SERNAGEOMIN reported continuing activity at Nevados de Chillán’s Nicanor Crater during 11-18 October. At 0043 on 12 October a long-period earthquake was recorded and was possibly associated with an emission, but weather clouds prevented visual confirmation. A long-period earthquake at 1504 on 13 October was followed by a dense gray-black ash plume that rose almost 2.3 km and drifted NNE. Pyroclastic flows descended the NNE flank. Another long-period event, at 2108 on 15 October, was followed by the ejection of incandescent material as high as 800 m above the crater rim and as far as 700 m NE onto the flank. Explosions at 1613 on 16 October produced a dense grayish-black ash plume that rose more than 400 m and drifted SE, though weather clouds inhibited views. A pyroclastic flow traveled more than 500 m NNE. The Alert Level remained at Yellow, the second lowest level on a four-color scale. Sistema Nacional de Prevención y Respuesta ante Desastres (SINAPRED) maintained an Alert Level Yellow (the middle level on a three-color scale) for the communities of Pinto and Coihueco, and reminded residents not to approach the crater within 2 km.

Geological Summary. The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The dominantly andesitic Cerro Blanco (Volcán Nevado) stratovolcano is located at the NW end of the massif. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The Volcán Nuevo lava-dome complex formed during 1906-1945 on the NW flank of Viejo. The Volcán Arrau dome complex was then constructed on the SE side of Volcán Nuevo between 1973 and 1986, and eventually exceeded its height. Smaller domes or cones are present in the 5-km valley between the two major edifices.

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