Mount Rainier National Park 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2005/007

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 

Mount Rainier National Park 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2005/007

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, Colorado 80225 

September 2005 

U.S. Department of the Interior 

Washington, D.C.
The Natural Resource Publication series addresses natural resource topics that are of interest 

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gre_publications) on the internet, or by sending a request to the address on the back cover. 

Please cite this publication as: 

Graham, J. 2005. Mount Rainier National Park Geologic Resource Evaluation Report. Natural 

Resource Report NPS/NRPC/GRD/NRR—2005/007. National Park Service, Denver, 

Colorado. 

NPS D-535, September 2005 
 MORA Geologic Resource Evaluation Report iii

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 
 NPS Geologic Resources Division iv 

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
 MORA Geologic Resource Evaluation Report 1

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 

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. 
 NPS Geologic Resources Division 2 

Introduction 

The following section briefly describes the regional geologic setting and the National 

Park Service Geologic Resource Evaluation program. 

Purpose of the Geologic Resource Evaluation Program 

Geologic resources serve as the foundation of park 

ecosystems and yield important information needed for 

park decision making. The National Park Service Natural 

Resource Challenge, an action plan to advance the 

management and protection of park resources, has 

focused efforts to inventory the natural resources of 

parks. The geologic component is carried out by the 

Geologic Resource Evaluation (GRE) Program 

administered by the NPS Geologic Resources Division. 

The goal of the GRE Program is to provide each of the 

identified 274 “Natural Area” parks with a digital 

geologic map, a geologic evaluation report, and a 

geologic bibliography. Each product is a tool to support 

the stewardship of park resources and each is designed 

to be user friendly to non- geoscientists. In preparing 

products the GRE team works closely with park staff and 

partners (e.g., USGS, state geologic surveys, and 

academics). 

GRE teams hold scoping meetings at parks to review 

available data on the geology of a particular park and to 

discuss specific geologic issues affecting the park. Park 

staff are afforded the opportunity to meet with experts 

on the geology of their park during these meetings. 

Scoping meetings are usually held for individual parks 

although some meetings address an entire Vital Signs 

Monitoring Network. 

For additional information regarding the Geologic 

Resources of Mount Rainier National Park, please 

contact the Geologic Resources Division, Denver, 

Colorado, or visit the National Park Service website at 

http://www2.nature.nps.gov/geology. 

Regional Location 

Towering 1.5 miles (2.4 km) above the surrounding 

mountains and about 3 miles (5 km) above the lowlands 

to the west, Mount Rainier is the second highest peak in 

the conterminous United States at 14,410 ft (4393 m). 

Mount Rainier also has the distinction of having the 

greatest single- peak glacial system in the United States. 

Over 35 square miles (91 sq km) of snow and ice cover 

this active volcano. Glaciers radiate from its summit so 

that its rocky, ice- mantled slopes above timberline 

contrast vividly with the green, verdant forests that 

include old growth trees. The snowfields, alpine tundra 

with vivid alpine flowers, and dense forests provide the 

park visitor with a variety of visitor experiences. In 1899, 

235,625 acres were set aside as Mount Rainier National 

Park and today, 97% of this area is designated wilderness 

(Figure 1). 

The Native Americans know the mountain as Tahoma or 

Takhoma or Ta- co- bet, names meaning “Snow 

Mountain” or the “Mountain that was God” or “Place 

where the Waters Begin”. These names are more 

descriptive and perhaps capture the mountain’s impact 

on the surrounding region better than the European 

moniker “Rainier”, a name bestowed on the mountain by 

Captain Vancouver in 1792 in honor of his friend and 

superior officer, Rear Admiral Peter Rainier. 

In terms of its potential impact on human populations, 

this “mountain of fire and ice” is the most dangerous 

volcano in the Cascade Range. In the shadow of Mount 

Rainier, live over 1.5 million people. The glaciers on 

Mount Rainier provide a steady flow of water for 

hydroelectric power in the region, regardless of the 

season. However, should an eruption occur, these 35 

acres of ice and snow could melt and send debris flows 

towards Puget Sound and the Seattle/Tacoma 

metropolitan area. 

General Geology 

Compared to the total age of the earth, the rocks 

exposed within Mount Rainier National Park are 

relatively young. Earth formed about 4600 million years 

ago (4.6 billion years ago), but the rocks in the park 

formed within the last 60 million years, during the 

Tertiary and Quaternary Periods (Figure 2). By the time 

Mount Rainier formed, the dinosaurs were extinct and 

primitive ancestors of many of today’s familiar mammals 

roamed the Earth. The trees and plants growing in 

Tertiary forests were clearly forerunners of today’s 

forests. 

Mount Rainier is a stratovolcano, a composite volcano 

created through successive eruptions of lava and 

pyroclastic flows. It is one of more than a dozen 

stratovolcanoes perched on older rocks of the Cascade 

Range (Figure 3). The impressive eruption of Mount St. 

Helens in 1980, demonstrated the explosive nature of 

these types of volcanoes. 

The Cascade volcanoes are aligned in a north- south 

direction that roughly parallels the Pacific coastline for 

about 500 miles (800 km). The volcanic mountains of the 

Cascade Range are a small segment of the circum- Pacific 

volcanic belt, or “Ring of Fire,” that encircles the Pacific 

Ocean. Volcanoes in the Ring of Fire mark converging 

lithospheric plate boundaries where dense, oceanic crust 

is subducted beneath the less dense, overriding 

continental crust or an island arc. The volcanoes in 

Washington and Oregon are the result of the collision 

between the oceanic Juan de Fucca plate, traveling 

northeast, and the continental North American plate, 

moving westward. 
 MORA Geologic Resource Evaluation Report 3

The prevailing rock type of the Cascade volcanoes is 

andesite, an igneous rock of intermediate composition 

between light- colored, silica- rich rocks (e.g., rhyolite) 

and dark, basaltic rocks that contain very little silica. 

Andesite is typically dark gray or greenish black in color 

and is composed of approximately equal amounts of 

light- colored minerals like plagioclase feldspars and 

dark minerals like hornblende, olivine, and pyroxenes. 

The north- south trend of Cascade volcanoes is believed 

to be located above the zone of melting deep within the 

crust where rocks in the subducting plate begin to melt. 

Magma rises from this zone to erupt at the surface as 

lava. 

Lithospheric plates moving past one another generate 

earthquakes. Few large- scale earthquakes have occurred 

in historic time along the Pacific Northwest coastal area, 

but severe earthquakes accompanied by tsunamis have 

occurred in prehistoric time. The Cascade subduction 

zone may be storing strain energy that, when released, 

could result in catastrophic earthquakes and tsunamis 

along the Washington and Oregon coasts. 

The landscape of Mount Rainier is complex, but its 

origins are simple: fire and ice. The mountain first 

erupted about half a million years ago and as recently as 

in the 1840s. Two large eruptions took place, first about 

2,300 years ago and another 1,000 years ago. About 90 

percent of Mount Rainier’s eruptions have been in the 

form of lava flows, which is unusual for a composite cone 

(Harris et al., 1995). In contrast, most of the other 

Cascade volcanoes, including Mount St. Helens, have 

had a more violent history with few lava flows and a high 

volume of pyroclastics. Much of the ash and pumice on 

Mount Rainier’s slopes came from Mount St. Helens 

during explosive episodes like the 1980 eruption. 

The mountain’s great height and northerly location 

allowed glaciers to cut deeply into its volcanic deposits. 

Today, steam from the volcano creates ice caves near the 

summit of the volcano, and in the past, devastating debris 

flows and mudflows were triggered by lava and rock 

debris from Mount Rainier’s eruptions. The consistency 

of these mudflows on Mount Rainier is like wet cement. 

The collapse of unstable parts of the volcano has led to 

additional debris flows. At one time, the summit rose 

perhaps 2,000 ft (600 m) higher than it does today. About 

5,700 years ago, an eruption took off the top of the 

mountain and left a depression 1.25 miles (2.01 km) in 

diameter. The mountain is a history of lava flows, lahars, 

mudflows, pyroclastic explosions, and ash falls mixed 

with glacial debris, glacial outwash floods, and rockfalls. 
 NPS Geologic Resources Division 4 

Figure 1: Location of glaciers, campgrounds, streams, and visitor centers at Mount Rainier National Park. 
 MORA Geologic Resource Evaluation Report 5

Figure 2: Geologic time scale. Red lines indicate major unconformities between eras. Absolute ages shown are in millions in years. 

Scale is from the U.S.G.S. 
 NPS Geologic Resources Division 6 

Figure 3: Volcanoes on the west coast of the conterminous United States. Green areas on the map represent units of the National Park 

Service. 
 MORA Geologic Resource Evaluation Report 7

Geologic Issues 

A Geologic Resource Evaluation scoping session was held for Mount Rainier National 

Park on September 10- 12, 2002, to address the status of geologic mapping pertinent to the 

park. Resource management issues and needs were not discussed in depth. As a result, 

the following section only preliminarily discusses geologic resources management issues 

that may require attention from resource managers. 

On clear days, about 2.5 million people of the greater 

Seattle- Tacoma metropolitan area can see Mount 

Rainier. About 150,000 live in areas swept by lahars and 

floods that emanated from the volcano during the last 

6,000 years (Sisson et al., 2001). The large population at 

risk and the lack of information about Mount Rainier’s 

edifice geology, pre- Holocene history, and 

hydromagmatic system prompted its inclusion as one of 

16 volcanoes worldwide targeted for intense research as 

part of the United Nations’ International Decade for 

Natural Disaster Reduction (IDNDR). 

Decade Volcano designation led to new research and 

substantial progress in understanding hazards from 

Mount Rainier. In general, collapse hazards are greatest 

on the west flank and future edifice stability modeling 

promises to quantitatively assess collapse risks (Sisson et 

al., 2001). The likelihood of lahars formed by magma- ice 

interaction chiefly by pyroclastic flows is higher than was 

previously supposed. Such eruption- generated lahars 

threaten all valleys that radiate from the volcano. Mount 

Rainier has erupted more frequently than was previously 

known and the association between eruptions and lahars 

is stronger than previously thought. Although seismic 

and other eruption precursors serve to alert communities 

to increased risks, some sizeable lahars were shown to 

have no known eruptive triggers. 

Results from geologic mapping, remote sensing, 

geotechnical, and geochemical studies show that 

geologic features controlling the most potentially 

destructive volcanic hazard types lie primarily in the east 

and west sectors of the volcano (Zimbelman et al., 

2000B). The east and west sectors are more deeply 

dissected by glaciers, have hosted numerous historic 

debris avalanches and flows, and contain active 

fumaroles, large areas of hydrothermally altered rock, 

near- vertical fracture systems, and radial dikes. All of 

these geologic features offer the potential for large 

edifice- collapse events. In contrast, the north and south 

sectors of the volcano generally lack these features. 

Fewer collapse events have occurred in the north and 

south sectors. Risk mitigation efforts, therefore, will be 

most effective if they reflect this east- west distribution of 

the geologic controls on volcanic hazards. 

Volcanic hazards from Mount Rainier include those that 

occur during eruptions such as tephra falls, pyroclastic 

flows and surges,, volcanic projectiles, and lava flows and 

those that occur during dormant periods such as debris 

avalanches, lahars, and floods. The National Research 

Council (1994) included the following volcanic hazards 

or volcanic related events as potential threats to persons 

or property: 

• Volcanic eruptions – the eruption of ash flows and 

tephra (ash or pumice) 

• Edifice failure – the gravitational collapse of a portion 

of the volcano 

• Glacial outburst floods – the sudden release of 

meltwater from glaciers and snowpack or from glacier 

dammed lakes on the edifice 

• Lahars or debris flows, and debris avalanches – 

gravitational movement of commonly water- saturated 

volcanic debris down the steep slopes of the volcano 

and into nearby valleys 

Although boundaries have been applied to these hazard 

zones at Mount Rainier, too many uncertainties exist 

about the source, size and mobility of future events to 

locate these zones with absolute certainly (Hoblitt et al., 

1998). 

Seismicity 

Earthquakes are precursors to volcanic eruptions 

although not every earthquake means an eruption is 

eminent. Mount Rainier is considered to be the second 

most seismically active volcano in the Cascades, second 

only to Mount St. Helens (Kiver and Harris, 1999). In a 

given month, an average of 1- 2 high- frequency volcanotectonic (VT) earthquakes occurs directly beneath the 

summit (Moran and Malone, 2000). Seismicity is 

concentrated both at the edifice and to the west in a 

broad north- south belt known as the west Rainier 

seismic zone (WRSZ) (Sisson et al., 2001). The frequent 

seismicity raises concerns that earthquakes might be 

produced that would be powerful enough to trigger 

edifice collapse. 

At Mount Rainier Moran and Malone (2000) showed 

that VT earthquakes occur from 0.6 mile to 1.2 miles (1 

km to 2 km) below the inferred base of the volcanic 

edifice. Nearly all edifice- centered earthquakes originate 

beneath the base of the volcano atop a 6- mile- thick (10-

km- thick) region of low seismic velocity. This low 

seismic velocity zone is interpreted to be nearly solidified 

small magma bodies and hydrothermally altered rocks. 

WRSZ earthquakes are most consistent with a network 

of relatively short faults that could produce an 

earthquake with a probable maximum magnitude of 

about 5.5 rather than the magnitude 7 earthquake 
 NPS Geologic Resources Division 8 

anticipated if the zone were a single long fault. 

Conclusions from this research reduce, but do not 

eliminate, concerns for edifice collapse triggered by local 

or regional seismicity (Moran and Malone, 2000; Sisson 

et al., 2001). 

Tephra (Volcanic Ash) 

Explosive eruptions, like Mount St. Helens, produce 

vertical plumes of hot gases mixed with volcanic rock 

particles (tephra). If less dense than air, the mixture rises 

over the volcano’s vent until it reaches an altitude at 

which it ceases to be buoyant. Fine tephra or volcanic ash 

in the plume will be carried downwind and will fall to 

produce a deposit that covers a broad area. Tephra 

thickness and particle size usually decrease with 

increasing distance from the volcano. 

