Olympic National
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Olympic National
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Geology of
Olympic Mountains

Glaciers of
Olympic National

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The Surficial Geology of the Hoh River Valley


 Hoh River Valley



 Geologic History

 Pleistocene Glaciation




 Works Cited


Major sections of the Olympic Mountains have gone through periods of glaciation and then ablation. Today, there are more than sixty glaciers scattered throughout the Olympics. The largest and most studied is Blue Glacier. Other prominent glaciers around Mt Olympus are White Glacier, Hubert Glacier, Hoh Glacier, Humes and Ice River Glaciers. Today these glaciers clustered collectively around Mt. Olympus cover approximately ten square miles in the Mt. Olympus area. Since the Pleistocene, the Blue, Hoh, and White Glaciers have played a dominant role in the shaping and molding of the Hoh River Valley. The glaciers have carved out cirques in the high country, and left glacial deposits scattered throughout the Hoh River area. The Olympic Peninsula has undergone glaciation on at least four separate periods during the last 1 million years. Even today, these glaciers play an immense role in the Quaternary geology of the Hoh River Valley.


The Olympic Mountains of the Olympic Peninsula contain 11% of Washington's glaciers (Spicer 1986). Unlike the larger glaciers of Washington's Cascade Range, the Olympic Mountains are surrounded on three sides by water and the fourth side by a river lowland. Another distinct feature of the Olympic Mountains is that they sit in the path of Pacific Ocean storm systems, which carry in much precipitation. The Olympics are noted for their marine west coast climate resulting from prevailing westerly to southwesterly winds from the Pacific Ocean (Renner 1992). These winds bring heavy precipitation in the form of rain or snows that have played a major role in the climatology of the Olympic Mountains. The tallest peak in the Olympic chain is Mount Olympus at 7,965 feet elevation. Though this elevation is not particularly high, the Olympics rise up from sea level. Mount Olympus plays a large role in the surficial geology of the Hoh River Valley. Nestled around Mount Olympus are several glaciers: the Blue, White, and Hoh. These glaciers have played a significant role in the geology of the Hoh River Valley both past and present. Since the early 20th century, the Blue Glacier has been intensely studied.

This paper will attempt to show the significant relationship between the climatology and physical responses of the glaciers affecting the Hoh River Valley.


The Olympic Peninsula forms an area greater than 6500 square miles (Richards 1984). The peninsula lies at 122 degrees west longitude and 47 degrees north latitude. The Olympic Peninsula consists of the Olympic Mountains, which are an extension of the Coast Mountains of British Columbia and Oregon. The Olympic Peninsula is known for lush rain forests, pristine coastlines and striking mountains. Within the borders of the peninsula lie the Olympic National Forest covering an area of 632,324 acres and the Olympic National Park claiming more than 923,000 acres or 1,400 square miles (Tabor 1987). Together, these two comprise more than 60% of the peninsula in area. The Olympic Peninsula is bordered to the north by Vancouver Island, British Columbia and the Strait of Juan de Fuca. To the west is the Pacific Ocean and to the east sits Puget Sound and the Cascade Mountains. The southern perimeter of the Olympics abuts the lowlands of the Grays Harbor basin. The Olympics can claim nearly four hundred miles in coastlines. Proximity to the Pacific Ocean leaves its distinct mark on the climate and ultimately the geology of the Olympic Peninsula.

The Olympic Mountains are not extremely tall. The highest point is Mount Olympus at 7,965 feet above sea level. The Olympics rise nearly from the waters of the Strait of Juan de Fuca. As these mountains rise, they intercept moisture rich air masses that move in from the Pacific Ocean. As this air is forced over the Olympic Mountains, it cools and releases moisture as rain or snow. At lower elevations, this rain sustains the great rainforests of the Olympics, while snowfall collects at higher elevations to add volume to the glaciers of the Olympic National Park. These glaciers have carved and shaped many features of the Olympic Mountains. The Olympic Mountains squeeze out much of the precipitation in the air, leaving areas of the northeast section of the peninsula with the effects of a rain shadow. For example, the Hoh rain forest averages 140 inches of rainfall each year, while the town of Sequim forty miles east receives an average of seventeen inches of rain and must irrigate to farm (Richards 1984).

