On 17 May, OVDAS-SERNAGEOMIN reported that seven hybrid earthquakes were detected beneath Chaitén at a depth of 1 km; the highest local magnitude recorded was 3.6. A second report on 19 May noted that seismicity had slightly increased during the previous few months, characterized by an increase in magnitude and occurrence of long-period events, volcano-tectonic events, and hybrid events. Thermal anomalies from the lava dome complex had also been detected although the report did not state when. The Alert Level was raised to Yellow, on a three-color scale.

Geological Summary. Chaitén is a small, glacier-free caldera with a compound Holocene lava dome located 10 km NE of the town of Chaitén on the Gulf of Corcovado. Early work had identified only a single explosive eruption during the early Holocene prior to the major 2008 eruption, but later work has identified multiple explosive eruptions throughout the Holocene. A rhyolitic obsidian lava dome occupies much of the caldera floor. Obsidian cobbles from this dome found in the Blanco River are the source of prehistorical artifacts from archaeological sites along the Pacific coast as far as 400 km from the volcano to the N and S. The caldera is breached on the SW side by a river that drains to the bay of Chaitén. The first historical eruption, beginning in 2008, produced major rhyolitic explosive activity and growth of a lava dome that filled much of the caldera.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)