While large tephra fragments are capable of causing 

death and injury by impact and may be hot enough to 

start fires where they land, these hazards are usually 

restricted to within 6 miles (10 km) of the vent (Hoblitt et 

al., 1995, 1998). Most tephra- related injuries, fatalities, 

and social disruptions occur farther away from the vent, 

where tephra fragments may be less than one inch (a few 

centimeters) across. Clouds of ash block sunlight, greatly 

restrict visibility, and impede travel. Frequent lightning 

commonly accompanies such clouds. Inhaling volcanic 

ash may create or aggravate respiratory problems. Roofs 

may collapse with an accumulation of 4 inches (10 cm) or 

more of ash. Thin accumulations may ruin crops. Wet 

tephra can short out power lines. Fine tephra (ash) is 

abrasive and can damage mechanical devices. Tephra 

clouds are extremely hazardous to aircraft. Engines may 

stop and pilots’ visibility may be reduced. 

Even thin accumulations of tephra can profoundly 

disrupt social and economic activity over broad areas. 

For example 0.25 to 3 inches (6 to 80 mm) of volcanic ash 

caused significant disruptions in transportation, business 

activity, and community services in the Washington 

communities of Yakima, Ritzville, and Spokane when 

Mount St. Helens erupted in 1980. 

Relative to other Cascade volcanoes, Mount Rainier is a 

moderate tephra producer. The average time interval 

between eruptions is about 900 years (Hoblitt et al., 

1998). At present, maps for tephra fallout hazard are not 

detailed enough to distinguish among park developed 

areas because Mount Rainier is within tephra fallout 

zones from several other Cascade Range volcanoes. In 

the past, however, tephra fallout from Mount Rainier 

eruptions has been largely confined to the east half of the 

park due to prevailing westerly winds (Crandell, 1967). 

While Mount St. Helens produced voluminous pumicefall deposits, Mount Rainier has erupted only modest 

amounts of pumice in the Holocene. The rock record 

suggests that voluminous pumice eruptions as at Mt. St. 

Helens are less likely. (Sisson et al., 2001). However, 

voluminous pumice- fall deposits are known from the 

Pleistocene record of Mt. Rainier. The conspicuous 60-

foot- thick (20- m- thick) white band in Sunset 

Amphitheater headwall that can be seen from the 

southern Puget Sound lowlands is one of these 

Pleistocene pumice deposits. 

Volcanic Projectiles 

Volcanic projectiles are particles thrown from the vent 

on ballistic arcs, like artillery shells. The range of these 

projectiles rarely exceeds 3 miles (5 km) from the vent 

(Hoblitt et al., 1998). Most projectiles are less than 3 feet 

(1 m) across. The primary hazard from volcanic 

projectiles is from direct impact. Because they may be 

quite hot when they land, the projectiles also may start 

fires if they land near combustible materials. 

Pyroclastic Flows and Pyroclastic Surges 

Pyroclastic flows are denser- than- air mixtures of hot 

rock fragments and gases whose down slope movement 

is controlled by topography. Pyroclastic flows are 

composed of particles and gas, but if the mixture is gasrich, it is called a pyroclastic surge. A pyroclastic surge is 

only weakly controlled by topography. The two often 

occur simultaneously. 

Both pyroclastic flows and pyroclastic surges are 

extremely hazardous. Their speeds typically exceed 20 

miles/hour (10 m/s) and sometimes exceed 200 

miles/hour (100 m/s), making escape from their paths 

difficult or impossible (Hoblitt et al., 1998; NPS, 2001). 

Temperatures in pyroclastic flows are usually greater 

than 570o

 Fahrenheit (300o Celsius). Because of their high 

densities, high velocities, and high temperatures, 

pyroclastic flows can destroy all structures and kill all 

living things in their paths. Although they have lower 

densities and temperatures, pyroclastic surges may also 

be quite destructive and lethal. Animals may be killed by 

direct impact by rocks, severe burns, or suffocation. 

Deposits of pyroclastic flows and surges exist at Mount 

Rainier, but not in abundance (Figure 4). Pyroclastic flow 

deposits about 2,500 years old are exposed in the South 

Puyallup River valley, about 7.5 miles (12 km) southwest 

of the volcano’s summit. A thin surge deposit about 1,000 

years old was discovered in White River valley about 7 

miles (11 km) northeast of the summit (Hoblitt et al., 

1998). Pyroclastic flows that travel across glaciers, 

however, do not weld and so do not leave long- lasting 

deposits. The dearth of pyroclastic flows, therefore, may 

be the result of pyroclastic flows and surges passing over 

snow and ice and being converted to debris flows 

(Hoblitt et al., 1998; Sisson et al., 2001). Hot rock 

fragments melt snow and ice, mix with the meltwater, 

and form lahars. Because Mount Rainier supports 

glaciers on all its sides, pyroclastic flows and the lahars 

they produce threaten all the valleys that originate on the 

volcano.
 MORA Geologic Resource Evaluation Report 9

The types of pyroclastic flows at Mount Rainier are 

termed “block- and- ash” pyroclastic flows that are 

generally the result of lava dome collapse. Since Mount 

Rainier has only one lava dome exposed, the pyroclastic 

flows probably derived from other processes such as 

vent clearing explosions, voluminous hydromagmatic 

eruptions, or the sudden failure of thick, viscous lavas 

flowing over steep headwalls (Sisson et al., 2001). 

Lava Flows 

Andesite lava flows compose much of Mount Rainier. 

Because of the chemical composition of andesite, lavas 

composed of andesite tend to be viscous and rather slow 

moving. On gentle slopes, andesite lava flows more 

slowly than a person can walk. Lava flows will, however, 

destroy everything in their paths either by fire, impact, or 

burial. While the hazard to people from lava flows is low, 

a more serious hazard results when lava comes in contact 

with snow and ice. Flowing lava on the ice- covered 

slopes of Mount Rainier may break up, avalanche, and 

form much larger lahars (Sisson et al., 2001). 

Unlike Mount St. Helens, Mount Rainier does not have 

significant lava domes. Two eruptive episodes in the past, 

one from 500,000- 420,000 years ago and one from 

280,000- 180,000 years ago, produced lava flows that 

extended up to 14 miles (22 km) radially from the present 

summit location with individual volumes of up to 9 km3

(cubic kilometers), but such voluminous and farreaching lava flows are unlikely today (Sisson et al., 2001). 

Lava flows erupting outside of the two periods 

mentioned above have generally traveled no farther than 

6 miles (10 km) from the summit and have volumes less 

than 0.5 km3

. 

Throughout the history of the volcano, pyroclastic flows 

accompanied lava eruptions and probably are a greater 

hazard to life and property than are lava flows. Lava 

flows will probably extend no farther than the present 

terminus of the glaciers. 

Volcanic Gases 

Magma contains dissolved gasses that are released during 

and between eruptions. Andesitic volcanoes contain 

gases composed primarily of water vapor. Secondary 

gases are carbon dioxide and sulfur compounds. Minor 

amounts of carbon monoxide, chlorine, fluorine, boron 

compounds, ammonia, and several other compounds 

may be present, as well (Hoblitt et al., 1998). 

Volcanic gases are distributed by wind. They may be 

concentrated near a vent and then diffuse rapidly 

downwind. Injuries to eyes and lungs from acids, 

ammonia, and other compounds and suffocation by 

denser- than- air gases, such as carbon dioxide, are 

possible. Metals can be severely corroded by volcanic 

gases. 

Information about volcanic gases at Mount Rainier 

comes from studies of the volcano’s hydrothermal 

system. In 1982, gas samples collected from fumaroles at 

Mount Rainier’s summit recorded air enriched with 

carbon dioxide but no sulfurous gases. Presently, 

volcanic gases are only a hazard to climbers who enter 

the summit ice caves. When the volcano erupts, however, 

the gas- emission rate will increase as will the potential 

hazard from volcanic gases. 

Mineral springs and meadows just northwest of the 

Longmire developed area in the park are potential 

hazards due to lethal volcanic gases. Carbon dioxide, 

carbon monoxide, and other potentially dangerous 

emissions are known to have killed animals at the site. 

However, the gases pose little risk to trail hikers passing 

through the area (NPS, 2001). 

Debris Avalanches, Debris Flows, and Lahars 

In 1980, at Mount St. Helens, rising magma created a 

bulge that broke away from the rest of the volcano and 

generated a rapidly moving landslide. Landslides caused 

by the failure of unstable slopes are called debris 

avalanches. A volcano’s slopes can also fail even if 

magma isn’t involved. Slopes may become unstable by 

melting of snow during periods of unusually high 

temperatures or unusually heavy rain in summer or early 

autumn, by glacial erosion, or as the strength of the rock 

is reduced by hydrothermal alteration. Hydrothermal 

alteration causes the rock to become weaker by 

chemically altering it to clay and other minerals. 

Eventually, the affected part of the volcano collapses 

under its own weight, generating a debris avalanche. 

Non- magmatic debris avalanches are especially 

dangerous because they can happen without warning. 

Debris avalanches may be triggered by earthquakes, 

steam explosions, and intense rainstorms affecting 

weakened slopes in the park. 

Debris avalanches can travel tens of kilometers at speeds 

of tens to hundreds of kilometers per hour. Like 

pyroclastic flows, escape from a debris avalanche is 

difficult to impossible. Topography controls a debris 

avalanche, which will destroy everything in its path and 

leave a deposit that is usually a few meters to hundreds of 

meters thick (Hoblitt et al., 1998). Large debris 

avalanches may block the mouths of tributary valleys and 

cause lakes to form. When impounded water spills over 

the dam formed by the debris avalanche, it can quickly 

cut a channel and cause the lake to drain 

catastrophically. 

Debris avalanches commonly contain enough water, 

snow, or ice to transform them into debris flows or 

lahars. Lahars are slurries of water and sediment (60 

percent or more by volume) that resemble flowing 

cement. Lahars are sometimes called mudflows and can 

travel at speeds reaching a few tens of kilometers per 

hour along gently sloping distal valleys to more than 100 

kilometers (60 miles) per hour on steep slopes near the 

volcano (Crandell, 1969A; Fiske et al., 1963, 1988; Scott et 

al., 1995; Hoblitt et al., 1998; Kiver and Harris, 1999). 

Water in reservoirs may be displaced by lahars and could 

cause floods farther downstream. 
 NPS Geologic Resources Division 10 

At least 60 lahars of various sized have flowed down 

valleys on Mount Rainier during the past 10,000 years 

(Figure 4). All of these lahars can be grouped into two 

general categories: cohesive and non- cohesive lahars. 

Cohesive lahars contain relatively large amounts of clay 

derived from chemically altered rocks. They form when 

debris avalanches originate from hydrothermally altered 

parts of the volcano. Non- cohesive lahars contain 

relatively little clay and are triggered whenever water 

mixes with loose rock debris. This can be caused by the 

mixing of pyroclastic flows or pyroclastic surges with 

snow or ice; relatively small debris avalanches; unusually 

heavy rain; or an abrupt release of glacier- stored water. 

The largest lahar at MORA in the last 10,000 years was a 

cohesive lahar known as the Osceola Mudflow. The 

Osceola Mudflow occurred about 5,600 years ago and 

was at least 10 times larger than any other known lahar 

from Mount Rainier. Perhaps triggered as magma forced 

its way into the volcano, the mudflow was the product of 

a large debris avalanche composed mostly of 

hydrothermally- altered material. Extending at least as 

far as the Seattle suburb of Kent and to Commencement 

Bay (now the site of the Port of Tacoma), the Osceola 

Mudflow left deposits that cover an area of about 212 

square miles (550 sq km) in the Puget Sound lowland 

(Hoblitt et al., 1998). The mudflow deposited more than 

4.9 billion cubic yards (3.7 billion cu meters) of material 

(NPS, 2001). Remnants of the mudflow on the sides of 

the White River and West Fork valleys show that both 

valleys were temporarily filled with streams of mud more 

than 500 feet (150 m) thick (Crandell, 1969B). 

Today, a similar event would produce a mudflow in the 

reservoir behind Mud Mountain Dam where it would 

acquire more water and thus increase its mobility. The 

reservoir dam would be destroyed and the mudflow 

would easily inundate the towns of Enumclaw, Buckley, 

Kent, Auburn, Sumner, and Puyallup, a combined 

population of 125,000 people in 1999. If an emergency 

warning sounded at the time the mudflow began, most 

people would have less than 2 hours to evacuate their 

homes. 

The Electron Mudflow originated from a slope failure on 

the west flank of Mount Rainier about 600 years ago and 

is unique in that it has not been correlated with a 

volcanic eruption. The mudflow reached the Puget 

Sound lowland along the Puyallup River. When the 

mudflow reached the community of Electron, it was 

more than 98 feet (30 m) deep. At Orting, mudflow 

deposits are as much as 20 feet (6 m) thick and contain 

remnants of an old- growth forest (Hoblitt et al., 1998). 

Large non- cohesive lahars are associated with 

volcanism. Valleys of both forks of the White River were 

filled to depths of 60 to 90 feet (20 to 30 m) about 1,200 

years ago by a non- cohesive lahar, which flowed 60 

miles (100 km) to Auburn. About 2,200 years ago, another 

lahar, named the National Lahar, inundated the 

Nisqually River valley to depths of 30 to 120 feet (10 to 40 

m) and flowed all the way to Puget Sound. These noncohesive lahars form as hot rock fragments flow over 

glacier ice and snow. The vast quantities of meltwater 

then mix with rock debris to form lahars. In the past 

6,000 years, periods of volcanism have produced more 

than a dozen non- cohesive lahars. 

Geologic circumstances conducive to debris avalanches 

and lahars include: 

• Substantial volumes of hydrothermally altered rock 

• Substantial topographic relief 

• Great volumes of ice 

• Potential for renewed volcanism 

All of these circumstances are present at Mount Rainier, 

making lahars a larger threat to communities down valley 

from Mount Rainier than any other volcanic 

phenomenon. 

Lahars at Mount Rainier can be classed in to three 

groups according to their genesis: 1) flank collapse of 

hydrothermally altered, water- saturated rock; 2) 

eruption- related release of water and loose debris; and 

3) hydrologic release of water and debris (Scott and 

Vallance, 1995; Scott et al., 1995; Vallance et al., 2003). 

Vallance and others (2003) distinguish lahars in the third 

category as debris flows. Debris flows are less 

voluminous than the other lahars, but occur frequently at 

Mount Rainier, often with little or no warning. 

