Sernageomin raised the technical alert for the Planchón-Peteroa volcanic complex from Green to Yellow (2 of 4) on July 6, 2018. The last eruption of this volcano took place in 2011.
The decision was made due increased seismic activity under the volcano, accompanied by episodes of vigorous degassing.
Officials warned there is a possibility of eruption, lahars and pyroclastic flows.
The Civil Protection Service recommends a safety zone of 3 km (1.8 miles) around active craters.
The last eruptive phase of this volcano started on February 17, 2011, and ended on June 26 (± 1 days), of the same year. It had Volcanic Explosivity of 3.
Planchón-Peteroa is an elongated complex volcano along the Chile-Argentina border with several overlapping calderas.
Activity began in the Pleistocene with the construction of the basaltic-andesite to dacitic Volcán Azufre, followed by formation of basaltic and basaltic-andesite Volcán Planchón, 6 km to the north. About 11 500 years ago, much of Azufre and part of Planchón collapsed, forming the massive Río Teno debris avalanche, which traveled 95 km (59 miles) to reach Chile’s Central Valley.
Subsequently, Volcán Planchón II was formed. The youngest volcano, andesitic and basaltic-andesite Volcán Peteroa, consists of scattered vents between Azufre and Planchón. Peteroa has been active into historical time and contains a small steaming crater lake. Historical eruptions from the complex have been dominantly explosive, although lava flows were erupted in 1837 and 1937.