Journal of Volcanology and Geothermal Research

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ISSN : 0377-0273
Published by: Elsevier BV (10.1016)
Total articles ≅ 7,171
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, Y. Qi, , M. Gresse
Journal of Volcanology and Geothermal Research; https://doi.org/10.1016/j.jvolgeores.2021.107410

Abstract:
Induced polarization is used to image the feeder dike of a monogetic dome thanks to the signature of pronounced alteration around these conduits. We performed a 3D tomography of the electrical conductivity and normalized chargeability of the 1630-monogenetic dome located inside the caldera of Furnas, a quiescent stratovolcano in the Eastern side of São Miguel Island (Azores volcanic archipelago, Atlantic Ocean). A total of 2634 apparent resistivity and chargeability data were collected and inverted using a classical regularized least-squares inversion (based on a quasi-Gauss-Newton approach). The 3D tomograms display an area of both high electrical conductivity and normalized chargeability. This area corresponds likely to the altered subvolume associated with the magmatic feeding conduit of the monogenetic dome. The same conduit can be also observed on a 2D magnetotelluric (MT) section, at least for the first 200 m below the ground surface. Assuming that the in-situ pore water conductivity is the same as in Furnas Lake (0.016 S m−1, 25 °C), the electrical conductivity and normalized chargeability are combined to obtain tomograms of the water content and cation exchange capacity of the monogenetic dome. The cation exchange capacity provides a proxy to image alteration associated with the formation of clay minerals and zeolites. This study highlights the usefulness of these imaging techniques to image the structure of monogenetic domes.
, F. Gil-Cruz, L. Franco-Marín, J. San Martín, O. Valderrama, J. Lazo, C. Cartes, S. Morales, E. Hernández, J. Quijada, et al.
Journal of Volcanology and Geothermal Research; https://doi.org/10.1016/j.jvolgeores.2021.107409

Abstract:
Nevados de Chillán volcanic complex (NChVC) is one of the most active volcanoes in Chile having 4 eruptive episodes within the previous century. All of this activity has been concentrated within Las Termas sub-complex, the last eruption before the current reactivation occurred in 2008 characterized by a lava flow toward the east side of the edifice. The first surficial manifestation was an explosive event occurred on January 8, 2016, NChVC has been in eruption since then and continuing today. Seismicity has shown a variety of waveforms and types: Long Period (LP), Tornillo (TO), Very Long Period (VLP), spasmodic tremor, harmonic tremor and Volcano Tectonic (VT) earthquakes. Reactivation was marked by an increase in LP seismicity accompanied by a more regular VT activity. Based on seismicity, morphological changes and some petrological features it has determined five phases of activity, from hydrothermal dominance up to different magmatic episodes. It includes a lava dome extrusion, alternate growing and destruction of it, effusion of four lava flows. It is remarkable the low flow rates observed on extrusion and effusion of lava bodies (0.008 m3/s-0.04 m3/s), the constant vulcanian type eruptions of low and middle intensity, the occurrence of piroclastic flows mainly toward north and northeast to the crater and deformation process absent in the lava dome extrusion and very clear during lava flows effusion. This work makes a broad description of multiparametric data acquired by the monitoring network from 2012 to 2020, in order to illuminate the internal and external processes acting during the NChVC crisis and a hypothetical model of the magmatic plumbing system is proposed. This model states the presence of a magma plug in the shallow (0.5–1.1 km) conduit reactivated by at least two intrusive processes from 4 to 6 km depth magma chamber following the trend of a major fault structure, Cortaderas fault, which controls the distribution of eruptive centers of the complex. Our results could contribute also, to understand the behavior of the magmatic systems that produce dacitic lava domes with low volume and low growing rates.
Journal of Volcanology and Geothermal Research, Volume 420; https://doi.org/10.1016/j.jvolgeores.2021.107407

Abstract:
A comprehensive heat flux assessment method that includes soil temperature measurement and a chloride-inventory method to evaluate the heat energy of a fissured geothermal area was developed. A novel optimized function was created to deal with the anisotropy of the sequential Gaussian simulation while calculating the conductive thermal energy release, and the accuracy of the result was improved. This method was applied to geothermal potential studies on the fracture-controlled Garze geothermal system in the western Sichuan Plateau, which belongs to the eastern Himalayan syntaxis. The field work was limited to the Garyungo Thermal Area (GYGTA), with an area of 0.91 km2. Soil temperature measurements in the field at more than 400 points and soil thermal conductivity measurements in the laboratory revealed that the conductive heat output accounts for 18.2 ± 0.2 MW. The convective heat output through soil evaporation comes up to 2.8 ± 0.5 MW. The heat output from the hot springs (seepage) accounts for 32.6 ± 6.2 MW. The total heat output reaches 53.6 ± 6.2 MW, with a heat flux of 59 ± 7 W m−2. The heat flux of the GYGTA was consistent with that of the Yangbajing geothermal area and some other high-temperature hydrothermal areas related to volcanic activities; therefore, the high-temperature nonvolcanic-hydrothermal area may produce significant geothermal energy.
Journal of Volcanology and Geothermal Research, Volume 420; https://doi.org/10.1016/j.jvolgeores.2021.107395