The Hoh River Valley lies on the western side of the Olympic National Park. The valley is generally recognized as stretching from Mount Olympus to its mouth at the Pacific Ocean. The length of the valley is approximately 56 miles and is one of the preeminent river valleys on the Olympic Peninsula along with the Elwha and Dungeness valleys. The Hoh River Valley has been glaciated on at least four known periods of time, and is quite unique. With the heavy precipitation from the Pacific Ocean, the Hoh has been home to the only temperate rain forest in the contiguous United States. top

Hoh River Valley:

The Hoh River Valley extends from the foothills of Mount Olympus to the Pacific Ocean. Some of the early geologic forces that shaped portions of the Olympics, also shaped the Hoh River Valley. Repeatedly during the Pleistocene, glaciers flowed down the valley from Mount Olympus, British Columbia, and eventually into the Pacific Ocean during each period of glacial advance and retreat. These glaciers formed the narrow valleys, giving them their U shape. Less than one mile from the river to the north and south, the ridges climb to more than three thousand feet in elevation. If you were hiking along the Hoh River enroute to higher elevations, you would find vast quantities of gravel. This gravel has its origins in Mesozoic-Tertiary graywacke, slate, argillite, volcanics, arkosic sandstone and was eventually deposited by the valley glaciers (Heusser 1974).The word Hoh is an Native American term meaning, "fast moving water"(Wood 1991).The Native Americans concluded correctly that the Hoh was truly a fast river. The Hoh is fed from the glaciers surrounding Mount Olympus. The Hoh receives 80% of the Mount Olympus glacial drainage from the Hoh, Blue, White, Black, Hubert, and Ice River glaciers (Wood 1991). The river attributes it's cold temperature and milky color to the glacial feed and silt. The Hoh river is a fairly large river as it departs the terminus of the Hoh glacier, and as it flows down the mountain, it collects water on the way downward from many smaller streams. As the Hoh continues its journey, it converges with Glacier Creek. Glacier Creek, is nearly the same size as the Hoh River and is fed by the Blue, White, and Black glacier. As the larger river continues downward, it flows to the west meandering eventually to the river valley floor. Several tributaries help feed the Hoh, by adding to it's volume; Mount Tom Creek, South Fork, Falls Creek, Lake Creek, Owl Creek, Maple Creek, Nolan Creek, and Braden Creek. top

Geologic History:

Though not old by geologic standards, the geology of the Olympic Peninsula is quite complex. The peninsula consists of two major rock groups. The Core rocks and the Peripheral rocks make up the foundation of the Olympics. The Core rocks make up the western, eastern, and central core of the peninsula and are made up of Upper Eocene and Oligocene rocks (23-40 million years ago) with well developed slaty cleavage in the eastern core (Tabor and Cady 1978). The Peripheral rocks form a horse shoe shape encircling the Core rocks from the south, east and north, with the open end of the horseshoe facing the Pacific Ocean to the west. The peripheral rocks are a much older, early-middle Eocene (43.6-57.8 million years ago) basaltic rocks making up the Crescent Formation. These were deposited close to North America in a marine environment (Tabor and Cady 1978). These Eocene lavas erupted from submarine volcanoes under the ocean and were later covered up by marine sediments of a similar age (Orr & Orr 1996). This formation is made up of thick submarine basalt flows, such as pillow lavas. The Crescent Formation was deposited upon aquatic sediments derived from the continent and is now interbedded with early Eocene limy red sediments that are now limestones (Lasmanis 1991).

