SERNAGEOMIN lowered the Alert Level for Cerro Hudson to Green (the lowest level on a four-color scale) on 7 September, based on decreased activity. Neither morphological changes nor thermal anomalies were visible in satellite images or webcam views during 16-31 August. Seismicity remained low and sulfur dioxide emissions were not recorded.

Geological Summary. The ice-filled, 10-km-wide caldera of 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 6,700 years ago was one of the largest known in the southern Andes during the Holocene; another eruption about 3,600 years ago also produced more than 10 km3 of tephra. An eruption in 1991 formed a new 800-m-wide crater in the SW portion of the caldera.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)