North Cascades & Oso Landslide
See some of America's best scenery at Mt. Adams and North Cascades National Park in Washington!
Travel to North CascadesThis field trip starts at Oso, Washington on state highway 530 northeast of Everett. We'll proceed east to Darrington, north to Rockport and Concrete on highway 20, and east on 20 through North Cascades National Park.
Time: This trip can be done in one day if you're short on time, but I recommend 2-4 days to soak it in. Hiking and backpacking opportunities are nearly limitless, so you may want to plan around those.
Lodging: Available along I-5 near Arlington, a motor inn in Darrington, a few options around Concrete, and scattered inns along highway 20 on the west and east sides of the national park.
Campgrounds are abundant in the park and in the region.
Vehicles: Any. Washington Pass on the east side of the park isn't particularly steep or challenging for RVs, but make sure your brakes and radiator are in good condition.
Food: Available in Darrington, Concrete, and along highway 20 west of the national park. Plan to take your own food while inside the park, because no facilities are available (a big oversight, in my humble opinion!).
Park Website: North Cascades National Park.
Seasons: Highway 20 through the national park is closed winters until May or June.
Hiking: See the park's website for fantastic trails!
Oso LandslideAmerica's deadliest landslide occurred on March 22, 2014 at about 10:30 in the morning. 43 people were killed. Landslide hazards in this canyon had been well known for decades, but the size and speed of this event were a complete surprise to even the experts.
I have created and taught a course in Natural Disasters and advised emergency responders and government officials on natural hazards for many years. When the Oso landslide happened, I was in shock along with everyone else. I use this tragic event to educate anyone who will listen and urge proper action by public agencies.
The 625 foot-tall hillside across the river from the Steelhead Drive neighborhood is made of glacial sand and gravel. Landslides had happened there before, but they were always small, and no one thought they threatened the houses. But over time, the north fork of the Stillaguamish River had been undercutting the hill, making it so steep it was unstable. Heavy rains leading up to March 22 had saturated the hill, further weakening it until it gave way. The slide began as a slump, more or less intact, but movement mobilized the water in the sediments to cause a phenomenon called liquefaction ("quick sand") in which the sediments flow like a milkshake. The mudflow spread across the valley at about 40 miles per hour, pushing and tumbling the houses in its path.
The landslide blocked the Stillaguamish River, making a bad situation even worse. USGS photo by Mark Reid.
This Google Earth image from 2011 shows the river undercutting part of the ancient landslide complex. Bare areas on the hill indicate previous land movement. Previous landslides had been restricted to the immediate hill slopes.
This Google Earth image from March, 2014 shows the landslide and mudflow.
The landslide was about 5340 feet (1630 meters) from top to toe, 625 feet (190 meters) tall, and it spread to be 3200 feet (975 meters) wide and up to 70 feet (21 meters) deep. The distance from the hill to this photo location is 3650 feet (1110 meters). 49 houses were destroyed in this view.
Memorials to the victims line the highway. It's a sobering reminder that we live on a dynamic planet with a wide variety of hazards. We need public awareness and education, action and funding by government leaders, and hard work by scientists and engineers to mitigate risks and try to avoid tragedies like this one.
The mudflow spread past the highway in several places, including this one where it destroyed two houses. Lawsuits blamed logging for the landslide, but in my opinion trees could not prevent a deep-seated landslide like this one. The heavy rains were to blame. But at least the victims and survivors were given some remittance, which is rare in landslide cases.
Darrington AreaThe Stillaguamish River valley is just heavenly! It was widened and flattened by glaciers from 2 million to about 12,000 years ago. Those glaciers filled the valley with sand and gravel, and the river has since excavated the valley, leaving remanants of glacial sediments in bluffs along the sides. On geologic maps, those bluffs are nearly all mapped as landslides.
Looks to me like Darrington has some interesting, creative residents!
With a view like this, I wonder where Darringtonians go for vacation? If I were in their places, I'd just sit on my back porch!
Glacially carved Whitehorse Mountain is made of a plagioclase feldspar-rich granite called tonalite, Oligocene in age (34 to 23 million years). A major fault, the Darrington-Devils Mountain fault, lies at the base of the mountains and extends westward parallel to the valley. The lower mountains at left are part of a tectonic melange, rocks accreted onto North America from the subducting oceanic plate several million years ago.
Lake Shannon - Baker Lake - Mount BakerLike most of the Cascades, Mount Baker is easiest to see from far away. Roads tend to be deep in canyons, providing only occasional glimpses of the high volcanic peaks. This view is from Baker Lake at Boulder Creek, coordinates 48.716938, -121.694210. Other access from the west side provides closer approaches and more views, including the top of Mount Baker ski area.
Mount Baker is 10,781 feet (3,286 m) high, and is the northernmost volcano in the conterminous United States. It holds the distinction of being the only Cascades volcano affected both by alpine (mountain valley) glaciers and continental (widespread ice sheets) glaciation. It is made mostly of andesite lavas and breccias (gravels) that began forming about 140,000 years ago. The most recent eruption was 6700 years ago, in which the side of the volcano collapsed in a giant landslide, sending mudflows down the river valleys and damming Baker Lake. The western shores of the lake are landslide debris from this event. Ash then blanketed the area. The volcano showed signs of activity in 1975-76, but no eruption occurred. It is expected to erupt again in the future, but there is no way of telling when. It poses high hazard risk to all surrounding communities, particularly in the river valleys.
When you look at a Cascades volcano, you're looking at a long series of events. First is the long-term eruption history that created the long plateau that the younger cones all sit on. Next was construction of the cone eruption by eruption, some of which were massive and catastrophic. Next came glaciation that carved the beautiful cirques and ridges, and which still fills them. And younger than the glaciation are more eruptions, including Baker's catastrophic collapse that dammed Baker Lake. Notice how very rocky Boulder Creek is in this view. That indicates violent floods during storms and rapid Spring run-off, and is a hazard concern.
North Cascades National ParkThis is the Gorge Lake dam on the Skagit River. The bedrock here is gneiss, the metamorphosed roots of older volcanoes.
Aptly named Gorge Creek plummets through the gneiss bedrock toward the lake. You can see some of the metamorphic banding in the rock.
Gorge Creek is easy to view from this see-through bridge. Coordinates 48.701089, -121.209260.
Farther east is beautiful Diablo Lake, which doesn't look so devilish on this gorgeous day. The turquois color comes from rock flour, which is bedrock ground into fine powder under glaciers.
From the same highway view area you can look southward to see Colonial Peak (left) and Pinnacle Peak (right), both glacial horns. Glaciers are still actively eating away at these mountains. Their bedrock is also gneiss.
To me, this is the must-see of North Cascades National Park!
Enter the observation site at Washington Pass. These are Liberty Bell Mountain and Early Winters Spires on the south side of the highway. They are made of 40-something million year old granite. Extensive joint (fracture) sets have given ice good foot-holds to break apart and carry away the rock, carving these wonderful spires.
The Washington Pass observation area features a wonderfully styled visitor center. I so appreciate the care and expense that goes into buildings like this in our National Parks! They show me that someone cares that my tax dollars are spent well so that I and all the visitors can have a great experience.
The short trail at the observation site puts you right on the edge of a 300-foot cliff with spectacular views! That's highway 20 going down the east side of Washington Pass. Look at the several high valleys still being carved out by snow and ice.
Liberty Bell Mountain and Early Winters Spires from the observation trail.
The highway barely avoids several debris chutes, where snow avalanches, flash floods, and debris flows deposit fans of rocks on the lower slopes. Ice constantly breaks apart the bedrock here, allowing snow and rain to do the rest. Debris flows typically form their own levees along the sides of their channels -- see them just beyond the bend in the road?
The granitic bedrock at Washington Pass has some fascinating fracture sets in it. The shallow-dipping set in the upper left indicates uplift and pressure relief, which caused the bedrock to expand and crack. This is similar to the exfoliation sheets you see at Yosemite National Park in California, and is a common phenomenon in igneous rocks and sandstones.
Highway 20 follows a deep glaciated canyon eastward from Washington Pass. Notice the very long debris chutes on the mountainsides where snow avalanches and debris flows (flash floods) strip out the vegetation and deposit piles of rocks and other debris at the slope bottoms.
Look where the observation area is! This is looking back up at Washington Pass from lower highway 20.
Related pages: Mt. Rainier, Rainier Sunrise, Glacier National Park, Yosemite National Park, Mouth of the Columbia River,
Geologic Map of the north Cascades from USGS