According to the Buenos Aires VAAC, a pilot observed a gray plume rising from Copahue to altitudes of 6.1-7.6 km (20,000-25,000 ft) a.s.l. and drifting NE on 11 October. Satellite images indicated no ash; the webcam recorded continuous emissions of water vapor and gas, and low-levels of ash. The next day the webcam recorded weak steam-and-gas emissions possibly with minor amounts of ash drifting SE.

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: Buenos Aires Volcanic Ash Advisory Center (VAAC)