Table of Contents


General Introduction


Impressions of the North Cascades
Essays about a Northwest Landscape

Part I: Landscapes of Memory

Keepers of the Beat


Jimmy Carter froze federal hiring in 1980, costing me an internship with the United States Geological Survey in Colorado. Election-year politics forced me to seek other employment. What I found was a volunteer position with the Student Conservation Association at North Cascades National Park. Little did I know, as my VW bug coasted into Colonial Creek Campground that June, that a very long chapter in my life had just begun.

When I think of seeing the Skagit Gorge and Jack Mountain that first day, I am reminded of Colin Fletcher's first impressions of the Grand Canyon. [1] He saw a mile of exposed rocks, some displaying brilliant color, others incredible detail of the past, tens of millions of years of earth history laid open like a book. After many days immersed in the Canyon, Fletcher wrote that "the rhythm of the rocks beats very slowly, that is all."

My first summer, the rhythms in the North Cascades seemed beyond comprehension. The easiest-to-reach rocks at lower elevations were obscured by dense vegetation. Well-exposed rock was a mile and a half straight up and surrounded by steep snow and ice. Only after fifteen years immersed in study of North Cascades glacial history can I begin to describe its rhythm of time and change.

The evidence of rock rhythms here is different than in the Grand Canyon because processes of landscape change are dominated by glaciers. Glaciers are elders of the landscape, having many stories to tell of rhythms spanning the past million years, tales written in glacial landforms and in the annual layers of glacial ice. The rhythms of the mountains recorded by glaciers are cycles of climatic change. They are the annual rhythm of seasons, climatic cycles spanning tens of thousands of years, the ultimate force shaping the mountains and causing change to land and life. The beats of these cycles could be so strong that they forced many creatures to abandon their homes as massive glaciers covered the landscape. Despite this power, the rhythms are imperceptible, the beat slow and complicated, but inexorable. They can be seen and heard only by those who take the time to look and listen for them. I have had the privilege and the resources, as a geologist, to listen and learn.

Let us journey to find these North Cascades rhythms. We begin at broad scales of space and time while exploring rhythms known as the great ice ages. These beats are marked by landforms of colossal, ice-age continental glaciers and alpine valley glaciers in the Fraser, Chilliwack, and Lower Depot Valleys. We move up Depot Creek to the Redoubt Glacier, traveling forward in time, and find the beat becoming more rapid as we come up to the present.

Stage One: Fraser and Chilliwack Valleys

Our search for the beat of the North Cascades begins from the northwest. We enter the mountains byway of the Fraser Valley, which is appropriate because the largest glaciers to occupy the North Cascades were born in this watershed. Landforms left by these glaciers reveal the rhythm of heating and cooling, of ice ages coming and going, of climate shaping the destiny of everything here.

Repeated periods of climatic cooling have been the dominant rhythms of the North Cascades, as deep cold has triggered ice ages at northern latitudes and high elevations. Massive glaciers grew during the ice ages, born of cooler summers that allowed snow and ice from previous winters to accumulate for thousands of years. The pulse of ice ages has been beating for at least 1 million years. Its rhythm is punctuated by periods of cooling that last 100,000 years, separated by periods of relative warmth lasting 10,000 years. [2]

Gazing across the lush, green expanse of vegetation surrounding the Fraser Valley today, we find it hard to believe that we maybe at the end of the warm spell that allowed habitation of these mountains and on the verge of another ice age. Only 15,000 years ago, the entire Fraser watershed and half the North Cascades were covered by ice more than a mile thick. [3] This colossal glacier is known as the Cordilleran Ice Sheet, which dwarfed alpine valley glaciers growing from the high summits of the North Cascades.

As we travel over the fertile floodplain and delta of the Fraser River, the scene 19,000 years ago when mammoths roamed this valley seems remote and scarcely possible. Sparse browse on cold, dusty, windswept tundra ended a few miles up the valley against the largest glacier this land had seen in 100,000 years. Change associated with these upheavals sealed the fate of many creatures; at least six waves of extinction are believed to have resulted from ice age changes. Between 12,000 and 10,000 years ago, at the end of the last ice age, at least fifty species of large mammals, including the mammoth, giant beaver, dire wolf, and saber-toothed cat became extinct. [4] At the mouth of Chilliwack Valley we pass the grave site of mammoths, whose bones were discovered beneath hundreds of feet of gravel on the north side of the road. [5]

The huge Cordilleran Ice Sheet had a tremendous impact on the landscape. At the international boundary, 6,000 feet of ice depressed the ground with its tremendous weight. The glacier was 600 feet thick near the mouth of the Chilliwack River. [6] This glacier was so massive that only the highest summits stood above its white expanse. For thousands of years during the ice ages, half the North Cascades mountain range slept beneath a 7,000-foot blanket of ice. Global growth of continental glaciers stored enough water to lower the sea level by several hundred feet, creating a land bridge between Alaska and Siberia that allowed humans to travel into North America from Asia. These nomads challenged mammoths and dodged saber-toothed tigers while migrating around the ice sheet. People came here with the last ice age—will they leave with the next?

