SERNAGEOMIN reported that during 1-15 November activity at Copahue decreased to low levels. Passive gas emissions generally rose 200-300 m above the vent, though on 15 November they rose 760 m. The report also noted no changes to deformation, low levels of sulfur dioxide emissions, low seismicity, partial restoration of the crater lake, and the absence of nighttime crater incandescence since late October. The Alert Level was lowered to Green (the lowest level on a four-color scale) on 15 November. ONEMI cancelled the Yellow Alert for the Alto Biobío municipality, but declared a “Preventive Early Warning” ensuring continued surveillance of the area and coordination within the Civil Protection System.

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)