SERNAGEOMIN and SEGEMAR reported that elevated seismicity (continuous tremor) at Copahue was recorded on 16 July and accompanied by ash emissions observed by local residents. Sulfur dioxide emissions were anomalous on 4, 6, and 20 July; values were 2,100 and 1,713 tons per day on 2 and 4 July, respectively, on the high end of normal values. On 20 July residents of La Araucanía described an odor indicating hydrogen sulfide gas emissions. On 23 July the Alert Level was raised to Yellow (the second lowest level on a four-color scale). ONEMI raised a Yellow Alert (the middle level on a three-color scale) for residents of the Alto Biobío municipality and access to an area within 1 km of El Agrio Crater was restricted to the public.

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