The last ice age brought impressive change to the Chilliwack River. Before that, the river flowed southwest to join the Nooksack River. Deposition of a glacial moraine approximately 12,000 years ago in the nearby Columbia Valley blocked its former route, sending the Chilliwack north to the Fraser instead. [7] Salmon entering the Nooksack for the first time after the ice age found their home waters no longer accessible along the route their ancestors had used for thousands of years. It was a change the salmon adapted to often as glaciers rearranged the courses of rivers throughout this area with the passage of ice ages.

Following the path of the ice sheet, we continue into the North Cascades up the Chilliwack Valley. Along with the Skagit and Pasayten Valleys to the east, the Chilliwack was one of the major routes the ice sheet took to invade the mountains. A few years ago, I began to wonder about the impacts of glaciers flowing up these deep mountain valleys.

After years of investigation, I now know that the ice sheets created dams preventing drainage north to the Fraser and Similkameen Valleys, and flooding the upper Chilliwack, Skagit, and Pasayten Rivers. Lakes created by these dams drained south across divides into the Skagit and Methow Rivers, cutting spectacular gorges along Lost River, Lightning Creek, Canyon Creek, and the Skagit River. Over the course of many ice ages, this drainage system had astounding effects. [8] Once-towering divides were reduced to valley-bottom swamps (Klesilkwa Pass) or shallow lakes (Lightning Lakes and Hidden Lakes). Ultimately, erosion at the outlets of these huge lakes caused the rearrangement of the drainage pattern of the entire area north of Newhalem. Indeed, the Pacific Crest of the northern North Cascades has shifted east at several locations. The largest shift may have reversed drainage of the entire upper Skagit watershed above Gorge Dam. Incredibly, the upper Skagit River, as told in Native lore, used to flow north to the Fraser. Like the glaciers and salmon, the original human inhabitants of these mountains remembered the ancient rhythms.

Crossing the wood-plank bridge over Paleface Creek, I see few signs of the old logging shacks that once stood here. I remember the old man and his son who called this place home while logging the shores of Chilliwack Lake and its tributary valleys. Their Dobermans surprised me walking one night on the shore of Chilliwack Lake. The encounter was worthwhile, however, as the dogs introduced me to the only humans living in the upper valley. I was comforted on later trips to know they were nearby and could help in case of an accident. Now the shacks and their friendly inhabitants are gone. The only sound is the stream, and alder and oil-stained soil are all that remain at the old logging site.

Vegetation change, associated with logging in this part of the valley, seems extreme. During the ice age, however, most plants moved far to the south to avoid the advancing ice sheet. Forests in the upper Skagit and Chilliwack Valleys were overrun and buried by the advancing ice. [9] This indicates that the ice age climate 20,000 years ago within the mountains was not radically different from the present, and that the turn toward a warmer climate had begun. Plant refuges from the ice sheet in this region included several high peaks that stood above the great glacier, as well as all of the southern North Cascades. What vegetation did survive on summits was certainly sparse. On the northeastern flank of the range, tundra and permafrost probably dominated in a cold, windy, dust-swept zone near the ice.

At the ends of the ice ages, summer warmth rapidly melted the continental glaciers, again bringing rapid change to the mountains. Landslides were large and frequent on the unstable glacial deposits until the return of soil-stabilizing plants. For several hundred years, at least, travel deep into the mountains would have been extremely dangerous. Trees returned to the landscape at different rates, advancing from a few hundred to a thousand or more feet per year in the wake of the retreating ice. [10] Mountain streams cut deeply into the glacial deposits, filling valleys. Eventually, stream channels stabilized and salmon returned to waters in which their ancestors had last spawned thousands of years earlier.

The slow, strong ice age rhythm dominates the natural history of this region by creating landscapes, extinguishing the lives of animals, and forcing migration of plants and people. We exist here now between the glacial beats of the ice age drum. As we hike deeper into the mountains, we find that the landforms left by alpine glaciers growing from the mountains record yet more detail of Earth's beat.

