Based on observations of satellite imagery and SIGMET reports, the Buenos Aires VAAC reported that during 14-19 May ash plumes from Chaitén rose to altitudes of 5.5-9.1 km (18,000-30,000 ft) a.s.l. and drifted N, NE, and E. Cloudy conditions often inhibited observations. A thermal anomaly was present in the crater on 19 May.

Based on estimates made during an overflight of the area, ONEMI reported on 14 May that about 90 percent of the town of Chaitén was flooded. SERNAGEOMIN reported that on 15 May ashfall accumulated up to 1 mm thick on a ship and an island to the W, and several areas inland were white due to ash cover. Lahars continued to cause the Chaitén and Blanco-Rayas rivers to overflow, affecting new areas in Chaitén town. The Alert Level remained at Red.

According to news articles, the military evacuated small groups of mostly journalists and troops remaining in areas near Chaitén on 19 May. A court ordered police to use force if necessary to move the few remaining people that refused to evacuate to areas outside of the 50 km high-risk zone.

Geological Summary. Chaitén is a small caldera (~3 km in diameter) located 10 km NE of the town of Chaitén on the Gulf of Corcovado. Multiple explosive eruptions throughout the Holocene have been identified. 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 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 recorded eruption, beginning in 2008, produced major rhyolitic explosive activity and building a new dome and tephra cone on the older rhyolite dome.

Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Reuters, Buenos Aires Volcanic Ash Advisory Center (VAAC), Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI)