Browsing by Author "Finizola, Anthony"
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Item Restricted Asymmetrical structure, hydrothermal system and edifice stability: The case of Ubinas volcano, Peru, revealed by geophysical surveys(Elsevier, 2014-04) Gonzales, Katherine; Finizola, Anthony; Lénat, Jean-François; Macedo Sánchez, Orlando Efraín; Ramos Palomino, Domingo A.; Thouret, Jean-Claude; Fournier, Michel; Cruz, Vicentina; Pistre, KarineUbinas volcano, the historically most active volcano in Peru straddles a low-relief high plateau and the flank of a steep valley. A multidisciplinary geophysical study has been performed to investigate the internal structure and the fluids flow within the edifice. We conducted 10 self-potential (SP) radial (from summit to base) profiles, 15 audio magnetotelluric (AMT) soundings on the west flank and a detailed survey of SP and soil temperature measurements on the summit caldera floor. The typical “V” shape of the SP radial profiles has been interpreted as the result of a hydrothermal zone superimposed on a hydrogeological zone in the upper parts of the edifice, and depicts a sub-circular SP positive anomaly, about 6 km in diameter. The latter is centred on the summit, and is characterised by a larger extension on the western flank located on the low-relief high plateau. The AMT resistivity model shows the presence of a conductive body beneath the summit at a depth comparable to that of the bottom of the inner south crater in the present-day caldera, where intense hydrothermal manifestations occur. The lack of SP and temperature anomalies on the present caldera floor suggests a self-sealed hydrothermal system, where the inner south crater acts as a pressure release valve. Although no resistivity data exists on the eastern flank, we presume, based on the asymmetry of the basement topography, and the amplitude of SP anomalies on the east flank, which are approximately five fold that on the west flank, that gravitational flow of hydrothermal fluids may occur towards the deep valley of Ubinas. This hypothesis, supported by the presence of hot springs and faults on the eastern foot of the edifice, reinforces the idea that a large part of the southeast flank of the Ubinas volcano may be altered by hydrothermal activity and will tend to be less stable. One of the major findings that stems from this study is that the slope of the basement on which a volcano has grown plays a major role in the geometry of the hydrothermal systems. Another case of asymmetrical composite cone edifice, built on a steep topography, is observed on El Misti volcano (situated 70 km west of Ubinas), which exhibits a similar SP pattern. These types of edifices have a high potential of spreading and sliding along the slope owing to the thicker accumulation of low cohesion and hydrothermally altered volcanic products.Item Restricted Deep electrical resistivity tomography along the tectonically active Middle Aterno Valley (2009 L'Aquila earthquake area, central Italy)(Oxford University Press, 2016-11) Pucci, Stefano; Civico, Riccardo; Villani, Fabio; Ricci, Tullio; Delcher, Eric; Finizola, Anthony; Sapia, Vincenzo; De Martini, Paolo Marco; Pantosti, Daniela; Barde-Cabusson, Stéphanie; Brothelande, Elodie; Gusset, Rachel; Mezon, Cécile; Orefice, Simone; Peltier, Aline; Poret, Matthieu; Torres Velarde, Liliana Rosario; Suski, BarbaraThree 2-D Deep Electrical Resistivity Tomography (ERT) transects, up to 6.36 km long, were obtained across the Paganica-San Demetrio Basin, bounded by the 2009 L'Aquila Mw 6.1 normal-faulting earthquake causative fault (central Italy). The investigations allowed defining for the first time the shallow subsurface basin structure. The resistivity images, and their geological interpretation, show a dissected Mesozoic-Tertiary substratum buried under continental infill of mainly Quaternary age due to the long-term activity of the Paganica-San Demetrio normal faults system (PSDFS), ruling the most recent deformational phase. Our results indicate that the basin bottom deepens up to 600 m moving to the south, with the continental infill largely exceeding the known thickness of the Quaternary sequence. The causes of this increasing thickness can be: (1) the onset of the continental deposition in the southern sector took place before the Quaternary, (2) there was an early stage of the basin development driven by different fault systems that produced a depocentre in the southern sector not related to the present-day basin shape, or (3) the fault system slip rate in the southern sector was faster than in the northern sector. We were able to gain sights into the long-term PSDFS behaviour and evolution, by