Causes, and impacts of lahars generated by the April, 2015 eruption of Calbuco volcano, Chile

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Calbuco is a 2015m high, glacier capped, stratovolcano in the heavily populated Los Lagos district of southern Chile (41 degrees 19'48"S 72 degrees 37'06"W) with a history of very large volcanic eruptions in 1893-95, 1906-7, 1911-12, 1917, 1932, 1945, 1961 and 1972. On 22 April, 2015 Calbuco experienced a powerful 90 minute eruption at 18:04h followed by additional major eruptions at 01:00h and 13:10h on 23 & 30 April, respectively, resulting in the evacuation of 6500 people and the imposition of a 20 km radius exclusion zone. These eruptions generated ash plumes up to 15 km high, causing widespread disruption and damage to property to the NE of Calbuco. Hot pyroclastic flows (glowing avalanches) descended into several river catchments radiating from the volcano transforming into hot floods of water and sediment known as lahars which travelled distances of up to 14 km, reaching surrounding populated areas resulting in extensive damage to infrastructure and property. Although Calbuco, along with other nearby glaciated volcanoes in the Andes, has experienced recent reductions in the size of its glaciers, the current eruption indicates that even volcanoes with small glacier ice volumes can generate significant lahars. Our scientific goal is to determine the causes, dynamics and impacts of lahars generated during the ongoing Calbuco eruption. To achieve our goals we will undertake fieldwork on the volcano as soon as is practically possible. In the field we'll catalogue the immediate geomorphic and sedimentary impact of lahars on the river valleys systems surrounding Calbuco. We'll Identify lahar wash marks and will survey these use differential satellite positioning systems and ground based laser scanning. We'll conduct a helicopter based laser scanning survey of the lahar channels and will also use an airborne Radar to determine the presence and thickness of any ice left on the mountain after these eruptions. We'll sample and describe the vertical characteristics of these fresh lahar deposits in detail. The Calbuco eruption provides an exceptional opportunity to examine the dynamics and sedimentary signature of rare hot lahars, as they are still cooling and degassing. We plan to conduct fieldwork as soon as possible before the onset of subsequent volcanic and rainfall-induced lahars which may mask the signature of these earlier events. Our research will contribute to a better understanding of hazardous lahar processes with the hope of reducing the risk to population.