe at least three discontinuities related with the oceanic crust and the overlying volcanic rocks layer. We compare the retrieved crustal structure with the seismicity recorded in recent years, showing how earthquakes have a radically different origin on these two islands. While in Tenerife they seem to be related to the dynamics of a shallow hydrothermal system, in La Palma they are related to magmatic intrusions in the upper mantle beneath the island.

References

Lodge, A., Nippress, S. E. J., Rietbrock, A., García-Yeguas, A., & Ibáñez, J. M. (2012). Evidence for magmatic underplating and partial melt beneath the Canary Islands derived using teleseismic receiver functions. Physics of the Earth and Planetary Interiors, 212, 44-54.

Martinez-Arevalo, C., de Lis Mancilla, F., Helffrich, G., & Garcia, A. (2013). Seismic evidence of a regional sublithospheric low velocity layer beneath the Canary Islands. Tectonophysics, 608, 586-599.

How to cite: Ortega, V., D'Auria, L., Cabrera-Pérez, I., Barrancos, J., Padilla, G. D., and Pérez, N. M.: Crustal structure of La Palma and Tenerife (Canary Islands) from receiver function analysis., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11140, https://doi.org/10.5194/egusphere-egu21-11140, 2021.

The Klyuchevskoy Volcanic Group (KVG) located in Kamchatka, Russia is one of the World’s most active clusters of subduction volcanoes. In order to investigate its structure and very intense seismovolcanic activity, an international collaboration designed the KISS experiment operating a dense temporary seismic network between August 2015 and July 2016. During this period, the main volcano of KVG – Kyuchevskoy entered into eruption in the spring 2016. The preparation and eruptive periods have been characterized by a large number of volcanic earthquakes and tremors.

We applied in this study three cross-correlations network-based methods to detect and locate seismovolcanic tremor sources. From these three methods we extract simple 1D functions: spectral width (averaging in the 0.5-5 Hz frequency band the width of the network covariance matrix eigenvalue distribution), network response function (performing the 3D back-projection of the inter-station cross-correlations) and correlation coefficient function (averaging correlation coefficient functions computed at single station that characterize the stability in time of the single-station intercomponent cross‐correlation function). The simultaneous application of these network features allowed us to classify the wavefield recorded by the dense seismic network. We then computed inter-station cross-correlations extracted from the first eigenvector filtered covariance matrix and generate time series of 3D spatial likelihood functions. Using output of our classification approach, we stack over time these 3D spatial likelihood functions for time windows containing tremor and we finally obtain a 3D Density Likelihood function imaging the seismovolcanic tremor sources distribution within KVG.

The addition of the temporary seismic stations from the KISS network greatly increased our detection and location resolution and thus allowed us to refine our knowledge about seismovolcanic tremor at KVG. Our results highlight a large distribution of tremor sources connecting different volcanoes and different depth levels. Most of tremor sources are located below the Klyuchevskoy volcano in a narrow zone vertically extended from the surface to the crust-mantle boundary and exhibit a highly intermittent behavior characterized by burst of activities and rapid upward and downward migrations between deep and shallow locations. Several tremor sources are also located along a SW-NE structure extending from Tolbachik to Klyuchevskoy volcanoes. We thus image the near-vertical quasi-open main conduit connecting the deep magmatic reservoir to Klyuchevskoy volcano in which very rapid pressure transfers might occur as well as a possible secondary conduit that links the marginal part of the deep reservoir to the Tolbachik volcanic system in which the system overpressure may be sometimes evacuated.

How to cite: Journeau, C., Shapiro, N., Seydoux, L., Soubestre, J., Koulakov, I., Jakovlev, A., Abkadyrov, I., Gordeev, E., Chebrov, D., Sens-Schönfelder, C., Luehr, B., Tong, F., Farge, G., and Jaupart, C.: Imaging seismovolcanic tremor sources distribution with seismic network-based methods reveals fluid pressure pathways within Klyuchevskoy Volcanic Group magmatic system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7871, https://doi.org/10.5194/egusphere-egu21-7871, 2021.

We analyze data from one tiltmeter and twelve broadband seismic stations recorded at the beginning of the 2018 Kilauea eruption, to provide an integrated view of distinct tremor sources that preceded and accompanied this eruption. Studying the beginning of the eruption is challenging because of the diversity and complexity of signals that were recorded during this phase. But such undertaking represents a key aspect for understanding the dynamics of the different processes that took place at the start of the lava lake withdrawal on May 2 and during the twelve major collapses that occurred in Halema‘uma‘u Crater through May 26. The application of a network-based method to automatically detect and locate seismic tremor, combined with physical modeling of the underlying source processes, enables a characterization of these tremor sources in unprecedented detail.

Our analyses document one tremor source active during the period preceding the eruption, which is attributed to the quasi-steady radiation from a shallow hydrothermal system located at the south-southwest edge of Halema‘uma‘u Crater. These analyses further document two newly described sequences of gliding tremor. The first sequence is attributed to progressive jerky intrusions of a rock piston into a shallow hydrothermal reservoir between May 7 and May 17. The second sequence is attributed to the gradual degassing of a bubbly magma within an east striking dike below Halema‘uma‘u Crater, impacted by repeated roof collapses, and resulting in a quasi to totally degassed magma by May 26.

How to cite: Soubestre, J., Chouet, B., and Dawson, P.: Characterizing volcanic tremor sources associated with collapses in Halema‘uma‘u Crater at the beginning of the 2018 Kilauea eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10723, https://doi.org/10.5194/egusphere-egu21-10723, 2021.

