Geology of Olympic

A Moving Landscape

The Olympic Peninsula is moving below your feet. Can you feel it? Perhaps not, unless a large earthquake occurs, but the land is moving: slowly, but drastically, today and for the past 50 million years.

This image depicts a person cross country skiing across a snow field towards frosted trees with the snowcapped Olympic mountains in the background.
Winter recreating in Olympic National Park

NPS Photo

The Olympic Mountains were born in the sea. The basalts and sedimentary rocks that form the mass of these peaks were laid down 18 to 57 million years ago offshore, then uplifted, bent, folded and eroded into the rugged peaks you see today.

Off the coast of the Olympic Peninsula, a dramatic story of epic proportions is slowly, yet steadily, occurring beneath the sea. Washington state boasts volcanoes from the north to the south that have made history. The Olympic range is not volcanic, but visitors may notice some geology that makes it seem as if they were. Years ago, underwater volcanoes erupted, gushing lava that cooled into basalt, a distinctly volcanic rock, on the ocean floor. This layer of sediment built up atop the tectonic plate below, blanketing the ocean depths. Then, a shift occurred. As the floor of the ocean shifted with the larger tectonic plate it rested upon, the basalt would become key to this hidden geologic past. Plates can move away from each other, parallel to each other, or into to each other. About 34 million years ago, just off of what was the former coastline, two massive tectonic plates, the North American Plate and the Juan de Fuca Plate, were sent into a collision that would literally shape the Olympic mountains.

The Juan de Fuca plate is currently being forced under the larger North American plate, causing uprising of the landscape, crumpling of rocks, and endless jagged peaks that inspire visitors to the peninsula every day.


Just how does subduction work?
Think of waking up on a chilly winter morning, getting ready for the day, and going outside to find a thick layer of frost on the windshield of your car. With no time to warm the car enough to melt the ice, you grab a scraper from the trunk. As the wide, blunt end of the scraper pushes into the sheet of ice, the solid windshield is stable below the scraper, but the weaker sediment lying on top of the windshield (the ice) starts to move, crinkling from a thin even layer into a condensed pile.

Now, replace your scraper with the North American plate, replace the windshield with the oceanic crust that goes beneath the North American plate as they meet, and replace the ice on your windshield with the layers of sediment lying thick on the ocean floor that are now being pushed up as mountains.

A series of images showing Jennifer Natoli's analogy of pushing up Oreo® filling off the bottom cookie by using the top cookie in order to demonstrate subduction.
Subduction shown with Jennifer Natoli's Oreo® cookie demonstration.

Image used from

"Ranger Jen’s Oreo Demo
Jennifer Natoli was a seasonal ranger at Redwood National and State Parks in California. In her version of the Oreo® cookie demonstration, the creamy filling is the layers of sediment and basalt on the ocean floor. As the Juan de Fuca Plate (lower cookie) subducts beneath the North American Plate (upper cookie), the layers are scraped off the ocean floor and pile up as the Coast Range.

Modified from “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest,” by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015,"

Taken from as an example of the geologic processes in Olympic National Park

Rising Mountains

Subduction is just the beginning of the monumental geologic story that is the Washington Peninsula. The mountains of today can be enjoyed from many viewpoints, but are changing each day. Over the course of millions of years, the immense weight of settling sand, mud, and debris on the ocean floor hardened into sedimentary rock. As the two tectonic plates of the area crash together, the Juan de Fuca Plate which holds the ocean and the Olympic Peninsula, is forced downward underneath the land-bearing North American Plate. However, not all of the crust on the oceanic plate makes its way further underground. Much of the built-up sedimentary rock on top of the tectonic plate continues to crumple against the landmass of North America and fold upwards out of the water, rising from the depths as time goes on.