Off the West Coast of Washington lies the Juan de Fuca Ridge, which is a divergent plate boundary. The Juan de Fuca Ridge is adding to the Pacific Plate on the west and is producing the Juan De Fuca plate to the east (formerly the Farallon plate between 25-150 Mya) (Riddihough 1984). While the Juan de Fuca plate and the North American plate converge, most of the oceanic plate subducts underneath the North American plate. This oceanic plate material is much more dense, consisting of heavier magnesium and iron bearing minerals which naturally sink down and under the more buoyant continental crust. Current geologic thought is that large portions of the Juan de Fuca plate have not subducted, but instead have been skimmed off, resulting in intense faulting and folding (Rau 1980). About 50 million years ago during the Eocene, the Crescent Formation became deformed due to it being accreted to North America. Those portions of the plate that were not subducted beneath North America, later became the altered sedimentary rocks (deep marine sandstones, siltstones and conglomerates) known as the Hoh Rock Assemblage. During middle-late Miocene (6.5-15 Mya), uplift of the Olympics became possible due to the subduction of the remaining Juan de Fuca Plate beneath North America (Lasmanis 1991). The subduction of the Juan de Fuca plate is currently occurring at a rate of 3-4 centimeters per year (Noson, Qamar, & Thorsen 1988). With this subduction, there have been relatively minor earthquake tremors on the peninsula ranging up to five on the Richter scale (Noson, et al. 1988). The most severe quakes traditionally have been along the Puget Sound basin, Cascade Mountain Range, and along the Juan de Fuca Ridge and Plate system at depths of 54-63 kilometers. (Noson, et al. 1988). The tectonic forces that created the Olympics and the Hoh River Valley have exposed a great variety of igneous, metamorphic, and sedimentary rock and mineral types. top


The climate of the Olympic Peninsula is mild, with both summers and winters being temperate. During winter, temperatures range from upper 20's-30's at night to 40 degrees during the day. Snow rarely falls on low elevations, but can be extreme in the mountains (Olympic National Park 1996). Spring is usually wet and windy with temperatures ranging between 35 degrees and 60 degrees Fahrenheit during day and night. Summer is generally warm and fair with daytime temperatures rising from 60-80 degrees Fahrenheit. Occasionally the temperature will rise to 85-90 degrees, however this is not common. Nights are a quite cool with evening temperatures between 45-60 degrees. Autumn is a carbon copy of spring with cool temperatures, and wet windy conditions. The climate is often unpredictable because of storms moving off the Pacific Ocean inland over the Olympics (Olympic National Park 1996). This same unforeseeable weather blowing in off the Pacific Ocean bringing in some of America's cleanest air. The air quality is similar to that found in Antarctica (Richards 1984). These Pacific storms are one reason that Hoh Head along the Washington coast receives 90 inches of rain annually and Mount Olympus receives an average of 240 inches of precipitation in the form of snow and rain at it's summit (Renner 1992). The Hoh Rain Forest shows some of this extreme precipitation. The following are average precipitation amounts for the Hoh River Valley.

12.48 inches per month
3.14 inches per month
13.15 inches per month
15.75 inches per month

Annual averages of precipitation for the Hoh Rain Forest and River Valley -133.58 inches. According to the Olympic National Park Headquarters, 76% of all Hoh precipitation falls between October 1st-April 1st. This precipitation is the result of prevailing winds from the west to southwest in late fall and winter. During the spring and summer, the prevailing winds are from the west and northwest (Renner 1992). Not only do these cyclonic storms bring rain and snow, but also strong winds from the Pacific Ocean and British Columbia. The Hoh Valley during the summer is usually warm and clear, however frequently at night ocean fog moves eastward from the ocean into the Hoh Valley until late morning of the next day. This meteorological feature is vital to the Hoh Rain Forest because it controls excessive evapotranspiration losses (Heusser 1974). top


Four types of glaciers are found in the Olympics today. Valley glaciers, mountain glaciers, rock glaciers and perennial ice patches.

