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Mount Rainier National Park Geologic Resource Evaluation Report

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Mount Rainier National Park Geologic Resource Evaluation Report National Park Service U.S. Department of the Interior Geologic Resources Division Denver, Colorado Mount Rainier National Park Geologic Resource Evaluation Report Mount Rainier National Park Geologic Resource Evaluation Geologic Resources Division Denver, Colorado U.S. Department of the Interior Washington, DC Table of Contents List of Figures .............................................................................................................. iv Executive Summary ...................................................................................................... 1 Introduction ................................................................................................................... 2 Purpose of the Geologic Resource Evaluation Program ............................................................................................2 Regional Location.......................................................................................................................................................2 General Geology ........................................................................................................................................................2 Geologic Issues............................................................................................................. 7 Seismicity ...................................................................................................................................................................7 Tephra ........................................................................................................................................................................8 Volcanic Projectiles ....................................................................................................................................................8 Pyroclastic Flows and Pyroclastic Surges ..................................................................................................................8 Lava Flows .................................................................................................................................................................9 Volcanic Gases...........................................................................................................................................................9 Debris Avalanches, Debris Flows, and Lahars ...........................................................................................................9 Lateral Blasts............................................................................................................................................................11 Hydrothermal Alteration Zones.................................................................................................................................11 Glacial Outburst Floods ............................................................................................................................................12 Flooding....................................................................................................................................................................12 Geologic Hazards During Dormant Periods..............................................................................................................13 Soils..........................................................................................................................................................................15 Sites at Mount Rainier within volcanic and non-volcanic hazard zones....................................................................18 Geologic Features and Processes............................................................................. 19 Glacial Features and Glacier Processes ..................................................................................................................19 Volcanic Features.....................................................................................................................................................20 Thermal Features and Ice Caves .............................................................................................................................21 Map Unit Properties .................................................................................................... 22 Map Unit Properities Table .......................................................................................................................................23 Geologic History.......................................................................................................... 25 Tertiary Period: Eocene Epoch.................................................................................................................................25 Tertiary Period: Oligocene Epoch.............................................................................................................................26 Tertiary Period: Miocene Epoch ...............................................................................................................................26 Granitic Intrusive Rocks of Miocene and Pliocene Age ............................................................................................27 Quaternary Period: Pleistocene Epoch.....................................................................................................................27 Quaternary Period: Holocene (Recent) Epoch .........................................................................................................27 Recent events associated with Mount Rainier..........................................................................................................34 Recent events associated with Mount Rainier (cont.)...............................................................................................35 Appendix A: Geologic Map Graphic .......................................................................... 38 Attachment 1: Digital Geologic Map CD MORA Geologic Resource Evaluation Report iii List of Figures Figure 1 Location of glaciers, campgrounds, streams, and visitor centers at Mount Rainier National Park. .................4 Figure 2 Geologic time scale.........................................................................................................................................5 Figure 3 Volcanoes on the west coast of the conterminous United States....................................................................6 Figure 4 Hazard zones for lahars and pyroclastic flows from Mount Rainier...............................................................17 Figure 5 Sites at Mount Rainier within volcanic and non-volcanic hazard zones ........................................................18 Figure 6 Paleogeographic map of the western margin of North America during the Paleocene and early Eocene ....29 Figure 7 Simplified geologic map of Mount Rainier National Park...............................................................................30 Figure 8 Paleotectonic map of western United States in the Miocene Epoch .............................................................31 Figure 9 Plate tectonic cross-section sketch ...............................................................................................................32 Figure 10 Generalized north-south geologic cross-section through Mount Rainier National Park ..............................32 Figure 11 Map of late Miocene and younger magmatic systems in the Cascade Mountains ......................................33 Figure 12 Recent events associated with Mount Rainier ............................................................................................35 Figure 13 Holocene tephras in Mount Rainier National Park ......................................................................................35 iv NPS Geologic Resources Division Executive Summary This report accompanies the digital geologic map produced by Geologic Resource Evaluation staff for Mount Rainier National Park. It contains information relevant to resource management and scientific research. Mount Rainier is the second highest peak in the Volcanic hazard mapping has identified areas in the park conterminous United States at 14,410 feet (4393 meters). that could be affected in the future by debris flows, Over 35 square miles (91 sq km) of snow and ice encase lahars, pyroclastic flows and surges, lava flows, volcanic Mount Rainier making it the largest single- peak glacial projectiles, tephra falls, and lateral blasts. Longmire system in the United States. Glaciers radiate from the Village and the Cougar Rock, Ohanapecosh, White summit masking its explosive potential. River, Ipsut Creek, and Sunshine Point campgrounds are all vulnerable to these hazards. Monitoring of volcanic Like the other volcanic peaks in the Cascade Range, activity is on- going. There is a need for an emergency Mount Rainier is a stratovolcano that formed through response plan to address these hazards. successive eruptions of lava and pyroclastic flows. These types of volcanoes have the most violent types of The reaction between groundwater and rising gas and eruptions as witnessed by the May 18, 1980, eruption of steam from the underlying magmatic system creates Mt. St. Helens. Large eruptions of Mt. Rainier took place zones of hydrothermally altered rock. Fumeroles at the as recently as 1,000 years ago. Today, steam from the summit of the volcano are one result of this reaction. volcano generates ice caves and fumeroles
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