In the past, glacial outburst floods, torrential rains, and 

stream capture have caused small- to moderate- size 

debris flows. Commonly, debris flows occur in drainages 

that have large glaciers in them. However, a drainage 

diversion may trigger a debris flow in an unglaciated 

drainage basin such as the diversion of Kautz Glacier 

meltwater into Van Trump basin on the south side of 

Rainier which occurred in August, 2001 (Vallance et al., 

2003). 

At Mount Rainier, many of the developed sites are 

located in valley bottoms on historic debris flow and 

lahar deposits. Seventeen of twenty- three developed 

sites in the park are within mapped debris flow hazard 

zones (Hoblitt et al., 1995, 1998; NPS, 2001). These hazard 

zones identify where debris flows could occur and at 

what frequency (recurrence interval) and magnitude they 

might occur (Figure 5). For the purpose of hazard 

assessment, four classes of lahars have been designated: 

Case M, Case I, Case II, and Case III lahars (Hoblitt et al., 

1998). 

Case M flows (not shown on Figure 5) are extreme flows 

such as the Osceola mudflow. Lahars of this magnitude 

are too infrequent to estimate an annual probability 

(Hoblitt et al., 1998). 

Case I flows originate from debris avalanches of weak, 

chemically altered rock. Case I debris flows have a 

recurrence interval of 500 to 1,000 years, an annual 

probability of 0.1 to 0.2 percent. The Electron Mudflow 

is an example of a Case I debris flow. The Electron 
 MORA Geologic Resource Evaluation Report 11

Mudflow, however, inundated floodplains that were 

covered by a mature old- growth forest. Today, an 

Electron- size mudflow would spread farther and faster 

across floodplains that are now deforested and thus 

hydraulically smoother. Consequently, hazard zone 

maps reflect this modern scenario that might inundate 40 

percent more area than the original Electron Mudflow 

(Hoblitt et al., 1998). A Case I lahar could destroy all or 

parts of Orting, Sumner, Puyallup, Fife, the Port of 

Tacoma, and possibly Auburn. 

Case II flows are relatively large non- cohesive flows 

containing coarser materials and lower clay contents 

than Case I flows. They occur on an estimated 

recurrence interval of 100 to 500 years, analogous to the 

100- year flood commonly considered in engineering 

practice. As with Case I flows, both eruptive and noneruptive origins are possible for Case II flows. For 

example, in 1947, a Case II flow occurred at Kautz Creek 

due to heavy rain and the release of water stored within a 

glacier. The National Lahar, which occurred in the 

Nisqually River valley less than 2,000 years ago, is 

considered a characteristic Case II flow. The Case II 

inundation zone of Hoblitt and others (1998) reflects the 

recent discovery of lahar- related deposits from Mount 

Rainier that apparently filled the lower Duwamish River 

valley from wall to wall as far as Elliott Bay in Puget 

Sound. 

Case III flows may be moderately large debris avalanches 

or small, non- cohesive debris flows that typically extend 

to the base of the volcano near the park boundary. The 

recurrence interval for Case III flows is 1 to 100 years. 

This class includes small debris avalanches as well as 

lahars. Most commonly, Case III flows are lahars 

triggered by a sudden, unpredictable release of water 

stored by glaciers. For the purposes of hazard 

assessment, the lahar that occurred about 500 years ago 

in the Tahoma Creek valley is considered a characteristic 

Case III flow (Hoblitt et al., 1998). 

The revised hazard maps of Hoblitt and others (1998) 

also reflect the potential failure of Alder Lake on the 

Nisqually River. Since Alder Dam exists for power 

generation, the lake is never empty. Should a Case I flow 

enter the reservoir, the dam might fail or a significant 

volume of water in storage could be displaced, causing 

catastrophic downstream flooding. The inundation zone 

would, therefore, be similar to that determined for a 

sudden failure of the dam (Hoblitt et al., 1998). 

Facilities at the Paradise area of the park are located on 

the south flank of Mount Rainier about 5,260 feet (1,604 

m) above sea level and less than 6.5 miles (10 km) from 

the summit crater. Because Paradise is located on a 

bench above the floors of the Paradise and Nisqually 

Valleys, it is not in a debris flow inundation area. Its 

location near the summit, however, makes it one of the 

most vulnerable sites for volcanic hazards associated 

with eruptions. 

Sunrise is also located on a ridge top, well above the 

debris flow hazard zones on the Whiter River valley 

floor. However, like Paradise, Sunrise is near the summit 

and may be impacted by a volcanic eruption (NPS, 2001). 

Research has shown that eruptions can trigger lahars 

either directly by hot rock avalanches and pyroclastic 

flows, or indirectly when volcanic unrest dislodges 

unstable edifice flanks (Sisson et al., 2001). Spontaneous, 

unheralded collapses of Mount Rainier’s flanks appear 

less common than was previously supposed. Preeruptive seismicity, enhanced gas emissions, or edifice 

deformation may precede and warn of future large 

lahars. The alteration- rich Electron Mudflow of about 

560 years ago, however, is an exception to this rule as no 

evidence of an associated eruption has yet been found. 

Lateral Blasts 

All of the parks’ developed areas are within a 22- mile 

(35- km) diameter lateral blast zone (Crandell and 

Hoblitt, 1986; Hoblitt et al., 1995). Lateral blasts occur 

when the side of a shallow magma body or hydrothermal 

system is suddenly depressurized. The explosion 

produces a pyroclastic surge that can travel tens of miles 

(tens of kilometers) from the volcano. In 1980, a body of 

magma accumulated within Mount St. Helens over a 

period of 52 days and caused the north flank to bulge 

outward. The bulging enlarged and the northern sector 

broke away from the rest of the volcano, producing a 

great debris avalanche, and the depressurized magma 

body exploded, producing a lateral blast (Hoblitt et al., 

1998). A lateral blast also was associated with the debris 

avalanche that produced the Osceola Mudflow. 

Lateral blasts caused by magma moving into a volcano 

can be predicted with adequate monitoring. Lateral 

blasts may occur, however, without the movement of 

magma if a non- magmatic debris avalanche uncovers an 

active hydrothermal system, which then explodes. Three 

factors, all of which are present at Mount Rainier, 

include: 

• Substantial volumes of weak hydrothermally altered 

rock 

• Substantial topographic relief 

• An active hydrothermal system 

Hydrothermal Alteration Zones 

The Osceola Mudflow, the signature event in the 

Holocene history of Mount Rainier, was remarkable in 

its volume, abundance of hydrothermal clay, and its 

nearly immediate transformation to a mobile lahar 

(Sisson et al., 2001). Several other far- reaching Holocene 

lahars from Mount Rainier also contain clays and other 

hydrothermal minerals, raising the concern that the 

volcano’s edifice is composed of widespread weak 

altered rocks. However, detailed geologic mapping, 

remote sensing, and geochronology showed that intense 

and pervasive alteration of edifice rocks is confined to a 

relatively narrow east- northeast to west- southwest 

trending belt that passes through the summit (Sisson et 

al., 2001). In contrast to the narrow belt of 
 NPS Geologic Resources Division 12 

hydrothermally altered rock, the dominant unaltered 

portions of the edifice have been stable, as is shown by 

widespread preservation of rocks as old as 200,000 years 

above 13,780 feet (4,200 m) elevation on the volcano’s 

northwest face. 

High- resolution aeromagnetic and electrical resistivity 

surveys and three- dimensional slope stability models 

further assessed the distribution of altered, structurally 

weak rocks and the consequences if they collapse at 

Mount Rainier. Research showed that large volumes of 

highly altered rock are restricted to Mount Rainier’s 

upper west flank and to smaller bodies in the subsurface 

that partially ring the Osceola collapse crater. Only very 

small amounts of extremely altered rock underlie the 

volcano’s summit and upper northeast slope (Sisson et 

al., 2001). Mount Rainer’s upper west flank has the 

greatest likelihood of gravitational failure and the lahars 

produced from this potential collapse pose the greatest 

risk to the Puyallup River valley that heads on the 

volcano’s altered west flank. 

Recent geologic mapping has identified valleys in the 

park that might host a large debris flow or small debris 

avalanche (Sisson, 1995; Zimbelman, 1995; Crowley and 

Zimbelman, 1997). Mapping included zones of rock 

weakened by fractures, faults, and the alteration of 

minerals to weak clay minerals by hot gases 

(hydrothermal alteration). Areas containing fractures 

caused by down slope movement of hydrothermally 

altered rocks include Little Tahoma Peak, the east side of 

the volcano, and the west side of Sunset Amphitheater 

(Figure 5). 

Glacial Outburst Floods 

Glacial outburst floods are a type of flood that is caused 

by a massive, sudden release of water from a glacier. 

These may occur on sunny or rainy days in the summer 

or fall (Walder and Driedger, 1993). Outburst floods pose 

a serious hazard to life and property. Peak discharge of 

an outburst flood may be greater than the 100- year flood 

commonly considered in engineering practices. Since 

1926, bridges, roads, and National Park visitor facilities 

have been destroyed or damaged on about ten occasions 

by outburst floods. Rarely, however, are the effects of 

outburst floods noticeable outside the park boundaries 

(Hoblitt et al., 1998). 

Outburst floods have occurred from the Kautz, 

Nisqually, South Tahoma and Winthrop glaciers. Many 

of these outburst floods became lahars as they 

incorporated large quantities of sediment in their flows. 

Sediment is available since the glaciers on Mount Rainier 

have retreated substantially since the mid- 19th century 

(Hoblitt et al., 1998). Upon glacial retreat, stagnant 

masses of sediment- rich glacial ice become stranded in 

valleys downstream from present- day glaciers. Floods 

easily erode these stagnant ice masses. Over a period of 

decades, as the stagnant ice melts, stream channels 

should become more stable and less affected by outburst 

floods. Nisqually Glacier produced outburst floods in 

the 1950s and 1960s, but the glacier has not produced a 

flood since 1990. 

Glacial outburst floods are not related to volcanic 

activity at Mount Rainier (Hoblitt et al., 1998). Rather, 

studies show that outburst floods are correlated with 

periods of unusually high temperatures or unusually 

heavy rain in summer or early autumn. 

Flooding 

Rivers that drain Mount Rainier are on the steep- slopes 

of the volcano. They carry vast amounts of water, sand, 

gravel, and boulders. Streams in the park generally have a 

braided channel pattern and highly unstable and eroding 

banks because of the large volume of sediment and 

debris carried by the rivers. Stream channel instability in 

valleys throughout the park is caused by deposition of 

glacial sediments by floods and debris flows. Because 

channels are not stable, the 100 and 500- year floodplains 

associated with Mount Rainier rivers are not static and 

continue to change over time. 

Floods can occur in MORA year- round and can be 

triggered by a number of events, including glacial 

outbursts, precipitation, melting of snow and ice, and 

volcanic activity. Debris flows and precipitation- induced 

flooding are two end members on a continuum of 

hydrologic and geologic events. 

On average, precipitation- induced flooding occurs twice 

a year on rivers at MORA. The largest and most frequent 

precipitation- induced floods occur during late fall and 

early winter, when heavy rainfall melts snow at higher 

elevations. High peak flows in these floods have 

damaged both the Carbon River Road and Westside 

Road. Rapid melting of snow produces spring floods in 

April and May. Spring floods have smaller peak flows but 

longer duration than do the fall and winter floods (NPS, 

2001). 

Melting glacial ice (meltwater) produces floods primarily 

during the summer and fall, primarily in late July and 

August. Daily cycles of high afternoon discharge rates on 

glacial meltwater streams also pose a safety hazard for 

hikers. 

Extreme floods trigger debris flows (or lahars) composed 

of water, ice, sediment, and other debris. Debris flows 

can begin as outburst floods from glaciers and then 

transform into sediment- laden debris flows as they flow 

down slope. They occur less frequently than other types 

of floods, but are far more destructive than waterdominated floods. 

Floodplain assessments conducted at the 13 developed 

sites with overnight housing and sensitive facilities at 

MORA showed that 9 of the 13 sites were outside their 

regulatory floodplains (100- or 500- year floodplain). 

The Carbon River entrance and the Ipsut Creek 

campground appear to be within the regulatory 

floodplain. The Longmire complex and Sunshine Point, 
 MORA Geologic Resource Evaluation Report 13

although outside the regulatory floodplain, are prone to 

outburst flooding (NPS, 2001). 

Although a flood in 1959 inundated the Longmire 

compound, a 1994 hydraulic model showed that 100-

year and 500- year floods would be contained within the 

Nisqually River channel and would not flood the 

Longmire compound. Flood velocities, however, would 

cause severe erosion along unvegetated channel banks, 

such as along the levee constructed to protect Longmire. 

The model further indicated that flood flows from a 

500- year outburst flood would overflow the channel and 

flood the Longmire compound. Results from the model 

indicated that the 1959 flood was probably a small debris 

flow that may have started as an outburst flood from the 

Nisqually Glacier rather than a precipitation- induced 

event. Sediment deposited in the Nisqually River where 

the river exits a canyon near Longmire may have caused 

floodwater to be diverted into the compound (NPS, 

2001). Longmire is in a Case III debris flow inundation 

zone (Figure 4). 

Like Longmire, Sunshine Point campground was 

affected by prior flooding along the Nisqually River as a 

result of outburst flood activity from the Nisqually 

Glacier. However, outburst flooding from the glacier has 

decreased over the past few decades so that the 

probability that the campground would flood from such 

an event is small. Continued sediment deposition in the 

Nisqually River could cause higher flood elevations and 

require continued maintenance within the regulatory 

floodplain to avoid erosion of the campground’s 

protective levees. 

Ipsut Creek campground is in a high flood hazard area 

adjacent to the floodplain of the Carbon River. The 

channels within this large braided channel network shift 

constantly. Depths of flow for the 50- year and 100- year 

floods in the main channel of the Carbon River are 

shallow, only 3.5 feet (1 m), but velocities are rapid, 

estimated to be 8 feet per second (146 m/ min). 

Parts of Ipsut Creek campground, former walk- in sites, 

and the entrance road occupy very low parts of the 

floodplain. Most of the campground is located on a low 

terrace rising 5 to 6 feet (1.8 m) above the current 

channel. The walk- in sites were permanently closed in 

1997 after it was shown that these sites were isolated by 

swift water in a side channel during even small flood 

events. Discharges of 1,000 cubic feet per second or 

greater generate a high flood hazard for this area. 

