OVDAS-SERNAGEOMIN and ONEMI reported that during 2-7 October a webcam at Copahue recorded white and gray emissions rising as high as 300 m above the El Agrio Crater rim and drifting ENE, SE, and SSE. By 7 October the number and intensity of seismic events detected at Copahue had decreased to low levels. The volcano Alert Level was lowered to Yellow (second lowest level on a four-color scale). ONEMI maintained the Yellow Alert (the middle level on a three-color scale) for residents, and stated that the public should stay at least 1 km away from El Agrio Crater.

Geological Summary. Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Sources: Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), Servicio Nacional de Geología y Minería (SERNAGEOMIN), Servicio Geológico Minero Argentino (SEGEMAR)