Surficial Extent And Conceptual Model Of Hydrothermal System At Mount Rainier, Washington

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Journal Article: Surficial Extent And Conceptual Model Of Hydrothermal System At Mount Rainier, Washington

Abstract
A once massive hydrothermal system was disgorged from the summit of Mount Rainier in a highly destructive manner about 5000 years ago. Today, hydrothermal processes are depositing clayey alteration products that have the potential to reset the stage for similar events in the future. Areas of active hydrothermal alteration occur in three representative settings: 1. (1) An extensive area (greater than 12,000 m2) of heated ground and slightly acidic boiling-point fumaroles at 76-82°C at East and West Craters on the volcano's summit, where alteration products include smectite, halloysite and disordered kaolinite, cristobalite, tridymite, opal, alunite, gibbsite, and calcite.2. (2) A small area (less than 500 m2) of heated ground and sub-boiling-point fumaroles at 55-60°C on the upper flank at Disappointment Cleaver with smectite alteration and chalcedony, tridymite, and opal-A encrustations. Similar areas probably occur at Willis Wall, Sunset Amphitheater, and the South Tahoma and Kautz headwalls.3. (3) Sulfate- and carbon dioxide-enriched thermal springs at 9-24°C on the lower flank of the volcano in valley walls beside the Winthrop and Paradise Glaciers, where calcite, opal-A, and gypsum are being deposited. In addition, chloride- and carbon dioxide-enriched thermal springs issue from thin sediments that overlie Tertiary rocks at, or somewhat beyond, the base of the volcanic edifice in valley bottoms of the Nisqually and Ohanapecosh Rivers. Maximum spring temperatures of 19-25°C and 38-50°C, respectively, and extensive travertine deposits have developed in these more distant localities. The heat flow, distribution of thermal activity, and nature of alteration minerals and fluids suggest a conceptual model of a narrow, central hydrothermal system within Mount Rainier, with steam-heated snowmelt at the summit craters and localized leakage of steam-heated fluids within 2 km of the summit. The lateral extent of the hydrothermal system is marked by discharge of neutral sulfate-enriched thermal water from the lower flank of the cone. Simulations of geochemical mass transfer suggest that the thermal springs may be derived from an acid sulfate-chloride parent fluid which has been neutralized by reaction with andesite and highly diluted with shallow groundwater. The model may accomodate some of the thermal springs beyond the base of the edifice. Present heat flow from Mount Rainier is substantial relative to other Cascade Range volcanoes and does not appear to have diminished since at least the late 19th century. Evidence of older hydrothermal processes found in Holocene lithic tephra and debris avalanches record activity more extensive but similar in chemical composition to that of today.

Author 
David Frank








Published Journal 
Journal of Volcanology and Geothermal Research, 1995





DOI 
Not Provided
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Citation

David Frank. 1995. Surficial Extent And Conceptual Model Of Hydrothermal System At Mount Rainier, Washington. Journal of Volcanology and Geothermal Research. (!) .