Cerro Blanco volcanic complex: a collapsing caldera in the Southern Central Andes?

JOSÉ VIRAMONTE; J.M. ARNOSIO; PABLO EUILLADES; MAURO BLANCO; G. ASH; B. HEIT; M. POODTS; S. CASTRO GODOY; R. BECCHIO; G. GROPELLI; J. KLOTZ

Pucón, Chile

Congreso; IAVCEI General Assembly 2004; 2004

International Association of Volcanology and Chemistry of the Earth’s Interior

Cerro Blanco volcanic complex (S 26° 45` - W 67° 45`) is the youngest (200.000 – 150.000 years) caldera in the Southern Central Andes. A perfect piston-like 5 km in diameter caldera is associated to a large (45 km long) pyroclastic flow, post caldera domes with associate pyroclastic flow with big pumice fragments (up 5 m in diameter) that filled the caldera. However, several previous collapse structures and rock units can be recognized forming a nested caldera complex. The youngest piroclastic flow (Campo de la Piedra Pomez flow) is ryolitic in composition (70-74.4 %SiO2) and shows a variation from co-lag ignimbritic proximal facies to a pumice rich distal facies. A thermal anomaly (~ 100°C) was detected in the central part of the caldera. Pritchard & Simons (2002), from radar interferometry reported a subsidence of 2,5 cm/year for an area of 10 km in diameter related to the Cerro Blanco Caldera. In order to validate this data, and modelate the possible collapse of the caldera, a high precition 5 benchmarks GPS network was monumented and measured for the first time in April 2004 and 5 broad band digital continuous seismometer network was installed in February 2004. Seismic station will be recorded during 1 year. New GPS network measurement is planned for the next year. Geological mapping using ASTER images, petrological, geochemical, and isotopic studies are in course.