This image shows compressed layers of rock standing vertical to form a slight peak with spruce trees in the foreground
Standing vertically, the many layers of former sea rock show the rise in the Olympic Range

NPS Photo

Hurricane Ridge and Mt. Angeles
Millions of visitors each year traverse the high and winding road up to Hurricane Ridge. This ridgetop and corresponding trails up Hurricane Hill and Mt. Angeles are popular daytime destinations to get far ranging views of the widespread mountains of Olympic. However, while the panoramic distant peaks may draw the eye and drop the jaw, taking a moment while standing on the “hill” to ponder the ridges and folds right below the feet allows for a close-up peep into the lost chapters of the peninsula. As hikers follow the ridge on the Hurricane Hill trail, they pass by what appears to be slices of stone all pressed together into a tall standing ream of rock. If one could peel apart these “pages” they would see a very different story of what the mountain has looked like before. These segments are former pieces of the ocean floor, now standing just shy of 6,000 feet above sea-level! The former ocean bed crumples and folds as it crashes into the North American Plate, rising from below. As this happens, the stone is tilted almost vertical, now thousands of feet above the sea as we know it today.


Mount Olympus

Mountains are one of Olympic National Park’s most prominent geologic features, including Mt. Olympus, the tallest of the Olympic range. This giant reaches 7, 979 feet high at its summit. The Olympic Mountains are still being uplifted as the plates continue to converge. However, as changes from environmental factors continue to occur, erosion happens at such a rate that makes this uplift insignificant in sum.

While many will view mountains from a distance, others seek to conquer the views from atop by mountaineering. No matter the angle, Olympic National Park offers incentive for all to visit.


Glaciers of Olympic

This image depicts the Hoh Glacier with a blue-ish white tint viewed from the terminus with grey rocky slopes on both sides and snow fields beyond it.
A view from the terminus of the Hoh Glacier

NPS Photo

Geology is not just about sediment, but about the shaping and forming of it, as well. Over the past tens of millions of years, the earth has been rising from below. However, it has also been shaped from above. While today we may stand on soil, only 14,000 years ago, if visitors could have come to the region, they would have been standing atop ice thousands of feet high before it started to recede and release the land below from its icy weight.

About 2.1 % of the Earth’s water is held in glaciers around the world. Glaciers have had an impact for millions of years, although what that looks like is changing. As of 2020, Washington is the state with the second largest number of glaciers in the US, after Alaska. The number and size change each year as climate change continues to impact them. Even from the vantage point of a moraine, you can experience this change by listening to the creaks and groans, almost as if the glacier were telling its own story.

This image depicts the crevasses of a glacier, showing a blue hue.
Glacial crevasses show the blue hue of the ice

NPS Photo

Recognizing a Glacier Today
You look at the mountains, dotted with white. What do you see? Snow from the previous winter? Or a glacier that has existed for years? Whether hiking to the end of the Hoh River Trail and standing on the lateral moraine of Blue Glacier or taking in distant view from Hurricane Ridge visitor center, visitors to the park may wonder what they are actually looking at. Unlike a snowpack, glaciers have a few distinctive characteristics to search for:

  • Glaciers will have a blue hue to them because longer wavelengths of light, like the reds, are absorbed quickly into ice and snow, whereas shorter wavelengths, however, like the blues, are spread throughout.
  • Crevasses, or large cracks and gaps, can be seen in glaciers. These are evidence of glaciers shifting and moving. Not all parts will move at the same rate, creating friction and cracking. This is particularly indicative of faster movement from a glacier.

  • Moraines are piles of sediment that build up after being deposited or moved from the melting of a glacier. Typically, they are on the boundaries of a glacier, like at the edge (a lateral moraine) or at the end (a terminal moraine).

  • Lakes and ponds can be created by glacial melt. As a glacier melts, water can collect at its terminus and will form a lake. Many alpine lakes show where there were glaciers in the past. Glaciers can also form surface ponds in their divots.

Defining a Glacier
The key characteristics above can help to recognize a glacier, but glaciers must have a few distinct elements not as recognizable by the eye. Glaciers are persistent year to year, not melting out. They also must also have some flow of water. Glaciers flow is subject to gravity. While all mass is affected by gravity, a glacier must have enough mass and weight to move from the effects of gravity. Typically, this will be at least 100 ft (30.5 m) thick and 25 acres (0.1 km2) in size.
How a Glacier Forms
Many parts of the world see seasons, where snow will fall and melt away. Imagine a climate cold enough that the snow doesn’t melt away and winter freezes last most of the year. Instead, it piles on top of previous snow, year after year. This is what happened to create ice caps and glaciers over time. With more snow and more weight, the snow at the bottom compresses and becomes ice. However, a glacier is not permanent in its makeup. Flowing, shifting, and growing or shrinking, the water molecules move. Just as water can seep through rocks, it can move through a glacier. While some glaciers do have ice that is thousands of years old, many will continue to be replenished by fresh snowfall. In only 100 years, water could make its way through a glacier. As you stand at the bank of the Hoh River, imagine the first known people to Summit Mt. Olympus in 1907. The snow that they walked over may just be flowing past you today.
This image depicts the Blue Glacier taken from a plane. The glacier is shown in a basin between rocky mountain peaks.
The Blue Glacier recedes

