At Chaiten Volcano, Chile
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rim and on the north flank of the volcano, Interdisciplinary Studies of Eruption and thick volcaniclastic fill in channels on the east and south flanks. The northward blast leveled forest over 4 square kilome- at Chaiten Volcano, Chile ters and left a narrow, outer zone of standing trees with scorched foliage and limbs (see PAGES 381-382 and associated wood and sediment deposi- Figure S1b in the online supplement). tion, especially along the Rio Chaiten, which Altogether, approximately 400 square High-silica rhyolite magma fuels Earth's drains the southern sector of the volcano. kilometers of forest in rugged terrain to the largest and most explosive eruptions. Recur- Floodwater and sediment devastated much north, east, and south of the volcano expe- rence intervals for such highly explosive of the town of Chaiten (population -5000), rienced severe damage. Forest damage in eruptions are in the 100-to 100,000-year a coastal village built on a fan of older vol- proximal areas beyond the blast-affected time range, and there have been few direct canic flood and lahar deposits 10 kilometers area resulted trom a rain of tephra that observations of such eruptions and their south of the volcano. Collapse of about 10% stripped foliage and branches from the for- immediate impacts. Consequently, there of the new lava dome on 19 February 2009 est canopy; from tephra deposition in tree was keen interest within the volcanology sent a hot pyroclastic flow, which charred crowns, leading to limb fall; and from possi- community when the first large eruption trees, to within 3 kilometers of the town ble but as yet unknown physiological effects of high-silica rhyolite since that of Alaska's [Duhart et aI., 2009; SERNAGEOMIN, 2009]. of tephra and volcanic gases on foliage Novarupta volcano in 1912 began on 1 May Field teams investigated and sampled and of burial of the soil surface by tephra 2008 at Chaiten volcano, southern Chile, a eruption products on and flanking the lava fall deposits. Many species in these native, 3-kilometer-diameter caldera volcano with dome and volcano, conducted stratigraphic broadleaf, evergreen forests have the capac- a prehistoric record of rhyolite eruptions studies of the 2008-2009 deposits, sur- ity to sprout from scorched, delimbed, and [Naranjo and Stern, 2004; Servicio Nacio- veyed thermal and gas fluxes from the lava fallen trees, which is influencing ecological nal de Geologia y Miner(a (SERNAGEOMIN). dome, and investigated ecologic and hydro- responses to the eruption. The diverse taxa 2008; Carn et al., 2009; Castro and Dingwell, logic impacts of the eruption. Researchers and suite of ecological disturbance mecha- 2009; Lara, 2009; Munoz et al., 2009]. Vig- mapped and sampled multiple lava lobes nisms operating at Chaitenmake it a rich orous explosions occurred through 8 May on the dome using short-duration helicopter environment for extending knowledge of vol- 2008, after which explosive activity waned landings within the caldera's moat and hell- cano ecology. and a new lava dome was extruded, copter dredging of areas that were otherwise Sedimentological observations show that In early 2010, seismicity, sulfur dioxide inaccessible. Fieldwork confirms that alter during the explosive phase of the erup- emissions of less than 100tons per day, the initial explosions, the volcano erupted a tion, volcaniclastic deposits to 8 meters thermal imagery, and visual observations rhyolite lava dome, which grew to a size of thick choked the upper reaches of Rio Chai- showed that the lava dome was still grow- approximately 500 million cubic meters (see ten, and at least 6 meters of sediment filled ing slowly, but there was no indication of an Figure Sla in the online supplement) within the fiver channel in and near the lown of impending explosion or dome collapse. Cap- about 3 months [Carn et al., 2009). Like the Chaiten during a period of intense rain- italizing on this relative quiescence of the prehistoric lava dome at Chaiten, the cur- fall in the waning stages of the explosive volcano, an interdisciplinary team of 21 geol- rent dome is composed of rhyolite obsidian phase (see Figures S1c and S1d in the online ogists, geophysicists, geochemists, hydrolo- and microcrystalline rhyolite lava. The rapid supplement), Sediment transport, stor- gists, and ecologists from Chile, the United eruption rate (averaging -60 cubic meters age, and flooding in the river system have States, Mexico, Australia, and Italy (for a per second) is unusual for rhyolite magma, been strongly alfected by newly introduced complete list of participants, see the online which is generally considered too viscous to woody debris and local diversion of the river supplement to this Eos issue (http://www sustain such high rates without fragmenting. through extensive floodplain forest cover. .agu.org/eos_elec/)) conducted an inten- Photogrammetric analysis of oblique aerial Sediment overwhelmed the Chaiten airport sive, helicopter-supported field campaign at photographs and satellite imagery