Observatorio Volcanológico de los Andes del Sur (OVDAS)-SERNAGEOMIN and ONEMI reported increased activity at Planchón-Peteroa beginning in the morning of 16 December. Low-intensity pulses of tremor were detected by the seismic network and associated with pulsating grayish gas emissions which rose no higher than 800 m above the vent rim. Webcams recorded crater incandescence during the night of 15-16 December. The Alert Level remained at Yellow (the middle level on a three-color scale) for the volcano, and ONEMI maintained Alert Level Yellow for the communities of Molina (66 WNW), Curicó (68 km NW), Romeral (75 km NW), and Teno (68 km NW).

Geological Summary. Planchón-Peteroa is an elongated complex volcano along the Chile-Argentina border with several overlapping calderas. Activity began in the Pleistocene with 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 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.

Sources: Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), Servicio Nacional de Geología y Minería (SERNAGEOMIN)