We investigate the geometry of the metamorphic basement of the Santorini volcanic island using ambient noise data to determine the pre-Alpine/pre-volcanic bedrock structure. The geometry of pre-volcanic Santorini is important in order to constrain the recent volcanic history of the island and also to study the site-effect of the volcanic formations on seismic motions. Santorini is the most active volcano of the Southern Aegean Volcanic Arc and is the southernmost island of the Cyclades islands metamorphic complex. As a result, the volcanic material that has accumulated during the last 600+ Kyrs has been superimposed on the pre-volcanic Santorini (Cycladic) island. To map the thickness of volcanic material, we have performed a large number (>200) of single-station noise measurements in the Santorini area.  Measurements were mainly performed using conventional acquisition systems (Guralp-40T 30sec seismometer and Reftek-130A digitizer). We also employed additional single-station noise data from several previous studies (Dimitriadis et al. 2006, PROTEUS Project 2015), as well as permanent stations from the Hellenic Seismological Network in the same region. HVSR curves were calculated using single-station noise data and were used to estimate the fundamental frequency, f₀, as well as the corresponding maximum HVSR amplitude, A₀^HVSR. The majority of HVSR curves showed prominent peaks (A₀^HVSR locally larger than 7-8), indicating a clear impedance contrast between volcanics and metamorphic formations. To map the bedrock depth, we estimated the thickness of the upper volcanic formations using the quarter-wavelength approximation for each site. For this assessment, the average shear-wave velocity (Vs) of the volcanic formations was estimated from the inversion of several passive ambient noise array data, as well as additional constraints from selected MASW measurements. Where possible, the reliability of the spatial variation of volcanic formation thickness was checked with independent geological information. Using the digital elevation model and the volcanic formation thickness for each site of the single-station noise data, we estimated the spatial distribution of the pre-Alpine, metamorphic bedrock depth. The resulting geometry of the pre-volcanic Santorini island shows very deep basins (now filled with volcanic formations) around the pre-Alpine bedrock outcrop in the southern part of Santorini (Profitis Ilias), increasing to 100+ meters in the Kamari-Perissa basin area (southeastern Santorini) and to more than 400+ in the central (Fira-Imerovigli) and the north Santorini areas (Oia), in agreement with recent larger-scale tomographic results (Heath et al., 2019). The results are also in very good agreement with the pre-Alpine bedrock geometry independently inferred from gravity data inversion (Tzanis et al., 2019.)

This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning» in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432), implemented by the State Scholarships Foundation (ΙΚΥ), the Hellenic Foundation for Research and Innovation (HFRI) under the “First Call for HFRI Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (Project Number: 2924) and the Institute for the Study and Monitoring Of the SAntorini Volcano (ISMOSAV).

How to cite: Chatzis, N., Papazachos, C., Theodulidis, N., Hatzidimitriou, P., Anthymidis, M., Vougioukalakis, G., Panagiotopoulos, D., Hooft, E., Heath, B., Toomey, D., Paulatto, M., Morgan, J., and Warner, M.: Investigation of the bedrock (metamorphic basement) geometry of Santorini island using single-station ambient noise data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7968, https://doi.org/10.5194/egusphere-egu21-7968, 2021.

The island of Gran Canaria is located in the Canarian Archipelago, with an area of 1560 km² and a maximum altitude of 1956 m.a.s.l., being the third island of the archipelago in terms of extension and altitude. The island has two very well differentiated geological domains: the southwest domain or Paleo-Canarias, which is the geologically oldest part, and the northeast domain or Neo-Canarias, where are located the vents of the most recent Holocene eruptions. This volcanic island hosted Holocene eruptions. Therefore, apart from being affected by volcanic risk, it potentially hosts geothermal resources that could be exploited to increase the percentage of renewable energy in the Canary Islands.

The main objective of this work is to use Ambient Noise Tomography (ANT) for retrieving a high-resolution seismic velocity model of the first few kilometres of the crust, to improve local earthquake location and detect anomalies potentially related to active geothermal reservoirs. Currently, the 1-D velocity model of the island does not allow a correct determination of the hypocenters, being unable to take into account the substantial horizontal velocity contrasts correctly.

To realize the ANT, we deployed 28 temporary broadband seismic stations in two phases. Each campaign lasted at least one month. We also exploited data recorded by the permanent seismic network Red Sísmica Canaria (C7) operated by INVOLCAN. After applying standard data processing to retrieve Green’s functions from ambient noise cross-correlations, we retrieved the dispersion curves using the FTAN (Frequency Time ANalysis) technique. The inversion of dispersion curves to obtain group velocity maps was realized using a novel non-linear multiscale tomographic approach (MAnGOSTA, Multiscale Ambient NOiSe TomogrAphy). The forward modelling of surface waves traveltimes was implemented using a shortest-path algorithm that allows the topography to be taken into account. The MANgOSTA method consists of successive non-linear inversion steps on progressively finer grids. This technique allows retrieving 2-D group velocity models in the presence of substantial velocity contrasts with up to 100% of the relative variation. Then, we performed a depth inversion of the Rayleigh wave dispersion curves using a transdimensional Bayesian formulation. The final result is a 3-D model of P- and S-wave velocities of the island. The preliminary results show the presence of a low-velocity zone in the eastern part of the island that coincides spatially with anomalies observed in previous geophysical and geochemical studies and which could be related to actual or fossil geothermal reservoirs. Furthermore, the model shows the presence of high-velocity anomalies that are associated with the mafic core of the island.

How to cite: Cabrera Pérez, I., Soubestre, J., D'Auria, L., Cervigón-Tomico, G., Martínez van Dorth, D., Barrancos, J., Padilla, G. D., and Pérez, N. M.: Ambient noise tomography of Gran Canaria island (Canary Islands), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10957, https://doi.org/10.5194/egusphere-egu21-10957, 2021.

In May 2018, a seismic crisis started in the Comoros archipelago, East of Mayotte, which was widely felt on the Island. The related discovery of a new, 800-m high, submarine edifice 50 km East of Mayotte showed that the seismicity was caused by the birth of a volcano. The eruption is still on going at the time of writing and has sparked a large interest in the scientific community.

The seismicity is still active and is being continuously monitored thanks to several seismic stations installed on the island of Mayotte. The oceanographic campaigns that were carried out since the beginning of the crisis deployed a number of ocean bottom seismometers directly above the seismicity, to accurately understand the crisis and particularly its location. A new technique of automatic detection based on Machine Learning enabled to considerably increase the number of earthquakes that can be used to constrain the extent of the seismicity. Furthermore, the development of a new velocity model for the region allowed a precise location of these earthquakes.

These new developments permitted to reconstruct the seismicity evolution during two years of this seismic crisis and to complete the seismicity map associated with the new seismic activity. These results provide more details on the active structures to study the evolution in time as well as their precise spacial variations, allowing the analysis of the daily-to-yearly timescales of this unprecedented eruption. This is crucial to understand the dynamics of the volcanic and magmatic processes beneath Mayotte island. Linking these spatial and time variations with the real-time data, as well as the deformation and petrology evolutions, will provide crucial details on the dynamics of submarine eruptions.

How to cite: Lavayssière, A. and Retailleau, L.: Short- and long-term evolution of the seismicity associated with the New Volcanic Edifice offshore Mayotte island, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2769, https://doi.org/10.5194/egusphere-egu21-2769, 2021.

