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The newly formed crater lake of Chiginagak volcano, located on the Alaska Peninsula, tunneled through the glacier/crater rim interface in the summer of 2005 producing a flood and minor lahar. The crater lake water was acidic due to dissolved fumarolic gases, and the flood damaged and killed vegetation along the channels through which it flowed. The drainage event at Chiginagak volcano is unique among observed crater lake breakouts in that the flood was accompanied by a dense gas flow that killed vegetation in a large swath over 150 m above the flood path. The airborne agents responsible for the vegetation damage are likely sulfuric acid and HF dissolved in water droplets, carried along by a dense gravity current of CO2. Prior to the formation of the crater lake, the summit crater at Chiginagak was filled with snow and ice. The presence and subsequent melting of this ice cover may be an important factor in explaining how a large volume of CO2 and acidified water could coexist and be released simultaneously. A model for the conditions at Chiginagak that can explain this phenomena will be proposed. A hydrodynamic model will be used to simulate the water flood and a heavy gas dispersion model will be used to simulate the transport of the gas. Simulations performed with these models will aim to reveal whether the gas traveled independently of the flood water or coupled to the flood surface; to estimate a reasonable initial concentration of the phytotoxic gases in the crater lake water prior to the breakout; and to determine whether there is something distinctive about the topography at Chiginagak that allowed this event to occur or if there is a danger of similar events at other volcanoes.
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