Report on Nevados de Chillan (Chile) — 5 May-11 May 2021
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 5 May-11 May 2021
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2021. Report on Nevados de Chillan (Chile) (Sennert, S, ed.). Weekly Volcanic Activity Report, 5 May-11 May 2021. Smithsonian Institution and US Geological Survey.
Nevados de Chillan
36.868°S, 71.378°W; summit elev. 3180 m
All times are local (unless otherwise noted)
SERNAGEOMIN noted that sulfur dioxide emissions and thermal anomalies at Nevados de Chillán’s Nicanor Crater had both increased in March, and inflation began on 27 March. During the second half of April the dome grew at a higher rate, with growth concentrated on the W part. The dome was 66 m high at the center. The L5 lava flow advanced and was about 940 m long, and 50 m thick near the flow front. The effusion rate increased on 28 April. During 2-5 May activity was characterized by increased crater incandescence and a series of intense explosions that destroyed part of the summit lava dome. Dense ash plumes rose above the crater. Block-and-ash flows traveled less than 400 m down the NE flank and pyroclastic flows traveled short distances SW. During 4-5 May the effusion rate increased and the L5 lava flow advanced. A new lava flow (L6) emerged on 5 May from the summit crater and descended 100 m down the NE flank. A high-temperature elongated deposit in between the L5 and L6 flows was visible in infrared images. 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.