The topic of my work is a seismic tomography which has as object the investigation of Southern Tyrrhenian. This tomography has been obtained by means of inversion of teleseismic data to investigate subduction zones in the Southern Tyrrhenian oceanic back-arc basin. The subducting lithosphere has been mostly consumed along the Tyrrhenian-Apennine system has been consumed with the exception of the Calabrian arc sector. This kind of inversion could provide a good resolution to depth of 500-600 km, whereas previous local tomographies of Southern Tyrrhenian show results to depth of 250-300 km. The adopted database consists of 1929 teleseisms  recorded in period 1990-2012 by 122 southern Italian seismic station directly connected to ISC (International Seismological Centre). The software FMTT was employed for the inversion of these arrival times. I have implemented a grid of 0-500 km in depth, 7°E-20°E in longitude and 35°-48° in latitude, with a grid spacing of 50 km in depth, 0.8 degrees in longitude and 0.4 degrees in latitude. I have made 10 horizontal sections of final model from 50 km of depth to 500 km of depth, with an interval of 50 km of depth from each other. I have made 8 vertical sections, 4 NS vertical sections at fixed longitude and 4 WE vertical sections at fixed latitude. Finally, I have made 3 transversal sections. Summarising, the horizontal sections show an evolution of the high velocity body that represents the Ionian slab. It is visible both at depth of 50 km and at depth of 100 km, beneath the Calabrian arc and extends to northern Sicily beneath the Aeolian arc with a maximum of 0.6-0.8 km/s. At depth of 250 km, the tomography evidences a sort of “transition” due to the absence of the Southern Tyrrhenian HVA and the occurrence of a low velocity region with maximum of -0.5 km/s scattered between the Aeolian Islands and Calabria. In the depth interval from 250 km to 400 km, there are two impressive high velocity areas in northern Sicily and along southern Campania with a value of 0.3 km/s, separated by a low velocity area (LVA) along the Calabrian arc and the Aeolian Islands in the range [0.4 ; 0.6] km/s. Extensions of HVAs and LVAs previously mentioned have been estimated by means of vertical and transversal sections. This evidence could be interpreted as the effect of a three-dimensional circulation of astenospheric flow provoked by slab roll-back. A new evidence from the tomography is the presence of a LVA in the [250 ; 400] km depth interval with an extension of 100-150 km that practically splits the Tyrrhenian slab into two parts, in Neapolitan region and in the southern Calabria-northern Sicily region. The presence of this “window slab” could be interpreted as a tear in which unperturbed mantle insert itself.

How to cite: Pucciarelli, G.: Seismic Tomography of Southern Tyrrhenian by means of teleseismic data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1752, https://doi.org/10.5194/egusphere-egu21-1752, 2021.

The highly productive high temperature geothermal fields in Iceland are located within active volcanic systems on the plate boundaries. When an earthquake swarm or an unusual surface uplift or subsidence occur, it is important to assess the hazards and whether the unrest is triggered or controlled by volcanic or anthropogenic processes, or a combination of both.

On January 22nd, 2020, a rapid, large-scale uplift (14 km x 12 km) started at the Svartsengi geothermal field on the plate boundary of the Reykjanes Peninsula, along with an intense earthquake swarm that began simultaneously about 3 km east of the centre of uplift. The centre of uplift was located about 1 km west of Mt. Thorbjörn, in the middle of the Svartsengi geothermal field, close to the reinjection wells. Over a period of 6 months, three such uplift cycles occurred, each lasting for several weeks and followed by periods of relatively rapid subsidence. The duration and timing of the uplift-subsidence cycles appears to follow a clear trend where the successive inflation episodes lasted longer but with lower inflation rate.

The centres of uplift and the deflation cycles are the same and remained stationary. The accompanied intense earthquake swarms migrated along the 40 km long oblique plate boundary of the Reykjanes Peninsula, demonstrating a major plate tectonic event. The maximum depth of earthquakes was close to 4.5 km directly above the centre of uplift but extending to 6-7 km in the surroundings where the maximum magnitudes reached M_W 4.8.

A few weeks after the onset of the unrest, nine additional seismic stations were deployed to densify the local seismic network in place. In addition, complimentary data from an existing 21 km long fibre optics cable were used to monitor high-frequency linear strain rates. Both measures led to a significant improvement in the earthquake detection and location which predominantly occurred in swarms. Likewise, InSAR data analysis of temporal uplift cycles was performed, repeated gravity measurements at permanent sites were performed, and resistivity was remeasured at chosen sites.  

Multiple different elementary models were developed and tested to explain the cyclic excitation of the uplift, subsidence, and seismicity. While the individual unrest episodes might be controlled by possible magma intrusions into the lower crust, our favoured model explains the spatio-temporal pattern of ground uplift by the rise and diffusion of pore pressure in a 4-5 km deep geothermal aquifer. To distinguish between different models, we use multi-disciplinary geophysical datasets, such as deformation, seismicity, and gravity.

How to cite: Flóvenz, Ó., Wang, R., Hersir, G. P., Ágústsson, K., Vassileva, M., Drouin, V., Heimann, S., Isken, M., Hainzl, S., Gudnason, E. Á., Ágústsdóttir, T., Magnússon, I., Horalec, J., Milkereit, C., Motagh, M., Walter, T., Rivalta, E., Jousset, P., and Dahm, T.: The possible role of magma and geothermal fluid in the episodic uplift cycles and intense seismicity beneath the Svartsengi high temperature geothermal field, Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7870, https://doi.org/10.5194/egusphere-egu21-7870, 2021.

Modern UAS (unmanned aircraft system), light weight sensor systems and new processing routines allow us to gather optical data of volcanoes at a high resolution. However, due to the typically poor colorization, our ability to investigate and interpret such data is limited. Further, the information stored in the red, green and blue channel (RGB) is correlated. This makes any analysis a 3 dimensional task. Principal Component Analysis (PCA) helps us to overcome these problems by decorrelating the original band information and generating a variance representation of the original data. Therefore PCA is a suitable tool to detect optical anomalies, as might be caused by volcanic degassing and associated processes.

Applied in a case study at La Fossa Cone (Vulcano Island - Italy), the PCA showed a high efficiency for the detection and pixel based extraction of areas subject to hydrothermal alteration and sulfur deposition. We observed a broad alteration zone surrounding the active fumarole field, but also heterogeneities within, indicating a segmentation. Systematic variations in color and density distribution of sulfur deposits have implications for structural controls on the degassing system.

Combining the efficiency of PCA with the high resolution of UAS derived data, this methodology has a high potential to be employed in the spatio-temporal monitoring of volcanic hydrothermal systems and processes at surface.