Stage Two: Up Depot Creek

Fifteen miles of cross-country travel into one of America's great wilderness areas begins in a clearcut. Alder, fireweed, and other pioneer plants choke the old logging road. Many of these hill slopes have been stable since the end of the ice age, but logging has reactivated old landslides and started many new ones. Sediment surging down these valleys is part of a chain reaction felt all the way down to Chilliwack Lake. Evidence from the adjacent Silver-Hope Valley indicates that sedimentation of Silver Lake increased ten to a hundred times with the advent of clearcut logging. [11] The ancient rhythms seem to be muddled by the cadence of modern life.

After a mile or so in "alderland," the trail crosses the international boundary into North Cascades National Park. A single row of trees was spared on the south edge of the clearcut to define the north edge of the international boundary border cut. It seems the boundary clearcut would have been enough. Most of the remaining buffer strip of trees has fled to the United States, with the help of the wind. The panic also seems to have spread to many American trees. Wrestling through this border tangle provides time to reflect on the incredible contrast between the two sides of the border: hot, fly-infested clearcuts to the north, cool hemlock forest to the south. Dense vegetation on the west side of the North Cascades limits geologic interpretation of the landscape. On this hike, however, I welcome the physical comfort of the dense forest at the expense of geology—at least for a few strides.

In the forest permeated by the rumble of Depot Creek, my thoughts are drawn back to the ice age. The cold caused the expansion of glaciers in the mountains as well as in interior British Columbia. It triggered a relatively rapid reaction by the smaller, more sensitive alpine glaciers. They grew much more quickly than their continental-sized cousins because they were fed by abundant Pacific storms, in contrast to the dry interior plateaus that were the source of the ice sheet. Somewhere farther up the valley ahead of us, the continental and alpine glaciers collided. Discovering the exact location of the great crash is a continuing interest of mine. All I know right now is that it occurred closer to the head of this valley than its mouth because by the time the ice sheet was beginning to cross into what is now the United States, the alpine glaciers were retreating from their maximum down-valley positions. [12]

Nervous about a cross-country hike in a valley I had never seen, I barely took notice of a narrow ridge stretching across the valley floor on my first trip here in 1985. Eleven years and two dozen trips later, I am now convinced the ridge is an alpine glacial moraine. Its exact age is unknown, but I believe it represents the last advance of alpine glaciers, approximately 12,000 years ago, at the end of the most recent ice age. Other moraines from the Depot Valley glacier were probably obliterated by the ice sheet. A complete record of moraines from the last ice age is found in the Yakima and Wenatchee watersheds.

These moraines record rhythms of climate change more frequent than the 100,000-year ice age cycle. The moraines tell us that alpine glaciers advanced four times during the last ice age, and that retreat between at least one of the advances was significant. This geologic evidence indicates that the ice age climate was not uniformly cold, but was punctuated by brief periods of relative warmth. The elevation of these moraines also allows us to determine that average summer temperature was as much as 12°F colder 20,000 years ago. [13] This was enough to drop the snowline by 2,500 feet, which means skiing should be excellent in the next ice age.

Long tongues of blue glacier ice filled the upper reaches of nearly every North Cascades valley in the ice age cold. The largest valley glacier systems were fed by extensive ice caps and ice fields at a dozen locations scattered throughout the range. The alpine glaciers were long, but not as thick as the ice sheet. At this location, the Depot Creek Valley glacier was approximately 1,500 feet thick, only one fifth the thickness of the larger glacier.

The pattern of alpine glaciation is important to mountaineers and those interested in the varied climate of the North Cascades. Trails and well-planned, cross-country routes don't follow deep, winding, narrow canyons carved by streams. Preferred routes are the wide, flat-floored, straight, U-shaped valleys carved by glaciers. This valley up which we travel was glaciated from top to bottom, making the hike easy. The pattern of alpine valley glacier systems across the mountains also teaches us a great deal about the climate of the region. The glaciers in this valley were much larger than those in the Ross Lake drainage 15 miles to the east. This asymmetry was caused by the rapid decrease in precipitation across the North Cascades. Played out over many ice ages, this climatic wrinkle created two startlingly different landscapes on either side of Ross Lake. [14] Glaciers entering from the wetter west side were large and flowed all the way to the Skagit Valley. As a result, the west side valleys have classic U shapes for their entire lengths. Glaciers on the east side of Ross Lake were smaller and did not make it to the Skagit. As a result these valleys have narrow, V-shaped river canyons at their junction with the Skagit Valley.

