Geologic Publications for Mount Rainier
Hydrothermal processes at Mount Rainier Washington
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David G. Frank
University of Washington
Field studies and thermal-infrared mapping at Mount Rainier indicate areas of active hydrothermal alteration where excess surface heat flux is about 9 megawatts. Three representative settings include:
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. 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, and other probably similar areas at Willis Wall, Sunset Amphitheater, and the South Tahoma and Kautz headwalls;
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 where maximum spring temperatures are 19-25°C and 38-50°C respectively and where extensive travertine deposits have developed.
The heat flow, distribution of thermal activity, and nature of alteration products indicate that a narrow, central hydrothermal system exists within Mount Rainier forming steam-heated snowmelt at the summit craters and localized leakage of steam-heated fluids within 2 kilometers of the summit. The lateral extent of the hydrothermal system is limited in that only sparse, neutral sulfate-enriched thermal water issues 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 ground water.
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.
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In Text Citation:
Frank (1985) or (Frank, 1985)
Frank, D.G., 1985, Hydrothermal processes at Mount Rainier Washington: Ph.D Dissertation, University of Washington, 218 p..