Browsing by Author "Cruz, Vicentina"
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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 Open Access Caracterización geoquímica de las fuentes termales y frías asociadas al volcán Ubinas en el sur del Perú(Sociedad Geológica del Perú, 2009) Cruz, Vicentina; Gonzales, Katherine; Macedo Sánchez, Orlando Efraín; Fournier, NicolasEl volcán Ubinas (16°22’S, 70°54’O; 5672 msnm) se encuentra ubicado en la Zona Volcánica de los Andes Centrales y es considerado como el más activo en el sur del Perú, por sus 23 episodios de alta actividad fumarólica y emisiones de cenizas reportado desde el año 1550 D.C. La caracterización geoquímica de las aguas termales y frías asociadas al sistema hidrotermal del volcán Ubinas muestra una relación entre las diferentes aguas y se clasifican como aguas NaCl y Ca (Mg)-Cl(SO₄). Su composición resulta de la mezcla de tres miembros externos: 1) Un reservorio clorurado profundo (RCP), 2) Un reservorio de agua fría (RAF), y 3) Un componente de fluidos volcánicos (FV). El modelo conceptual de circulación de los fluidos asociados al sistema hidrotermal del Ubinas, muestra que las aguas se mezclan de la siguiente manera: 1) Una “mezcla a nivel regional”, que corresponde a las fuentes cloruradas, y 2) Una “mezcla local”, que corresponde a las demás muestras. Las aguas ricas en Cl, comúnmente relacionadas a un reservorio clorurado profundo de fluido geotermal, parecen ser totalmente equilibrados en el sistema Na-K-Mg. A la inversa, las aguas de las fuentes Mariposa y Salinas Huito, parecen lograr un equilibrio parcial químico. Las aguas de baja salinidad presentan una química típica de aguas inmaduras que muestran relativamente altas concentraciones de Mg causadas por la disolución isoquímica de las rocas. Por lo tanto, un sistema hidrotermal bien desarrollado, afectado por entradas visibles de un sistema activo magmático, es comúnmente la principal fuente de descarga de fluidos en el volcán Ubinas. Por otro lado, en los años 1999 a 2006, el periodo de monitoreo de los iones Cl y SO₄, presentó variaciones en la concentración, con incremento de SO4 a mediados del 2000, y luego, en el 2001 se observa otra anomalía que es la disminución de SO₄, posiblemente asociado al terremoto de 23 de Junio del 2001. Posteriormente desde el 2002 hasta el 2006 se notó una considerable disminución del ion SO₄ y el aumento de Cl- en menor escala, así como el incremento de la actividad fumarólica en la cumbre, antes de la crisis volcanica del Ubinas, que se inició en Marzo del 2006 con emisión de cenizas.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 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.