OVDAS-SERNAGEOMIN reported that during 29 January-4 February the web camera near Copahue recorded white gas plumes rising 350-1,550 m above the crater and drifting E and SE. Seismicity fluctuated but mostly remained at low levels. The Alert Level was lowered to Yellow on 4 February.

The Buenos Aires VAAC noted that although a pilot reported an ash plume between the altitudes of 3-4.6 km (10,000-15,000 ft) a.s.l., no ash was detected in mostly clear satellite images. The VAAC also noted that steam with possible diffuse ash was recorded by the OVDAS webcam.

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), Buenos Aires Volcanic Ash Advisory Center (VAAC)