SERNAGEOMIN reported that a phreatic explosion from Copahue occurred at 2023 on 4 July that deposited bombs (less than 12 cm in diameter), lapilli (less than 4 cm), ash, and gray clay smelling strongly of sulfuric acid along the E flank of the crater. During an overflight on 7 July, OVDAS officials observed the deposit and measured a moderate amount of gas emissions (an average of 4,000 tons per day of SO2), a relatively low level of water in the crater, and low temperatures of the fumaroles within El Agrio crater. DOAS stations had measured up to 18,000 tons/day of SO2 on the day of the explosion. An anomalous tremor signal was detected at 0823 on 5 July that was associated with an explosion from El Agrio crater; a microphone installation 13 km E also detected an acoustic signal. The explosion generated a plume 1,000 m above the crater. The Alert Level remained at Yellow.

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)