SERNAGEOMIN reported that during 29 April-4 May gas-and-ash plumes rose up to 2 km from Chaitén's growing Domo Nuevo 1 and Domo Nuevo 2 lava-dome complex. Collapses originating from unstable slopes generated block-and-ash flows. An overflight on 1 May revealed a large central spine fractured into three main blocks. The surface of the lava dome complex was very irregular and several spines had grown 100 m above the dome surface. Seismicity remained high. The Alert Level remained at Red. Based on analysis of satellite imagery, SIGMET notices, web camera views, and information from the Puerto Montt Flight Information Region (FIR), the Buenos Aires VAAC reported that during 5 and 10-12 May, ash plumes rose to altitudes of 2.1-4.6 km (7,000-15,000 ft) a.s.l. and drifted N, NE, and ENE.

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