All images are public domain NPS taken by Janis Burger on fixed wing glacier monitoring flight 10-18-10, high overcast from about 1100-1400 hrs.

Where Did They Come From, Where Did They Go?
Where Did They Come From, Glacier on the Hoh?

Mountains have been rising on the Olympic Peninsula for over 30 million years. Now dotted with moving ice, we can see influences from above the sea over the years as well. Today’s glaciers were created in the ‘geologically recent’ cold period, known as the Pleistocene Epoch, which began about 2.5 million years ago. Ice sheets, or large glacial masses, covered entire continents. Chunks occasionally split off as smaller individual glaciers and ice sheets that then advanced to other areas. According to Central Washington University’s geologist, Nick Zenter, at least seven of these advances came down from the Canadian Ice Sheet and onto what is now known as Washington State. The most recent, the Cordilleran Ice Sheet, advanced about 16,900 years ago, blanketing the region until about 14,000 years ago when it began to retreat with warming climates. With a thickness of about 3,500 feet (1,100 meters), this and previous ice sheets carved and changed the landscape drastically. The Puget Sound was dug out, valleys were created, and glaciers were left to mystify us still to this day.

As the ice advanced, it would move, but also grow. Like mold that spreads over the landscape, snow would continue to fall and accumulate, coming together to blanket the region as a whole. Glaciers would join together, split apart, and move wherever they could.

The glaciers present today continue to move, but in a different fashion. Glaciers can grow and advance or shrink and retreat. With the current warming climate and more melting periods than freezing periods throughout the year on average, the glaciers are melting, causing them to shrink and retreat. Due to their size, glaciers are subject to gravity that move them downhill, often moving the landscape with them.

Within these paths lie clues and evidence we can recognize today to imagine a past, frozen world.

Evidence of the Past
While many glaciers have melted, we can still see evidence of their influence across the landscape:

  • Glacial erratics are large boulders and rocks that were not formed where they rest today, but instead were moved to that location by a glacier. Sediment can fall on a glacier and move with it or be picked up as a freeze happens. Areas were carved out by glaciers' weight and friction, but the sediment moved doesn’t disappear. Instead, it is pushed aside or picked up and moved to other places. As they melt, glaciers drop sediment, sometimes carried for thousands of miles. The cycle of melting, moving, and refreezing has helping to track the former paths of these glacier.

  • Scree fields can be created in the moraines, shaping basins and sediment.

  • Basins formed by sediment buildup often leave behind glacial lakes.

  • When the glaciers were much larger, they would extend down into the rainforest valleys of today. These valleys are U-shaped with wide, flat bottoms and tall cliff sides as the glacier moved across the entire valley, spreading its weight and grinding action evenly across. This is distinctly different to V-shaped, river carved valleys, where the water is fluid and concentrated as it takes the smallest path of least resistance.

  • As a glacier melts, the water flows through these valley watersheds. The Hoh River today is fed by water from Blue Glacier, White Glacier, and Hoh Glacier. The sediment flowing out of the geologic giants above creates the iconic blue, silty look of the massive river today.


A Landlocked Island
While today, visitors fly and drive from around the world, this landscape was not always so accessible. The density in which the ice moved over the Peninsula created a sort of ‘island’ of land, inaccessible to other parts of land further away. People could not access the ocean and rivers at the time. Even animals could not encroach. However, this meant that other animals could not expand. Today, Olympic National Park is home to five species of endemic mammals, meaning the only place on Earth they are found is here, including the Olympic Marmot. Thanks to the rich diversity and accessibility of waterways, the Olympic Peninsula became home to people almost as soon as it was accessible and livable. Even some animals are relatively new to the area including coyotes and foxes.

