Abstract:
Despite volcanic quiescence, several glaciers on volcanic edifices and constrained within volcanic craters are influenced by subglacial thermal activity including direct or indirect degassing, heat output, and hydrothermal changes within the volcanic edifice. One unique feature from these interactions is subglacial caves formed due to thermal gradients between the lithosphere and the cryosphere. The Cascade Volcanic Arc includes the best studied examples and stretches more than 1,100 km from Mount Garibaldi in British Columbia (Canada) to Lassen Peak in northern California (USA). This presentation will outline examples of volcano-ice interactions and explain the dynamics of the subglacial voids formed. While strong glacier retreat has occurred at Mount Hood (Oregon), subglacial hydrothermal springs resulted in the formation of caves in ice at the rock-ice margin. The glacial plug and cave system on top of Mount Rainier (Washington) appears to hold a dynamic equilibrium over five decades. These passages, more than 3.8 km surveyed in the dual summit craters, also host a melt- and condensate-formed subglacial lake. Mount St. Helens (Washington) represents an unique environment with an expanding glacier. Glacial advance towards the new lava dome and subsequent dome-glacier interaction resulted in the formation of subglacial cave passages extending up to 82 m deep into the glacier. The slowly decreasing heat transfer since 2008, clearly evident in colder and inactive fumaroles, has led to a significant decrease in cave expansion and simultaneous glacier enlargement over the past year. At Mount Meager in Canada, subglacial fumaroles created a void which became subaerial by glacial ablation, with passages now maintained by air advection and heat output. Finally, at Mount Baker (Washington), a significant cave system appears to be maintained by a combination of fumarolic activity, subglacial warm springs, and meltwater which is thermally influenced by warm subglacial sediments. These environments have proven valuable for additional studies in astrobiology and testing instruments for extraplanetary life detection.
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