Browsing by Author "Thouret, Jean-Claude"
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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 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 Open Access Genèse et évolution pétrologique des magmas émis au cours de l’histoire éruptive récente du volcan Ubinas (Pérou méridional): contribution à l’évaluation des aléas éruptifs(Universidad Blaise Pascal, 2000-06-29) Rivera, Marco; Gerbe, Marie Christine; Thouret, Jean-Claude; Gourgaud, AlainLa genèse des magmas dans les zones de subduction est considérée comme un processus complexe. Les hypothèses actuelles peuvent être résumées soit par (1) cristallisation fractionnée à partir d’un magma basaltique primaire, soit par (2) fusion partielle de la croûte continentale inférieure, soit par (3) fusion partielle du coin de manteau situé au-dessus de la zone de subduction sous l’effet des fluides libérés par la déshydratation de la plaque plongeante, soit par (4) fusion partielle de la croûte océanique subductée. De plus, des phénomènes postérieurs de contamination crustale et de mélange magmatique compliquent le modèle de genèse de ces magmas (Wilson, 1994). Au Pérou, en Bolivie et un nord du Chili, la subduction de la plaque de Nazca sous la marge sud-américaine donne naissance à un volcanisme plio-quaternaire très important constituant la Zone Volcanique Centrale des Andes (CVZ), dont fait partie le strato-volcan Ubinas (16º 22' S, 70º 54' W; 5672 m). Ce volcan est considéré comme le plus actif du Pérou méridional avec 23 épisodes d'intense activité fumerollienne et d'émissions de cendres répertoriés depuis 1550 (Rivera et al., 1998).Item Open Access Geología, historia eruptiva y evaluación de peligros del volcán Ticsani (sur del Perú)(Instituto Geofísico del Perú, 2003) Mariño Salazar, Jersy; Thouret, Jean-ClaudeEl volcán poligénico Ticsani se encuentra ubicado en el segmento norte de la Zona Volcánica de los Andes Centrales (70°36’W, 16°44’S, 5408 m.s.n.m.) y comprende dos edificios: “Ticsani antiguo” y “Ticsani moderno”. El edificio “Ticsani antiguo” es un estratovolcán formado por flujos de lavas, rocas volcanoclásticas e ignimbritas. Es cortado por un anfiteatro en forma de “herradura” abierto hacia el oeste y de 3 km de radio, el cual marca el inicio de extensos depósitos de avalanchas de escombros de aproximadamente 12 km3 de volumen. Se originaron por el colapso de gran parte del edificio volcánico y son los mayores depósitos de avalancha de edad Pleistocena del sur del Perú. Dicha avalancha de escombros fluyó en dirección oeste, llegando hasta la confluencia de los ríos Tambo y Omate, situado a 44 km de la cicatriz del colapso. A partir de allí, se transformó en lahar y se desplazó a lo largo del río Tambo hasta el Oceano Pacífico, recorriendo más de 150 km. El edificio “Ticsani moderno”, está conformado por tres grupos de depósitos: A) Lavas en bloques encauzados en paleo-valles y cubriendo laderas proximales, que sobreyacen a los depósitos de avalanchas de escombros probablemente del Pleistoceno medio; y domos alineados en dirección N325°, emplazados posterior a los flujos de lavas en bloques. B) Flujos piroclásticos de bloques y cenizas ligados al colapso sucesivo de domos, canalizados en quebradas cercanas al volcán, hacia el SO y NO del cráter más reciente. C) Tres depósitos (preservados entre otros) de caídas piroclásticas recientes: depósito de lapilli pómez “Ticsani gris” emplazado hace aproximadamente 10600 ± 80 años BP, depósito de ceniza “Ticsani gris” y depósito de pómez “Ticsani pardusco”. Este último corresponde a una erupción ocurrida hace menos de 400 años y precedió al emplazamiento del último domo. El más voluminoso de los depósitos de caída, es el depósito de pómez “Ticsani gris”. Forma un lóbulo cuyo eje mayor de dispersión tiene una orientación N103°. En áreas proximales tiene de 2 a más de 4 m de espesor y la isópaca de 1 cm cubre un área de aproximadamente 806 