Servicio Nacional de Geología and Minería (SERNAGEOMIN) Observatorio Volcanológico de Los Andes del Sur (OVDAS) reported continuing activity during 11-17 July associated with growth of the Gil-Cruz lava dome in Nevados de Chillán’s Nicanor Crater. Seismicity consisted of long-period events and tremor associated with explosions. The webcam recorded pulsating white gas emissions, nighttime incandescence, and intermittent ejection of ballistics from explosions. A local M3.7 earthquake recorded at 2055 on 13 July was associated with an explosion, and located 430 m below Nicanor Crater. Another earthquake associated with an explosion was recorded at 1530 on 14 July. The event was a local M3.9 and occurred at a depth of 1.4 km. Weather conditions inhibited visual observations of the crater, though a thermal camera measured increased thermal output with a max temperaturs of 300 degrees Celsius. A third earthquake, a M3.8 located at a depth of 1.8 km, was recorded at 0324 on 15 July. Incandescent material was ejected 340 m high. These three explosions partially destroyed the lava dome, ejecting material onto the N and NE flank. The Alert Level remained at Orange, the second highest level on a four-color scale, and residents were reminded not to approach the crater within 3 km. ONEMI maintained an Alert Level Yellow (the middle level on a three-color scale) for the communities of Pinto, Coihueco, and San Fabián.

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)