Landslides in the western U.S. are very much in the news lately, so I thought I’d put together a brief listing of some data, images and video on a few of them. Most of the listings below are related to the Oso, Washington landslide. But because of unusually wet conditions that have occurred during the past several months throughout parts of the western U.S., I’m also including information on yesterday’s landslide in northwestern Montana and on the Colorado Front Range storm event of September 2013.
The Oso, Washington Landslide:
The landslide near Oso, Washington happened on Saturday, March 22, 2014, when an unstable hillside collapsed and propelled mud and debris across the North Fork of the Stillaguamish River. The 1-square-mile (2.6-km2) slide obliterated property and also created an earthen dam and a barrier lake. The slide is known as the “Hazel Landslide” and has reportedly been an active area of earth movement since at least 1937.
In a Washington Post video, David Montgomery, a geology professor at the University of Washington, briefly outlines the cause of the Oso landslide:
Past landslides in the Oso area are delineated in a new US Geological Survey report based on a 2013 high-resolution lidar survey of the North Fork Stillaguamish River Valley which was acquired by the Tulalip Tribes in partnership with the Puget Sound Lidar Consortium:
Snohomish County, Washington, released video of a March 23, Sunday afternoon flight over the mudslide area. The video was taken with Washington State Patrol equipment aboard a Washington State Patrol aircraft:
Landslide debris covered part of Interstate 90 near northwestern Montana’s Lookout Pass (mile marker 6.5) late Sunday afternoon (March 30). As a result, west-bound traffic was detoured from St. Regis, Montana (mile marker 33) along Montana 135 and Highway 200 north to the Sandpoint, Idaho area until this afternoon. Currently westbound traffic on I-90 is diverted to an eastbound lane in the slide area. The cause of the slide is basically an unstable slope that was activated during wet conditions. Rock debris continues to move downslope as Montana Department of Transportation crews attempt to clean up the slide area – see the video posted by NBC Montana at: Lookout Pass Landslide
Colorado Front Range Storm Event:
Lastly, the Colorado Front Range storm event of last September is yet another example of geologic hazards generated by record rains that send water cascading through mountainous narrow valleys, producing landslides. I wrote an earlier Geopostings blog on this event and posted photos that I took of some of the flood-damaged areas. The link to my earlier Colorado Front Range storm event blog is: Front Range Storm Event
The northern Colorado Front Range area was hit with flooding and hundreds of landslides that were triggered by record rains that fell throughout this area from September 9 through 13, 2013. U.S. Geological researchers from the Landslide Hazards Group in Golden, Colorado, presented their findings to-date on landslide hazards associated with this storm event at the Geological Society of America’s (GSA) annual meeting in late October. A summary of their findings is available in the pdf online – Landslides in the northern Colorado Front Range caused by rainfall between September 9 and 13, 2013. The Figure 1 map from this pdf is shown above (red depicts the extent of the landslide area and 2000-2010 fire areas are in gray) and is a good reference map to use in understanding that the storm event damage happened inside a triangle along Colorado’s Front Range Mountains, spanning an area of approximately 1,150 square miles. As noted by the USGS researchers:
The combination of landslides and flooding was responsible for eight fatalities and caused extensive damage to buildings, highways, and infrastructure (fig. 2). Three fatalities were attributed to a fast moving type of landslide called debris flow (fig. 3). One fatality occurred in Jamestown, and two occurred in Pinebrook Hills immediately west of the City of Boulder. All major canyon roads in the northern Front Range were periodically closed between September 11 and 13. Some canyon closures were caused by undercutting of roads by landslides and flooding, and some were caused by debris flows and rock slides that deposited material on road surfaces (fig. 4). Most of the canyon roads, with the exceptions of Highway 6 (Clear Creek Canyon), Highway 46/Jefferson Co. Rd. 70 (Golden Gate Canyon), and Sunshine Canyon in Boulder County, remained closed at the end of September 2013. A review of historical records in Colorado indicates that this type of event, with widespread landslides and flooding occurring over a very large region, in such a short period of time, is rare.
I took an afternoon off from the GSA meeting and went to the flood damaged area to look at flood-related deposits and debris flows. At that time, most major canyon roads were still closed. I was able to go up Fourmile Canyon Road, which is west of Boulder, just off Highway 119, and then drove up towards Estes Park on Highways 72 and 7. The flood/landslide damage even in the areas I could get to was extensive. Below are several photos from these areas.
If this blog has peaked your interest in the September storm event, you should also read both a High Country News (HCN) blog and article written by Cally Carswell about Colorado Front Range flood events. In her HCN Goat Blog, Carswell tells why Front Range flooding is an inevitable event. She follows up the blog writing with a HCN article on lessons that should be learned by us all with this flood/landslide event. And – the flooding was not confined to just the immediate Front Range area. As flood waters cascaded out of the mountainous areas, they engulfed towns and farmlands further east. National Public Radio ran a news segment on 11/19 that’s well worth listening to about how Colorado farmers are trying to recover from the historic flood event.