km2. Se estima que la columna eruptiva alcanzó 16.5 km de altura y que la erupción tuvo un Índice de Explosividad Volcánica (IEV) 4. Estudios petrográficos y geoquímicos efectuados, muestran que los depósitos pertenecen a un vulcanismo calco-alcalino con alto contenido de K y con ciertas características adakíticas. Las lavas del edificio “Ticsani antiguo” son andesitas, mientras que los piroclastos y lavas del edificio “Ticsani Moderno” son dacitas. Basado en las tres erupciones explosivas y en el emplazamiento de dos flujos piroclásticos debloques y cenizas, ocurridos todos en los últimos 11 000 años, consideramos tres escenarios eruptivos probables: erupción peleana, erupción freatomagmática y erupción sub-pliniana. Se han identificado los siguientes peligros volcánicos principales: peligros por caídas de tefras; por flujos y oleadas piroclásticas asociados al crecimiento de domos; y por deslizamientos y/o flujos de lodo y escombros. Los centros poblados que se hallan a menos de 15 km del volcán (Calacoa, San Cristóbal, Carumas, Cuchumbaya, Soquezane, entre otros), donde viven más de 5000 personas, se hallan amenazados por los peligros potenciales antes citados.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 Open Access Huaynaputina volcano, south Perú: Site of the major explosive eruption in historic times in the Central Andes(Instituto Geofísico del Perú, 1996-11) Thouret, Jean-Claude; Davila, Jasmine; Rivera, Marco; Juvigné, Etienne; Eissen, J.; Cotten, Jo; Gourgaud, Alain; Woodman Pollitt, Ronald FranciscoLa erupción violenta (IEV 6) del pequeño centro volcánico Huaynaputina empezó el 19 de Febrero de 1600, duró 16 días y liberó una recaída pliniana sobre más de 20000 km2, luego ignimbritas, oleadas piroclásticas y otras recaídas menores de lapilli y cenizas. El edificio pre-existente fue destruido en parte, formando un complejo de tres cráteres y conos de cenizas adyacentes. Además, flujos de escombros devastaron los 120 km del trayecto del Rio Tambo hasta el Océano Pacífico. Los depósitos sugieren que procesos de interacciones hidromagmáticos han jugado un papel en desencadenar la erupción Pliniana y que se han formado luego cráteres semejantes a un mar de gran tamaño. Aunque tan violenta erupción no involucró el colapso de una caldera, varias fracturas concéntricas recortan el complejo de cráteres y el piso de la caldera de avalancha.Item Restricted In situ cosmogenic 3He and 36Cl and radiocarbon dating of volcanic deposits refine the Pleistocene and Holocene eruption chronology of SW Peru(Springer, 2019-11-07) Bromley, Gordon R. M.; Thouret, Jean-Claude; Schimmelpfennig, Irene; Mariño, Jersy; Valdivia, David; Rademaker, Kurt; Vivanco López, Socorro del Pilar; ASTER Team; Aumaître, Georges; Bourlès, Didier; Keddadouche, KarimConstraining the age of young lavas, which generally fall outside the effective range of traditional geochronology methods, remains a key challenge in volcanology, limiting the development of high-resolution eruption chronologies. We present an in situ cosmogenic ³He and ³⁶Cl surface-exposure chronology, alongside new minimum-limiting ¹⁴C ages, documenting young eruptions at five sites in the Western Cordillera, southern Peru. Four ³He-dated lavas on the Nevado Coropuna volcanic complex (hitherto thought to be dormant) indicate that the central dome cluster is young and potentially active; two Holocene lavas on the easternmost dome are the youngest directly dated lavas in Peru to date. East of Coropuna, lava domes and block-lava flows represent the most extensive output to date of Nevado Sabancaya, one of Peru’s most active volcanoes. Two ³He measurements confirm the Holocene age of these deposits and expand the chronology for one of the youngest major lava fields in Peru. ³⁶Cl surface-exposure ages from the Purupurini dome cluster and Nevado Casiri document middle-late-Holocene episodes of effusive activity, while basal ¹⁴C ages from a lavadammed wetland