SERNAGEOMIN reported that on 19 February a partial lava-dome collapse of the S flank of Chaitén's Domo Nuevo 1 and Domo Nuevo 2 lava-dome complex generated lateral explosions, block-and-ash flows, and pyroclastic flows. A pyroclastic flow traveled S down the Chaitén (Blanco) River valley, stopping within about 5 km of Chaitén town (10 km SW). Ash plumes rose to an altitude of 9.1 km (30,000 ft) a.s.l. and drifted W and SE. Ash fell in Futaleufú (about 65 km ESE), and, according to ONEMI, accumulated to thicknesses of 3-5 mm. Overflights revealed that the tree leaves in a forest near the S flank were burned and steam rose from new deposits in the Chaitén River valley. Ash-and-steam plumes rose to altitudes of 7.1-9.1 km (23,300-30,000 ft) a.s.l. A 500 x 500 m scar from the partial dome collapse was seen on the S flank. Seismicity decreased to pre-collapse levels by the afternoon. The steaming from pyroclastic flow deposits was again seen in the channel and on the shores of the Chaitén River valley during an overflight the next day, but had greatly decreased by 21 February. Using photos taken during 19 and 20 February overflights, scientists estimated that 10 million cubic meters of material was removed from the S flank of the dome complex. According to a news article, about 200 people were living in Chaitén town on 19 February. ONEMI reported that many of those people self-evacuated, but about 46 people remained in the town, refusing to leave. On 23 February, lahars traveled down river valleys and an off-white plume was seen on the web camera rising about 1 km above the lava domes.

Based on SIGMET notices, analysis of satellite imagery, and web camera views, the Buenos Aires VAAC reported that during 23-24 February ash plumes rose to altitudes 2.1-3 km (7,000-10,000 ft) a.s.l. and drifted NE and E.

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