RECENT ERUPTIVE ACTIVITY AT EL-MISTI VOLCANO (SOUTH PERU) - IMPLICATIONS FOR HAZARD ASSESSMENT IN AREQUIPA AREA

About 1 million people live at risk in Arequipa city which lies 15 km from the vent of the active El Misti stratovolcano (5,825 m), in the P liocene to Holocene Central Andean Volcanic Zone. Built on volcaniclas tic bedrock, El Misti encompasses a stratovolcano of Pleistocene age a nd a modern stratocone. The bulk of the modern strato-cone consists of a series of stubby lava flows and pyroclastic debris reaching 2,800 m in thickness. The interpretation of eighteen tephra profiles situated in gorges of the western to southeastern foot of the El Misti volcano shows that the volcano has erupted repeatedly during the upper Pleist ocene, the more recent products corresponding to repeated plinian erup tions. The uppermost huge tephra sequence lies on a poorly developed p alaeosol containing charcoal that was dated by C-14 method at 1,920 +/ - 200 yrs BP. Historical data refer to some volcanic activity at AD 14 40-1470. Based on the tephrostratigraphic study, the most important vo lcanic hazards for the 900,000 inhabitants of Arequipa are four-fold: tephra fallout as thick as 50 cm falling from high plinian columns, py roclastic flows expected in any valley towards the northern suburbs, l ahars during the wet season (December to March), and uncommon debris a valanches.