The Origin of an Alpine Lake

Despite the area’s formidable topography, the North Cascades are filled with lakes. On a hike late last summer, I glimpsed how many of them formed.

Monogram Lake sits in a small basin perched a few thousand feet above Cascade River. At this elevation, just shy of 5,000 feet above sea level, it’s surrounded by blueberry meadows and scattered woodlands of mountain hemlock and Pacific silver fir. It’s an inviting place to camp for a couple of nights, no matter if you want to lounge by the lakeside or strengthen your quads further by climbing to the surrounding ridges.

small lake surrounded by meadows and mountains

I hiked there late last August hoping to watch black bears feeding on blueberries. The blueberries were reaching peak ripeness when I arrived, but I found no black bears or even any fresh bear sign, so instead of relaxing at the lake I decided to explore the surround terrain and take in some of the iconic alpine views that make the North Cascades so famous.

Not having a specific destination in mind, I was free to wander. These are my most favorite hikes, when I travel more to see what might lie in front of me instead fixating on a pre-determined destination.

Bushwhacking around the lake, I passed through quiet sedge-filled wetlands…

sedge meadow and small pond in mountain basin

…stopped frequently to eat blueberries…

blueberry plants with ripe blueberries

…wandered over a gently sloping boulder field…

meadow and boulder field looking up to a mountain ridge

…to a glacier tucked in a pocket just south of Little Devil Peak.

small, mostly snow free glacier tucked in a basin below a mountain peak

Here, I ate my lunch while contemplating the scene. It was a near perfect analog for the formation of the Monogram Lake basin.

Glaciers form when snow is compressed into mostly air-free ice and attains enough mass to deform and flow. Under the influences of gravity, ice deformation (high pressure within a glacier causes deeply buried ice to behave plastically), and lubrication from water at the its bed, glaciers move along the paths of least resistance. Due to their mass and size, they become powerful agents of erosion. They entrain rock, sand, and anything else as they flow. Forced along by moving ice, rocks at a glacier’s bed are especially erosive. Glacial erosion mills rock so effectively that much is pulverized into a microscopic powder called rock flour. This is the substance that gives glacial runoff it’s milky appearance and can color lakes turquoise.

Where ice had only recently receded at this particular glacier, the bedrock recorded plenty of evidence of the glacier’s past movement.

hiking pole lying on bare rock. Rock shows faint horizontal striations.

Many faint striations were scored into the bedrock near the glacier. The striations run roughly parallel to the hiking pole.

concentric gouges in metamorphic rock

Chatter marks are small, crescentic grooves formed in bedrock by rocks frozen in ice. The rocks chip the glacier’s bed as they are forced forward. The convex face of the marks point in the direction of movement.

Since glacial erosion is most pronounced at a glacier’s base, if topography forces ice through a pinch point then it causes the glacier to carve the underlying land more deeply and quickly than at the glacier’s sides, a process called overdeepening. As ice retreats, overdeepened basins often fill with water. This is the origin of fjords and deep lake basins as well as cirques high on mountainsides.

Monogram Lake occupies a cirque, a half open and steep-sided valley or basin on the side of a mountain. Instead of a clear lake surrounded by meadows, it was once filled with ice just like the basin below Little Devil Peak.

View looking toward a lake in a glacial cirque. Deep valley and snow covered peaks on horizon.

Monogram Lake

view of glacier in mountain basin. Snow covered mountains on horizon.

The glacier south of Little Devil Peak as seen from an unnamed peak above Monogram Lake.

Uniformitarianism is a geologic principle that, in sum, means the key to interpreting the past is to understand processes that occur today. Excluding the three hydroelectric reservoirs in the Skagit Valley, glaciers carved the basins for nearly every lake in North Cascades National Park and Lake Chelan National Recreation area. Even though I wasn’t around to see Monogram Lake emerge in the wake of glacial retreat, all the evidence I needed for this process was right before me.

Fault Creep

The San Andreas Fault may be the most famous fault on Earth. For roughly 750 miles (1200 km), it creases California and marks part of the tectonic boundary between the North American and Pacific plates. It creates tangible examples for us to see plate tectonics in action.