constrain an effusive eruption at Mina Arcata, north of Coropuna, to the late-glacial period. These new data advance the recent Western Cordillera volcanic record whilst demonstrating both the considerable potential and fundamental limitations of cosmogenic surface-exposure methods for such applications.Item Restricted Largest explosive eruption in historical times in the Andes at Huaynaputina volcano, A.D. 1600, southern Peru(Geological Society of America, 1999-05) Thouret, Jean-Claude; Davila, Jasmine; Eissen, Jean-PhilippeThe largest explosive eruption (volcanic explosivity index of 6) in historical times in the Andes took place in a.d. 1600 at Huaynaputina volcano in southern Peru. According to chronicles, the eruption began on February 19 with a Plinian phase and lasted until March 6. Repeated tephra falls, pyroclastic flows, and surges devastated an area 70 × 40 km2 west of the vent and affected all of southern Peru, and earthquakes shook the city of Arequipa 75 km away. Eight deposits, totaling 10.2–13.1 km3 in bulk volume, are attributed to this eruption: (1) a widespread, ∼8.1 km3 pumice-fall deposit; (2) channeled ignimbrites (1.6–2 km3) with (3) ground-surge and ash-cloud-surge deposits; (4) widespread co-ignimbrite ash layers; (5) base-surge deposits; (6) unconfined ash-flow deposits; (7) crystal-rich deposits; and (8) late ash-fall and surge deposits. Disruption of a hydrothermal system and hydromagmatic interactions are thought to have fueled the large-volume explosive eruption. Although the event triggered no caldera collapse, ring fractures that cut the vent area point to the onset of a funnel-type caldera collapse.Item Restricted Multidisciplinary study of the impacts of the 1600 CE Huaynaputina eruption and a project for geosites and geo-touristic attractions(Springer, 2021-07) Mariño, Jersy; Cueva, Kevin; Thouret, Jean-Claude; Arias, Carla; Finizola, Antony; Antoine, Raphael; Delcher, Eric; Fauchard, Cyrille; Donnadieu, Franck; Labazuy, Philippe; Japura, Saida; Gusset, Rachel; Sanchez, Paola; Ramos, Domingo; Macedo Franco, Luisa Diomira; Lazarte, Ivonne; Liliane, Thouret; Del Carpio Calienes, José Alberto; Jaime, Lourdes; Saintenoy, ThibaultThe Huaynaputina volcano, southern Peru, was the site of the largest historical eruption (VEI 6) in the Andes in 1600 CE, which occurred during the historic transition between the Inca Empire and the Viceroyalty of Peru. This event had severe consequences in the Central Andes and a global climatic impact. Spanish chronicles reported that at least 15 villages or settlements existed around the volcano, of which seven of them were totally destroyed by the eruption. Multidisciplinary studies have allowed us to identify and analyze the characteristics of six settlements buried by the eruption. Tephra fallout and pyroclastic current deposits (PDCs) had different impacts according to the settlement distance from the crater, the location with respect to the emplacement of PDCs along valleys, the geomorphological characteristics of the site, and type of constructions. Thus, Calicanto, Cojraque, and San Juan de Dios, located beneath the main axis of tephra dispersal lobe due west and/or on valley edges, were buried under several meters of pyroclastic deposits, while the villages of Estagagache, Chimpapampa, and Moro Moro, located to the S and SE of the lobe, were partially mantled by tephra. The 1600 CE Huaynaputina eruption created an important geological and cultural heritage, which has scientific, educational, and touristic values. Geo-touristic attractions are proposed based on identification, characterization, and qualitative evaluation of four groups totaling 17 geosites: volcanic geosites, volcanic-cultural geomorphosites, and hot springs. Seven geological roads along with seven viewpoints are proposed, which allow to value the most relevant landscapes, deposits and geological structures.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.