Results from a hydraulic model indicated that most of 

the Ipsut Creek campground is outside the 100- year 

floodplain. However, the model’s boundaries for the 

100- year floodplain may need to be adjusted due to the 

unstable nature of braided channels and the location of 

parts of the campground at lower elevations than the 

active river channel. 

Continued deposition in the modern channel and 

upstream channel alignment may cause the Carbon River 

to shift to the south. If the channel does shift, it would 

isolate and claim all or parts of the campground and 

cause considerable damage to roads, trails, and other 

facilities (NPS, 2001). 

Hydraulic models indicate that all the facilities at the 

Carbon River entrance are outside the 100- year 

regulatory floodplain. Historic flooding may have been 

caused by a shift in the channel of June Creek, a tributary 

to the Carbon River, to the west of the entrance area. 

Flooding that does occur at the entrance is shallow, less 

than 2 feet (0.6 m) of standing water, with very low 

velocities. 

Other evidence, however, indicates that the Carbon 

River entrance facilities are within the floodplain. 

Floodplain soils, a levee, and an apparent absence of 

volcanic tephra point to larger floods that might have 

occasionally inundated this site in the recent past. 

Although the hydraulic model suggests otherwise, the 

entrance facilities have been placed within the regulatory 

floodplain because of the erosion of soils and the 

potential for floods to inundate the site (NPS, 2001). 

Bank erosion over the next few decades also could 

threaten Carbon River entrance facilities. Channel 

changes have resulted in the migration of the Carbon 

River from its north bank to its south bank over the past 

few years. Because of this change, the road, which lies 

below the river in some places, has been flooded with 

smaller flood discharges. 

Geologic Hazards During Dormant Periods 

Snow avalanches, rockfalls, and landslides are geologic 

hazards that occur throughout MORA during dormant 

periods (termed “non- volcanic geologic hazards” in 

Figure 5). In 1963, the largest rockslide ever recorded in 

the park occurred on the east flank of Mount Rainier. A 

series of avalanches from the steep side of Little Tahoma 

Peak carried 4 billion cubic feet (113 cu m) of rock onto 

the Emmons glacier and to within 0.6 miles (1 km) of the 

White River campground (Crandell, 1969B). 

Unstable bedrock on the slopes of Mount Wow have 

sent several mass movements into the Tahoma Creek 

valley and this area still remains a geologic hazard (Scott 

et al., 1995). Westside road crosses a small talus field and 

rockfall hazard east of Lake Allen and a larger talus field, 

rockfall and snow avalanche area between Dry Creek 

and the former picnic area. Visitors who park at the 

current end of the road (Dry Creek) are exposed to 

potential rockfall hazards. 

The location of the White River campground poses 

major safety hazards to both overnight and daytime 

visitors (NPS, 2001). The site is in a Case III inundation 

zone for debris flows and in the pyroclastic flow zone 

(Figure 5). The campground rests on a terrace only 35 

feet (11.5 m) above the White River. The terrace was 

formed by a debris flow deposit estimated to be 500-
 NPS Geologic Resources Division 14 

2,000 years old (Crandell, 1971). A large mass of 

fractured, hydrothermally altered rock is perched just 

above the campground on Little Tahoma Peak. These 

weakened rocks were the source of a 1963 debris 

avalanche that stopped about 3,000 feet (0.6 mile or 600 

meters) short of the campground after it had already 

traveled 4.3 miles (7 km). 

The proximity of Cougar Rock campground to the 

volcano and the site’s location on a low- elevation debris 

flow terrace within the Case III inundation zone makes 

overnight use at the campground highly hazardous. 

Several debris flows formed the terrace, including the 

National and Paradise lahars that inundated the site in 

the last 5,000 years. 

Cliffs on a ridge descending from Rampart Ridge pose a 

potential rockfall hazard at the southwest end of the 

campground. A potential landslide 1.5 miles (2.5 km) 

upstream on the west side of the Nisqually River at an 

elevation of 5,600 feet (1,700 m) could threaten Cougar 

Rock Campground. The Nisqually Glacier undercut this 

slope, which is now covered with unstable glacial 

sediments. 

Rockfall also is a potential non- volcanic geologic hazard 

at the Stevens Canyon entrance and in the Stevens 

Canyon area. 

Park facilities at Ohanapecosh are located in a Case II 

inundation zone on a series of river terraces and bedrock 

benches along the Ohanapecosh River. Potential failure 

of the weak rocks of the Ohanapecosh Formation on the 

east valley wall threatens visitors and employees at the 

site. The presence of hot springs indicates the continued 

hydrothermal alteration and weakening of the host rock. 

While the ridge top location of Mowich Lake is well 

above the valley floor where debris flows could occur, 

debris flows may block roads in the Carbon River valley 

and affect evacuation efforts. 

Glacial Monitoring 

The glaciers on Mount Rainier are important sources of 

streamflow for several rivers, including some that 

provide water for hydroelectric power and irrigation. 

They also pose geologic hazards in the form of glacial 

outburst floods. Glaciers are sensitive indicators of 

climate changes and affect the distribution of aquatic and 

terrestrial habitat through their advance and retreat. 

Because Mount Rainier glaciers are a significant 

component of the regional hydrologic system and have 

both immediate and long- term impacts on the local and 

regional environment, glacial monitoring becomes an 

important issue for MORA. 

Measuring and monitoring glacial response to climate is 

commonly accomplished by measuring the terminus 

position and surface elevation of a glacier. Nisqually 

Glacier has the lengthiest surface- elevation record of 

any in North America. Begun in 1931, the record shows 

the glacier’s responses to small but significant climatic 

variations.

In 2004, data from maps and aerial photographs were 

compiled into a geographic information system (GIS) 

database (Nylen, 2004). The spatial and temporal 

variations of Mount Rainier glaciers from 1913 to 1994 

show that: 

• the glaciers on Mt. Rainier have decreased in area, 

volume, and length; 

• the retreat of the glaciers from 1913- 1994 was not 

continuous; 

• the temporal changes in area, volume and terminus 

position of the glaciers are driven by climate 

variations; 

• spatial differences affected the response of the glaciers 

to climate variation. 

Between 1913- 1994, the total area and volume of Mount 

Rainier glaciers shrank by 21 percent and 25 percent, 

respectively. The average retreat of the 11 largest glaciers 

was 3,737 feet (1,139 m), an average of 46 feet per year (14 

meters/year). South Tahoma Glacier had the largest 

retreat of 8,334 feet (2,540 m) (Nylen, 2004). 

The 11 monitored glaciers in Nylen’s study advanced an 

average of 1,280 feet (390 m) between the mid- 1950s and 

the mid- 1980s. High snowfalls during the 1960s and 

1970s led to the advance of the Carbon, Cowlitz, 

Emmons, and Nisqually Glaciers during the 1970s and 

early 1980s (Driedger, 1992; Nylen, 2004). Except for 

Emmons and Cowlitz glaciers, the glaciers retreated after 

the mid- 1980s. Debris cover on Emmons and Cowlitz 

glaciers may have slowed melting. 

Some glaciers have retreated more than two miles (3.2 

km) up their valleys since reaching their maximum postPleistocene extent during the Little Ice Age (between the 

14th century and 1850 A.D.) (Driedger, 1986). At the time 

of the Little Ice Age, the Nisqually Glacier advanced to a 

position 650- 800 feet (183- 244 m) down valley from the 

site of the Glacier Bridge. Tahoma and South Tahoma 

Glaciers merged at the base of Glacier Island, and the 

terminus of Emmons Glacier reached within 1.2 miles (1.9 

km) of the White River Campground. 

Between 1954 and 1994, winter snowfall at the Paradise 

Station decreased by 5.1 cm/year. A corresponding 

retreat in the terminus position of Mount Rainier glaciers 

correlates with this drop in precipitation (Nylen, 2004). 

At Mount Rainier, southern glaciers decreased in area, 

volume, and length more than the northern glaciers. The 

southern glaciers are smaller than the northern glaciers, 

and size appears to be the controlling factor on area 

decrease. Smaller glaciers have small elevation ranges 

and are, therefore, more sensitive to climate changes 

than larger glaciers. 
 MORA Geologic Resource Evaluation Report 15

Cloud cover increased by 45 percent between 1963 and 

1983 and decreased by 69 percent between 1983 and 1992. 

Glacial advance and retreat can be correlated with these 

time periods. Nylen also showed that aspect and cloud 

cover are directly related. Fewer clouds mean relatively 

more energy available to melt the southern glaciers. 

Nylen’s research demonstrated that monitoring only one 

glacier is not adequate when trying to determine regional 

variations in glacial response to climate change. At 

MORA, a long- term monitoring protocol is being 

developed that will identify a number of index glaciers to 

represent the larger population of MORA glaciers (Paul 

Kennard, MORA Regional Geomorphologist, personal 

communication). Measurable objectives of this protocol 

include: 

• determining summer, winter and net mass balance at 

index glaciers; 

• determining glacial contribution to summer runoff for 

two MORA watersheds; 

• assessing surface features changes related to glacial 

hazards at MORA; 

• determining glacier volume and area for index glaciers 

at 10 year intervals, and for all glaciers every 20 years 

• tracking annual surface elevation changes across 3 

fixed lateral transects at Nisqually Glacier, in order to 

track trends in kinematic waves; 

• determining relationships among surface elevation 

data, mass balance data, and glacier dynamics and 

movement. 

Implementation of these protocols will help track the 

response of glaciers to variations in both temperature 

and precipitation and thus record regional and global 

climate change over longer time periods than most other 

climate measures. 

Soils 

Cryptobiotic soil crusts are the foundation of highelevation ecosystems. Cryptobiotic soil crusts bind soil 

particles together, thus increasing soil stability, and have 

been shown to increase rainfall infiltration, to reduce 

sediment production and runoff, and to facilitate the 

establishment of vascular plants by enhancing nutrient 

and water availability for these plants. 

No systematic soil mapping project has been conducted 

for Mount Rainier National Park (NPS, 2001). Solid rock 

and talus slopes with virtually no topsoil occupy the 

higher elevations of Mount Rainier while lower 

elevations are composed of glacial till. Valley bottoms 

contain layers of mixed rocks and benches of silt 

deposited by streams and glaciers. Subalpine meadows 

have very shallow, loose, friable soils that are easily 

eroded by foot and horse traffic. 

A classification system developed for forest soils and 

based on the geological origin, relief, and drainage 

features of the park identified the following four most 

common soil groups in the forested areas of Mount 

Rainier(Hobson, 1976). 

• Tephra soils: pyroclastic deposits 

• Colluvial soils: unstable soils 

• Alluvial soils: formed from river deposition, glacial 

outburst floods, and ephemeral streams carrying 

snowmelt discharge 

• Mudflow soils: result of lahars 

Tephra soils are identified by individual ash layers and 

are the result of volcanic eruptions of Mount Rainier, 

Mount St. Helens, and to a lesser extent, Mount Mazama 

(the volcano that erupted about 7,000 years ago to form 

Crater Lake). Although thin, these soils support the 

subalpine and alpine meadows in the park. 

Colluvial soils are rapidly drained and consist of coarse, 

unconsolidated, mixed parent materials. These soils are 

found on slopes at all elevations. They are especially 

prevalent on steep slopes and south- facing areas of the 

park. 

Alluvial soils are often found in major river valleys, along 

streams, on wet benches, and on alluvial slopes and fans. 

Mudflow soils are surface or subsurface parent materials 

within the rooting zone. Mudflow soils may contain 

tephra W, a volcanic ash layer from a Mount St. Helens 

eruption, as well as alluvial or colluvial surface deposits. 

The destruction of cryptobiotic soil crusts by visitor use 

is a geologic issue at MORA (NPS, 2001). The most severe 

damage is in subalpine and alpine meadows. In these 

areas, the “damage ranges from trampled vegetation in 

campsites or informal (social) trails to severely eroded 

social or designated trails, some over 3 feet deep” (NPS, 

2001, p. 139). 

In Paradise Meadows, approximately 89 percent of the 

human impacts were in the form of social trails. Of 1,126 

social trails studied in 1987, high elevation trails were 

found to be more susceptible to erosion than middle and 

low elevation trails while slope was the variable 

accounting for the most variance in trail depth (Fritzke, 

1992). In the same study, five plant communities were 

evaluated, and the heath shrub community was found to 

be the most susceptible to damage when a social trail was 

established.
 NPS Geologic Resources Division 16 

The remaining impacts were large bare areas used as rest 

stops and viewpoints. Many of these impacts were over 

20 years old. The Paradise Meadow Plan (Rochefort, 

1989) identified 913 human- caused bare ground impacts, 

with 28.5 miles (46 km) of social trail compared to 13.5 

miles (22 km) of maintained trails. 

Studies of human impacts have been done since the late 

1960s above Paradise in the Muir corridor. Unauthorized 

campsites and social trails have been documented in 

these studies. Most of the campsites were found in rocky 

areas. 

Intensive human use also has led to severely eroded areas 

and bare ground in Spray Park, Mowich Lake, Reflection 

Lake, and Tipsoo Lake. 
 MORA Geologic Resource Evaluation Report 17

Figure 4: Hazard zones for lahars and pyroclastic flows from Mount Rainier (Hoblitt et al., 1998). The map shows areas that could be 

inundated if events similar in size to those of the past occurred today. Puyallup Valley is the valley most susceptible to lahars caused 

by flank collapse. MMD: Mud Mountain Dam. 
 NPS Geologic Resources Division 18 

Sites at Mount Rainier within volcanic and non-volcanic hazard zones 

Park Site Case I 

Debris Flow 

Zone 

Case II 

Debris Flow 

Zone 

Case III 

Debris Flow 

Zone 

Hydrothermally 

altered rock 

Nonvolcanic 

geologic 

hazard 

Pyroclastic 

Flow Zone 

Tahoma 

Woods X X 

Nisqually 

entrance X X X X 

Sunshine Pt. 

Campground X X X X 

Kautz Creek X X X 

Westside Rd X X X X X 

Longmire X X X 

Cougar Rk 

campground X X X 

Paradise X 

Camp Muir X X 

Narada Falls 

picnic area X X X 

Box Canyon 

picnic area X X X 

Ohanapecosh X X X 

Stevens 

Canyon 

entrance 

 X X 

White River 

entrance X X X 

White River 

campground X X X 

Camp 

Schuman X X X 

Sunrise X X 

Mowich 

Lake X 

Carbon River 

entrance X X X 

Falls Creek 

picnic area X X X 

Ipsut Creek 

campground X X X 

Figure 5: Reproduced from the Mount Rainier National Park General Management Plan, page 156 (2001). 
 MORA Geologic Resource Evaluation Report 19

Geologic Features and Processes 

This section provides descriptions of the most prominent and distinctive geologic features 

and processes in Mount Rainier National Park. 