Valley glaciers have:

(a) a steady accumulation of snow and ice for at least two years;
(b) terminal or lateral moraines, trimlines, fluting or other proglacial features;
(c) crevasses of any type, firn layers, medial moraines, meltwater with glacial flow or any other feature showing evidence of active glacial flow (Hambrey & Alean 1994).

Mountain glaciers have:

(a) accumulations of snow and ice for at least two years;
(b) crevasses, firn layers, medial moraines;
(c) meltwater with glacial flour and maintain their shape continuously for at least two years.

Rock glaciers possess:

(a) a mass of angular rock shaped glacially in a cirque or valley with interstitial ice, firn, snow or dead ice moving slowly downslope (currently there are no active rock glaciers in the Olympics, the largest inactive rock glacier is on Gray Wolf Ridge and is an unusual feature to the Pacific Northwest).

Perennial ice patches exhibit:

(a) only an accumulation of ice and snow for two years or more (Hambrey & Alean 1994).

By comparison, the Cascade glaciers to the east are much larger than the Olympic glaciers. The Olympic Mountains do not form a linear chain like the Cascades and are not as tall. They are instead lumped together in the center of the Olympic Peninsula. With the Pacific Ocean nearby to the west, the maritime climate glaciers tend to form at much lower elevations in the Northern Hemisphere than their more distant cousins. Glacier heads can be found at elevations between 5900-7500 feet in the Olympics with their terminus ranging from 3200-4430 feet elevation (Hubley 1955).

The glaciers in the Olympics are susceptible to temperature fluctuations especially in the winter. Warmer temperatures than normally expected for winter can be devastating to the long term health of the low altitude glaciers. They will continue to receive precipitation, but it is in the form of rain, not snow. The result is lack of snow accumulation. The largest Olympic glaciers radiate in all directions from the top of Mount Olympus and are drained by the Hoh and Queets Rivers. Due to their large size, the Blue, Hoh and White glaciers radiate from the north and east slopes of Mount Olympus. However, it is the Hoh river basin that contains more than half (57.4 %) of the total glaciated area and (74.5%) of the estimated total glacier volume (Spicer 1986). The Hoh glacier is the longest at 4.93 km, and the Blue glacier the largest by volume (0.57 km3) and by area at (5.31 km2) (Spicer 1986).

Because of their remoteness, there was very little information was known on the Olympic glaciers till the 20th century. Not till the 1950's did the Blue Glacier become the object of much international glacial research, much which continues today. Only in the 20th century, when the Blue glacier became the object of attention, did research reveal the recent advances and retreat of the Blue glacier and others. For example, between 1938 and 1953 the Blue glacier receded continuously. During 1941 and again in 1951, the Blue's terminus retreated 56 meters and 22.9 meters respectively (Spicer 1986). In 1954, the terminus did not change it's position, and in 1955 it advanced 3 meters. Five years later, the Blue had retreated again losing over 15 meters in length (Spicer 1986). From 1960-1980, the Blue advanced a total of 164 meters. The period from 1980 to 1986 has shown a rough equilibrium (Spicer 1986). top

Pleistocene Glaciation:

The Hoh River Valley and the other parts of the peninsula have experienced on several occasions geologic events which have shaped the peninsula as it is known today. These periods of glaciation have left their mark by carving out the landscape and transporting rock debris over vast distances. The most climactic modification to the topography was huge troughs nearly 1,200 feet deep, that were carved into the level outwash plain beneath the Puget ice lobe. The thrust of ice through the lowlands left deep gouges or channels known today as Puget Sound, Strait of Juan de Fuca, and Hood Canal (Orr & Orr 1996).