combined and parts of the town, rerouted the river Chalten volcano from 19January to 8 Febru- with studies of the petrology of the rhyolite through the middle of town, and nearly bur- ary 2010. are under way to better quantify and under- ied the highway bridge on the only Chilean stand the conditions that enabled the rapid land route to southern Patagonia, graphi- Observations of the Eruption and Aftermath eruption rate. cally illustrating the hazards posed by vol- Curiously, the eruption severely damaged canic flooding and sedimentation to a vul- extensive tracts of forest despite producing nerable downstream community. The river only limited column collapse pyroclastic is delivering sediment and felled logs to flows but left trees standing on caldera walls the Gulf of Corcovado, building a delta that within hundreds of meters of vents opened extends more than a kilometer from the orig- through the prehistoric lava dome. Field inal shoreline, and threatening the only ferry observations documented a directed blast port in the region. Additional studies are deposit (similar to, but 2 orders of magnitude needed to evaluate and forecast the long- smaller than, that from the 1980 eruption of term impacts of sediment delivery on local Mount St. Helens) within and on the caldera river systems and the gulf. It has been widely reported that 2008 technology officer Mary Brett Rogers-Springs; Guarda. G., and R. Moreno (2008), Monumenta marked the first eruption at Chaiten in 9400 and economic and political affairs officer Cartogmphica Cbiloensia, 205 pp., Corp. Patrimo- nio Cult. de Chile, Santiago, years [Naranjo and Stern, 2004; Carn et al., Grace Choi of the U.S.Embassy, Santiago, for Lara, L. E. (2009). The 2008 eruption f the Chaiten 2009: Castro and Dingwell, 2009]. Volcanoes their keen interest and support. We also thank o volcano, Chile: A preliminary report, Andean former national director Alejandro Vio Grossi that erupt after long dormant periods tend Geol., 36(1), 125-129. to have large eruptions [Blong, 1984],a rela- and geological branch director Waldo Vivallo Munoz, J., D. Basualto, C. Delgado, C. Gallegos, tionship to which Chaiten appears to con- Sandoval of SERNAGEOMIN, and Fernando and H. Moreno (2009), Asistencia geologica form. However, observations of fresh rhyolite Gil, chief of SERNAGEOMIN's Observatorio durante la fase explosive inicial de mayo 2008 de pyroclastic deposits, ash beds, and appar- Volcanologico de los Andes del Sur (OVDAS), la erupcion del volcan Chaiten, Andes del Sur, ently eruption-related flood deposits newly for their strong support and ongoing collabo- paper presented at the XII Congreso Geologico exposed near the surface but below the 2008 ration. We acknowledge exceptional helicop- Chileno, Soc. Geol. de Chile, Santiago, Chile, deposits raise doubts about the presumed ter support from pilot Roberto Prieto of FAASA 22-26 Nov. Naranjo, J. A.. and C. R. Stern (2004), Holocene length of dormancy since the last eruption. Aviacion. Funding to support our work was tephrochronology the southernmost art provided by the USGSVolcano Hazards Pro- of p Observations, as well as hislorical records (42o30' -45oS) of the Andean Southern Volcanic [Guarda and Moreno, 2008], suggest the pos- gram, SERNAGEOMIN's Chilean Volcano Mon- Zone, Rev. Geol. Chile, 31(2), 225-240. sibility that the volcano may have been active itoring Network (RNVV) and Puerto Varas Servicio Nacional de Geologia y Mineria much more recently. Radiometric dating and Technical Office, Chilean Fondecyt projects (SERNAGEOMIN) (2008), Erupcion del volcan additional stratigraphic and petrologic stud- 1080249 and 1090774, the U.S.National Sci- Chaiten: Informes tecnicos, Obs, Volcanol. de los ies are needed to better understand the vol- ence Foundation International Program, and Andes del Sur, Temuco, Chile. (Available at www cano's eruptive history. the U.S.Forest Service International Program. .sernageomin.cl) Current goals in this continuing proj- Servicio Nacional de Geologia y Mineria ect are to better understand the magmatic (SERNAGEOMIN) (2009), Erupcion del volcan References Chaiten: Informes tecnicos, Obs. Volcanol, e los and eruptive processes at this rhyolite vol- d Andes del Sur, Temuco, Chile, (Available at www cano and the sedimentological and ecologi- Blong, R. J. (1984), Volcanic Hazards: A Sourcebook .sernageomin.d) cal impacts of its eruption, to glean insights on the Effects of Eruptions, 424 pp., Academic, regarding rhyolite eruptions in general, and Sydney, N. S. W, Australia. to forecast probable future activity includ- Carn, S. A., J. S. Pallister, L. Lara, J. W. Ewert, -JOHN S. PALLISTER, JON J. MAJOR, THOMAS C, ing downstream hazards and patterns and S. Watt, A. J. Prata, R. J. Thomas, and G. ViI· PIERSON, and RICHARD P. HOBUTT,USGS, Vancouver, trends of ecologic change. Efforts are under larosa (2009), The unexpected awakening of Wash.; E-mail: [email protected]; JACOB B. LoWEN- ST RN, USGS, Menlo Park, Calif.; JOHN C. EICHELBERG- way to promote further discussion of the Chaiten volcano, Chile, Eos Trans.AGU, 90(24), E 205-206.