At present, the Cascade Province contains four national 

parks and one volcanic monument: Mount Rainier 

National Park (WA), North Cascades National Park 

(WA), Crater Lake National Park (OR), Lassen Volcanic 

National Park (CA) and Mount St. Helens Volcanic 

Monument (WA), managed by the U.S. Forest Service. 

These parks, as well as other Cascade Mountain areas, 

contain world- class examples of volcanic and glacial 

features. The geologic features and processes in MORA 

are divided into the following sections: 

• Glacial Features and Glacier Processes 

• Volcanic Features 

• Thermal Features and Ice Caves 

Glacial Features and Glacier Processes 

Glaciers are highly effective erosional agents, shaping 

mountains into picturesque landforms with such 

distinctive erosional features as horns (peaks), cirques 

(deep, bowl- shaped, steep- walled recesses in a 

mountain), glacial valleys (U- shaped valleys), and arêtes 

(rugged crests or ridges between two mountains). Tipsoo 

Lake, Crescent Lake, and Mowich Lake are examples of 

cirque lakes at MORA. Some tributary streams end as 

waterfalls at the mouth of hanging valleys like Christine 

Falls and Comet Falls. Carved by glaciers, hanging valleys 

are erosional features in which the floor of the valley is 

notably higher than the level of the valley to which it 

leads. Most of the glacial landforms on Mount Rainier 

are the result of Pleistocene glaciers that formed 25,000 

to 10,000 years ago and continue to erode the mountain 

today. 

Depositional features are formed from material eroded 

from the mountain that is transported down valley and 

deposited as rock debris termed drift. Glacial till is 

unconsolidated, poorly sorted drift that forms end and 

lateral moraines, undulating mounds composed of 

boulders, cobbles, pebbles, sand, silt, and clay clasts. 

Many of the deposits left by mudflows, debris flows, and 

avalanches also are associated with the glaciers on 

Mount Rainier. 

The valley glaciers that create the backcountry of Mount 

Rainier radiate like spokes on a wheel from the summit 

of the volcano (Figure 1). About 35,000 years ago, the 

Cowlitz Glacier on the southeast side of the mountain 

extended 65 miles (105 km) from the mountain and about 

8 miles (13 km) west of the present town of Randle (Kiver 

and Harris, 1999). The end of the Pleistocene Ice Age 

came about 10,000 years ago, about the same time as the 

eruptive event that formed the main cone of Mount 

Rainier. 

The extreme height and massive character of the volcano 

allows it to intercept moisture- laden westerly winds 

from the Pacific and to receive abundant snowfall that 

helps maintain glacial cover. For example, during the 

winter of 1971- 1972, slightly more than 102 feet (31 m) of 

snow fell on the mountain, setting a world’s record at an 

official weather station (Kiver and Harris, 1999). Since 

the mid- 1800s, however, the glaciers have lost as much as 

35 percent of their surface area. This trend is 

synchronous with glacier retreat recorded elsewhere 

around the world and reflects global warming trends 

from natural perturbations and human influences. From 

1900 to 1960, the Nisqually Glacier retreated about 1 mile 

(1.6 km) upstream from the old highway bridge (Kiver 

and Harris, 1999). Paradise Ice Caves, once a major 

attraction for visitors, collapsed in the fall of 1991 due to 

the effects of global warming. 

The glaciers of Mount Rainier form the largest glacier 

system in the conterminous United States. Some of the 

glaciers originate from the summit of the volcano while 

others extend down the mountain flanks from cirques 

located in the high- precipitation zone at middle 

elevations. Linear rock ridges or arêtes, locally known as 

cleavers, separate the glaciers. The Willis Wall is the 

3,600- foot- high (1,100 m) vertical headwall that marks 

the Carbon Glacier cirque. Over a mile wide, the Carbon 

Glacier cirque is the largest in the Cascade Mountains 

(Kiver and Harris, 1999). 

Over one cubic mile of snow and ice is estimated to 

perpetually cover Mount Rainier. Only a relatively thin 

veil separates this ice from the “Mountain of Fire”. If this 

ice were to melt during an eruption, huge floods and 

mudflows would easily reach the densely populated 

areas in the Puget Lowland. 

The following points of interest are associated with 

Mount Rainier glaciers or glacial processes. Emmons, 

Ingraham (Cowlitz- Ingraham), Nisqually, Tahoma, and 

Winthrop glaciers are the predominant glaciers 

originating on the summit of Mount Rainier. 

Emmons Glacier: Named for geologist, Samuel F. 

Emmons, the Emmons Glacier is the largest glacier in the 

contiguous United States. Located on the east slope of 

Mount Rainier, the Emmons Glacier covers 4.3 square 

miles (11.1 sq km). A landslide in 1963 covered the lower 

glacier with rock debris, which insulates the ice from 

melting. As a result if irregular melting, a vast hummocky 

topography has formed over the area. 

Cowlitz- Ingraham Glacier: The Cowlitz- Ingraham 

Glacier is currently thinning and retreating although it 
 NPS Geologic Resources Division 20 

made a notable advance in the mid- 1970s and continued 

to slowly advance until the mid- 1980s. 

Nisqually Glacier: One of the most accessible glaciers on 

Mount Rainier, Nisqually glacier can be viewed from 

Nisqually and Glacier Vistas. Nisqually Glacier holds the 

record for the fastest measured downhill movement for a 

Mount Rainier glacier: 29 inches per day (74 cm/d). The 

glacier thinned by 53 feet (16 m) in the region 

immediately west of Glacier Vista between 1985 and 1991, 

but the retreat may be slowing. 

Winthrop Glacier: With an area of 3.5 square miles (9.1 sq 

km), the Winthrop Glacier is the second largest glacier 

on Mount Rainier. The glacier extends from the summit 

to the 4,700- feet level (1,433 m) of the West Fork White 

River Valley. Winthrop Glacier was named for Theodore 

Winthrop who visited the mountain in 1853, described his 

experiences in his book Canoe and Saddle, and died on 

the field of battle during the Civil War. 

Carbon Glacier: Measurements of the Carbon Glacier, 

the largest in the park, recorded a thickness of over 700 

feet (215 m). Although the third largest glacier by area on 

Mount Rainier, Carbon Glacier has the greatest 

thickness and volume (0.2 cubic miles) of any glacier in 

the contiguous United States. It is 5.7 miles long (9.2 km), 

which makes it also the longest glacier on Mount Rainier. 

Beginning just below the imposing 4,000- foot- high 

(1,219 m) Willis Wall, the glacier’s terminus is surrounded 

by mature forest and shrubbery at an altitude of 3,500 

feet (1,067 m). 

Kautz Glacier: Kautz Glacier, named in honor of 

Lieutenant (later General) A.V. Kautz, is one of the 

primary glaciers on the mountain. In 1857, Kautz made 

the first attempt to scale the peak by climbing along the 

edge of the glacier that bears his name. He failed to reach 

the summit by only a few feet. Kautz Creek originates in 

the Kautz Glacier and flows into the Nisqually River. 

Paradise Glacier: The Paradise Glacier area was one of 

the main attractions for visitors in the early part of the 

twentieth century. Because of this attraction, the 

Paradise Inn was built and opened for business in 1917. 

Russell Glacier and Wilson Glacier: These two glaciers are 

tributary glaciers of major glaciers in the park. Russell 

Glacier is named after Professor Israel C. Russell, the 

first scientist to describe the glaciers of the park, and is 

one of the largest inter- glaciers of the park. It is a 

tributary to the Carbon Glacier on the north side of 

Mount Rainier. 

Wilson Glacier is a tributary to the Nisqually Glacier on 

the mountain’s south side. It was named for A.D. Wilson. 

In 1870, Wilson and Professor S.F. Emmons made the 

second successful ascent of Mount Rainier. 

Stevens Glacier, Van Trump Glacier, and Sluiskin Falls: 

The Stevens Glacier and the Van Trump Glacier are on 

the southern slope of the mountain. In 1870, Philemon 

Beecher Van Trump and General Hazard Stevens made 

the first successful ascent to the summit of Mount 

Rainier. The Yakima Indian brave, Sluiskin, guided the 

two men. They named the falls at the head of the 

Paradise River after their guide. 

Sunset Amphitheatre: Chiseled and dredged by 

rockslides, glacial erosion, and frost action, Sunset 

Amphitheatre is a cirque- like gouge near the summit of 

the mountain. Puyallup Glacier originates in Sunset 

Amphitheatre. A cliff collapse that formed this cirque 

may have triggered the Electron Mudflow about 500 

years ago. This mudflow inundated at least 14 square 

miles (36 sq km) of Puget Sound Lowland and formed 

the valley surface around Orting, Washington. 

Volcanic Features 

The eruption of Mount Rainier also left some distinctive 

volcanic features. Summit features, rock walls, and 

satellite volcanoes rim the mountain. 

Columbia Crest, Liberty Cap, Point Success: These three 

distinct summits are high points at the top of Mount 

Rainier. At 14,410 feet (4,392 m), Columbia Crest is the 

highest and lies in the rim of a small recent lava cone. 

The cone is indented by two craters. The larger of the 

two is about one- quarter mile (0.4 km) in diameter, and 

both craters are nearly filled with snow and ice. Volcanic 

heat and steam have melted a system of tunnels and caves 

in the ice. Liberty Cap and Point Success are remnants of 

the sides of an old, high cone. 

Echo Rock and Observation Rock: Echo Rock and 

Observation Rock are dissected satellite volcanoes. 

Olivine andesite erupted from these satellite volcanoes 

on the northwestern flank of Mount Rainier. 

Little Tahoma and McClure Rock: Northwest American 

Indians named the mountain Takhoma, Tahoma, Taco- bet and other names that mean “big mountain”, or 

“snowy peak”, or “place where the waters begin”. Little 

Tahoma is a prominent rock outcrop on the east side of 

Mount Rainier. 

McClure Rock is a prominent point on the southern 

shoulder of the mountain. The point was named for 

Professor McClure, University of Oregon, who fell and 

died while doing scientific research on the mountain. 

Ptarmigan Ridge and Wapowety Cleaver: The rugged 

surface surrounding Mount Rainier is evidence of thick 

intra- canyon flows. At least 1,200 feet (366 m) thick, 

Ptarmigan Ridge is an example of a thick flow that was 

once confined in a canyon. Since deposition, the canyon 

walls have eroded away, leaving the flow as a resistant 

ridge in the surrounding landscape. 

Wapowety Cleaver is another ridge of rock located 

between the Kautz and the Wilson Glaciers. Kautz 

climbed the ridge in 1857 and the ridge was named after 

Kautz’s Indian guide. 
 MORA Geologic Resource Evaluation Report 21

The Palisades: Located at the northwestern corner of 

White River Park, The Palisades form a great cliff of 

columnar- jointed black rock that rises abruptly from the 

headwaters of Lost Creek. The cliff is composed of a 

rhyodacite welded tuff that is as much as 800 feet (244 m) 

thick. 

Willis Wall: Willis Wall forms the rear wall of the cirque 

of the Carbon Glacier. Named in honor of California 

geologist, Bailey Willis, the wall is an almost sheer wall of 

lava some 3,600 feet (1.097 m) high. Willis explored the 

north side of the mountain and blazed the first trail to the 

Carbon Glacier in 1881. He was also influential in 

securing the passage of the bill that created Mount 

Rainier National Park. 

Thermal Features and Ice Caves 

In 1870, active fumaroles were recognized at the summit 

of Mount Rainier during the first authenticated climb to 

the top of the volcano (Crandell, 1971). These summit 

fumaroles, ice caves associated with the fumeroles, and 

Ohanapecosh Springs are hydrothermal features listed in 

the Geothermal Steam Act (Barr, 2001). In response to 

the Geothermal Steam Act, Amendments of 1988, an 

evaluation of “significant thermal features” in MORA 

was conducted by the Bureau of Land Management 

(Korosec, 1989). Thermal features of the park fall into six 

separate groups: 

• Summit thermal area 

• Upper- flank thermal areas 

• Winthrop Springs 

• Paradise Springs 

• Longmire Mineral Springs 

• Ohanapecosh Hot Springs 

Fumeroles at the summit of Mount Rainier are small 

vents that release steam in an area where the ground 

temperature is 174o

 to 185o F (65o to 71o C). The summit 

thermal area, upper- flank thermal areas, and the 

Winthrop and Paradise Springs on the lower flanks are 

thought to be part of a single geothermal system within 

the edifice of the volcano (Korosec, 1989). Hot acid 

sulfate- chloride water flows from the upper part of the 

cone outward toward areas of leakage on the lower 

flanks (Frank, 2000). 

Thermal groundwater flowing from the cone appears to 

be neutralized by reaction with andesite and cooled by 

dilution with cold groundwater prior to being discharged 

into surface waters. Elevated sulfate and chloride were 

found in two sets of thermal springs near Paradise and 

Winthrop Glaciers. Cold neutral water with elevated 

sulfate and chloride discharges was found issuing from 

Winthrop Glacier (Frank, 2000). 

The vented steam at the summit continues to melt ice to 

form ice caves. The creation of ice caves by the steam 

vents in an active glacier area represents an unusual 

geologic feature. The two craters atop the summit of 

Mount Rainier contain the world’s largest volcanic icecave system (Zimbelman et al., 2000A). In 1997, two 

active fumeroles were sampled for stable isotopic, gas, 

and geochemical studies. Data indicate that the 

hydrothermal system in the edifice of Mount Rainier 

consists of shallow, meteoric water reservoirs that 

receive gas and steam from an underlying magmatic 

system. 

In the eastern crater, 2,300 feet (700 m) of caves were 

mapped in 1997- 1998 (Le Guem et al., 2000). Researchers 

found the main fumaroles located at the eastern 

entrance. Very few fumeroles were observed deep within 

the cave. No sulfur was detected in the gases and CO2

concentration in the cave atmosphere was close to 300 

ppm and around 1 percent in the fumaroles. 

