Instituto Geofísico del Perú (IGP) reported that lahars descended the SE flanks at El Misti at 1448 on 23 January and at 1642 on 25 January. The report noted that possible areas of impact included the Andamayo and Agua Salada river drainages in the Chiguata District. The public was warned to stay away from the drainages and roads on the SE flank.

Geological Summary. El Misti is a symmetrical andesitic stratovolcano with nested summit craters that towers above the city of Arequipa, Peru. The modern symmetrical cone, constructed within a small 1.5 x 2 km wide summit caldera that formed between about 13,700 and 11,300 years ago, caps older Pleistocene volcanoes that underwent caldera collapse about 50,000 years ago. A large scoria cone has grown with the 830-m-wide outer summit crater. At least 20 tephra-fall deposits and numerous pyroclastic-flow deposits have been documented during the past 50,000 years, including a pyroclastic flow that traveled 12 km to the south about 2000 years ago. The most recent activity has been dominantly pyroclastic, and strong winds have formed a parabolic dune field of volcanic ash extending up to 20 km downwind. An eruption in the 15th century affected nearby Inca inhabitants. Some reports of historical eruptions may represent increased fumarolic activity.

Source: Instituto Geofísico del Perú (IGP)