On 17 June OVDAS-SERNAGEOMIN reported increased activity at Copahue during the previous days, characterized by low-altitude gas emissions containing particulate matter. A period of increased seismicity was recorded in the afternoon on 16 June accompanied by crater incandescence and emissions visible in webcam images.

The report noted that very-long-period earthquakes had been recorded in previous months, and a series of volcano-related seismic events were detected in an area SSW of the volcano on 20 March. Additionally, satellite images showed a reduction in the size of the crater lake. These recent changes coupled with increased seismicity prompted SERNAGEOMIN to raise the Alert Level to Yellow (second lowest level on a four-color scale) and restrict access to an area within 1 km of El Agrio Crater. ONEMI raised a Yellow Alert (the middle level on a three-color scale) for residents of the Alto Biobío municipality.

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), Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI)