Landslide

Sandhill cranes frolic in the fields of the Danielson farm, with the Saddle Mountain cliffs looming over it. Photograph by Phyllis Danielson.

Sandhill cranes frolic in the fields of the Danielson farm, with the Saddle Mountain cliffs looming over it. Photograph by Phyllis Danielson.

The communities of Oso and Darrington were devastated by the recent landslide, in which around fifty houses and more than thirty people were annihilated in the space of a couple of minutes. It will be a long time before life can return to anything like it used to be, with Darrington’s main artery to the rest of the world cut off. Now commuters from Darrington have to head north, past our Sauk River cabin, to get to their jobs, shops and supplies. It takes a lot of time and gas. My son’s scout troop raised cash and supplies that we took to Darrington last weekend, and I’ve been watching the news about the landslide daily.

Pictures of the Oso landslide reminded me very much of the landslide my family and I used to climb around on when I was a kid. One of our favorite hikes was to the cliffs at the top of Saddle Mountain, where you can climb down to a ledge where sandstone exposures have been carved by the winds and graffito-ed by generations of local visitors. You used to be able to read my dad’s name from his visit in the 1920s, but I’m pretty sure the wind has scoured it out by now.

The headscarp of an Ice Age landslide exposes layers of Columbia River basalt and sandstone laid between some of the flows.

The headscarp of an Ice Age landslide exposes layers of Columbia River basalt and sandstone laid between some of the flows.

The mechanics of the Oso landslide are still being worked out, but the Stillguamish River undercutting a notoriously unstable and steep slope is undoubtedly a major contributing factor.  Other factors might include the extraordinary amount of rain we received in the weeks before the slide, and perhaps some logging on the flats above the slide.

The cliffs on Saddle Mountain mark the eastern edge of five miles of tumbled mountainside, larger by seven or eight times than the deadly slide at Oso. Saddle Mountain is mostly made out of basalt, with some sedimentary layers between some of the flows. The mountain at Oso was glacial till: cobbles and sand, far more unstable than you’d expect from a mountain made of rock. Yet Saddle Mountain collapsed the same way the mountain at Oso did.

At Oso you can see how the top of the mountain slammed down on the layers beneath it, remaining largely intact. It acted like a sledgehammer dropped on a pudding cup, spewing liquified mud, clay and sand across the valley in a powerful, fast moving stream. Almost everything it encountered was destroyed. There are indications that Saddle Mountain collapsed much the same way. In places along the headscarp you can see where hunks of the mountain slipped down, intact, pushing debris across the slopes below.

The rugged debris field left in the wake of the Ice Age landslide that broke Saddle Mountain along the Corfu fault. In the distance the cliffs mark the edge of the original smooth slopes of the mountain.

The rugged debris field left in the wake of the Ice Age landslide that broke Saddle Mountain along the Corfu fault. In the distance the cliffs mark the edge of the original smooth slopes of the mountain.

An estimated 13,000 to 15,000 years ago the north face of Saddle Mountain began collapsing. Rushing floods of water from glacial Lake Missoula slammed into the mountain, parting where our farm is located. Some of the water scoured out channels around the east end of Saddle Mountain, while a strong flow carved out a series of canyons along the foot of the mountain, headed west towards Sentinel Gap. This flow undercut the mountain face, which collapsed time and again, up to an estimated 24 times. This probably occurred over the course of a number of Lake Missoula releases, although geologists have been pointing out that catastrophic flood releases probably could have also come from sources other than Lake Missoula. The last of the collapses released muddy flows that filled in the canyons on the east side of Corfu, but the canyons are still visible to the west.

From a sandstone ledge west of the cliffs you get an overlook of the tumbled debris field that ends below the saddle. The canyon below the mountain was filled in by mud and debris from later landslides.

From a sandstone ledge west of the cliffs you get an overlook of the tumbled debris field that ends below the saddle. The canyon below the mountain was filled in by mud and debris from later landslides.

NASA scientists who published a report on the Corfu Slide Complex in 1983 compared it to landslides visible in the Vales Marieneris on Mars. In addition to the undercutting of Saddle Mountain by the flood waters, they indicated that  local tremors, the unlucky tilt of slip surfaces (probably some of those sandstone or soil layers sandwiched between the lava flows) and a wetter climate contributed to the mountainside’s failure. They concluded that similar conditions were probably responsible for the Martian landslides.

Doubt has been expressed that all of the bodies of victims of the catastrophe will ever be found. There has been some talk of designating the disaster scene a monument to the victims. Discussions about what will happen to the land that was devastated by the Oso landslide seem premature, especially in light of legal actions that will likely wind up in court for years to come.

The Corfu Slide complex has received more and more public attention lately, partly because of the growing awareness of the Ice Age Floods. Dr. Bruce Bjornstad has authored several popular books on the subject and remains active in research connected to it. He has also hidden a number of geo-caches along the routes of the proposed Ice Age Floods interpretive trails. One is at the Saddle overlook at the west end of the Corfu Slide.

Bjornstad contributed to government studies that established rules of use for the Hanford Reach National Monument (created by Presidential Proclamation in the year 2000). In a comment he made on the Final Comprehensive Conservation Plan & EIS (2008), Bjornstad called the Corfu Landslide “a prominent and significant topographical feature.” He also points out that most of the Landslide falls outside the Monument, but that access to the Saddle overlook is by way of roads originating inside the boundaries of the National Monument.

Senator Clarence C. Dill and Wenatchee irrigation promoters celebrate the passage of the 1927 appropriation of funds to investigate  placement of dams on the Columbia River. The picnic took place at the Saddle Gap overlook.

Senator Clarence C. Dill and Wenatchee irrigation promoters celebrate the passage of the 1927 appropriation of funds to investigate placement of dams on the Columbia River. The picnic took place at the Saddle overlook.

The feature he refers to as an overlook is in itself a historical site. Besides hosting the remnant of a missile defense site from the Cold War, this was the location of the 1927 picnic at which farmers, politicians and businessmen celebrated the passage of an appropriation of funds allowing the investigation of the Columbia River from the British Columbia boundary to the mouth of the river for power, navigation, flood control and reclamation. Eastern Washington farmers and ranchers believed it was the first step in bringing irrigation waters to the Columbia Basin. And so it proved to be.

This pass through the anticline of the Saddle Mountains is a notch in the ridgeline created by the collapse of the northern face of the mountain during the landslides. It is the only place where the summit of the mountain was swept away. In profile from the Crab Creek valley, the shape of the gap resembled the profile of a roper’s saddle, so pioneer ranchers gave the mountain range its name from that feature. But the pioneer trail crossed Saddle Mountain in the pass east of the landslide, beyond the cliffs. Originally, that pass was referred to as Low Gap, but contemporary sources call it Saddle Gap. I’ve always found that confusing, if not downright wrong.

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