CURRENT ACTIVITY OF THE NEVADO SABANCAYA STRATOVOLCANO (SOUTH PERU) -GEOLOGICAL FRAMEWORK AND VOLCANIC HAZARD-ZONE MAPPING

The May 28, 1990, eruption of Nevado Sabancaya volcano (south volcanic zone of Peru) ended a dormant stage of about 200 year duration. This ice-clad stratovolcano still poses a threat to about 35,000 people and to irrigated tilled land in the Rio Colca and Siguas valleys. This st udy aims to develop a model for volcanic hazards appraisal and hazard- zone mapping available for remote stratovolcanoes like Nevado Sabancay a which lack geological information. The method is based on remote sen sing using 5 SPOT images collected during 1990, geological and geomorp hological survey of the summit volcano, and calculation of parameters for tephra dispersal and pyroclastic flowage. Nevado Sabancaya is pote ntially hazardous because it was active 200 years ago, and because it is still ice-clad despite its three years of recent activity. In addit ion, recent tephra-fall deposits on similar volcanoes in this area poi nt to the occurrence of Plinian eruptions during the past 500 years. T wo maps showing hazard zones for tephra fallout, pyroclastic flows, la hars, and potentially catastrophic events are presented. Hazard zones are portrayed according to three types of behaviour: moderate-magnitud e vulcanian activity (e.g. june 1990-december 1992), violent explosive activity, and a potentially paroxysmal Plinian event.