comparing throw rates at different timescales and discriminating the splays that lead deformation. Some fault splays exhibit large cumulative throws (>300 m) in coincidence with large displacement of the continental deposits sequence (>100 m), thus testifying a general persistence in time of their activity as leading splays of the fault system. We evaluate the long-term (3–2.5 Myr) cumulative and Quaternary throw rates of most of the leading splays to be 0.08–0.17 mm yr−1, indicating a substantial stability of the faults activity. Among them, an individual leading fault splay extends from Paganica to San Demetrio ne’ Vestini as a result of a post-Early Pleistocene linkage of two smaller splays. This 15 km long fault splay can explain the Holocene surface ruptures observed to be larger than those occurred during the 2009 L'Aquila earthquake, such as revealed by palaeoseismological investigations. Finally, the architecture of the basin at depth suggests that the PSDFS can also rupture a longer structure at the surface, allowing earthquakes larger than M 6.5, besides rupturing only small sections, as it occurred in 2009.Item Open Access Disruptions in the hydrothermal water geochemistry inside Misti volcano in coincidence with the 8.4 Mw earthquake of June 23rd, 2001, in southern Peru(Instituto Geofísico del Perú, 2001) Cruz, Vicentina; Finizola, Anthony; Macedo Sánchez, Orlando Efraín; Sortino, FrancescoMisti volcano (16°18'S, 71°24'W and 5822 in elevation) is located 17 km from Arequipa (-800000 inhabitants). It is characterized by two concentric summit craters. The youngest one hold lava dome, 130m wide, with fumarolic activity and temperature higuer than 200°C, geochemical techniques turn out to be very effective for the monitoring of active volcanoes. The ascent of a magmatic gases and their interactions with aquifers induce changes in the chemical composition and physical properties of the waters that can be sampled at the surface.The geochemical monitoring of the Misti volcano began in 1998 with a systematic sampling of the hot spring of "Charcani V", located to 6 Km of the active crater at 2960 meters in elevation.Item Open Access Estudio estructural y del sistema hidrotermal de los volcanes Sabancaya y Hualca-Hualca mediante el método de Potencial Espontáneo(Instituto Geológico, Minero y Metalúrgico - INGEMMET, 2018) Puma Sacsi, Nino; Macedo Sánchez, Orlando Efraín; Álvarez, Yovana; Finizola, Anthony; Ramos Palomino, Domingo A.El volcán Sabancaya, considerado el segundo volcán más activo del Perú forma parte del complejo Volcánico Ampato-Sabancaya (CVAS), está ubicado a 80 Km en dirección NNO de la ciudad de Arequipa (15°47’ S; 71°72’W; 5976 msnm) en el sur del Perú. El presente estudio tiene como finalidad determinar estructuras importantes que se encuentran ocultas por material volcánico y el efecto que generan estas estructuras sobre la señal del Potencial Espontaneo (PE); además, estudiar el sistema hidrotermal del volcán Sabancaya, aplicando uno de los métodos geofísicos más antiguos y conocidos, pero poco usado en la vulcanología, como es el PE. La aplicación de este método nos ha permitido conocer la estructura interna del área del CVAS y volcán Hualca-Hualca, así como determinar las dimensiones del sistema hidrotermal.Item Open Access Estudio estructural y del sistema hidrotermal del volcán Ubinas por métodos geofísicos y geoquímicos(Sociedad Geológica del Perú, 2002) Macedo Sánchez, Orlando Efraín; Gonzales Zuñiga, Katherine; Finizola, Anthony; Métaxian, Jean-Philippe; Fournier, Nicolas; Sortino, FrancescoEl volcán Ubinas (16° 22’ S, 70° 54’ W; 5672 m.s.n.m.) ubicado en el sur del Perú y dentro de la ZVC o Zona Volcánica Central de los Andes (Fig. 1), es considerado como el más activo del Perú, con hasta 23 erupciones menores registradas históricamente en los últimos 450 años. Estudios geológicos recientemente realizados sobre este volcán han puesto en evidencia su condición de peligro potencial (Rivera, 1997; Rivera et al., 1997). Poco se conoce, sin embargo, acerca de su estructura interna. Este trabajo muestra los resultados de la aplicación de diferentes métodos geofísicos, geoquímicos, de la realización de mediciones de temperatura del suelo, y observaciones detalladas del interior del cráter activo, realizadas en el volcán Ubinas entre 1997 y 1999. Tales resultados han permitido proponer un modelo de estructura y de circulación de fluidos propio a este volcán andesítico. Se ha efectuado principalmente un amplio trabajo de investigación por potencial espontáneo (PE) con mediciones a lo largo de 9 perfiles radiales que cubren todo el edificio y con mediciones detalladas del PE sobre el piso de la