SERNAGEOMIN reported that during 14-20 October a gas-and-ash plume from Chaitén rose to an altitude of 3.1 km (10,200 ft) a.s.l. The lava dome continued to grow, especially the E side. The Volcanic Alert level remained at Red. Based on web camera views, information from the Puerto Montt Flight Information Region (FIR), analysis of satellite imagery, and SIGMET reports, the Buenos Aires VAAC reported that during 14-18 and 21 October continuous ash plumes from Chaitén rose to altitudes of 2.1-4 km (7,000-13,000 ft) a.s.l. and drifted N, NE, and ESE.

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.

Sources: Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Nacional de Geología y Minería (SERNAGEOMIN)