SERNAGEOMIN and SEGEMAR reported increased activity at Copahue, beginning with minor, sporadic increases in tremor first detected at the end of May. During 30 June-2 July tremor was elevated and volume of water in the crater lake decreased significantly. Coincidently crater incandescence was visible in nighttime webcam views and gas emissions increased. Residents reported volcanic gas odors. Increased gas-and-steam emissions during 1100-1400 on 2 July contained minor amounts of ash that left visible deposits on the SE and ENE flanks. The Alert Level remained at 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.

Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Servicio Geológico Minero Argentino (SEGEMAR)