How to cite: Müller, D., Bredemeyer, S., Zorn, E., De Paolo, E., and Walter, T.: Detection and monitoring of hydrothermal alteration by Principal Component Analysis applied on UAS derived optical data, Vulcano Island - Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4291, https://doi.org/10.5194/egusphere-egu21-4291, 2021.

The ability to accurately and reliably obtain images of shallow subsurface anomalies within the Earth is important for hazard monitoring at many geologic structures, such as volcanic edifices. In recent years, the use of machine learning as a novel, data-driven approach to addressing complex inverse problems in the geosciences has gained increasing attention, particularly in the field of seismology. Here we present a physics-based, machine learning method to integrate disparate geophysical datasets for shallow subsurface imaging. We develop a methodology for imaging static density variations at a volcano with well-characterized topography by pairing synthetic cosmic-ray muon and gravity datasets. We use an artificial neural network (ANN) to interpret noisy synthetic datasets generated using theoretical knowledge of the forward kernels that relate these datasets to density. The deep learning model is trained with synthetic data from a suite of possible anomalous density structures and its accuracy is determined by comparing against the known forward calculation. 

In essence, we have converted a traditional inversion problem into a pattern recognition tool, where the ANN learns to predict discrete anomalous patterns within a target structure. Given a comprehensive suite of possible patterns and an appropriate amount of added noise to the synthetic data, the ANN can then interpolate the best-fit anomalous pattern given data it has never seen before, such as those obtained from field measurements. The power of this approach is its generality, and our methodology may be applied to a range of observables, such as seismic travel times and electrical conductivity. Our method relies on physics-based forward kernels that connect observations to physical parameters, such as density, temperature, composition, porosity, and saturation. The key benefit in using a physics-based approach as opposed to a data-driven one is the ability to get accurate predictions in cases where the amount of data may be too sparse or difficult to obtain to reliably train a neural network. We compare our approach to a traditional inversion, where appropriate, and highlight the (dis)advantages of the deep learning model.

How to cite: Cosburn, K. and Roy, M.: Using artificial neural networks with joint muon-gravity datasets for shallow subsurface density prediction at volcanoes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-717, https://doi.org/10.5194/egusphere-egu21-717, 2021.

Recent volcanic activity of La Palma island, the fifth in extension (706 km²) and the second in elevation (2,423 m a.s.l.) of the Canarian archipelago, has taken place exclusively in the last 123 ka at the southern part of the island, where Cumbre Vieja volcano, the most active basaltic volcano in the Canaries, has been constructed. A total of seven volcanic eruptions have been reported along the main north-south rift zone of Cumbre Vieja in the last 500 years. On October 7^th and 13rd, 2017, two remarkable seismic swarms interrupted a seismic silence of 46 years in Cumbre Vieja volcano with earthquakes located beneath Cumbre Vieja volcano at depths ranging between 14 and 28 km with a maximum magnitude of 2.7. Five more seismic swarms were registered in 2020.

³He/⁴He ratio has been monitored at Dos Aguas cold mineral spring in La Palma Island since 1991 to date as an important volcano monitoring tool able to provide early warning signal of future volcanic unrest episodes. Magmatic helium emission studies have demonstrated to be sensitive and excellent precursors of magmatic processes occurring at depth. The highest ³He/⁴He ratio reported to date from the Canarian archipelago has been measured at Dos Aguas: 10.24 R_A (being R_A the ratio in atmospheric helium) (Padrón et al., 2015). This value is higher than any value found either in the lavas or terrestrial fluid in the Canary Islands, and indicates an important mantle contribution.  According to the temporal evolution of the magmatic component of helium at Dos Aguas, we suggest the occurrence of aseismic magma rising episodes beneath La Palma within the upper mantle towards an ephemeral magma reservoir in the period 2007-2017. However, in the period 2017-2020, magma rising have produced seismic swarms that were accompanied also by the highest ³He/⁴He ratio measured at Dos Aguas (10.42 R_A); both geochemical and geophysical signals confirm an upward magma migration towards a subcrustal magma reservoir beneath La Palma island.

Padrón et al., (2015). Bull Volcanol 77:28. DOI 10.1007/s00445-015-0914-2

How to cite: Padrón, E., Pérez, N. M., Melián, G. V., Sumino, H., Alonso, M., Recio, G., Asensio-Ramos, M., Rodríguez, F., and D’Auria, L.: Temporal evolution of 3He/4He isotopic ratio at Dos Aguas cold mineral spring, La Palma, Canary Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14994, https://doi.org/10.5194/egusphere-egu21-14994, 2021.

Significant temporal variations in the chemical and isotopic composition of Taal fumarolic gas as well as in diffuse CO₂ emission from Taal Main Crater Lake (TMLC) have been observed across the ~12 years of geochemical monitoring (Arpa et al., 2013; Hernández et a., 2017), with significant high CO₂ degassing rates, typical of plume degassing volcanoes, measured in 2011 and 2017. In addition to these CO₂ surveys at the TCML, soil CO₂ efflux continuous monitoring was implemented at Taal volcano since 2016 and a clear increasing trend of the soil CO₂ efflux in 2017 was also observed. Increasing trends on the fumarolic CO₂/St, He/CO₂, CO/CO₂ and CO₂/CH₄ ratios were recorded during the period 2010-2011 whereas increasing SO₂/H₂S, H₂/CO₂ ratios were recorded during the period 2017-2018. A decreasing on the CO₂/CH₄ and CO₂/St ratios was observed for 2017-2018. These changes are attributed to an increased contribution of magmatic fluids to the hydrothermal system in both periods. Observed changes in H₂ and CO contents suggest increases in temperature and pressure in the upper parts of the hydrothermal system of Taal volcano. The ³He/⁴He ratios corrected (Rc/Ra), and δ¹³C of fumarolic gases also increased during the periods 2010-2011 and 2017-2018 before the eruption onset. During this study, diffuse CO₂ emission values measured at TMCL showed a wide range of values from >0.5 g m⁻² d⁻¹ up to 84,902 g m⁻² d⁻¹. The observed relatively high and anomalous diffuse CO₂ emission rate across the ~12 years reached values of 4,670 ± 159 t d^-1 on March 24, 2011, and 3,858 ± 584 t d^-1 on November 11, 2017. The average value of the soil CO₂ efflux data measured by the geochemical station showed oscillations around background values until 14 March, 2017. Since then at 22:00 hours, a sharp increase of soil CO₂ efflux from ~0.1 up to 1.1 kg m^-2 d^-1 was measured in 9 hours and continued to show a sustained increase in time up to 2.9 kg m^-2 d^-1 in 2 November, that represents the main long-term variation of the soil CO₂ emission time series. All the above variations might be produced by two episodes of magmatic intrusion which favored degassing of a gas-rich magma at depth. During the 2010-2011 the magmatic intrusion of volatile-rich magma might have occurred from the mid-crustal storage region at shallower depths producing important changes in pressure and temperature conditions, whereas a new injection of more degassed magma into the deepest zone of the hydrothermal system occurring in 2017-2018 might have favored the accumulation of gases in the subsurface, promoting conditions leading to a phreatic eruption. These geochemical observations are most simply explained by magma recharge to the system, and represent the earliest warning precursor signals to the January 2020 eruptive activity.