The advent of the Ice Age occurred during the Pleistocene Epoch. As global temperatures plummeted, ice and snow became the end products in a worldwide drop in temperature. The Cordilleran ice sheet covered the northwestern section of North America during the most recent glaciation. The ice sheet sprung from the initial merging together of two separate mountain glaciers on Vancouver Island and the British Columbian mainland. With the merging of these two glaciers, the Cordilleran ice sheet advanced southward into the modern day United States over a period of between 10,000-15,000 years (Boothe 1987). The most widely investigated record of Ice Age advances and retreat are found along the southern boundary of the Cordilleran ice sheet, especially in the Fraser and Puget bottom lands. This ice sheet southern border extends into present day southern Washington state. The advances and retreats of the ice sheets are quite clear based on their lasting impression made on the vegetational history and coastal sea cliffs.

The pollen stratigraphy and radiocarbon dating of various bogs and parkland tundra along with a diamicton of glacial origin found and tested have provided the evidence needed for verification of age and deposition (Heusser 1974). As the ice caps advanced southward, they progressed into the Georgia Depression and eventually splintered into two separate lobes. The western lobe in Washington became known as the Juan de Fuca lobe, whereas the eastern lobe became the Puget lobe during the Salmon Springs and Fraser Glaciations (Florer 1972). Glacial tills have been deposited by pre-Salmon Springs, Salmon Springs, and Fraser glaciations (Florer 1972). The western side of the Olympics has been glaciated on at least four specific periods (Crandell 1964).

1. Pre-Salmon Springs Glaciation (Puget lobe)
2. Late Salmon Springs Glaciation (Puget lobe)
3. Fraser Glaciation (Vashon Stade)
4. Neoglaciation

On the coast, valley glaciers flowed in the direction of the Pacific Ocean. These glaciers converged to form large piedmont lobes concluding at sea level, while the Hoh Glacier may have reached the shore. To the north and east of the Olympics, lobes of ice blocked the drainage of most Olympic valleys after the glacial retreat during the end of the last glacial flow (Spicer 1986). The last advance of the Puget Lobe occurred approximately 14,000 years ago. Remnants of stationary pockets of ice continued to linger behind for an additional 1400 years (Spicer 1986). The Juan de Fuca lobe began it's southward trek by about 14,460 years ago and the last straggling portions of dead ice vanished before 9380 years before present (Spicer 1986).

Based on the depth of area glacial till that is exposed, the Hoh glacier is the first and largest glacier to occupy the Hoh valley and is thought to be pre-Puyallup in age (Heusser 1974). The Pre-Salmon Springs Glaciation left its imprint on the Hoh Valley and the Olympics at least 50,000 years ago, and is based on the depth of area glacial till and radiocarbon dating of flora in the valley (Heusser 1974). Additional proof of glaciation can be found at many locations in the sea cliffs between the Hoh River and a point eleven kilometers south of the river's mouth (Heusser 1974).

These glacial deposits were subject to being submerged underwater during the Puyallup Interglaciation and were later misshapen and entombed by gravels of Salmon Springs age (Heusser 1974). The pre-Puyallup glacier may have been tidal by virtue of the glacier having reached the shoreline of the Pacific. However, no proof is available to substantiate the existence of a tidewater terminus. Coastal processes such as erosion, changes in sea level and uplift may have destroyed record of the coastal terminus of the glacier (Heusser 1974). If the pre-Puyallup was definitely a tidal glacier, then it would have been the most southerly West Coast glacier to empty into the Pacific Ocean during the Quaternary Period (Heusser 1974).

Late Salmon Springs Glaciation is apparent from an end moraine on the Hoh-Bogachiel drainage divide at an elevation of 183 feet. This event is dated at 18,800 + years by carbon-14 dating of bog sections in the area (Heusser 1974). This is evidence that alpine glaciers of Fraser age had withdrawn on the western slope of the Olympic Mountains. Fraser glaciation was defined by an area approximately 20 kilometers east of the Pacific Ocean as a moraine marking the terminal wastage area of the Hoh Glacier (Heusser 1974).