Aerial view of landscape with fault line at center right.

The San Andreas Fault cleaves the land on the Carrizo plain. Photo courtesy of Ikluft and Wikipedia.

For about 75 miles, California State Route 25 (CA 25) roughly traces the path of the San Andreas Fault as the highway passes through an open valley filled with cattle ranches. (If you’re visiting the east side of Pinnacles National Park, you’ll drive this road.) From the ground, the fault is relatively hidden in most places even though the highway crosses it several times. On Google Earth, it shows a bit more clearly.

Google Earth image of creek valley with buildings at center.

A group of buildings, sitting just to the east of CA 25, is bisected by the San Andreas Fault. The red line marks the fault’s approximate location.

This part of the fault creeps along at a slow rate, maybe an inch per year. When covered by soil and vegetation, the resulting displacement would be nearly invisible on a yearly basis. When we pave the landscape with asphalt or concrete, however, the fault’s movement can manifest itself in ways that are easy to see.

About a ten-minute drive north of Pinnacles National Park’s east entrance the San Andreas Fault crosses CA 25. Here, the San Andreas Fault is slowly tearing the pavement apart.

Road with crack running from middle left to lower right.

This is essentially the boundary between the Pacific and North American tectonic plates. Land and water on the fault’s west and south side is moving north relative to the North American continent.

Person standing on road. Land to right is North American plate. Land on lower left is Pacific plate.

Yours truly straddles the plate boundary between North America and the Pacific.

According to Greg Hayes on his Geotripper blog, this section of road was repaved in 2008. When he visited this site in 2017, the yellow center line paint had not yet split. When I stopped on the morning of January 31, 2018, the paint was clearly cracked.

Crack in pavement across yellow line.

View is looking north.

This movement has been going on for millions of years. The rocks of Pinnacles National Park, now most famous for scenery and condors, are part of a volcanic field that erupted almost 200 miles to the south. Since then, movement along the San Andreas has displaced the rocks northward, leaving about a third of the volcanic field behind.

Road pavement with crack. Text reads "To Alaska" and "North"

Land on the south and west side of the San Andreas Fault is on track to meet Alaska in a couple hundred million years.

The crack in the pavement is the current surface expression of the fault’s movement. Fault creep is evident elsewhere in California. In Hayward, creep along the Hayward Fault is splitting the city hall in half.

This section of the San Andreas provides a rare opportunity to observe the Earth’s tectonic plates in motion. Because it happens over immense time scales, geologic change is most often undramatic and unnoticed. It happens slowly in rivulets of erosion on a hillside, waves reworking sand on a beach, dust blown in the wind, and creep along faults. As passengers on Earth’s brittle crust, we’re always moving relatively speaking.

Google Earth image of road moving north to south.

You can visit this site on CA 25 at 36°35’54.27″N, 121°11’40.19″W. Please be cautious though; this is a busy highway with a high speed limit. It’s also surrounded by private land, but you can find a couple of small pullouts about a hundred yards from the fault.

Burpee Hill

Dry weather has been infrequent in western Washington this fall, so when a clear day dawned earlier this week I couldn’t resist the opportunity to take a wandering bike ride, one of my favorite pastimes. Over the last several years, my bicycle rides and hikes have become far more leisurely since I have become more prone to distraction. Without a fixed agenda though, I’m more open to discovery. Why, for example, would anyone pass on the chance to see a baby snake?

tiny snake in palm of gloved hand

This tiny garter snake was basking on the side of the road on a warm fall day in late October. Concerned it might become road kill, I moved it off of the pavement.

With temperatures near freezing on Monday, I wasn’t going to find any snakes, but over a fifty mile round trip—from Skagit River to the end of the road near Baker Lake—I found more than enough to hold my attention. After a mere two miles of pedaling, I found a reason to pause.

I began at the old concrete silos in Concrete, a small town along the middle reaches of Skagit River…

Concrete silos. Text on silos reads,

Why was Concrete named Concrete? You only get one guess.

