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Mount Rainier National Park geologic resource evaluation report

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Author(s): J Graham

Document Type: Natural Reource Report NPS/NRPC/GRD/NRR-2005/007
Publisher: National Park Service
Published Year: 2005
Pages: 46
DOI Identifier:
ISBN Identifier:

Mount Rainier is the second highest peak in the conterminous United States at 14,410 feet (4393 meters). Over 35 square miles (91 sq km) of snow and ice encase Mount Rainier making it the largest single- peak glacial system in the United States. Glaciers radiate from the summit masking its explosive potential.

Like the other volcanic peaks in the Cascade Range, Mount Rainier is a stratovolcano that formed through successive eruptions of lava and pyroclastic flows. These types of volcanoes have the most violent types of eruptions as witnessed by the May 18, 1980, eruption of Mt. St. Helens. Large eruptions of Mt. Rainier took place as recently as 1,000 years ago. Today, steam from the volcano generates ice caves and fumeroles near the summit of the volcano.

In 2002 a scoping meeting for MORA was held to discuss geologic maps available for conversion to a digital format. The identification of park specific geologic issues was only addressed in a cursory manner. Nonetheless, some of major geologic management issues in the park include:

• Potential volcanic eruptions, producing tephra (ash), volcanic projectiles, pyroclastic flows and surges,lateral blasts, lava flows, and volcanic gases
• Edifice failure and debris avalanches
• Glacial outburst floods
• Lahars and debris flows
• Hydrothermal alteration zones
• Seismicity
• Snow avalanches, rock falls, ice falls, and landslides
• Cryptobiotic soils and soil erosion
• Glacial Monitoring

Due to the proximity of over 1.5 million people living within the shadow of Mount Rainier, it is considered the most dangerous volcano in the Cascade Range. A major eruption melting the ice and snow could send debris flows, pyroclastic flows, and lahars towards Puget Sound and the Seattle/Tacoma metropolitan area.

Volcanic hazard mapping has identified areas in the park that could be affected in the future by debris flows, lahars, pyroclastic flows and surges, lava flows, volcanic projectiles, tephra falls, and lateral blasts. Longmire Village and the Cougar Rock, Ohanapecosh, White River, Ipsut Creek, and Sunshine Point campgrounds are all vulnerable to these hazards. Monitoring of volcanic activity is on- going. There is a need for an emergency response plan to address these hazards.

The reaction between groundwater and rising gas and steam from the underlying magmatic system creates zones of hydrothermally altered rock. Fumeroles at the summit of the volcano are one result of this reaction. Another result is the largest volcanic ice- cave system in the world at the summit of Mount Rainier.

Earthquakes are also geologic hazards associated with Mount Rainier. Earthquakes precede a volcanic eruption although not every earthquake means an eruption is imminent. Other than Mt. St. Helens, Mount Rainier is the most seismically active volcano in the Cascades.

The destruction of cryptobiotic soils and general soil erosion by human impacts are important issues. A systematic soil survey is needed to identify and characterize soil types.

The glaciers of Mount Rainier are hydrologically significant and have both immediate and long- term impacts on the local and regional environment. Recent changes in glacial extent and volume make glacial monitoring an important issue for MORA.

Mount Rainier is known for interesting geologic features. Glacial features on Mount Rainier include horns, cirques and cirque lakes, glacial valleys, arêtes, and characteristic glacial topography defined by glacial moraines and glacial drift.

Volcanic processes have left many volcanic features, as well. Lava cones and flows, satellite volcano structures, rock walls, and summit features are present on Mount Rainier.

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Suggested Citations:
In Text Citation:
Graham (2005) or (Graham, 2005)

References Citation:
Graham, J., 2005, Mount Rainier National Park geologic resource evaluation report: Natural Reource Report NPS/NRPC/GRD/NRR-2005/007, National Park Service, 46 p..