caldera. Asimismo, se ha efectuado un breve monitoreo de la actividad sísmica instalándose sismómetros sobre la parte superior del cono volcánico, un análisis de la concentración de CO2 en los gases del suelo tanto sobre el edificio como al interior de la caldera, detalladas mediciones de la temperatura sobre el piso de la caldera, y finalmente, un análisis geoquímico preliminar de aguas termales y frías próximas a la zona del volcán.Item Restricted Fluid circulation and structural discontinuities inside Misti volcano (Peru) inferred from self-potential measurements(Elsevier, 2004-08) Finizola, Anthony; Lénat, Jean-François; Macedo Sánchez, Orlando Efraín; Ramos Palomino, Domingo A.; Thouret, Jean-Claude; Sortino, FrancescoOne of the seven potentially active andesite stratovolcanoes in southern Peru, Misti (5822 m), located 17 km northeast and 3.5 km above Arequipa, represents a major threat to the population (∼900,000 inhabitants). Our recent geophysical and geochemical research comprises an extensive self-potential (SP) data set, an audio – magnetotelluric (AMT) profile across the volcano and CO2 concentrations in the soil along a radial profile. The SP survey is the first of its kind in providing a complete mapping of a large andesitic stratovolcano 20 km in diameter. The SP mapping enables us to analyze the SP signature associated with a subduction-related active volcano. The general SP pattern of Misti is similar to that of most volcanoes with a hydrogeologic zone in the lower flanks and a hydrothermal zone in the upper central area. A quasi-systematic relationship exists between SP and elevation. Zones with constant SP/altitude gradients (Ce) are observed in both hydrogeologic (negative Ce) and hydrothermal (positive Ce) zones. Transition zones between the different Ce zones, which form a concentric pattern around the summit, have been interpreted in terms of lateral heterogeneities in the lithology. The highest amplitudes of SP anomalies seem to coincide with highly resistive zones. The hydrothermal system 6 km in diameter, which extends over an area much larger than the summit caldera, may be constrained by an older, concealed collapse caldera. A sealed zone has apparently developed through alteration in the hydrothermal system, blocking the migration of CO2 upward. Significant CO2 emanations are thus observed on the lower flanks but are absent above the hydrothermal zone.Item Restricted Geology of El Misti volcano near the city of Arequipa, Peru(Geological Society of America, 2001-12) Thouret, Jean-Claude; Finizola, Anthony; Fornari, Michel; Legeley-Padovani, Annick; Suni, Jaime; Frechen, ManfredApproximately 750 000 people live at risk in the city of Arequipa, whose center lies 17 km from the summit (5820 masl [meters above sea level]) of the active El Misti volcano. The composite edifice comprises a stratovolcano designated Misti 1 (ca. 833– 112 ka), partially overlapped by two stratocones designated Misti 2 and Misti 3 (112 ka and younger), and a summit cone Misti 4 (11 ka and younger). Eight groups of lava flows and pyroclastic deposits indicate the following volcanic history. (1) Three cones have been built up since ca. 112 ka at an average eruptive rate of 0.63 km3/k.y. (2) Several episodes of growth and destruction of andesitic and dacitic domes triggered dome-collapse avalanches and block-and-ash-flows. Deposition of these flows alternated with explosive events, which produced pyroclastic-flow deposits and tephra-fall and surge deposits. (3) Nonwelded, dacitic ignimbrites may reflect the formation of a 6 × 5 km incremental caldera collapse on Misti 2 (ca. 50 000 and 40 000 yr B.P.) and a 2 × 1.5 km summit caldera on Misti 3 (ca. 13 700 to 11 300 yr B.P.). (4) Tens of pyroclastic flows and at least 20 tephra falls were produced by Vulcanian and sub-Plinian eruptions since ca. 50 ka. On average, ash falls have occurred every 500 to 1500 yr, and pumice falls, every 2000 to 4000 yr. (5) Misti erupted relatively homogeneous andesites and dacites with a few rhyolites, but Misti 4 reveals a distinct mineral suite. Less evolved andesites prevail in scoriaceous products of group 4–1 including historical ash falls. Scoriae of Misti 4 and the ca. 2300–2050 yr B.P. banded pumice commonly show heterogeneous textures of andesite and rhyolite composition. This heterogeneity may reflect changes in physical conditions and magma mixing in the reservoir. (6) Deposits emplaced during the Vulcanian A.D. 1440– 1470 event and the sub-Plinian eruption(s) at ca. 2050 yr B.P. are portrayed on one map. The extent and volume of these deposits indicate that future eruptions of El Misti, even if moderate in magnitude, will entail considerable