The 2005 catastrophic acid crater lake drainage, lahar, and acidic aerosol formation at Mount Chiginagak volcano, Alaska, USA: Field observations and preliminary water and vegetation chemistry results

mass of snow and ice 400-m-wide and 105-m-thick began melting in the summit crater of Mount Chiginagak volcano sometime between November 2004 and early May 2005, presumably owing to increased heat flux from the hydrothermal system, or possibly from magma intrusion and degassing. In early May 2005, an estimated 3.8 106 m3 of sulfurous, clay-rich debris and acidic water, with an accompanying acidic aerosol component, exited the crater through a tunnel at the base of a glacier that breaches the south crater rim. Over 27 km downstream, the acidic waters of the flood inundated an important salmon spawning drainage, acidifying Mother Goose Lake from surface to depth (approximately 0.5 km3 in volume at a pH of 2.9 to 3.1), killing all aquatic life, and preventing the annual salmon run. Over 2 months later, crater lakter sampled 8 km downstream of the outlet after considerable dilmeltwater was a weak sulfuric acid solution (pH = 3.2, SO4 = 504 = 7.92 mg/L). The acid flood waters caused severe vegetation daand leaf kill along the flood path. The crater lake drainage was accompanied by an ambioructic flow of acidic aerosols that follrotic leaf damage to vegetation in a 29 km2 area along and above affected streams, in areas to heights of over 150 m above streaating extremely elevated atmospheric sulfur content. The most abundant airborne phytotoxic constituent was likely sulfuric acid ter lake drainage event. Two mechanisms of acidic aerosol formation are proposed: (1) generation of aerosol mist through turbuleenon of simultaneous vegetation damaging acidic aerosols accompanying drainage of an acidic crater lake has important implicatioAe waution from glacial mg/L, Cl = 53.6 mg/L, and Fmage, including plant death owed the flood path, contributing to defoliation and necm level. Moss species killed in the event contained high levels of sulfur, indicaerosols that were generated during the catastrophic partial crant flow of acidic water and (2) catastrophic gas exsolution. This previously undocumented phenomns for the study of hazards associated with active volcanic crater lakes.