The unexpected awakening of Chaitén volcano, Chile

CARN, SIMON; PALLISTER, J. S.; LARA, L.; EWERT, S.; PRATA, A. J.; THOMAS, R.J.; VILLAROSA, GUSTAVO

EOS TRANSACTIONS - AMERICAN GEOPHYSICAL UNION

American Geophisical Union

Lugar: Maryland, Estados Unidos; Año: 2009 vol. 90 p. 205 - 212

0096-3941

On 2 May 2008 a large eruption began unexpectedly at the inconspicuous Chaitén volcano in Chile?s southern volcanic zone (SVZ). Chaitén?s last known major eruption took place over 9000 years ago (Naranjo and Stern, 2004), although its recent eruptive history is still under investigation. Like the largest eruption of the 20th Century, at Katmai-Novarupta, Alaska in 1912, the 2008 Chaitén eruption discharged rhyolite magma, a high-silica composition associated with extremes of eruptive behavior ranging from gentle lava effusion to violent gas-driven explosions. As the first major rhyolitic eruption in the modern geophysical era, it is permitting observations that will be benchmarks for future such events. It reignites the debate on what processes rekindle long-dormant volcanoes, justifies efforts to mitigate rare but significant natural hazards through ground-based monitoring, and confirms the value of timely observations provided by satellite remote sensing. The eruption began abruptly with stratospheric (exceeding ~12 km altitude) ash columns, before transitioning into lava dome effusion accompanied by continuous low-altitude ash plumes (Basualto et al., 2008; Ewert et al., 2008; Prata et al., 2008a). Apocalyptic nighttime photographs of eruption plumes suffused with lightning were circulated globally. Three stratospheric tephra columns were generated during the first week of the eruption (Ewert et al., 2008; Prata et al., 2008a), which probably ranks between 4 and 5 on the volcanic explosivity index (VEI) scale, making it among the largest since the August 1991 eruption of Hudson (also in the SVZ ~300 kilometers south of Chaitén). The Chaitén eruption presents a rare opportunity to sample distal ashfall deposits on land, permitting evaluation of ash dispersion and fallout models (Folch et al., 2008; Watt et al., 2008), but no significant climate impact is expected due to low sulfur dioxide (SO2) emissions (Prata et al., 2008a, 2008b).           Impacts of the eruption were extensive (Ewert et al., 2008; Guffanti et al., 2008).  Floods and lahars inundated Chaitén town and its residents were evacuated; its future remains uncertain. Ashfall affected communities in Chile and Argentina, depositing over 10 centimeters of ash in Futaleufú, Chile and small amounts on Argentina?s Atlantic coast, 1000 kilometers from Chaitén. Drifting ash clouds and ashfall shut down regional airports and cancelled hundreds of domestic flights in Argentina and Chile and numerous international flights, and several aircraft encountered the ash clouds. Ash has heavily impacted the aquiculture industry in the nearby Gulf of Corcovado, curtailed ecotourism and closed regional nature preserves. The eruption spurred the Chilean government to boost support for monitoring and hazard mitigation at the 43 most hazardous of Chile?s 122 active volcanoes.