The Servicio Nacional de Geología y Minería (SERNAGEOMIN) reported lower levels of activity at Copahue during 16-30 November. Sulfur dioxide emissions were low, averaging 529 ± 79 tons per day (t/d) with a maximum value of 907 t/d detected on 24 November. No thermal anomalies were identified in satellite images. Gas plumes rose 280 m above the crater rim and did not contain ash. No crater incandescence was observed at night. Deformation data showed a minor change from deflation to inflation. Seismic data indicated a more stable pattern. The water lake in the summit crater had returned and grown to 9,340 square meters by 30 November. In general activity levels were low. On 6 December the Alert Level was lowered to Green (the lowest level on a four-color scale).

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.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)