A few miles past the moraine, the trail begins to climb steeply through a grove of huge cedars. The roar of Depot Creek is heard as it crashes 800 feet down a series of cliffs. At the base of the waterfall the sound is deafening. For hundreds of years these trees have listened patiently. On my first trip through here, I was not so patient, as the roar and icy blast spurred me to press ahead. Now, I enjoy this place as much as any on this journey, and often spend an hour or more listening to the sound of the water.

Above the waterfall, the route flattens out into a huge meadow covered by willow, alder, sedge, and grass. Towering above the meadow is the stunning north face of 8,985-foot Mount Redoubt. Ringed by blue glaciers, Redoubt is composed of many massive gray towers, flying buttresses, and steep, narrow couloirs. The desire for quick approaches to these inspiring peaks resulted in the cutting of an unofficial trail up this valley in the 1970s and 1980s. Similar expediency trails are beginning to scar many areas in the surrounding national park as people come in search of adventure, inspiration, and challenge.

Mount Redoubt is a testament to the legacy and powers of glaciers that have worked on this landscape for 2 million years and are alive today. This legacy defines the boundaries of the North Cascades Physiographic Province. [15] Unlike the Cascade Range south of Snoqualmie Pass, volcanic rocks have been mostly stripped from the North Cascades. Beneath the volcanic rocks, glaciers exposed the crystalline igneous and metamorphic rocks, seen on the flanks of Mount Redoubt, that form the backbone of the North Cascades.

Alpine glacial moraines record a more frequent beat emanating from deep within the mountains. Periods of glacial advance and retreat, recorded by lakes and moraines, identify at least four rhythms during the end of the last ice age. Superimposed on the slow, 100,000-year ice age rhythms, these more frequent cycles add tempo and complexity to the history of this place. The rhythms become more frequent and less powerful as we continue our climb higher and deeper into the mountains.

Stage Three: On Mount Redoubt

Sloshing along the flat meadow is a welcome change from the crawl up the waterfall. Adding to the comfort of this part of the journey is the solitude and warmth of the meadow, which contrasts sharply with the deafening sound and cold spray of the falls. This is a fitting place to reflect on the warming trend that caused the end of the last great ice age, which continued until approximately 4,000 years ago. In this 6,000-year warm spell, glaciers probably did not record climatic rhythms, as they disappeared from all but the high summits of Mount Baker and Glacier Peak.

Egyptians had built many of the great pyramids of Giza by the time glaciers again began to record the rhythms of these mountains. Pollen rained into lakes, and moraines shaped by readvancing glaciers provide evidence of colder and snowier periods between 4,000 and 3,000 years ago, 2,800 and 2,600 years ago, and within the last 800 years. [16] These shorter, more frequent cold climatic spells were caused by a 2,000-year cycle in sunspot activity, huge volcanic eruptions, and variations in global winds and sea-surface temperatures.

As our journey draws nearer to its conclusion, the glacial evidence we find is from the most recent cold wave, known as the Little Ice Age, when average annual temperatures were from 2°F to 3°F cooler than today. [17] The Little Ice Age began in the late thirteenth century and was known to people throughout the Northern Hemisphere. It forced the Vikings from Greenland and caused famine in Europe, but also made life in the North Cascades difficult. Historic accounts from the late 1800s describe snow 12 feet deep at the mouth of Ruby Creek. In the last fifteen years, I have not seen more than 2 feet of snow anywhere along the shores of Ross Lake. Heavy Little Ice Age snow caused bigger rain-on-snow and spring snowmelt floods. Travel through the mountains was more dangerous because of bigger and more frequent snow avalanches. Stories are told of the Skagit River freezing over in the 1800s.

Vegetation also reacted to the changing Little Ice Age climate. Tree line dropped with heavier snowfall, causing shifts in the range of a larger community of plants and animals. Today, tree line is charging up slope, glaciers are in retreat, and willow and alder flourish in the barren expanses. Avalanche chutes once swept clear of trees are now dotted with small silver fir and other montane species. I currently can grow a wide variety of fruits and vegetables in Marblemount, something I could not have done during the Little Ice Age.

Skagit Gorge with Skagit River at flood

One hundred years ago, the geologist R. A. Daly stood near the south end of this meadow, his path up valley blocked by a massive glacier that covered the remainder of the valley to the summit of Mount Redoubt. This was the Redoubt Glacier, and it was a half-mile longer during the late 1800s than it is today. [18] To Daly and his team, the elongated Redoubt Glacier was stark evidence of a glacial beat in a climatic rhythm much faster than any we have encountered thus far on this journey. The beat is felt at time scales of mere hundreds of years.