Cycling route profile from Google Maps.

No, I didn’t ride the hill as slowly as Google Maps says it will take.

…and immediately began a steep climb up Burpee Hill. In two miles, the road gains over 800 feet of elevation, although I didn’t mind the opportunity to warm up with frost lingering on the grass.

The North Cascades region is the sum of a complex geologic history. Large-scale mountain building, volcanism, and extensive glaciation created and shaped a landscape of unparalleled ruggedness in the Lower 48 states. This area’s geology is, well, complicated. Just take a look at the geologic map.

screen shot of geologic map of Mount Baker and Baker Lake area

Yikes.

On a bicycle, unlike in a car, stopping to check out roadside curiosities—wildlife, road kill, trees, wildflowers, rocks, scenery—is very easy and is an important reason why I enjoy it so much. About half way up the Burpee Hill climb, I stopped to ponder some interesting sediments exposed in a road cut. The coarse to fine grained sediments were well sorted, indicating flowing water had deposited them, and were capped by a mix of unsorted rocks. This is one piece of a grander glacial puzzle.

view of road cut

A few exposures of loose and coarse sediment can be found on the Burpee Hill Road.

Maps that outline the last glacial maximum in North America give the impression that ice flowed largely north to south. While generally true, the story is a bit more complex on a local scale, as Burpee Hill illustrates.

Glaciers are masses of ice that flow and deform, and they behave differently than ice from your freezer. Set an ice cube on a table and strike it with a hammer and it will fracture. Ice in a glacier’s interior, however, is under tremendous pressure. Ice crystals are altered and deformed like plastic putty, so much so that only the upper 30 meters of temperate glaciers are brittle. (The relatively consistent maximum depth of crevasses reveals this fact. Below 30 meters, deforming ice seals any crevasses. Cavities at the base of glaciers have been measured to seal as fast as 25 centimeters per day.) The ice is not impervious to liquid water though. Within temperate glaciers, ice remains at or slightly above freezing, which allows meltwater to percolate to the glacier’s base. Pressure from overlying ice also causes some water to melt at the bed. Once there, meltwater acts as a lubricant helping the glacier slide. These factors, combined with gravity’s pull, drive glaciers along the paths of least resistance, and sometimes these paths lead uphill.

Between 19,000 and 18,000 years ago, a broad lobe of the cordilleran ice sheet invaded the lowlands of Puget Sound. Fingers of the ice sheet reached into the North Cascades as it continued to advance southward. Around 16,000 years ago, the ice sheet reached its maximum extent in western Washington, reaching south beyond Seattle, Tacoma, and Olympia.

On the margin of the ice sheet, lowland valleys like the Skagit offered ice easy passage as it advanced. About 18,000 years ago in the lower and middle reaches of the Skagit valley, ice flowed in the opposite direction of the modern Skagit River. Burpee Hill is largely the result of this process. It’s a 200 meter-thick layer of glacial outwash, glacial lake sediments, and glacial till deposited at the front of ice as it advanced up the Skagit valley. The features are clearer in a LIDAR image.

LIDAR Image

Burpee Hill is the wedge-shaped feature in the center of the image.

LIDAR image with labels. From left to right:

Glacial ice from the Puget Sound area flowed east over the current location of Concrete. The sediments that make Burpee Hill were deposited in front of the advancing ice.

Since its formation, erosion and landslides have eaten away at Burpee Hill, and it is easy to overlook when the lure of craggy peaks and snow-capped volcanoes always dangles ahead. If volcanoes and orogenies are architects of this landscape, then glaciers are certainly its sculptor, reshaping landforms in profound ways. Stories like this are tucked away everywhere. Landforms are rarely ordinary.

Epilogue:
I continued my ride, which (in case you’re wondering) was wonderful even though temperatures remained near freezing. As I expected it to be on week day in early December, the road was quiet. The views of Mount Baker, pockets of old growth forest, and Baker Lake were worth the effort.
view of snow capped volcano and creek valley

Cross Country By Rail Day One

Since I live across the continent from most of my family, I’m obliged to return east periodically. During my time in Alaska I flew almost exclusively on this migration, primarily because it was the most expedient way to get to where I needed to go. If I have the time though, I’d rather travel by other means. With some time to spare before my summer job at North Cascades National Park begins, I traveled by train from Bellingham, WA to Pittsburgh, PA.

