Report on Cerro Hudson (Chile) — 16 December-22 December 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 December-22 December 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Cerro Hudson (Chile). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 16 December-22 December 2020. Smithsonian Institution and US Geological Survey.
45.9°S, 72.97°W; summit elev. 1905 m
All times are local (unless otherwise noted)
SERNAGEOMIN reported that a notable change in seismicity at Cerro Hudson was characterized by an increase in the frequency and magnitude of volcano-tectonic (VT), hybrid (HB), and long-period (LP) signals during 1-15 December. Two swarms of VT earthquakes were recorded during 10-11 December, with the largest event, a local M 2.9, located 4.7 km ESE of the caldera’s center at a depth of 4.6 km. The largest of five HB signals was a local M 3.1, located 4 km ESE at a depth of 4.3 km. The earthquake locations suggested a relatively shallow source SE of the caldera. No deformation or surficial changes were observed. The Alert Level was raised to Yellow (second highest level on a four-color scale) on 22 December, based on the increased seismicity. ONEMI warned the communities of Aysén and Río Ibáñez, declaring a status of “Preventive Early Warning”, a level in between Green and Yellow.
Geologic Background. The ice-filled, 10-km-wide caldera of the remote Cerro Hudson volcano was not recognized until its first 20th-century eruption in 1971. It is the southernmost volcano in the Chilean Andes related to subduction of the Nazca plate beneath the South American plate. The massive volcano covers an area of 300 km2. The compound caldera is drained through a breach on its NW rim, which has been the source of mudflows down the Río de Los Huemeles. Two cinder cones occur N of the volcano and others occupy the SW and SE flanks. This volcano has been the source of several major Holocene explosive eruptions. An eruption about 6700 years ago was one of the largest known in the southern Andes during the Holocene; another eruption about 3600 years ago also produced more than 10 km3 of tephra. An eruption in 1991 was Chile's second largest of the 20th century and formed a new 800-m-wide crater in the SW portion of the caldera.