hazards to the densely populated area of Arequipa.Item Restricted Influence of the regional topography on the remote emplacement of hydrothermal systems with examples of Ticsani and Ubinas volcanoes, Southern Peru(Elsevier, 2013-03) Byrdina, Svetlana; Ramos Palomino, Domingo A.; Vandemeulebrouck, Jean; Masias, Pablo; Revil, André; Finizola, Anthony; Gonzales Zuñiga, Katherine; Cruz, Vicentina; Antayhua Vera, Yanet Teresa; Macedo Sánchez, Orlando EfraínPresent work studies the influence of the regional topography on the hydrothermal fluid flow pattern in the subsurface of a volcanic complex. We discuss how the advective transfer of heat from a magmatic source is controlled by the regional topography for different values of the averaged permeability. For this purpose, we use a 2-D numerical model of coupled mass and heat transport and new data sets acquired at Ticsani and Ubinas, two andesitic volcanoes in Southern Peru which have typical topography, justifying this approach. A remarkable feature of these hydrothermal systems is their remote position not centered on the top of the edifice. It is evidenced by numerous hot springs located in more than 10 km distance from the top of each edifice. Upwelling of thermal water is also inferred from a positive self-potential anomaly at the summit of the both volcanoes, and by ground temperatures up to 37 °C observed at Ticsani. Our model results suggest that the regional topographic gradient is able to significantly divert the thermal water flow and can lead to an asymmetric emplacement of the hydrothermal system even considering a homogeneous permeability of the edifice. Inside the thermal flow, the hydraulic conductivity increases with the decrease of temperature-related viscosity, focusing the flow towards the surface and creating a hydrothermal zone at a large lateral distance from the heat source. The location and temperature of the hot springs together with the water table position given by self-potential data can be used to constrain the average permeability of the edifice, a key parameter influencing fluid flow and associated advective heat transfer in the direction opposite to the regional topographic gradient. Our study allows to explain the emplacement of the hydrothermal systems at volcanoes with asymmetric edifices or even the absence of a shallow hydrothermal system. These results can be generalized to the study of non-volcanic hydrothermal systems.Item Restricted Magma extrusion during the Ubinas 2013-2014 eruptive crisis based on satellite thermal imaging (MIROVA) and ground-based monitoring(Elsevier, 2015-09) Coppola, Diego; Macedo Sánchez, Orlando Efraín; Ramos Palomino, Domingo A.; Finizola, Anthony; Delle Done, Dario; Del Carpio Calienes, José Alberto; White, Randall; McCausland, Wendy; Centeno Quico, Riky; Rivera, Marco; Apaza, Fredy; Ccallata, Beto; Chilo, Wilmer; Cigolini, Corrado; Laiolo, Marco; Lazarte, Ivonne; Machaca, Roger; Masias, Pablo; Ortega, Mayra; Puma Sacsi, Nino; Taipe, EduAfter 3 years of mild gases emissions, the Ubinas volcano entered in a new eruptive phase on September 2nd, 2013. The MIROVA system (a space-based volcanic hot-spot detection system), allowed us to detect in near real time the thermal emissions associated with the eruption and provided early evidence of magma extrusion within the deep summit crater. By combining IR data with plume height, sulfur emissions, hot spring temperatures and seismic activity, we interpret the thermal output detected over Ubinas in terms of extrusion rates associated to the eruption. We suggest that the 2013–2014 eruptive crisis can be subdivided into three main phases: (i) shallow magma intrusion inside the edifice, (ii) extrusion and growing of a lava plug at the bottom of the summit crater coupled with increasing explosive activity and finally, (iii) disruption of the lava plug and gradual decline of the explosive activity. The occurrence of the 8.2 Mw Iquique (Chile) earthquake (365 km away from Ubinas) on April 1st, 2014, may have perturbed most of the analyzed parameters, suggesting a prompt interaction with the ongoing volcanic activity. In particular, the analysis of thermal and seismic datasets shows that the earthquake may have promoted the most intense thermal and explosive phase that culminated in a major explosion on April 19th, 2014. These results reveal the efficiency of space-based thermal observations in detecting the extrusion of hot magma within deep volcanic craters and in tracking its evolution. We emphasize that, in combination with other geophysical and geochemical datasets, MIROVA is an essential tool for monitoring remote volcanoes with rather difficult accessibility, like