Abstract:
A new submarine volcano has been discovered offshore Mayotte, a part of the Comoros volcanic archipelago located between Africa and Madagascar. The edifice arose from the sea-floor following a seismo-volcanic crisis that started in May 2018. This seismo-volcanic activity highlights very deep magma reservoirs and dykes in the East Mayotte volcanic system. Since the crisis, the region has experienced >2000 earthquakes with magnitude ≥3.5 and activity continues today (August 17, 2021). The earthquakes are unusually deep and distributed into two swarms: one 5–15 km east of Petite-Terre at 25–55 km depth and a second 25 km away at 30–50 km depth. Significant subsidence of Mayotte to the East has been assigned to the drainage of a deep magma chamber, inferred to be located 30 km from the coast. However, at present, the earthquake locations and geodetic observations have not been sufficient to image entirely the structure of the volcanic plumbing system. In this study, we construct Vp, Vs, dVp, dVs and Vp/Vs 3D velocity models to assess the deeper structure of the young volcano plumbing system, offshore and East of Mayotte. Using >3000 earthquakes from an ongoing monitoring effort, and a 1D velocity model determined onboard, we jointly inverted for velocity structures, earthquake locations, origin times, and station corrections using LOTOS software. The calculated 3D velocity models highlight a complex volcanic system down to 40 km depth. Specifically, we image 3 interpreted reservoirs, more or less consolidated/old. The main reservoir is located at about 30 km depth and deeper, making it one of the deepest magmatic chamber imaged. The reservoirs are connected by several old crystallized conduits, whose existence could have been influenced by the presence of an old fracture zone, globally oriented N130°, due to a regional strike-slip motion of the lithosphere. Moreover, gas-saturated rock may be present below the currently degassing Horse Shoe structure. We were unable to image connections between the new volcanic edifice and reservoirs or conduits due to a lack of resolution in that part of the study area.
Journal of Volcanology and Geothermal Research, Volume 420; https://doi.org/10.1016/j.jvolgeores.2021.107405

Abstract:
Merapi volcano is located in central Java and is the most active volcano in Indonesia. Many thousands live on the volcano's flanks which itself is 28 km (17 mi) north of Yogyakarta and its 2.4 million inhabitants. Given this population at risk, and a history of 73 recorded eruptions in the past 500 years, the hazards posed by Merapi are worthy of study. Merapi is monitored by networks of on-site seismology, deformation, and gas emission instruments and, like all volcanoes globally, is also routinely observed by satellite remote sensors. Here, we conduct a temporal and spatial time series analysis of land surface temperature (LST) observations of Merapi, as derived from MODIS (1 km spatial resolution), ASTER (90 m) and Landsat (30 m) thermal infrared imagery. The time series derived from MODIS is decomposed with the Seasonal Trend Decomposition using a Loess (STL) technique and this reveals thermal anomaly peaks caused by the eruptions and a subtle rising tendency in LST since the launch of MODIS in 2000. ASTER surface temperature time series is used for the cross validation of the MODIS LST time series and again, demonstrates thermal anomaly peaks and a longer term upward trend. For a detailed delineation of thermal features at Merapi, the 30 m pixel Landsat thermal imagery derived brightness temperature (BT) distribution during the period from 1988 to 2019 is presented. Finally, change detections (i.e., pixel-by-pixel comparison) of BT distribution from 1988 to 2019 are performed to inspect the spatial temperature variations of Merapi volcano. Positive thermal anomaly areas are identified and these correspond to local heat sources revealed by seismic imaging and resistivity tomography. In summary, the satellite remote sensing approach provides insights into thermal features at a higher spatial and temporal scale than has been conducted in the past and these observations complement ongoing ground-based measurements. The results of this study will feed into both an enhanced understanding of Merapi's thermally anomalous subsurface structures and facilitation of volcano monitoring and hazard assessment.
Argelia Silva-Fragoso, , Gianluca Norini, Teresa Orozco-Esquivel, Fernando Corbo-Camargo, Juan Pablo Bernal, Cesar Castro, Manuel Arrubarrena-Moreno
Journal of Volcanology and Geothermal Research; https://doi.org/10.1016/j.jvolgeores.2021.107396