At the same place today we see two long, stony glacial moraines deposited by the Redoubt Glacier. They record the fluctuations in the size of the Redoubt Glacier during the past several centuries. They illustrate that there were at least eight periods of glacial recession during the last 800 years. [19] The first moraine we crossed was deposited between 1760 and 1780. The glacier retreated from this position an unknown distance before finally depositing a second moraine 500 feet up slope between 1840 and 1860. When Daly's crew saw the glacier, it had retreated another 1,000 feet in fifty years, an average rate of 20 feet per year. After the surveyor's visit, retreat accelerated to 40 feet per year, and by 1947 the glacier had retreated a total of 2,000 feet. Between 1950 and 1990, a large mass of the glacier stagnated in a cirque, cut off from the main body of the Redoubt Glacier by a 400-foot headwall.

The moraines can be followed up the valley to a break in the slope of the valley wall where, above the lines of rocks, trees grow thickly. Below, a barren landscape composed of loose boulders and scoured bedrock stretches across the valley. Round rocks cover this 100-year-old landscape, making for tough travel with tired legs and a heavy pack. On one particularly long and arduous trip, I wondered if I had enough energy left to escape the glacier should it advance again down valley. Barren rock and glacial-till slopes like these throughout the North Cascades mark the extent of the last Little Ice Age glacial advance. In most cases, the change is astounding. What remains of the Little Ice Age Redoubt Glacier is a shallow puddle commonly known as Ouzel Lake. When I first visited here ten years ago, ice caves made Swiss cheese of the last part of the stagnant glacier. Today, there is no trace of the ice that covered the last half mile of our journey as little as fifty years ago.

We continue by climbing up the east wall of the cirque, the easiest way to gain access to the Redoubt Glacier. Granite, plucked and scoured by the glacier, makes a relatively easy climb. Finally, we stand on the glacier whose meltwater trail we have followed 50 miles into the mountains. Locked below our feet in annual ice layers is a record of the past 600 years: stories of cold, snowy winters and dry, fire-hazed summers. We hope to learn a great deal about the recent glacial rhythms of these mountains from a 600-foot-long ice core recently extracted from South Cascade Glacier. The age, memory, and beauty of all these glaciers command respect.

Throughout this area, glaciers have shrunk drastically since the end of the last century. The loss of these should not be taken lightly. As they melt, we lose a vital part of these mountains. Obelisks of time, elders of the landscape, glaciers add immeasurably to the North Cascades. In fact, the modern cover of glaciers defines the present boundaries of this region. Strung out like pearls on the backs of the mountains, the 700-plus glaciers in the North Cascades add greatly to the quality of our lives by providing challenge and inspiration, as well as consistent runoff for salmon runs, irrigation, and hydroelectricity.

We do not know if the glaciers will continue to wither, apparently in the heat of human consumption. Part of my current job is to monitor the health of four glaciers in North Cascades National Park. Silver Glacier, on the other side of the ridge, is one of the glaciers we visit three times a year. Since the late 1970s, there have been few good years for this glacier. Last year was the first in more than a decade that it gained more mass in winter snowfall than it lost in summer heat.

It is also possible that modern glaciers will stop shrinking and be the direct forebears of the next ice age. Many believe we are well on our way. It is estimated that a ten percent increase in winter precipitation or a 2°F to 3°F drop in average annual temperature would cause continual glacial expansion. [20] The glaciers are here, currently shrinking, but waiting to grow.

The rhythms of our lives may seem weak, especially in the din of the city. In these mountains the Earth's rhythm is strong, and its pattern is a big part of this place and our lives in it. Glaciers and their creations remind us of our helplessness in the face of ice ages, and of our dependence on the interglacial climate for food and the development of our civilizations and cultures. From this journey and place we can see very far in time and space. To Colin Fletcher I reply that the rhythm of the rocks in the North Cascades also beats slowly, but here we can find evidence of more rapid beats, recorded by the great dominance of glaciers in shaping this landscape. Here, the big ice ages dominate the rhythm at 100,000 year intervals. We exist here dependent on the warmth between ice ages. Fainter, less frequent beats remind us of other patterns to life here. Some come by the millennium, others the decade, but each is recorded in the glaciers and glacial landscapes of the North Cascades. They remind us of our past, and give perspective to our future.

JON L. RIEDEL has worked for the National Park Service in the North Cascades since 1980. He is a geologist at the North Cascades and other national parks in the Pacific Northwest. His professional interests include the glacial history and geology of the North Cascades, floodplain and geologic hazard management, and long-term monitoring of glaciers and streams.

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North Cascades Conservation Council
P.O. Box 95980
Seattle, WA 98145-2980