Assessment of volcanic hazards of El Misti and in the city of Arequipa, Peru, based on GIS and simulations, with emphasis on lahars

Our study aims to assess the volcanic and hydrological hazards and risks on El Misti volcano and in the city of Arequipa in southern Peru, which are exposed to the effects of tephra fall, pyroclastic flows, debris avalanches, lahars, and floods. Arequipa, Peru's second city, is home to approximately 850,000 people who live in the shadow of El Misti volcano whose summit is located approximately 3.5 km vertically and 17 km horizontally to the NE of the city centre. Since 1990, Arequipa has undergone unprecedented and largely uncontrolled urban expansion, with new settlements being constructed on the volcano's SW and S flanks and along radial valleys within 9-11 km of the summit. The purpose of this work is to assess hazards of tephras falls, pyroclastic flows, and lahars based on geologic record, mapping, statistical analysis, and GIS techniques. Three hazard zone maps portray a probable small-scale vulcanian eruption scenario, a mid-range sub-Plinian eruption scenario and a large-scale Plinian eruption scenario. Our emphasis here is on lahars and on simulating debris flows and hyperconcentrated flows by using the semi-empirical code LAHARZ. Output maps show that all simulated lahars with anticipated volumes in the range of 1.5 to 11 million m ³, can be conveyed across the city of Arequipa through the Rio Chili valley and three tributary drainages termed Quebradas San Lazaro, Huarangal, and Agua Salada.