Asymmetrical structure, hydrothermal system and edifice stability: The case of Ubinas volcano, Peru, revealed by geophysical surveys

Katherine Gonzales, Anthony Finizola, Jean François Lénat, Orlando Efrain Macedo Sánchez, Domingo Ramos, Jean Claude Thouret, Nicolas Fournier, Vicentina Cruz, Karine Pistre

Resultado de la investigación: Contribución a una revistaArtículorevisión exhaustiva

11 Citas (Scopus)

Resumen

Ubinas 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.

Idioma originalInglés
Páginas (desde-hasta)132-144
Número de páginas13
PublicaciónJournal of Volcanology and Geothermal Research
Volumen276
DOI
EstadoPublicada - 15 abr. 2014
Publicado de forma externa

Nota bibliográfica

Funding Information:
Geophysical surveys were funded by the Instituto Geofísico del Perú (IGP) and the Institut de Recherche pour le Développement (IRD) . We thank R. Pinto, P. Navarro, J. Taco, M. Uribe, V. Montesinos and the inhabitants of Ubinas village for field assistance. We thank IGP and Cooperation Office of the French Embassy that supported scientific exchanges between institutions. We thank Koki Aizawa and André Revil for the constructive reviews of our manuscript.

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