Arpa, M.C., et al., 2013. Bull. Volcanol. 75, 747. https://doi.org/10.1007/s00445-013-0747-9.

Hernández, P.A., et al.,  2017. Geol. Soc. Lond. Spec. Publ. 437:131–152. https://doi.org/10.1144/SP437.17.

How to cite: Hernández, P. A., Melian, G., Asensio-Ramos, M., Padron, E., Sumino, H., Perez, N. M., Padilla, G., Barrancos, J., Baldago, M. C., Rodriguez, F., Alonso, M., Amonte, C., Arcilla, C., and Lagmay, M.: Geochemical evidence of volcanic plumbing system processes from fumarolic gases and diffuse CO2 degassing of Taal volcano, Philippines, prior to the January 2020 eruption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15073, https://doi.org/10.5194/egusphere-egu21-15073, 2021.

The Cape Verde islands are located about 800 km west of Senegal, at 14°-17° latitude and 21°-25° longitude. The archipelago consists of a volcanic chain of 10 major islands and eight minor islands The only currently active volcano in the Cape Verde archipelago is Pico do Fogo, which is located on the island of Fogo. Rising to 2829 m a.s.l., it is the most active volcano of the Cabo Verde Island. We report the results of the geochemical monitoring of the fumarolic discharges at the Pico do Fogo volcano in Cape Verde from 2007 to 2016. During this period Pico do Fogo experienced a volcanic eruption (November 23, 2014) that lasted 77 days. Two fumaroles were sampled, a low (F1~100ºC) and a medium (F2~300ºC) temperature. The variations observed in the δ¹⁸O and δ²H in F1 and F2 suggest different fluid source contributions and/or fractionation processes. Although no significant changes were observed in the outlet fumarole temperatures, two clear increases were observed in the vapor fraction of fumarolic discharges during the periods 2008-2009 and 2013-2014. Also, two sharp peaks were observed in CO₂/CH₄ ratios at both fumaroles, in November 2008 and November 2013, coinciding with significant increases in the emission rate of diffuse CO₂ and He, and heat flow measured in the crater of Pico do Fogo volcano. This confirms that gases with a strong magmatic component rose towards the surface within the Pico do Fogo system during 2008 and 2013. Further, F2 showed two CO₂/St peaks, the first in late 2010 and the second after eruption onset, suggesting the occurrence of magmatic pulses into the volcanic system. Time series of He/CO₂, H₂/CO₂ and CO/CO₂ ratios are low in 2008-2009, and high in 2013-2014 period, supporting the hypothesis of fluid input from a deeper magmatic source. Regarding to the isotopic composition, increases in ³He/⁴He (R/R_A)_cor are observed in both fumaroles; F1 showed a peak in 2010 from a minima in 2009 during the first magmatic reactivation onset and another in late 2013, while F2 displayed a slower rise to its maximum in late 2013. The high ³He/⁴He ratios in both fumaroles are close to the magmatic end-member, indicating that He is predominantly of upper mantle origin. This work supports that monitoring of the chemical and isotopic composition of the fumaroles of the Pico do Fogo volcano is a very important tool to understand the processes that take place in the magmatic-hydrothermal system and to be able to predict future episodes of volcanic unrest and to mitigate volcanic risk.

How to cite: Melián, G. V., Hernández, P. A., Asensio-Ramos, M., Pérez, N. M., Padrón, E., Alonso, M., Padilla, G. D., Barrancos, J., Sortino, F., Sumino, H., Rodríguez, F., Amonte, C., Silva, S., Cardoso, N., and Pereira, J. M.: Insights from fumarole gas geochemistry on the recent volcanic unrest of Pico do Fogo, Cape Verde, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14763, https://doi.org/10.5194/egusphere-egu21-14763, 2021.

The Eastern Carpathians are characterized by intense gas emissions starting from the Neogene to Quaternary volcanic structures, especially the youngest dormant volcano, Ciomadul, but occurring also far away from these, in the Cretaceous flysch units. This is the most intensive degassing area from Romania. The gas emissions appear in different forms: dry gas, named mofettes and bubbling gas when they are accompanied by groundwater. The major components of these gas emissions are: CO₂, CH₄, N₂ and sometimes H₂S. Recent studies reveal a magmatic contribution up to 60% in these emissions (Vaselli et al., 2002, Kis et al., 2019). Gases are also present dissolved in groundwater and transported to the surface by CO₂-rich springs. Besides these visible emissions, the gases come to the surface as diffuse degassing from the soil. We started a systematic geochemical investigation of the gas emissions in the volcano-tectonic environment of the southern part of the Eastern Carpathians, together with a 5-year monitoring of the gas emissions. Our primary aims are to constrain the flux of CO₂, the origin of the different gas species, their interaction, and their relationship with the geodynamic background. Our findings could be integrated to the global carbon estimations, currently missing from the worldwide evaluations and could help the establishment of a long-term monitoring system of the gases in the area.

This work was supported by a grant of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN-III-P1-1.1-TE-2019-1908, within PNCDI III and the project GTC 32144 supported by Babes-Bolyai University, Romania.

How to cite: Kis, B.-M., Palcsu, L., Zsigmond, A.-R., Tamas, D. M., Szollosi, I., Szalay, R., and Harangi, S.: Geochemistry of gas emissions in the volcano-tectonic environment of the Eastern Carpathians, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13506, https://doi.org/10.5194/egusphere-egu21-13506, 2021.