Abstract:
The western slope of Cerro Domuyo in northern Patagonia is characterized by thermal springs with boiling waters, Quaternary silicic domes, and pyroclastic deposits that suggest the existence of a geothermal reservoir. According to geochemical studies, the reservoir may have a temperature of 220 °C and one of the largest advective heat fluxes reported for a continental volcanic center. In this paper, we propose a more refined conceptual model for the Domuyo geothermal area, based on a geological survey supported by UPb, UTh, and ArAr geochronology and by magnetotelluric and gravity surveys. Our study indicates that the Domuyo Volcanic Complex (DVC) is a Middle Pleistocene dome complex overlying middle Miocene to Pliocene volcanic sequences, which in turn cover: 1) the Jurassic-Early Cretaceous Neuquén marine sedimentary succession, 2) silicic ignimbrites dated at ~186.7 Ma, and 3) the Paleozoic metamorphic basement intruded by ~288 Ma granite bodies. The volcanic cycle in the DVC is distinctly bimodal, characterized by the emplacement of massive silicic domes and less voluminous olivine basalts on its southern slope. A major collapse of the central dome at ~600 ka produced a voluminous (19.4 km3 and 133 km2) block-and-ash flow, and associated pyroclastic flows, that filled a valley to the southwest at distances up to ~30 km from Cerro Domuyo summit. This was followed by a period of intense effusive activity that formed the Cerro Guitarra, Cerro Las Pampas, Cerro Domo, and Cerro Covunco silicic domes. The last two domes are the youngest and largest edifices, dated at 0.50 Ma (ArAr age) and 0.25 Ma (UTh age). Pre-Cenozoic successions were affected by N-S reverse and thrust faults that were later displaced by an ENE-WSW-trending transtensional belt. The basement rocks at the northern termination of the Cordillera del Viento anticlinorium were also displaced towards the east-northeast by this belt, which is observed NNW of Cerro Domuyo. The DVC was emplaced within this zone of crustal weakness. The integration of geologic observations with magnetotelluric and gravity data, allowed us to develop an updated conceptual model of the geothermal system. The geothermal reservoir is inferred at a depth of less than 2 km within pre-Pliocene fractured rocks, bounded by ~WSW-ENE trending faults and sealed by the pyroclastic deposits and rhyolitic lavas of the DVC. The location of most thermal springs is not directly controlled by faults. Instead, flows emerge at the contact between the fractured and faulted basement and the caprock.
, Michael J. Heap
Journal of Volcanology and Geothermal Research, Volume 420; https://doi.org/10.1016/j.jvolgeores.2021.107398

Abstract:
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.
, M. Rosi, A.B. Malaguti, F. Lucchi, C.A. Tranne, F. Speranza, P.G. Albert, V.C. Smith, A. Di Roberto, E. Billotta
Journal of Volcanology and Geothermal Research, Volume 420; https://doi.org/10.1016/j.jvolgeores.2021.107397

Abstract:
The youngest (last 1500 years) volcanic eruptions of Lipari, within the Aeolian Archipelago, produced the prominent pumice cone of Monte Pilato and the obsidian lava flows of Rocche Rosse and Forgia Vecchia, concentrated in the north-eastern sector of the island as well as highly dispersed white-coloured, fine-grained tephra layers of rhyolitic composition in terrestrial and marine settings on the regional scale. Here we describe in detail the stratigraphy of pyroclastic successions and lava flows erupted by different vents - Monte Pilato, Forgia Vecchia, Lami, and Rocche Rosse - combining field observations, sedimentological characteristics of the tephra deposits, and major and trace element compositions of the volcanic glass. All the pyroclastic materials consist of aphyric pumice lapilli and ash with a largely homogeneous rhyolitic composition. The Monte Pilato and Forgia Vecchia deposits primarily consist of highly vesicular pumice fragments and subordinate obsidian clasts, whilst Rocche Rosse and Lami are characterized by moderately vesicular juvenile fragments with a more significant fraction of obsidian. The Lami tephra also contains peculiar pumice clasts with a fibrous texture and breadcrust bombs.
, K.I. Konstantinou, P. Ranjan
Journal of Volcanology and Geothermal Research; https://doi.org/10.1016/j.jvolgeores.2021.107394

Abstract:
The Santorini-Amorgos zone is an area rich in microseismicity at the center of the Hellenic volcanic arc. The microseismicity of the zone is distributed along the Santorini-Amorgos ridge and Kolumbo submarine volcano. In this study, we utilized crustal events that were recorded by temporary networks during September 2002 to July 2004 and October 2005 to March 2007, and also by the permanent network from 2011 to 2020. These events were inverted for their moment tensors by using P-wave polarities as well as SV/P and SH/P amplitude ratios, yielding 74 well-constrained moment tensor solutions. Most of these moment tensors have significant CLVD and isotropic components that are positively correlated to each other (R2 = 0.68). Tensile faulting due to high pore pressure is considered as the most likely cause of the observed non-DC components. The positive and negative non-DC components observed in Kolumbo may be generated by the opening and closing of cracks beneath the shallow (6–7 km) magma chamber due to a steady migration of magmatic fluids from the deep reservoir into the chamber. In Anydros, most of the microearthquakes have positive non-DC components associated with the opening of cracks. It is possible that the extensional deformation and high pore fluid pressure in the area opens subvertical cracks that become pathways for upward migrating fluids. The upward migration of magmatic fluids in an extensional regime such as the Santorini-Amorgos zone can also be viewed as an indication of emerging volcanic activity in this area.
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