Report on Chaiten (Chile) — 30 April-6 May 2008

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 April-6 May 2008
Managing Editor: Sally Kuhn Sennert

Please cite this report as:

Global Volcanism Program, 2008. Report on Chaiten (Chile). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 30 April-6 May 2008. Smithsonian Institution and US Geological Survey.

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42.833°S, 72.646°W; summit elev. 1122 m

All times are local (unless otherwise noted)

SERNAGEOMIN reported that Chaitén erupted on 2 May, following increased seismicity in the region the day before. A pulsating white to gray ash plume rose to an estimated altitude greater than 21 km (68,900 ft) a.s.l. and drifted SSE. The Alert Level was raised to Red. Based on observations of satellite imagery and pilot reports, the Buenos Aires VAAC reported an ash plume at altitudes of 13.7-16.8 km (45,000-55,000 ft) a.s.l. drifted NE. According to news articles, Chile's government declared a state of emergency on 2 May and several hundred people were evacuated from the town of Chaitén (10 km SE). The eruption was initially thought to have been from Minchinmávida, about 17 km ENE, which last erupted in 1835.

According to news sources, ashfall was reported during 2-6 May both locally and up to hundreds of kilometers away, affecting water supplies and roads. Based on observations of satellite imagery and pilot reports, the Buenos Aires VAAC reported that during 3-6 May ash plume rose to altitudes of 7-10.7 km (23,000-35,000 ft) a.s.l. and drifted SE, E, W, and NE. News sources indicated that about 4,000-5,000 people were evacuated from the town of Chaitén and surrounding areas as the eruption continued. On 5 May, ONEMI (Oficina Nacional de Emergencia - Ministerio del Interior) reported that evacuations took place in Futaleufú, about 65 km ESE, where about 30 cm of ash accumulated. One elderly person died during the evacuation efforts. On 6 May, ONEMI and SERNAGEOMIN reported that the eruption became more forceful and generated a wider and darker gray ash plume to an estimated altitude of 30 km (98,400 ft) a.s.l. All remaining people in Chaitén were ordered to evacuate, as well as anyone within 50 km of the volcano.

Geologic Background. 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), Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), Buenos Aires Volcanic Ash Advisory Center (VAAC), Associated Press, Agence France-Presse (AFP)