Late Miocene to Pleistocene volcanism within the Vardar zone (N. Macedonia) covers a large area, has a wide range in composition and it is largely connected to the tectonic evolution of the South Balkan extensional system, the northern part of the Aegean extensional regime. A recent study indicated an increasing rate of mantle metasomatism towards the younger centers in the region [1]. During the last stage of activity, ultrapotassic (UK) centers that formed between ca. 3.2 and 1.5 Ma originated from the lithospheric mantle beneath the region [2]. Although there are no reported mantle xenoliths from these centers, the erupted mafic rocks contain abundant olivine as phenocrysts [3]. Noble gas isotopic characteristics of fluid inclusions in olivine can reveal important information about the origin of the fluid and the metasomatic state of the lithospheric mantle. We analyzed for the first time the noble gas composition of fluid inclusions of olivine phenocrysts from the Mlado Nagoričane volcanic center, the northernmost member of the UK centers with an eruption age of 1.8 ± 0.1 Ma [2]. The R/R_A ratios give a range of 3.1-4.5 with ⁴He/²⁰Ne values of 11.7-14.6. These R/R_A values are lower than the MORB and the averaged subcontinental lithospheric values, and considering the negligible amount of atmospheric contribution, imply a more metasomatized character for the underlying lithospheric mantle beneath the region. Mantle-derived noble gases were detected in a recent geochemical study on the thermal springs and gas exhalations in the region, with up to 20% of mantle contribution calculated based on their noble gas composition using the MORB R/R_A value [4]. These new Mlado Nagoričane fluid inclusion noble gas values indicate that the mantle contribution in the recent gas emissions in the region could be higher than what was thought.

This research was supported by the European Union and the State of Hungary, financed by the European Regional and Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’ project

[1] Molnár et al. 2020 – EGU2020-13101.

[2] Yanev et al., 2008 – Mineralogy and Petrology, 94(1-2), 45-60.

[3] Yanev et al., 2008 – Geochemistry, Mineralogy and Petrology, Sofia, 46, 35-67.

[4] Temovski et al. 2020 – EGU2020-2763.

How to cite: Molnár, K., Temovski, M., and Palcsu, L.: First noble gas results from fluid inclusions of the Late Miocene-Pleistocene Macedonian volcanics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9440, https://doi.org/10.5194/egusphere-egu21-9440, 2021.

Volcano monitoring is commonly performed through acquisition and interpretation of real-time signals able to track changes in the magmatic system and the eventual migration of magma toward the surface. Petrological monitoring, in particular,  focus on magma history in terms of depth of storage zones, transport pathways, mechanisms of differentiation, and timescales of involved processes with aim to extrapolate information about the trigger of magma ascent and the eruptive behaviour, and its possible variation over the course of an eruption.

In the present study, conducted in the framework of the EUROVOLC project, we developed a questionnaire that aims to survey the most common petrological monitoring procedures performed by volcano monitoring institutions, in order to identify prevailing techniques and most critical issues, and to rate the suitability of specific investigations in terms of costs versus benefit. The final goal is to identify essential and mandatory petrologic techniques to accomplish for an efficient petrological monitoring during ongoing eruptions, so that can be assessed the minimum logistic requirements (e.g., facilities, infrastructures, operators) and can be defined operative best practices protocols to achieve petrologic results in a timeframe short enough to be well of use for monitoring purposes.

The surveyed information, which resulted from a sample of eighteen interviewed institutions that deal with monitoring of active volcanoes with a variety of eruptive behaviour, provide insights about the whole steps of petrologic monitoring including sampling, sample preparations and analyses, data interpretation and dissemination. The survey reveals that efforts have been made to organize petrological monitoring with standardized procedures similarly to the other monitoring disciplines. For example, some institutions suffer lack of dedicated staff that can be operative with short forewarning. The objects of petrological investigation include all the types of volcanic products from lava to pyroclastic and there are attempts to deal with fixed sampling schedule. Moreover, there is consciousness that the capability to acquire and to interpret the most valuable analytical results at in situ institutions provide a quick image of ongoing eruptive processes and improve the interaction with other disciplines. Therefore, concerning the analytical procedures, which is the core of petrological monitoring, an important results is the cross correlation between the analyses that are easy to acquire (in terms of resources, equipment and time availability) and their effective role for the petrological monitoring.

The expectations include an augmented perception of the benefits that petrologic monitoring brings in the comprehension of eruptive processes. Filling the gap of the primary needs required to accomplish the identified best practices within a short timeframe is a compelling need to lead advancement of the volcano monitoring science.

How to cite: Re, G., Corsaro, R. A., D'Oriano, C., and Pompilio, M.: A review of petrological monitoring procedures: suggestion of best practice protocols for eruption monitoring, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5758, https://doi.org/10.5194/egusphere-egu21-5758, 2021.

One of the main volcano-structural and geomorphological feature in Tenerife (2,034 km²) is the triple rift system, formed by aligned of hundreds of monogenetic eruptive products of shield basaltic volcanism. At the intersection of this triple rift system rises the Teide-Pico Viejo volcanic complex. These volcanic rifts are considered as active volcanic edifices. The North East volcanic Rift Zone (NERZ, 210 km²) form a main NE-SW structure. The North West volcanic Rift Zone (NWRZ, 72 km²) is oriented in NW-SE direction and the North South volcanic Rift Zone (NSRZ, 325 km²) comprises a more scattered area on the south of these monogenetic cones. The most recent eruptive activity of Tenerife has taken place in these rift systems. NERZ host the fissural eruption of Arafo-Fasnia-Siete Fuentes (1704-1705). NWRZ host two historical eruptions: Arenas Negras in 1706 and Chinyero in 1909. Recently the eruption of Boca Cangrejo (1492) has been added to the historical register through ¹⁴C dating. NSRZ does not host historical volcanism, although it is recent, up to 10,000 years old.

In order to provide a multidisciplinary approach to monitor potential volcanic activity changes at the NERZ, NWRZ and NSRZ, diffuse CO₂ emission surveys have been undertaken since 2000, in general in a yearly basis, but with a higher frequency when seismic swarms have occurred in and around NWRZ volcano. Each study area for NERZ, NWRZ and NSRZ comprises hundreds of sampling sites homogenously distributed. Soil CO₂ efflux measurements at each sampling site were conducted at the surface environment by means of a portable non-dispersive infrared spectrophotometer (NDIR) LICOR Li820 following the accumulation chamber method. To quantify the CO₂ emission rate from the NERZ, NWRZ and NSRZ a sequential Gaussian simulation (sGs) was used as interpolation method.

