20 March 2016
Chelan County: A landslide near Wenatchee triggers evacuations
Posted by Dave Petley
Chelan County: A landslide near Wenatchee triggers evacuations
Near to Wenatchee in Chelan County, Washington State, in western USA, a large landslide has developed that is directly threatening 26 houses, leading to the evacuation of a number of families. KOMO News has the best account of this landslide:
Neighbors in the area have been asked to evacuate as the ground continues to shift and officials try to figure what has caused the potentially deadly disaster. Just above Wenatchee, the Whispering Ridge neighborhood provides a mountain top perspective. … Residents in 26 houses have been advised to leave. Roughly a dozen could take a direct hit from what has been described as a “potential massive landslide.” Two homes have already been declared unsafe to live in.
This landslide appears to have developed over the last few months at least, but to have become acute in the last few days, perhaps in response to recent heavy rainfall. KOMO News has a gallery of images of the landslide, including these two showing tension cracks running close to houses:
Chelan County landslide via KOMO News
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Chelan County landslide via KOMO News
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The location of this landslide appears to be the area on the map below:
Chelan County landslide location
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A Google Earth perspective view gives a better impression of the landscape in which this landslide has developed:
Chlean County landslide: a Google Earth perspective view
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The news reports suggest that there is now a geotechnical investigation of this site to determine the causes of the landslide. Washington State is of course prone to landslides, and indeed on the image above there is a very prominent landslide scar on the left side, and hints of others too. But the immediate cause of this landslide is less obvious. The Google Earth imagery extends back to 1998. In the intervening time there have been some minor changes to this area, but nothing obviously sufficient to trigger the landslide. The two ponds higher up on the slope, for example, were both present in 1998.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Looks like a small part of an old slide/earthflow complex is reactivating. To my eye, that entire neighborhood is on a large old, dissected slide mass. There is another geomorphically “fresher” slide complex over the ridge to the NE from Zimmerman Pond also.
[Yes, I agree, I think this is an old landslide complex, one of many in this landscape. D.]
I have heard from local sources that there have been 2 water main breaks in the area..we are looking to support with our monitoring unit.