SERNAGEOMIN reported continuing explosive and effusive activity at Nevados de Chillán’s Nicanor Crater during 16-30 June, alomg with increased sulfur dioxide emissions and thermal anomalies. Explosions generated ash plumes that rose as high as 1.4 km above the crater rim and crater incandescence at night; incandescent material was ejected as far as 500 m onto the N, E, and S flanks. The L5 and L6 lava flows continued to be active, with increased effusion rates during 17-19 and 27-28 June. During the periods of increased effusion rates the flow temperatures were higher, nighttime incandescence was more intense, emissions rose higher, and more pyroclastic flows were recorded. The pyroclastic flows traveled less than 500 m down the NE flank and were sourced from collapses at the sides of L6 and the front of L5. The average temperature was 131 degrees Celsius with a maximum of 174 degrees for L5 and an average of 163 degrees Celsius with a maximum of 181 degrees for L6. Temperatures at the vents at Nicanor Crater were as high as 360 degrees Celsius during explosive phases. Satellite images indicated that the L5 lava flow was 1,033 m long and L6 was 894 m long, and that the distal end of L6 had thickened. The average sulfur dioxide emission rate was 694 (± 43) tons/day, reaching a high value of 903 on 19 June. There was a total of 35 thermal anomalies. The Alert Level remained at Yellow, the second lowest level on a four-color scale. ONEMI stated that Alert Level Yellow (the middle level on a three-color scale) remained in place for the communities of Pinto and Coihueco, noting that the public should stay at least 2 km away from the crater.

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)