SERNAGEOMIN reported that during 12-16 April, seismicity from Chaitén's Domo Nuevo 1 and Domo Nuevo 2 lava-dome complex continued to increase. M 4-4.5 hybrid earthquakes occurred every 2-3 hours. Web camera views showed increased incandescence from the lava domes and gas-and-ash plumes that were wider at their base than previously seen. The plumes rose 1.5 km (4,900 ft) above the domes. The Alert Level remained at Red. Based on web camera views, analysis of satellite imagery, and a SIGMET notice, the Buenos Aires VAAC reported that during 16 and 18-19 April, ash plumes rose to altitudes of 1.8-2.4 km (6,000-8,000 ft) a.s.l. and drifted SE and N.

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)