The Evans Creek Stade was dominant from 25,000-15,000 years ago (Heusser 1974). After the earlier ice sheets retreated, and became known as part of the Vashon Stade, the Juan de Fuca lobe began its southward approach (Heusser 1974). Along the coast, including the mouth of the Hoh River lies loosely consolidated silt and gravel which covers the bedrock to depths of 100 feet. This silt and gravel was flushed out of the Olympic Mountains as glacial outwash (Orr & Orr 1996).

Another result of the Pleistocene glaciation was the worldwide lowering of the ocean by as much as 300 feet, because the ice caps, continental glaciers and ice sheets denied the oceans of large amounts of water (Orr & Orr 1996). During the periods of greatest glacial magnitude, the Pacific shorelines withdrew considerably farther west of the present coastline exposing thousands of square miles of the upper shelf to erosion (Orr & Orr 1996). top


To quote 18th century geologist James Hutton "the present is the key to the past", is so true in the Olympics. The constructional and erosional processes such as fluvial and glacial morphology continue to shape the landforms and topography today, as they did millions of years ago. Today with the warmer temperatures exhibited, fluvial and marine forces are the largest contributors to landform modifications. Higher temperatures may be a sign of a warming trend, which could have long term global effects of raising ocean levels through increased melting of glaciers worldwide. top

Works cited:

Boothe, Derek B. Timing and Processes of Deglaciation Along the Southern Margin of the Cordilleran Ice Sheet in: The Geology of North America; North America and Adjacent Oceans During the Last Deglaciation. The Geological Society of America. 1987.

Crandell, Dwight R. "Pleistocene Glaciations of the Southwestern Olympic Peninsula, Washington." U.S. Geological Survey Professional Paper 501B (1964): B135-B139.

Florer, Linda. "Quaternary Paleoecology and Stratigraphy of the Sea Cliffs, Western Olympic Peninsula, Washington." Quaternary Research 2 (1972): 202-216.

Hambrey, Michael, and Alean, Jurg. Glaciers.: Cambridge: 1994. Heusser, C.J. Quaternary Vegetation, Climate, and Glaciation of the Hoh River Valley, Washington. The Geological Society of American Bulletin (1974): vol. vol. 85, 1547-1560.

Hubley, Richard C. "Glaciers of the Washington Cascade and Olympic Mountains; Their Present Activity and Its Relation to Local Climatic Trends." Journal of Glaciology (1955): 669-675.

Lasmanis, Raymond. "The Geology of Washington." Rocks & Minerals 66 (1991): 262-276.

Noson, Linda L., Qamar, Anthony, and Thorsen, Gerald. Washington State

Earthquake Hazards. Washington State Department of Natural Resources: 1988.

Orr, Elizabeth and William N., Geology of the Pacific Northwest. McGraw-Hill: 1996.

Renner, Jeff. Northwest Mountain Weather: Understanding and Forecasting for the Backcountry User. The Mountaineers: 1992.

Richards, Bill. "The Olympic Peninsula." National Geographic (1984): 644-672.

Riddihough, Robin. "Recent Movements of the Juan de Fuca Plate System." Journal of Geophysical Research 89 (1984): 6980-6994.

Spicer, Richard C. "Glaciers in the Olympic Mountains, Washington: Present Distribution and Recent Variations." Thesis. University of Washington, 1986.

Tabor, Rowland W. Geology of the Olympic National Park. Northwest Interpretive Association: 1987.

Rowland W. Tabor and W.M. Cady. Geologic Map of the Olympic Peninsula Washington. Map Scale 1:125,000. 1978.

"Temperate Rain Forests, Climate and Seasons, Record Trees in the Olympic National Park, and Conifers of the Olympic National Park." Olympic National Park Handouts. No authors listed on handouts.1996.

Wood, Robert L. Olympic Mountains Trail Guide. The Mountaineers: 1991.


Revised April 14, 2001 
Page Design by David Garrett

This webpage submitted for ES 767 Quaternary Geology, Emporia State University, KS.