Servicio Nacional de Geología y Minería (SERNAGEOMIN) reported nighttime crater incandescence at Copahue on 16 October. According to Servicio Geológico Minero Argentino (SEGEMAR), webcam images recorded an increase in surface activity at 0430 on 19 October, which consisted of an ash emission that rose 200 m above the crater and drifted SE. The Alert Level remained at Green (the lowest level on a four-color scale) and the public was reminded to stay 500 m away from the 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: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Servicio Geológico Minero Argentino (SEGEMAR)