Andean Geology 40 (2): 324-358. May, 2013 doi: 10.5027/andgeoV40n2-a09
Andean Geology
formerly Revista Geológica de Chile www.andeangeology.cl
Pyroclastic density currents associated with the 2008-2009 eruption of Chaitén Volcano (Chile): Forest disturbances, deposits, and dynamics
Jon J. Major1, Thomas C. Pierson1, Richard P. Hoblitt1, Hugo Moreno2
United States Geological Survey, Volcano Science Center, Cascades Volcano Observatory, 1300 SE Cardinal Court, Vancouver, Washington 98683, USA.
[email protected];
[email protected];
[email protected] 2 Servicio Nacional de Geología y Minería, Observatorio Volcanológico de Los Andes del Sur, Dinamarca 691, Temuco, Chile.
[email protected] 1
ABSTRACT. Explosive activity at Chaitén Volcano in May 2008 and subsequent dome collapses over the following nine months triggered multiple, small-volume pyroclastic density currents (PDCs). The explosive activity triggered PDCs to the north and northeast, which felled modest patches of forest as far as 2 km from the caldera rim. Felled trees pointing in the down-current direction dominate the disturbance zones. The PDC on the north flank of Chaitén left a decimeters-thick, bipartite deposit having a basal layer of poorly sorted, fines-depleted pumice-and-lithic coarse ash and lapilli, which transitions abruptly to fines-enriched pumice-and-lithic coarse ash. The deposit contains fragments of mostly uncharred organics near its base; vegetation protruding above the deposit is uncharred. The nature of the forest disturbance and deposit characteristics suggest the PDC was dilute, of relatively low temperature (