I’m not a train fanatic, but the railroad allows me see a good deal of the landscape and perhaps some wildlife without the risks involved with highway driving. On the train, I could sit in my seat and gaze eagerly out the window to watch the landscape pass by. My first wildlife sighting began even before I stepped onboard.

While waiting for the train in Bellingham, I watched a crow land in a parking lot with something large in its bill. This was nothing unusual as crows are fond of scavenging garbage, but as soon as the crow landed I noticed its prize was moving. I hurriedly yanked my binoculars out of my daypack to get a better look.

The crow had caught and was killing a semi-neonate cottontail rabbit. After it dispatched and partly consumed its prey, the crow returned to catch and kill another kit. With more than it could eat, the crow cached pieces of the rabbits in nearby trees and shrubs. It was a fairly gruesome death for the rabbits, but crows gotta eat too.

view through fence of crow

Life and death struggles happen even in city parking lots.

Once onboard the train and traveling from Bellingham to Seattle, I witnessed no more battles between predator and prey. The rest of the ride, in fact, was quite pleasant. The Cascade route provided plenty of views of Puget Sound, where many birds lounged and fished in the water near shore. I enjoyed glimpses of birds like blue herons, cormorants, gulls, more crows, and brant.

view of water with clouds and boulder in middle foreground

Puget Sound is a glacially carved trough. The boulder in the middle foreground is likely a glacial erratic.

Where I couldn’t see the water, the route often passed through rich farmland where large rivers like the Skagit and Snohomish have deposited broad floodplains.

Fallow farm fields and farmhouseAfter transferring to the Empire Builder in Seattle, my route reversed north before it turned east up the Snohomish and Skykomish rivers valleys toward the Cascade Mountains, which were quite showy under clear skies.

Farmland with view of tall snowcapped mountains in backgroundThis section of rail, besides letting me enjoy scenes of lush forest, provided a conspicuous example of habitat changes due to climate, particularly the Cascades’ rain shadow effect. When moisture-laden storms from the Pacific reach the Cascades, the rising air cools and drops a considerable amount of its moisture on the west side of the mountains. Far less remains to wet the mountains’ eastern slopes.

Skykomish, WA at 900 feet in elevation, for example, receives a whopping 91 inches of precipitation per year. The forests of this valley, except where recently clear-cut, are lush and thick and moss hangs prominently from stout big leaf maple branches.

Forests on snow-covered mountainside

Lush forest cloak the western slopes of the Cascades.

 

Around 2900 feet in elevation, the train entered an eight-mile long tunnel and passed underneath the Cascade crest. When the train exited the tunnel on the east side of the Cascades, the forest was noticeably different. Trees were sparser and included a higher proportion of drought tolerant species like ponderosa pine.

Sparsely snow covered mountain

Many mountainsides east of the Cascade crest are noticeably drier and less forested than equivalent areas to the west.

As the train descended the Wenatchee River valley to the Columbia River, the climate became drier and drier. Soon enough, sagebrush and bitterbrush mixed with widely scattered trees as we approached Wenatchee around sunset. About 780 feet in elevation, Wenatchee receives only 11 inches of annual precipitation. Along the Columbia River, as night fell, the route crossed a dramatically drier environment compared to the lush forests not far to the west. I could see few trees except those planted by people.

Darkness concealed central and eastern Washington’s landscape, which I knew would happen but was still disappointing because I missed viewing any of the unique and spectacular channeled scablands. I went to bed looking forward to more sightseeing.

In a future post, I’ll describe days two and three on the train where the land continued to offer more reasons to be glued to the window.