The diffuse CO₂ emission rate for the NERZ ranged from 532 up to 2823 t d^-1 between 2001 and 2020, with the highest value measured in 2020. In the case of NWRZ, the diffuse CO₂ emission rate ranged from 52 up to 867 t d^-1 between 2000 and 2020, with the highest value measured in one of the surveys of 2005. Finally, and for NSRZ, the diffuse CO₂ emission rate ranged from 78 up to 819 t d^-1 between 2002 and 2020, with the highest value measured in 2019. The temporal evolution of diffuse CO₂ emission at the NERZ, NWRZ and NSRZ shows a nice and clear relationship with the volcanic seismicity in and around Tenerife Island, which started to take place from the end of 2016. The good temporal correlation between the volcanic seismicity and the increase trend observed in the time series of diffuse CO₂ emission rates at NERZ, NWRZ and NSRZ is also coincident with the observed increase of diffuse CO₂ emission rate at the summit crater of Teide. This work demonstrates the importance of performing soil CO₂ efflux surveys at active rift systems in volcanic oceanic islands as an effective geochemical monitoring tool.

How to cite: Rodríguez, F., Padrón, E., Melián, G., Asensio-Ramos, M., Alonso, M., Amonte, C., Martín, A., Hernández, P. A., Pérez, N. M., Barrancos, J., Padilla, G., and D'Auria, L.: Monitoring of diffuse CO2 degassing at NERZ, NWRZ and NSRZ volcanic systems of Tenerife, Canary Islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15427, https://doi.org/10.5194/egusphere-egu21-15427, 2021.

In seismic active areas, the primary composition of natural gas emissions can be modified upon migration to the surface and storage in crustal reservoirs as the result of secondary chemical processes at shallow levels that can change the pristine composition of the fluids creating misunderstanding in the evaluation of the contributions due to different sources. Noble gases are among the most powerful indicators of such natural processes.  In particular, Helium (hereafter He) is a reliable geochemical tracer for discriminating the crustal and mantle components in the outgassing gases due to the different origin of its two isotopes (³He has a primordial origin, whereas ⁴He is continuously produced by radioactive α-decay of ^235,238U and ²³²Th).  Therefore, the ³He/⁴He ratio is considered one of the most efficient geochemical tracers, whose variations can be directly ascribed to magmatic/crustal dynamics and therefore it is of primary importance in volcanic and seismic forecasting. In this study, we report chemical and isotopic (helium and carbon) data of gases and water emitted from three areas characterized by a high seismic hazard and located within the southern Apennines seismogenic belt. Through two fieldwork campaigns in 2019-2020, about 15 sites were inspected. Carbon dioxide is the main component in most of investigated sites (> 90 vol.%), except for Pozzo Tramutola, that is CH₄-dominated. He and N₂ concentrations are significantly variable (from 6 to 260 ppm and from 0.22 to 12.78 vol%, respectively). In agreement to previous investigations (Italiano et al., 2001; Caracausi and Paternoster, 2015), the sites in the Matese area are characterised by typical metamorphic [MOU1] N₂ values and low content of He and Ar and seem to be the result of mixing processes between crustal and/or metamorphic and atmospheric or ASW end-member. The sampled fluids have ³He/⁴He ratios from 0.02 to 2.92 Ra with corresponding He/Ne ratios in the range of 0.353-508.10. These ⁴He/²⁰Ne ratios are much higher than the same ratio in the atmosphere (He/Ne=0.318; Ozima-Podosek, 2002) supporting that atmospheric He component in the sampled fluids is negligible for most sites. In general, we recognized that ³He/⁴He ratios indicate mixing between radiogenic and mantle end-members and Mefite site has highest mantle values that are close to the ratio at Mt Vesuvio and Pleghreian volcanic systems (< 60 from the study area). The ⁴⁰Ar/³⁶Ar ratios show a small range from values close to atmosphere up to ⁴⁰Ar/³⁶Ar = 325. We also investigated the carbon species and their isotopes. To investigate the genetic origins of the methane we have used web-based machine learning tool that determines the origin of natural gases (Snodgrass-Milkov, 2020) and the results shown that methane is mainly thermogenic even if we also recognized an abiotic component in a few of sites. This study will provide data for the reconstruction of a basic model for interpreting the relationships between outgassing and tectonics, and further for interpreting possible seismic-induced variation

Ozima & Podosek. 2002. Noble Gas Geochemistry.

Tsunogai & Wakita. 1995. Science

Snodgrass and Milkov, 2020. Comput. Geosci

How to cite: Buttitta, D. and Paternoster, M.: Noble gases and carbon isotopes in natural gas samples from seismic active areas of southern Apennines (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15484, https://doi.org/10.5194/egusphere-egu21-15484, 2021.

Volcanoes are inherently unstable structures that spread and frequently experience mass wasting events (such as slope failure, rockfalls, and debris flows). Hydrothermal alteration, common to many volcanoes, is often invoked as a mechanism that contributes significantly to volcano instability. We present here a study that combines laboratory deformation experiments, geophysical data, and large-scale numerical modelling to better understand the influence of hydrothermal alteration on volcano stability. La Soufrière de Guadeloupe (France) is a hazardous andesitic volcano that hosts a large hydrothermal system and therefore represents an ideal natural laboratory for our study. Uniaxial and triaxial deformation experiments were performed on samples prepared from 17 variably-altered (alteration minerals include quartz, cristobalite, tridymite, hematite, pyrite, alunite, natro-alunite, gypsum, kaolinite, and talc) blocks collected from La Soufrière de Guadeloupe. Our uniaxial compressive strength experiments show that strength and Young’s modulus decrease as a function of increasing porosity and increasing alteration. Triaxial deformation experiments show that cohesion decreases as a function of increasing alteration, but that the angle of internal friction does not change systematically. We first combined recent muon tomography data with our laboratory data to create a 3D strength map of La Soufrière de Guadeloupe. The low-strength zone beneath the southern flank of the volcano exposed by our 3D strength map is coincident with the hydrothermal system. We then assigned laboratory-scale and upscaled mechanical properties (e.g., Young’s modulus, cohesion, and angle of internal friction) to zones identified by a recent electrical survey of the dome of La Soufrière de Guadeloupe. Numerical modelling (using the software LaMEM) was then performed on a cross-section of the volcano informed by the recent electrical data, and on a cross-section in which we artificially increased the size of the hydrothermally altered zone. Our modelling shows (1) the importance of using upscaled values in large-scale models and (2) that hydrothermal alteration significantly increases the surface velocity and strain rate of the volcanic slope. We therefore conclude, using models informed by experimental data, that hydrothermal alteration decreases volcano stability and thus expedites volcano spreading and increases the likelihood of mass wasting events and associated volcanic hazards. Hydrothermal alteration, and its evolution, should therefore be monitored at active volcanoes worldwide.