This image depicts a ranger carrying scientific equipment over a glacier.
Collecting data ensures a deeper understanding of the past and the future of glaciers

NPS Photo

Our Glaciers Today and Tomorrow
Glaciers are a popular destination and sought after sight for many of the visitors to Olympic National Park. While they may not be the first feature that comes to mind when you think of the ocean and rainforest ecosystems of the Pacific Northwest, they are an important component to the geologic and ecologic story, even today. That story has always consisted of change, and the rate of that change is only increasing as climate change affects the glaciers of these mountains. The Blue Glacier is the largest glacier in the Olympic Mountain Range and, while snow still flies many months of the year, the warmer temperatures more often mean that it, too, will continue to shrink. However, the story of geologic change is one that is still growing.


Coastal Geology

Geology is prevalent along the Olympic Coast as it is marveled at in the high cliffs, the tidal pools, and the depths of the ocean. Geologic processes have shaped and influenced them all. The coast of the Olympic Peninsula is particularly famous for some of this distinct geology, the history the rock preserves, and the incredible views they create today.

Underneath a pink and orange sunset, six sea stacks can be seen. The stone tower in the foreground bears several evergreen trees on top.
Sunset provides a stunning view of the many volcanic sea stacks of Third Beach

NPS Photo

Sea Stacks

The coastline of Olympic National Park draws visitors for its rugged views. Notable for its sea stacks, which tower several stories overhead, the Pacific Coast truly is a mystifying sight to see. These towers of rock that make the peninsula coastline so famous define the views from beaches such as Ruby Beach, Ozette Beach, Shi Shi Beach, Rialto, La Push, and First, Second and Third Beach. Not only shrouded in salty water, but in history and mystery as well, the geology behind these majestic rock outcroppings lies just as much in what we see today as it does in what is no longer there.

The jagged sea stacks are a part of the Hoh Rock Assemblage. Long ago, this “Rock Assemblage” would have resembled a sort of geologic chocolate chip cookie dough. Throughout several millennia, there have been a great variety of rock types in the area. The dense volcanic and marine sedimentary rocks would be the chocolate chips amidst the cookie batter of the softer mudstone. At that time, the high cliffs now seen above the beach were sitting at sea level. The driving power of the ocean waves pummeled and weakened the mudstone, washing it away, but the sturdy volcanic chocolate chips remained. The cliffs rose with the same tectonic forces that rose the mountains of the peninsula, and alongside them rose the same volcanic outcroppings that were left behind.

Varying layers of smooth flat rock are fused together by dark bands of gray sediment, appearing like a multilayered cake of stone turned on its side
Beach 4 provides an interesting look into the geologic past of the area

NPS Photo

Tilted Rocks
Walking down from the parking lot at Beach 4, visitors are greeted by a unique view. The rocks on which they stand appear to be fully tilted as they jut from the sand. Not only are these panels of sandstone tilted, but they are also upside down!

A few geologic processes are at work to make the unique formations at Beach 4. The formation of these rock layers happened by sediment settling after the occurrence of a natural phenomenon known as a “turbidity current.” Turbidity currents are essentially massive underwater landslides. As sections of the steep continental shelf give way—due to earthquakes or other disturbances—the main body of sand, mud, and debris forces its way to the bottom of the slope first. As the finer particles finally settle in the water, a layered gradient of particle size occurs, with the larger particles at the bottom of the pile. Overtime this mix of debris compresses into sandstone.

To better imagine this in action, one may picture kicking up a pile of dead leaves in autumn. As they do so, the wetter, denser leaves along with heavier sticks and twigs fall to the ground first. Afterwards, having been caught in the wind, the lighter, crisper, or smaller leaves lightly drift and land atop the pile. A look inside this new pile would show layers of the larger sticks and denser leaves at the very bottom and the lighter debris on top. In this very same way, we can tell even with the naked eye that the rock layers at Beach 4 have fully overturned. How? Because the smaller particles are at the bottom!

These layered sandstone formations eventually uplifted towards the surface of the ocean. The power of the waves ultimately planed off and flattened the top of the rocks before they rose more, eventually escaping the rage of the sea altogether as they now rest well out of reach of high tide.