Lake Chelan

If you’ve never been to Stehekin, it takes some time to get to. Lying at the head of Lake Chelan, Stehekin is only accessible on foot, by boat, or plane. I’ve traveled in and out many times over Lake Chelan in the past year and each time, it gave me time to witness the climatic, topographic, and glacial changes that make this area biologically diverse.

View from ridge looking into deep valley with lake

Upper Lake Chelan and the lower Stehekin River valley seen from a ridge above Rainbow Creek.

Lake Chelan is cleaved into the heart of the North Cascades and is one of the more spectacular places in the area, biologically and geologically. Most people who arrive in Stehekin in Lake Chelan National Recreation Area do so via ferry. When the ferry motors away from Fields Point Landing, about one third the distance from Chelan to Stehekin, it leaves a relatively dry habitat with sparse tree cover, but this can look lush compared to areas farther down lake. At the lake’s outlet, the town of Chelan receives only 11.4 inches (29 cm) of precipitation per year. It is a downright arid place.

Mountain slopes with few trees above lake

Sparse vegetation along the lower half of the lake is the result of an arid climate with hot, dry summers.

As the boat continues up lake, stands of ponderosa pine and Douglas-fir slowly thicken. At the elevation of the lake (1,100 feet, 335 meters) however, several factors continue to limit tree growth even along the lake’s upper reaches. Fires frequently burn the slopes while bare rock and sheer walls inhibit soil formation. Summer drought is common with scant rain and hot, dry temperatures that bake the lake’s western and south facing slopes. During spring, the mountainsides are flush with water from snow melt, but in late July and August the soil will become so desiccated it rises like powder under your footsteps.

Snow covered mountain with dead standing trees

In 2015, wildfires burned large areas near Lucerne, a small village on the lake.

Mountainside with dead standing trees and snow filled gullies

With ample snow melt, water is easy to find on the mountainsides next to the lake. In mid to late summer however, many of the gullies will become completely dry.

The North Cascades are famous for prodigious snowfall and plenty still clings to the mountains at this time of year. During the last glacial maximum, nearly the whole lake basin was filled with a glacier that carved it into a land-locked, steep-walled fjord.

In its middle reaches, Lake Chelan plunges to great depths. The mountain topography on either side of the valley restricted the glaciers outward flow, but not its forward movement. The tight topographic pinch created by the mountains enhanced downward erosion by the glacier. The lake basin, averaging only a mile wide over 50 miles, was greatly over-deepened, even reaching below sea level. At its deepest point the lake is almost 1500 feet (456 meters) deep. (More info about Lake Chelan’s underwater topography.)

Diagram of lake basin. Y axis is depth in feet and and X axis is length in miles

The upper basin of Lake Chelan is its deepest and most voluminous. Near mile 16 on the horizontal axis lies a submerged glacial moraine.

Section of bathymetric map of Lake Chelan. Contour Lines in 100 foot intervals. Greatest depth 1486 feet.

The steep mountain topography continues underneath the lake.

Steep mountain above lake

Sheer cliffs plunge steeply into Lake Chelan above the deepest areas of the lake. Below the boat on which I stand, the water is over 1,000 feet deep.

The volume of the former glaciers is apparent by looking at the shape of the mountains. Where glaciers overran the mountains, the ridges and peaks are smoothed over and somewhat rounded. Mountains that were tall enough to escape complete glaciation remain craggy and jagged. Measured perpendicularly from the deepest area on the lake to the crest of nearby mountains, vertical relief can reach 9,000 feet (2,744 m) and glaciers filled most of the space in between.

Snow covered mountain peak and ridgeline

Knife-edged ridges and peaks were not completely glaciated. Glacier ice eroded lower ridges, smoothing them over.

Looking at a map of Washington before I arrived here, I didn’t fully understand or appreciate the area’s diversity or its glacial story. Here, arid adapted species like sagebrush can live on hot, dry rocky outcrops just a short distance away from a cool, moist ravine with western red cedar and thimbleberry. Glaciers left their mark up and down the lake, accentuating topography even further. Lake Chelan is Washington’s inland fjord surrounded by, perhaps, the most diverse habitats in the whole North Cascades ecosystem.