those of the Andes that reach remarkably high altitudes.Item Open Access Physical impacts of the CE 1600 Huaynaputina eruption on the local habitat: geophysical insights(Sociedad Geológica del Perú, 2017-11) Finizola, Anthony; Macedo Franco, Luisa Diomira; Antoine, Raphael; Thouret, Jean-Claude; Delcher, Eric; Fauchard, Cyrille; Gusset, Rachel; Japura Paredes, Saida Blanca; Lazarte Zerpa, Ivonne Alejandra; Mariño Salazar, Jersy; Ramos Palomino, Domingo A.; Saintenoy, Thibault; Thouret, Liliane; Chávez, José Antonio; Chijcheapaza, Rolando; Del Carpio Calienes, José Alberto; Perea, Ruddy; Puma Sacsi, Nino; Macedo Sánchez, Orlando Efraín; Torres Aguilar, José Luis; Vella, Marc-AntoineThe February-March CE 1600 eruption of Huaynaputina (VEI 6) has a well-documented worldwide climatic impact but the regional consequences of this eruption on climate, habitat and inhabitants are poorly known. The location of several villages buried below the Huaynaputina erupted deposits exceeding one meter in thickness is not clearly mentioned in the historical early Spanish chronicles. Geophysical investigations carried out during the20 15-2016 period on three different sites (Coporaque, Calicanto and Chimpapampa within 16 km from the volcano summit/crater) are the initial stage and part of a large project termed <Item Restricted Ubinas: the evolution of the historically most active volcano in southern Peru(Springer, 2005) Thouret, Jean-Claude; Rivera, Marco; Wörner, Gerhard; Gerbe, Marie-Christine; Finizola, Anthony; Fornari, Michel; Gonzales Zuñiga, KatherineUbinas volcano has had 23 degassing and ashfall episodes since A.D. 1550, making it the historically most active volcano in southern Peru. Based on fieldwork, on interpretation of aerial photographs and satellite images, and on radiometric ages, the eruptive history of Ubinas is divided into two major periods. Ubinas I (Middle Pleistocene >376 ka) is characterized by lava flow activity that formed the lower part of the edifice. This edifice collapsed and resulted in a debris-avalanche deposit distributed as far as 12 km downstream the Rio Ubinas. Non-welded ignimbrites were erupted subsequently and ponded to a thickness of 150 m as far as 7 km south of the summit. These eruptions probably left a small collapse caldera on the summit of Ubinas I. A 100-m-thick sequence of ash-and-pumice flow deposits followed, filling paleo-valleys 6 km from the summit. Ubinas II, 376 ky to present comprises several stages. The summit cone was built by andesite and dacite flows between 376 and 142 ky. A series of domes grew on the southern flank and the largest one was dated at 250 ky; block-and-ash flow deposits from these domes filled the upper Rio Ubinas valley 10 km to the south. The summit caldera was formed between 25 and 9.7 ky. Ash-flow deposits and two Plinian deposits reflect explosive eruptions of more differentiated magmas. A debris-avalanche deposit (about 1.2 km³) formed hummocks at the base of the 1,000-m-high, fractured and unstable south flank before 3.6 ka. Countless explosive events took place inside the summit caldera during the last 9.7 ky. The last Plinian eruption, dated A.D.1000–1160, produced an andesitic pumice-fall deposit, which achieved a thickness of 25 cm 40 km SE of the summit. Minor eruptions since then show phreatomagmatic characteristics and a wide range in composition (mafic to rhyolitic): the events reported since A.D. 1550 include many degassing episodes, four moderate (VEI 2–3) eruptions, and one VEI 3 eruption in A.D. 1667. Ubinas erupted high-K, calc-alkaline magmas (SiO₂=56 to 71%). Magmatic processes include fractional crystallization and mixing of deeply derived mafic andesites in a shallow magma chamber. Parent magmas have been relatively homogeneous through time but reflect variable conditions of deep-crustal assimilation, as shown in the large variations in Sr/Y and LREE/HREE. Depleted HREE and Y values in some lavas, mostly late mafic rocks, suggest contamination of magmas near the base of the >60-km-thick continental crust. The most recently erupted products (mostly scoria) show a wide range in composition and a trend towards more mafic magmas. Recent eruptions indicate that Ubinas poses a severe threat to at least 5,000 people living in the valley of the Rio Ubinas, and within a 15-km radius of the summit. The threat includes thick tephra falls, phreatomagmatic ejecta, failure of the unstable south flank with subsequent debris avalanches, rain-triggered lahars, and pyroclastic flows. Should Plinian eruptions of the size of the Holocene events recur at Ubinas, tephra fall would affect about one million people living in the Arequipa area 60 km west of the summit.