Lakes and Rivers

Water has directed and been directed in turn by the geologic processes of Olympic National Park that are highlighted below. Each water feature is bound in shape and flow by its geologic past. However, all of these lakes and rivers continue to reveal more about the ecologic and human past, present, and future with every passing droplet.

This photo depicts the colors of the sunset enclosed between to mountains and reflecting on Lake Crescent in the foreground.
The sun sets on another beautiful day at Lake Crescent

J Preston; NPS Photo

Lake Crescent
As massive glaciers slowly crept across the Olympic Peninsula and began to recede, a deep scar in the Earth filled with crystal clear water. This cut in the land came to be known as Lake Crescent. The largest lake in the park, Lake Crescent is unique for many reasons. It tells many stories within its shape, color, depth and makeup, yet still holds many mysteries for the same reasons. In the summer, recreational swimmers and boaters need only paddle a few yards from the beach and look down to witness the cobbled shore as it gives way to the intimidating darkness below. The sheer depth of the lake is one factor that lends to the lake’s deep hue. Officially reaching down 624 feet (190 meters) below the surface, the waters are cold and have limited nitrogen. The lack of this chemical prohibits the growth of most algae, which leaves the waters with glass-like clarity. On top of the vertigo-inducing depths, Lake Crescent is also 11.8 miles long. However, it used to be much larger. Geologic record shows that approximately 7,000 years ago a cataclysmic landslide event occurred. The immense boulders and debris cut the glacial lake in two, leaving behind both Lake Crescent and the neighboring, much smaller, Lake Sutherland in the process.


Other Lowland Lakes
Olympic National Park is home to many notable lakes known for their beauty and recreation. From Lake Cushman in the southeast to Lake Quinault in the southwest to Ozette Lake along the coast, water invades the landscape, providing for enjoyment and park life alike. As all water tells a story on the peninsula, so do these bodies of water. Lake Quinault rests within the glacially carved valley of the Quinault River in the park's southwest corner. Lake Ozette's surface is less than 30 feet (9 meters) above sea level, which means that its bottom is over 300 feet (91 meters) below sea level. Lake Cushman is not within the boundary of the park, but does derive its water source from the peaks and flows within. While the basin in which Lake Cushman lies is naturally glacially carved, the lake basin itself is human-made and kept up by a dam that regulates water and provides power to the Southeast. The lowlands indicate the story being passed down from the heights of the watershed and the past that made them.

The image depicts alpine lakes in a rocky basin with clouds and a ridge behind them and snow on the ground around them.
Aptly named "Seven Lakes Basin" boasts a glacially carved geologic past

NPS Ranger Karl Rand

Alpine Lakes
Hiking higher into the Olympic wilderness can lead to different ecosystems than those seen from the roads. In higher heights, open meadows, scree slopes, and alpine lakes abound. Hiking trails such as Seven Lakes Basin lead past lakes of varying sizes, left behind to tell a story of what once dominated the towering peaks. These glacial lakes show where there was change in the landscape as glaciers came through, carved natural basins in the land, and filled them back in with melt over the years. Many glaciers have melted away, but visitors are invited to enjoy a glimpse of the frozen past within the beauty of today's geology. By studying these lakes, the park can better understand the weather patterns based on when they freeze and melt out as well as water quality and content. Many of these lakes were stocked with fish, changing the ecosystem within and around it. Look for signs of birds and other predators that may take advantage of the human influence left behind.


River Valleys
Rivers define Olympic National Park from the human history, to the geologic history, to the ecosystems that rely on them. Geology defined the rivers as they are today. As many streams spiral out from the tallest peaks in the center of the Olympic Wilderness, they come together in larger watersheds with glacially carved river valleys that continue to reach and wind their ways down to the ocean coast. River and lakes of Olympic are not only defined by the geologic makeup, but by the past, present, and future of the balance in the ecosystem as a whole.


The Foundation of a Park

Geologic processes founded the land that exists today as the Peninsula and forms the continued foundation of the park as a whole. The geology defines the park. It has uplifted and eroded the peaks and valleys alike. It creates alpine habitats, lush forests, and coastal cliffs. It lends shelter to resident animals. It provides beauty and recreation to millions of visitors each year. Without the geologic uplift and creation of the Olympics, where would we be today? At the bottom of the ocean floor.

Last updated: September 29, 2020

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