How to cite: Heap, M., Baumann, T., Rosas-Carbajal, M., Komorowski, J.-C., Gilg, H. A., Villeneuve, M., Moretti, R., Baud, P., Carbillet, L., Harnett, C., and Reuschlé, T.: The influence of hydrothermal alteration on volcano stability: a case study of La Soufrière de Guadeloupe (France), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-151, https://doi.org/10.5194/egusphere-egu21-151, 2021.

Despite the well-established interest of Synthetic Aperture Radar data for volcanoes study and monitoring, their integration to operational monitoring activities in volcanoes observatories remains limited so far. We here describe the effort in progress to integrate in near real time the information derived from Sentinel-1 satellites into the monitoring devices at BBPTKG in charge of Merapi volcano survey as well as the use of Sentinel-1 data during the recent period of  unrest. Merapi (7°32.5’ S and 110°26.5’ E) located in the densely populated Province of Yogyakarta in Central Java is one of the most active volcanoes in Indonesia. The eruptive history of Merapi is characterized by two eruptive styles: 1) recurrent effusive growth of viscous lava domes, with gravitational collapses producing pyroclastic flows known as « Merapi-type nuées ardentes » (VEI 2); 2) more exceptional explosive eruptions of relatively large size (VEI 3-4), associated with column collapse pyroclastic flows reaching distances larger than 15 km from the summit. The eruptive periodicity is 4 to 5 years for the effusive events and 50 to 100 years for the explosive ones. The last explosive events (VEI 3-4) occurred in November 2010 and was followed by a period of limited activity. In August 2018, a new dome was observed inside the summit crater, thus marking the start of a new phase of effusive activity. A new period of unrest then started in mid-October 2020, characterized by an increase in seismic activity as well as large and localized displacements in the summit area. Magma finally reached the surface on 4  January 2021. Deformation is currently recorded by EDM and tiltmeters together with a network of 10 permanent GNSS stations. GNSS data are automatically processed and inverted for a pressure source at depth. Both displacement time series as well as spatial probability distribution are directly available through WebObs (Beauducel et al., Frontiers, 2020), an integrated web-based system for monitoring. Sentinel-1 data are acquired over the volcano every 12 days on descending track 76 and every 6 days on ascending track 127. Since mid 2017, Sentinel-1 data are automatically downloaded on a local server at BPPTKG. Interferograms and coherence images are then produced using the NSBAS processing chain (Doin et al, 2012) and automatically integrated to WebObs to enable detection of potential rapid and significant changes in signal. Mean velocity maps are also produced as well as time series of surface displacement at given location enabling direct comparison with GNSS measurements. The descending InSAR time series shows a strong displacement away from the satellite in a 1.5 km wide area located on the north-eastern part  of the crater. This signal became significant in September 2020. It is consistent with field measurements recorded and allows to map the affected area. In mid-November 2020, Sentinel-1 data thus provided the first information on the spatial extent of the ongoing surface displacements, which was useful for crisis management.

How to cite: Pinel, V., Beauducel, F., Putra, R., Sulistiyani, S., Nandaka, G. M. A., Nurnaning, A., Budi Santoso, A., Humaida, H., Doin, M.-P., Thollard, F., and Laurent, C.: Monitoring of Merapi volcano, Indonesia based on Sentinel-1 data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10392, https://doi.org/10.5194/egusphere-egu21-10392, 2021.

Ground deformation is frequently one of the first detectable precursors alerting scientists to changes in behavior or the onset of unrest at active volcanoes. GNSS, InSAR, strain and tilt measurements are routinely used by volcano observatories for monitoring pre-eruptive, co-eruptive and post-eruptive deformation. In addition to monitoring signals related to magma migration, deformation observations are used as an input into geodetic modeling to determine the location and rate of magma accumulation and help define the structure of magma plumbing systems beneath active volcanoes.

This presentation will provide an update of how geodetic observations are being used in conjunction with seismicity and gas measurements, for the near-real time monitoring of key Icelandic volcanoes; to determine their current status, identify the onset and likely cause of unrest, locate magmatic intrusions, determine magma volumes and supply rates and assess the likelihood of eruption. An overview of the current status of the following active volcanoes will be provided: Hekla, Bárðarbunga and Grímsvötn, along with an update of the recent volcano-tectonic unrest on the Reykjanes Peninsula.

Hekla is one of the most active and dangerous volcanoes in Iceland with approximately 18 eruptions since 1104. Over the past few decades, Hekla erupted at almost regular ~10 year intervals, with the last four eruptions occurring in 1970, 1980–1981, 1991 and 2000. Previous geodetic studies have suggested magma storage at depths of 12-25 km directly beneath the volcanic edifice. However, recent InSAR analysis has detected a localized inflation signal to the west of the volcano. A regional borehole strain meter network has proven instrumental for real-time eruption forecasting at Hekla.

In the Bárðarbunga volcanic system, the six-month long effusive 2014-2015 Holuhraun eruption was accompanied by gradual caldera collapse of up to 65 m and was preceded by a two-week period of 48 km long lateral dyke propagation with extensive seismicity and deformation. Geodetic observations indicate that Bárðarbunga began to slowly inflate in July 2015. This may be explained by a combination of renewed magma inflow and viscoelastic readjustment of the volcano.

The Grímsvötn subglacial volcano is the most frequently erupting volcano in Iceland, with eruptions in 1998, 2004 and 2011. A GPS station shows a prominent inflation cycle prior to eruptions. Observations during the 2011 eruption suggest a pressure drop at a surprisingly shallow level (about 2 km depth) during the eruption, in a similar location as in previous eruptions. Deformation at this volcano has now surpassed that observed prior to historic eruptions and its aviation color code is currently elevated to yellow.

In December 2019, the Reykjanes Peninsula entered a phase of volcano-tectonic unrest characterized by seismic swarms, followed in late January 2020 by inflation detected in near-real time by GNSS and InSAR observations. At the time of writing (mid-January 2021) there have been three magmatic intrusions in the vicinity of Svartsengi, an intrusion beneath Krýsuvík and indications of magma migration at depth along the entirety of the Peninsula.

How to cite: Parks, M., Ófeigsson, B., Geirsson, H., Drouin, V., Sigmundsson, F., Hooper, A., Hreinsdóttir, S., Li, S., Ducrocq, C., Sturkell, E., Vogfjord, K., Hjartardóttir, Á. R., Fridriksdóttir, H. M., Þrastarson, R., Barsotti, S., Pfeffer, M., and Roberts, M.: The application of geodetic observations for near-real time monitoring of Icelandic volcanoes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14271, https://doi.org/10.5194/egusphere-egu21-14271, 2021.