155 meters (508 feet) of caves were mapped in the western 

crater. H2

S concentrations in the cave atmosphere were 2 

to 5 ppm, giving it a rotten egg odor, and 0.3 percent CO2

(Le Guem et al., 2000). Isotope data indicate that 

meteoric groundwater has diluted the H2

S 

concentrations, but samples taken from incrustations 

around a dormant vent record a past history of magmatic 

components episodically venting at the surface 

(Zimbelman et al., 2000A). 

Ice caves also are usually visible at the base of Paradise, 

Carbon, and other glaciers. However, these caves formed 

as a result of glacial meltwater rather than hydrothermal 

processes. 

Longmire Mineral Springs are part of a separate 

geothermal system. The heat source is probably related 

to the volcano’s magmatic system at depth and may be 

fault and/or fracture controlled. This system is of limited 

extent and has a volume of perhaps three cubic 

kilometers covering about three square kilometers. 

Ohanapecosh Hot Springs consists of 25 springs, ranging 

from small seeps to small springs. The springs are located 

near the base of Mount Rainier in the southeast part of 

the park and like the Longmire Mineral Springs are part 

of a separate geothermal system, also of limited extent. 

The springs are indicators of subsurface thermal 

processes. Temperatures have been reported as high as 

122o

 F (50o C). Flows have been measured between 110-

250 liters per minute. 

Yellow- orange to white travertine deposits of unknown 

thickness underlie parts of a meadow at Longmire and a 

small area near Ohanapecosh campground (Crandell, 

1969B). Travertine is a calcium carbonate mineral and 

has formed by warm spring water present at both 

localities. 
 NPS Geologic Resources Division 22 

Map Unit Properties 

This section provides a description for and identifies many characteristics of the map 

units that appear on the digital geologic map of Mount Rainier National Park. The table 

is highly generalized and is provided for informational purposes only. Ground 

disturbing activities should not be permitted or denied on the basis of information 

contained in this table. More detailed unit descriptions can be found in the help files that 

accompany the digital geologic map or by contacting the NPS Geologic Resources 

Division. 

The rocks exposed at MORA fall into three main groups: 

• Bedded rocks of Eocene, Oligocene, and Miocene age 

• Granitic intrusive rocks of Miocene and Pliocene age 

• Lava flows and related Quaternary- age rocks of 

Mount Rainier volcano 

The bedded rocks include the Puget Group (exposed 

west of the park), Ohanapecosh Formation, Stevens 

Ridge Formation, and the Fifes Peak Formation. A brief 

description of the three main groups of rocks is given in 

the following Map Unit Properties Table. 

The table is a stratigraphic column and itemized list of 

features for each rock unit. The table includes properties 

specific to each unit such as: geologic map symbol, 

formation name, rock description, resistance to erosion, 

suitability for development, hazard potential, mineral 

resources, and global significance. 

Resistance to erosion is a subjective category. In general, 

igneous rocks such as andesite and basalt are more 

resistant to erosion relative to sedimentary rock types 

and soil. In the wet climate of the Pacific Northwest, 

however, chemical weathering of less stable minerals in 

igneous rocks such as olivine, augite, and plagioclase 

feldspar, might contribute to enhanced erosion rates. 

In addition, glacial weathering processes may accelerate 

erosion. Glacial plucking of formations immediately 

adjacent to the glacial ice may destabilize the formations 

and lead to over steepening and ultimately, rockfall. 
Map Unit Properties Table 

Period Epoch Map Unit (symbol) Rock/Unit Description Resistance to Erosion Haza

Surficial Deposits (Qs) Alluvium, mudflows, lahars, & glacial deposits; variable thickness Low 

May be into glacflows & 

Holocene 

Landslides (Qls) Unconsolidated, poorly sorted deposits; variable thickness Low 

Inactive reactivaactively BackbonNisqual

Mount Rainier plugs and dikes (Qrp) 

Central plug of opalized andesite in Sunset Amphitheater; satellite plugs of olivine andesite at Observation Rock & Echo Rock; radial dikes Variable Limited 

rockfall

Andesite of Mt. Rainier volcano (Qra; Qroa) 

Qra: chiefly hypersthene- augite andesite & minor olivine andesite in thick intracanyon lava flows & associated mudflows near base of volcano: thinner flows & interlayered breccia on upper slopes; up to 2000 ft (610 m) thick Qroa: olivine andesite flows from Echo Rock & Observation Rock vents 

Variable; glacial plucking forms “cleavers.” 

May be into debavalanch

Quaternary 

Pleistocene 

Regional Unconformity 

Tatoosh granodiorite and quartz monzonite (Tg) 

Subordinate amounts of quartz diorite, contact breccia, & fine- grained border rocks; central pluton & associated stocks High R

Pliocene 

Andesite of Bee Flat (Tha) Intracanyon lava flow of hypersthene- hornblende High R

Tatoosh diorite, quartz diorite, granodiorite, and quartz monzonite porphyries (Tdi) 

Subordinate amount of microgranite, porphyritic granophyre, and felsite; swarms of sills, dikes, & irregular small intrusive bodies clustered mainly near borders of the Tatoosh pluton and associated stocks; poor exposures in valleys of Panther, Laughingwater, and 

Chenuis Creeks. 

High 

Limited rockfall underlieWhite R

Welded tuff of The Palisades (Tw) Pyroclastic rocks that grade downward into The Palisades plug; 800+ feet (240+ m) thick. High R

Regional Unconformity 

Pre- Tatoosh diabase & basalt (Td) Chiefly in dikes and sill swarms; the Box Canyon sill complex along Cowlitz River. Limited aerial extent Limited 

Miocene 

Stevens Ridge Fm. (Ts) Fifes Peak Fm. (Tf) 

Ts: Rhyodacitic ash flows; subordinate amounts of volcanic breccia, sandstone, and siltstone of epiclastic & pyroclastic origin; 450- 3000 feet (137- 914 m) thick. Tf: Basalt, basaltic andesite, & andesite flows; minor rhyolite flows, ash flows, & tuff breccia, volcanic sandstone, & volcanic siltstone of epiclastic & pyroclastic origin; 24,000+ feet (730+ m) thick. 

Low : Tf mostly removed from park by erosion. 

Regional Unconformity 

Oligocene Ohanapecosh Fm. (To, 

Tol, Tor) 

To: volcanic breccia, sandstone, & siltstone of epiclastic & pyroclastic origin, Tol: local thick accumulations of basaltic andesite flows & coarse mudflows, Tor: rhyolite Total formation thickness: 10,000+ feet (3,000 m) 

Variable: To exhibits vertical fractures on cliffs 

Variablerockfall

Regional Unconformity 

Pre- Tatoosh basaltic andesite & rhyolite (Tar) 

Plugs of massive & brecciated basaltic andesite which supplied lava & fragmental material to the Ohanapecosh Formation. South Cowlitz Chimney is a flow- banded rhyolite plug 

Very limited aerial extent R

Eocene 

Puget Group Sandstone, claystone, coal exposed west of Mount Rainier National Park; thickness 10,000+ feet (3,000+ m). Less resistant than igneous rocks No

Tertiary 

Paleocene Regional Unconformity 

Cretaceous/ Jurassic Russell Ranch Fm? (KJvb) Basalt flows of fault- bounded greenstone unit consisting of pillow lavas and minor shale interbeds; not exposed in MORA. Not in MORA No

 MORA Geologic Resource Evaluation Report 25

Geologic History 

This section highlights the map units (i.e., rocks and unconsolidated deposits) that occur 

in Mount Rainier National Park and puts them in a geologic context in terms of the 

environment in which they were deposited and the timing of geologic events that created 

the present landscape. 

The volcanoes in the north- south trending Cascade 

Province evolved through a history of complex plate 

tectonic processes and glaciation. Different tectonic 

models have been proposed for the development of the 

Cascades, but all models include subduction, addition of 

exotic terranes, and oblique plate movements as 

important components in creating today’s Cascade 

Range (Kiver and Harris, 1999). In general, the North 

American plate edge was located farther east during the 

Mesozoic in Nevada, western Idaho, and eastern 

Washington. Subduction processes added larger masses 

of continental materials, island- like masses called 

microcontinents, microplates, or exotic terranes to the 

western margin of North American. Addition of these 

microplates shifted the plate edge westward. 

The first Cascade volcanoes erupted about 42 million 

years ago (Ma), forming the older Western Cascades. At 

the time, the range was oriented northwesterly but would 

later rotate clockwise to achieve today’s north- south 

orientation. Continued subduction formed rows of 

volcanic vents that become younger to the east. As a 

result of clockwise rotation, extensive fissures opened up 

to the east and voluminous eruptions of the Columbia 

River Basalt occurred about 17 Ma. 

Subduction and accompanying volcanism continued for 

some 25 million years in the older Cascade Range. As 

magma rose, rocks were heated and began to expand. 

Large lithospheric blocks dropped downward along 

north- south oriented faults creating linear depressions, 

or grabens (fault- bounded basins). The faults opened 

pathways that enabled large volumes of magma to rise. 

The grabens filled and overflowed with overlapping 

shield and cinder cones to form a volcanic plateau called 

the Eastern, or High, Cascades. 

The present generation of volcanoes is believed to be no 

more than 400,000- 600,000 years old. Mount St. Helens 

was formed only 40,000 years ago. Coincident with the 

growth of these recent volcanoes was the Pleistocene Ice 

Age, which began about 1.6 Ma. Glaciers formed on each 

volcanic cone when it reached sufficient height. At the 

peak of glaciation, a continuous icecap buried the upper 

Cascades from Canada to northern California, broken 

only in the Columbia Gorge area where elevations 

approached sea level (Kiver and Harris, 1999). Alpine 

glaciers on Mount Rainier flowed as far as 65 miles (105 

km) from the mountain. Most of the glacial sculpturing 

seen today occurred during the Wisconsin glacial stage, 

which reached its maximum only 15,000- 20,000 years 

ago. 

For Mount Rainier National Park, the terrestrial history 

begins in the Tertiary Period of the Cenozoic Era in the 

Eocene Epoch, 36.6- 52 Ma. 

Tertiary Period: Eocene Epoch 

Western Washington looked far different in the Eocene 

than it does today. Mount Rainier and the Cascade 

Mountain Range did not exist. Rather, deltas, swamps, 

and inlets formed a broad lowland bordering the Pacific 

Ocean. Rivers drained into this lowland from the east. 

The sand, clay, and peat that accumulated were 

compacted into the 10,000- foot (3,000 m) sequence of 

sandstone, shale, and coal of the Puget Group, exposed 

west of the park (Harris et al., 1995; Kiver and Harris, 

1999). 

On the western margin of North America, a complex 

tectonic framework created a complex sedimentary 

assemblage. In Oregon, Eocene deep- sea sedimentary 

fans developed west of an accreted and subsiding 

seamount chain in a new fore- arc basin (the Tyee forearc basin in Figure 6). The basin developed in the Coast 

Range, west of the older Mesozoic fore- arc basin of 

central Oregon (Miller et al., 1992). In the Klamath 

Mountains, Hornbrook Basin area, and northern part of 

the Great Valley fore- arc basin (California), regional 

uplift during the Paleocene to early Eocene caused nonmarine Eocene strata to unconformably overlie 

Cretaceous marine rocks. Sedimentation continued in 

the Great Valley fore- arc basin. 

Middle and upper Eocene submarine sedimentary fans 

and continental- slope deposits that graded eastward 

into shallow- marine, deltaic, and fluvial equivalents 

buried newly accreted, subsiding terranes in the Pacific 

Northwest from about 55- 43 Ma (Christiansen and 

Yeats, 1992). Pull- apart basins created by oblique 

subduction on the northwest flank of the North 

Cascades were filled with thick nonmarine arkosic 

sandstones and conglomerates. From the North 

Cascades to central Idaho, extensional faulting 

juxtaposed upper- crustal sections against mid- crustal, 

metamorphic rocks in relatively continuous metamorphic 

core complexes. These metamorphic core complexes 

formed domes between which graben- like basins 

formed and filled with thick sediments and 

contemporaneous volcanics. 

In latest Eocene (about 43 Ma), the coastal region rotated 

clockwise at a rate of one degree per million years. Lakes 

and alluvial basins occupied the area east of the 

continental divide while the Cascade Arc, an arcuate 
 NPS Geologic Resources Division 26 

trend of offshore volcanoes, extended from British 

Columbia southward into southern Oregon. South of the 

arc, most of California was either eroding upland or 

coastal plain that bordered a continental shelf and slope 

to the west. 

Tertiary Period: Oligocene Epoch 

Ohanapecosh Formation: Beginning in the Oligocene 

about 35 Ma and continuing until 28 Ma, plate movement 

along the western subduction zone increased, the 

descent of the oceanic plate became less steep, and the 

rigorous movement generated abundant magma. Large 

lakes or embayments of the sea inundated the lowland, 

and clusters of volcanoes erupted under the sea and on 

land. Breccia from volcanic explosions and material from 

lava flows, mudflows, and ash falls, all of which 

accumulated in shallow water, comprise the 

Ohanapecosh Formation (Harris et al., 1995; Kiver and 

Harris, 1999). 

The most explosive volcanoes were underwater where 

percolating water triggered steam- blasted eruptions. 

Andesites, rhyolites, and volcanic breccia are well 

exposed in the eastern part of the park where, locally, 

layer upon layer of volcanic debris may reach over 10,000 

feet (3,000 m) thick (Kiver and Harris, 1999). These 

layers are exposed in highway road cuts on the east side 

of Backbone Ridge, and remnants of volcanic centers are 

well exposed in the steep cliffs below the Sarvent 

Glaciers, just east of Mount Rainier. Volcanic vents, now 

plugged with masses of solidified lava, are visible at the 

South Cowlitz Chimney, Double Peak, and Barrier Peak. 

After the volcanic activity subsided, the Ohanapecosh 

Formation was compressed into broad folds. Zeolites (a 

group of hydrous aluminosilicate minerals common as 

replacement minerals in volcanic rocks) and other 

minerals replaced most of the original minerals, and 

these new minerals firmly cemented the fragmental 

debris into hard rocks. They also imparted the dark gray 

and green colors typical of Ohanapecosh deposits. Uplift 

of the entire area followed. In the warm, wet climate, 

streams and rivers carved deep valleys into this hilly 

terrain. Valleys as deep as 1,500 feet (457 m) were eroded 

into the underlying Ohanapecosh Formation. 

Stevens Ridge Formation: During the Oligocene and 

Miocene (Figure 2), thin layers of pumice and ash were 

deposited over the hilly terrain. These layers are the 

initial deposits of the Stevens Ridge Formation 

(Figure 7). The first thin ash falls had little affect on the 

many trees growing on the hills, but that was about to 

change. The most catastrophic event ever to befall the 

area blasted a series of searing hot ash flows over the area 

and smothered the former landscape. The ash flows 

consisted of mixtures of volcanic dust, bits of pumice, 

and other hot volcanic fragments buoyed up and greatly 

mobilized by hot volcanic gases that expanded and 

lubricated the flows so that flow velocities may have 

reached 60 or 80 miles per hour (97- 129 km/hr). Flowing 

into the valleys carved in the underlying Ohanapecosh 

Formation, the first ash flows choked streams, disturbed 

the soil, and killed trees that stood in their path. 

Subsequent ash flows eventually filled the valleys with 

deposits hundreds of feet thick and completely covered 

the pre- existing hills. When the hot volcanic ash was 

deposited, the heat fused the small bits of volcanic glass 

and pumice together into a rock known as welded tuff. 

Only remnants of the Stevens Ridge ash flows survive in 

the park. Highway road cuts near the top of Backbone 

Ridge contain pieces of wood, bits of soil, and other 

debris chaotically mixed into the lower part of the basal 

Stevens Ridge ash flow. This ash flow can be traced 

northwestward to the lower slopes of Stevens Ridge 

where it is visible along the Stevens Canyon highway. 

Other ash flows are well exposed in the cliffs on the 

southern slope of Stevens Ridge. 

Tertiary Period: Miocene Epoch 

Fifes Peak Formation: The Fifes Peak Formation is 

primarily composed of andesite and basalt lava that 

erupted directly on top of the Stevens Ridge Formation 

(Figure 7, Appendix A). Rather than erupting bits of ash 

and pumice, the volcanoes responsible for the Fifes Peak 

Formation produced streams of lava that built low, 

overlapping volcanic cones. Up to 2,400 feet (730 m) of 

interfingering lava flows covered the area although 

erosion has removed all but a small remnant of this lava 

field from the park. The largest remnant of the Fifes Peak 

Formation underlies much of the rugged area near 

Mowich Lake, northwest of Mount Rainier. 

Although the volcanoes have been dissected and mostly 

removed by erosion, feeder dikes to the volcanoes still 

remain. The dikes can be traced for about a mile along 

the surface and vary from 6 inches (15 cm) to 20 feet (6 

m) thick. Swarms of dikes that cut the Stevens Ridge and 

Ohanapecosh Formations may be found on Backbone 

Ridge and on Stevens Peak, Mount Wow, and in the 

headwaters of the North Fork of the Puyallup River. 

Lava also was forcefully injected between underground 

layers of Ohanapecosh and Stevens Ridge strata, which, 

when cooled, formed tabular bodies known as sills. 

These sills can be found in the low country along the 

Muddy Fork of the Cowlitz River and near Longmire. 

The Box Canyon of the Cowlitz slices into one of these 

thick Fifes Peak Formation sills. 

Following the eruptions of Fifes Peak lava, the area was 

once again compressed and folded. The folds that 

formed after deposition of the Ohanapecosh Formation 

became tighter. Faults broke the strata of the 

Ohanapecosh, Stevens Ridge, and Fifes Peak Formations 

as the rocks shifted to relieve the compressive stresses. 

For example, near vertical movement caused 910 meters 

(3,000 feet) of displacement between the base of the 

Stevens Ridge Formation and the Stevens Ridge 

Formation strata in Stevens Canyon. Continued plate 

collisions on the western margin caused this folding and 

faulting and set the stage for the second major episode in 

the geologic history of MORA – the emplacement of the 

Tatoosh pluton. 
 MORA Geologic Resource Evaluation Report 27

Granitic Intrusive Rocks of Miocene and Pliocene Age 

By 20 Ma (early Miocene), only remnants of the Farallon 

plate remained (Figure 8). Most of western Washington 

and Oregon had emerged above sea level by late Miocene 

time. Upper Miocene and lower Pliocene nonmarine 

sediments accumulated locally in basins in the Puget 

Lowland, in the Willamette Valley, and along the 

Columbia River. 

Tatoosh Pluton and Associated Intrusives: About 9 Ma 

(late Miocene), the rate of collision between lithospheric 

plates slowed and the angle of descent of the subducting 

plate steepened, like it is today (Figure 9). In the Miocene 

and Pliocene, a great upward surge of molten rock 

stopped short of the surface and intruded the rocks of 

the Ohanapecosh, Stevens Ridge, and Fifes Peak 

Formations, solidifying as intrusive igneous bodies, 

called plutons (Figures 7, 10) (Fiske et al., 1963, 1988). 

Dikes and sills riddle the bedded formations. Some of 

these intrusive bodies are large enough to be mapped; 

some are not. Some of the magma erupted onto the 

surface although all but the welded tuff at The Palisades 

has been eroded from the park. 

Igneous activity such as eruption of the lava flow at Bee 

Flat occurred sporadically throughout the rest of the 

Pliocene time. But uplift and erosion were the dominant 

processes at the time, and these processes developed the 

unconformity that separates the Pliocene from the 

Pleistocene (Map Unit Properties Table). Over time, the 

thin roof of older rocks was partly eroded away to 

expose the top of a large and complex granitic pluton. 

Some of the best exposures are found in the rugged 

cirques and peaks of the Tatoosh Range, from which the 

pluton is named (Appendix A). The granodiorite of the 

Tatoosh pluton is also exposed in the Carbon and White 

River valleys and part of the upper Nisqually River valley. 

Mapping reveals that the Tatoosh pluton completely 

underlies Mount Rainier and forms a platform upon 

which the volcano grew (Figure 10) (Fiske et al., 1988). 

Quaternary Period: Pleistocene Epoch 

The eruptive centers that would create North Cascades 

National Park, Mount Rainier National Park, Crater 

Lake National Park, and Lassen Volcanic National Park 

erupted from 7 to 2 Ma (Figure 11). 

At the time of the great Pleistocene Ice Age, the Tatoosh 

Mountains were undergoing glaciation in a very cold 

climate. A series of relatively fluid andesitic lava flows 

early in the Pleistocene flowed onto the rugged terrain 

carved into the mountain (Figure 7; Appendix A). Intracanyon lava flows filled ancient canyons to depths of 

2.000 feet (610 m) and traveled up to 15 miles (24 km) 

from the young volcano (Fiske et al., 1988). Evidence of 

mudflow and glacial deposits interlayered with the lava 

flows indicates that glaciation was ongoing throughout 

this time. 

These intra- canyon flows now form ridges or flat 

benches far above today’s canyons. Originally, the flows 

filled the canyons, but the lava was more resistant to 

erosion than the surrounding strata. The vigorous 

erosion by rivers and glaciers preferentially cut the 

weaker rocks, excavating far below the floors of the old 

filled canyons. 

Good exposures of old intra- canyon flows can be seen at 

Burroughs Mountain and the flat surface of Yakima Park 

where a stream of lava flowed about 7 miles (11 km) down 

the canyon of the ancestral White River. The end of this 

flow is exposed in the highway road cuts below Sunrise 

Ridge. The present- day canyon cut by the White River 

lies to the south side of the intra- canyon flow. The thick 

lava flow that underlies Rampart Ridge, just west of 

Longmire, is another example of a ridge that was once a 

canyon. Originally, the flow poured into the upper 

canyon of the Nisqually River. The ridges of old intracanyon flows stand in stark contrast to the younger flows 

that now lie at the bottom of a few present- day canyons. 

The projecting fingers of intra- canyon lava lie in the 

shadows of the main cone of Mount Rainier. The cone is 

built from hundreds of thin lava flows, breccia deposits, 

and debris and mudflows. The cone began to be built 

from short streams of lava interspersed with ejections of 

breccia and ash. About 75,000 years ago, the volcano 

reached its greatest height of perhaps 15,500 to 16,000 

feet (4,700 to 4,900 m) (Harris et al., 1995). Dikes 

radiated from the center of the volcano, like spokes in a 

wheel, and a plug of solidified magma filled the central 

vent. 

Quaternary Period: Holocene (Recent) Epoch 

Figure 12 summarizes the lahars, mudflows, debris flows, 

avalanches, and recent eruptions of Mount Rainier over 

the past 70,000 years that are listed on the USGS website, 

http://vulcan.wr.usgs.gov/Volcanoes/Rainier/framework

.html. The recent eruptions have ejected minor amounts 

of pumice and ash high into the air to be deposited in the 

park. Figure 13 breaks out the recent eruptions from the 

list of events in Figure 12. Although eleven eruptions 

from Mount Rainier, two eruptions from Mount St. 

Helens, and one eruption from Mount Mazama have 

deposited pumice in the Mount Rainier area, the total 

thickness of these deposits ranges from less than an inch 

to a few feet, and this unconsolidated material has been 

completely eroded away from many areas. 

About 5,000 years ago, the weak clay zones, steep slopes, 

high elevation, and abundant water and ice combined 

with a volcanic eruption to produce the Osceola 

Mudflow, one of Earth’s largest known mudflows. The 

upper 3,000 feet (910 m) of Mount Rainier collapsed as 

distinct blocks of rocks quickly disintegrated into a giant 

debris avalanche, and mixing with abundant water and 

clay particles, transformed into a wall of mud cascading 

down the White River drainage. Thinning away from the 

mountain, the Osceola Mudflow deposited 100 feet (3o 

m) of mud near the present site of Enumclaw, 35 miles 

(56 km) downstream (Figure 4). Traveling at about 40 

miles per hour (64 km/hr), the mudflow buried the site of 

an Indian village and eventually poured into Puget 
 NPS Geologic Resources Division 28 

Sound, 75 miles (120 km) from the mountain (Kiver and 

Harris, 1999). 

Mount Rainier was built from material erupting from a 

central vent. A plug of solidified lava now fills this vent 

and is exposed in the precipitous east wall of Sunset 

Amphitheater (Appendix A). Two small plugs on the 

northwestern flank of Mount Rainier denote satellite 

volcanoes and three thick radial dikes extending 

outward from the summit area mark locations where lava 

erupted and flowed onto the lower slopes of the volcano. 

Two prominent dikes can be seen at Puyallup Cleaver 

and St. Elmo Pass where they stand as resistant ribs 

above the rocks they intrude. 

Although Mount Rainier is the second highest peak in 

the conterminous United States, the mountain’s peak 

was once considerably higher than it’s 14,410 feet (4,390 

m) today. The truncated lava flows in the upper part of 

the mountain slant upward to a former summit that was 

at least 100 feet (30 m) higher than the present summit 

(Fiske et al., 1988). Three hypotheses have been proposed 

as reasons for the summit’s removal. Some geologists 

believe the pinnacle of Mount Rainier was removed by a 

violent explosive eruption, but fragments from this 

eruption have not been found. Others believe that 

avalanches and glacial erosion rapidly ate away the upper 

part of the mountain. Still others see the former summit 

collapsing into the central vent when the column of lava 

temporarily subsided. 

The largest rockfalls on Mount Rainier in historic time 

occurred in December 1963, when a series of rockfalls, 

hundreds of feet across, fell from the steep north face of 

Little Tahoma Peak onto Emmons Glacier (Crandell, 

1969A, B; Kiver and Harris, 1999). When the rock hit the 

glacier, it shattered into dust and countless fragments 

and then avalanched down the steep ice surface at a 

tremendous speed. At the end of the glacier, the rock 

debris traveled toward the valley floor over a layer of 

compressed air that reduced the friction and permitted 

the avalanche to move almost 2 miles (3 km) beyond the 

end of the glacier. This avalanche passed over a small 

wooden gage house about 5 feet (1.5 m) high without 

damaging it and then slammed into the north base of 

Goat Island Mountain. The force of the avalanche 

scraped away trees and bushes in the path of the flow. A 

later avalanche stopped just short of the gage house, but 

unfortunately, when the trapped wind was expelled from 

beneath the rock debris, the gage house was destroyed. 

At least seven rockfalls and avalanches from Little 

Tahoma Peak occurred in a matter of minutes or hours 

and some came to rest only a short distance up- valley 

from the White River Campground. 

Today, fumaroles and occasional steam explosions on 

the flanks of Mount Rainier indicate continued heat 

flow, and seismic tremors suggest that future volcanic 

eruptions are possible. 
 MORA Geologic Resource Evaluation Report 29

Figure 6: Paleogeographic map of the western margin of North America during the Paleocene and early Eocene time. Modified from Miller 

and others, 1992. 
 NPS Geologic Resources Division 30 

Figure 7: Simplified geologic map of Mount Rainier National Park showing rock units and the location of the synclines, anticlines, faults, and 

dip of beds. 
 MORA Geologic Resource Evaluation Report 31

Figure 8: Paleotectonic map of western United States approximately 15 Ma in the Miocene Epoch. Initiation of basin and range faulting and 

the San Andres fault system takes place about this time. Modified from Dickinson, 1976. 
 NPS Geologic Resources Division 32 

Figure 9: Plate tectonic cross-section sketch illustrating the general tectonic setting for the present northwestern margin of the United 

States. Modified from Dickinson (1976). 

Figure 10: Generalized north-south geologic cross-section through Mount Rainier National Park showing the central vent, glaciers, Tatoosh 

pluton, and adjacent bedded strata. Modified from Crandell (1969A) and Fiske and others (1988). 
 MORA Geologic Resource Evaluation Report 33

Figure 11: Map of late Miocene and younger magmatic systems in the Cascade Mountains. Light coloring indicates volcanic rocks of 7 to 2 

Ma age; dark coloring indicates volcanic rocks of 2 to 0 Ma age. The arrow indicates relative convergence between the Juan de Fuca and 

North American Plates. Modified from Christiansen and others, 1992. 
 NPS Geologic Resources Division 34 

Recent events associated with Mount Rainier 

Event Age/Date Description and Comments 

Glacial outburst floods Late 1960s Geothermal (?) melting of South Tahoma Glacier 

Little Tahoma Peak 

avalanche 1963 

Extended as far as 4.3 miles down valley; impacted Inter Fork and 

White River valleys; lahar from main avalanche was <2- 4% clay; extent 

to White River Campground 

Kautz Creek Mudflow Oct. 2- 3, 1947 Rain induced lahars; extent to Nisqually River 

Tahoma Glacier 

avalanche 1910- 1930 Small debris flow; Puyallup River drainage; extent below glacier 

terminus 

Pumice layer G 1820- 1860 

Pumice layer X 1820- 1860 Scattered pumice lapilli 

West Fork White River 

debris flow 1570- 1695 Lahar extended at least 18 mi beyond Winthrop Glacier 

White River debris 

flow 1550 Large gravel- rich debris flow & flood gravel aggraded present channel; 

non- volcanic in origin; extent to Mud Mountain Reservoir 

Tahoma Lahar Post- pumice 

layer W Tahoma Creek & Nisqually River drainages; 3- 4% clay; extent to Elbe 

Pumice layer W 

(from Mt. St. Helens) 1480- 1520 Pumice ash; white; fine to med sand size; thickens from 0.25 inches on west side to 3 inches near SE corner 

Electron Mudflow 1400- 1420 

Subrounded to subangular pebbles, cobbles, and boulders in plastic 

matrix of clayey sand; 200+ million cubic yards at average thickness of 

15 ft; extended about 30 miles down South Puyallup River Valley; 

underlies about 14 sq mi of the Puyallup River Valley in the Puget 

Sound lowland 

1,000- year- old lahar 900- 970 Extended at least 14 miles beyond Tahoma Glacier (South Puyallup 

River Valley); 5- 12% clay 

National Lahar Post- pumice 

layer C, pre- W 

Runout phase inundated all valley bottoms above Alder Reservoir to at 

least 9 ft depth; extent to Puget Sound 

Columbia Crest 

Summit Cone 

33 A.D.; Postpumice layer C, 

pre- W 

Pyroclastic surge; lava flows forming summit cone 

Pumice layer C 

2,200 yearsbefore- present 

(BP) 

Pumice lapilli & scattered blocks; widely distributed over most of park 

east of the volcano; 1 to several inches thick; most widespread & 

voluminous of Mt. Rainier tephras 

Block- and- Ash flow 2,350 BP Extended about 3 miles beyond Tahoma Glacier (South Puyallup River 

Valley) 

Lahar 2,533- 2,833 BP Extended at least 3 miles beyond Tahoma Glacier (South Puyallup 

River Valley) 

Round Pass Mudflow 2,170- 2,790 BP 

Extended at least 7 miles beyond South Tahoma Glacier and 15 miles 

beyond Tahoma Glacier (Tahoma Creek & Puyallup River drainages); 

4- 5% clay 

Pumice layer P 

(from Mt. St. Helens) 2,500- 3,000 BP 

Pumice layer Y 

(from Mt. St. Helens) 3.400 BP Pumice ash; light yellow- brown; med to very coarse sand size; thickens 

from 1 inch near east edge of park to 12 inches near SW corner 

Pre- Y lahar at 

Round Pass >3,400 BP About 3% clay; Puyallup River drainage & Tahoma Creek; unknown extent 

Pumice layer B 4,000- 4,500 BP Pumice ash & scattered lapilli, scoria, lithic fragments 

Pumice layer H 4,033- 5,000 BP Scattered pumice lapilli, lithic fragments 

Osceola Mudflow 4,500- 5,000 BP 

Probable total volume of a little more than half a cubic mile; largest 

mudflow of postglacial age at Mt. Rainier; covers an area of over 100 sq 

miles; extends down the White River to the Puget Sound lowland; 

deposits range in thickness from a few feet to over 200 feet; 2- 15% clay 

Greenwater Lahar 4,500- 5,000 BP 

Extended at least 28 miles down valley from volcano (Inter Fork and 

White River valleys); <3% clay; probably part of Osceola; extent to 

Puget Sound lowland 
 MORA Geologic Resource Evaluation Report 35

Recent events associated with Mount Rainier (cont.) 

Event Age/Date Description and Comments 

LOSS OF SUMMIT 5,733 BP 

The present summit of Mt. Rainier is at the top of a young lava cone 

constructed within a large depression about 1.25 miles across; high 

points on the rim of this depression are Point Success, Gibraltar Rock, 

and along the ridge between Liberty Cap and Russell Cliff; these high 

points record the removal of the volcano’s summit above an altitude of 

14,000 feet; material removed from the summit may have formed very 

large rockslides and avalanches that led to the Osceola Mudflow 

Pumice layer F 5,700- 5,800 BP 

Montmorillonite- rich lithic ash; lithic fragments, pumice, crystals, 

clay; similar clay contents and age of Osceola Mudflow; supposition is 

that Layer F records phreatic activity preceding or accompanying 

generation of the avalanche and resulting debris flow 

White River flows 5,700- 6,600 BP Bomb- bearing flows in White River Valley 

Pumice layer S 5,200 BP Sand- to block- sized lithic rubble; angular rock fragments as large as 

1.5 feet across; 

Pumice layer N 5,500- 6,500 BP Lithic fragments, ash 

Pumice layer D 5,500- 6,500 BP Pumice lapilli, scoria, lithic fragments; basaltic andesite 

Pumice layer L 5,500- 6,500 BP Pumice lapilli; silicic andesite 

Pumice layer A 5,500- 6,500 BP Pumice ash and scattered lapilli, lithic fragments 

Paradise Lahar 5,833- 6,633 BP 

Unsorted deposit of angular to subrounded rock fragments in a plastic 

matrix consisting of a mixture of sand, silt, and clay; extended at least 

18 miles down Nisqually River valley; younger than pyroclastic layer O 

and predates pyroclastic Layer D; 1- 6% clay; Paradise River and 

Nisqually River drainages 

Pumice layer O 

(from Mt. Mazama) 6,633- 6,900 BP Pumice ash; blankets entire park and adjoining area to depth of 1- 2 

inches; distinctive yellow- orange color 

Pumice layer R >8,750 BP Pumice, lithic fragments 

Main Cone of Mount 

Rainier About 10,000 BP 

Flows and breccia eventually built a cone standing 6,900 to 7,900 feet 

(2,100 to 2,400 m) above its surrounding topography before the end of 

the latest glaciation 

Ash layer 30,000- 70,000 

BP 

A thick pumice layer northeast, east, and southeast of the volcano may 

have been erupted from Mount Rainier; 

Figure 12: Summarized from USGS website. Blue signifies floods; orange signifies avalanches; yellow signifies debris flows, lahars, or 

mudflows; gray signifies pumice deposits; white represents a constructive phase of the volcanic cone; and red represents a destructive 

phase of the summit cone. 

Layer Age 

(years BP) Dominant Materials Source 

Thickness 

in inches 

West/East 

Volume in 

millions of 

cubic ft (m3

) 

X +/- 150 Pumice Mt. Rainier 0 / 1 35 (1) 

W 485 Pumice Mt. St. Helens 0- 1 / 1- 3 ? 

C 2200 Pumice, scoria, lithic fragments Mt. Rainier 0 / 1- 8 10,000 (300) 

Y 3250- 4000 Pumice Mt. St. Helens 5- 20 / 1- 5 ? 

B >4000 Scoria, lithic fragments Mt. Rainier ? 180 (5) 

H >5000 Pumice, lithic fragments Mt. Rainier ? 35 (1) 

F 5000 Lithic fragments, pumice, clay Mt. Rainier ? 880 (25) 

S 5200 Lithic fragments Mt. Rainier ? 700 (20) 

N 5500 Lithic fragments, pumice Mt. Rainier ? 70 (2) 

D 6000 Scoria, lithic fragments Mt. Rainier 0 / 0- 6 2,600 (75) 

L 6400 Pumice Mt. Rainier 0 / 0- 8 1,800 (50) 

A 6500 Pumice, lithic fragments Mt. Rainier ? 180 (5) 

O 6600 Pumice Mt. Mazama 1- 3 / 1- 3 ? 

R >8750 Pumice, lithic fragments Mt. Rainier 0 / 0- 5 880 (25) 

Figure 13: Holocene tephras in Mount Rainier National Park. Data from USGS website and Crandell (1969B). Age is in radiocarbon years 

before present (BP) except for Layer X, which was dated using tree rings. 
 NPS Geologic Resources Division 36 

References 

This section provides a listing of references cited in this report. A more complete geologic 

bibliography is available and can be obtained through the NPS Geologic Resources 

Division. 

Barr, D.L., 2001, The Geothermal Steam Act and the 

National Park Service: Department of Energy, Yucca 

Mountain Project, p. 38- 40. 

Christiansen, R.L., and Yeats, R.S., 1992, Post- Laramide 

geology of the U.S. Cordilleran region, in B.C. 

Burchfiel, P.W. Lipman, and M.L. Zoback, eds., The 

Cordilleran Orogen: Conterminous U.S.: Geological 

Society of America, the Geology of North America, v. 

G- 3, p. 261- 406. 

Crandell, D.R., 1967, Potential Effects of Future Volcanic 

Eruptions in Mount Rainier National Park, 

Washington: Unpublished report prepared for the 

National Park Service, U.S.G.S. Administrative Report, 

on file at Mount Rainier National Park, Ashford, WA. 

Crandell, D.R., 1969A, the Geologic Story of Mount 

Rainier: U.S.G.S. Bulletin 1292, 43 p. 

Crandell, D.R., 1969B, Surficial Geology of Mount 

Rainier National Park Washington: U.S.G.S. Bulletin 

1288, 41 p. 

Crandell, D.R., 1971, Postglacial Lahars from Mount 

Rainier Volcano, Washington: U.S.G.S. Professional 

Paper 677, 73 p. 

Crandell, D.R., and Hoblitt, R.P., 1986, Lateral Blasts at 

Mount St. Helens and Hazard Zonation: Bulletin of 

Vulcanology, v. 48. p. 27- 37. 

Crowley, J.K., and Zimbelman, D.R., 1997, Mapping 

Hydrothermally Altered Rocks on Mount Rainier, 

Washington with Airborne visible/Infrared Imaging 

Spectrometer (AVIRIS) Data: Geology, v. 26, p. 559-

562. 

Dickinson, W.R., 1976, Sedimentary basins developed 

during evolution of Mesozoic- Cenozoic arc- trench 

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Driedger, C., 1986, A Visitor’s Guide to Mount Rainier 

Glaciers: Pacific Northwest National Parks and 

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Driedger, C., 1992, Glaciers on Mount Rainier: U.S.G.S. 

Open- File Report 92- 474, Fact Sheet. 

Fiske, R.S., Hopson, C.A., and Waters, A.C., 1963, 

Geology of Mount Rainier National Park Washington: 

U.S.G.S. Professional Paper 444, 93 p. 

Fiske, R.S., Hopson, C.A., and Waters, A.C., 1988, 

Geologic Map and Section of Mount Rainier National 

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Frank, D., 2000, Hydrothermal Indicators in Streams and 

Springs at Mount Rainier: Washington Geology, v. 28, 

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Fritzke, S.L., 1992, Soil Erosion and Vegetation Loss 

Accelerated by Visitor Use of Paradise Meadows, 

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Pringle, P.T., and Vallance, J.W., 1995, Volcano 

Hazards from Mount Rainier, Washington: U.S.G.S. 

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Pringle, P.T., and Vallance, J.W., 1998, Volcano 

Hazards from Mount Rainier, Washington, Revised 

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 MORA Geologic Resource Evaluation Report 37

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Report 03- 368. 

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volcanic Debris Avalanches as Displayed at Mount 

Rainier, Washington: Paper presented at Mount 

Rainier – Decade Volcano I session, Fall meeting, 

American Geophysical Union, San Francisco, CA. 

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Fumaroles in Ice Caves on the Summit of Mount 

Rainier: preliminary Stable Isotope, Gas, and 

Geochemical Studies: Journal of Volcanology and 

Geothermal Research, v. 97, p. 457- 473. 

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p. 29. 
 NPS Geologic Resources Division 38 

Appendix A: Geologic Map Graphic 

This image provides a preview or “snapshot” of the geologic map for Mount Rainier 

National Park. For a detailed digital geologic map, see included CD. 

The original map digitized by NPS staff to create the above surficial map was: Crandell, D.R., 1969, Surficial geology of Mount Rainier 

National Park, Washington, USGS, Bulletin 1288, 1:48,000 scale. In addition a bedrock geologic map: Fiske, R.S., Hopson, C.A., and 

Waters, A.C., 1964, Geologic map and section of Mount Rainier National Park, Washington, USGS, I-432, 1:62,500 scale, was digitized 

as part of the GRE program. For detailed digital geologic data and cross sections, see included CD. 
The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and other 

information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and affiliated Island 

Communities. 

Mount Rainier National Park 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2005/007

NPS D-535, September 2005 

National Park Service 

Director • Fran P. Mainella 

Natural Resource Stewardship and Science 

Associate Director • Michael A. Soukup 

Natural Resource Program Center 

The Natural Resource Program Center (NRPC) is the core of the NPS Natural Resource Stewardship and 

Science Directorate. The Center Director is located in Fort Collins, with staff located principally in 

Lakewood and Fort Collins, Colorado and in Washington, D.C. The NRPC has five divisions: Air 

Resources Division, Biological Resource Management Division, Environmental Quality Division, Geologic 

Resources Division, and Water Resources Division. NRPC also includes three offices: The Office of 

Education and Outreach, the Office of Inventory, Monitoring and Evaluation, and the Office of Natural 

Resource Information Systems. In addition, Natural Resource Web Management and Partnership 

Coordination are cross-cutting disciplines under the Center Director. The multidisciplinary staff of NRPC 

is dedicated to resolving park resource management challenges originating in and outside units of the 

national park system. 

Geologic Resources Division 

Chief • David B. Shaver 

Planning Evaluation and Permits Branch Chief • Carol McCoy 

Credits 

Author • Dr. John Graham

Editing • Lisa Norby and Sid Covington 

Digital Map Production • Victor DeWolfe, Stephanie O’Meara, Josiah Engblom, and Melissa Copfer 

Map Layout Design • Melanie Ransmeier
Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, CO 80225 

http://www.nature.nps.gov/geology/inventory/ 

(303) 969-2090 

EXPERIENCE YOUR AMERICATM 

National Park Service 

U.S. Department of the Interior