Sunday, May 20, 2012

Deep-Seated Landslide in Upper Trout Creek, Lewis County

I was doing some landslide evaluation off of aerial imagery. When I focused down on the image below to determine if a bare area was a landslide, I noted that the logging road was criss-crossed with arcuate fractures of a large deep-seated slide. 

High view of upper Trout Creek, Lewis County
Red dots denote probable landslide initiation locations (my own designations)
 (image 2009 via USGS)

Close up of the above image with arcuate surface fractures of a deep-seated landslide
 (image 2009 via USGS)

Topographic map of the area (USGS)
Red dots denote recent landslides (my own designations)

I pulled up the Department of Natural Resources FRAP map to see if this deep-seated slide area showed up on the map.

Slope designation map of section showing slide site
The locations shows as a mix of medium stability (green) and stable (white) landforms
outside of designated high hazard areas (Map is WADNR)

Plenty of shallow landslides within landform areas designated as high instability and moderate instability, but this deep-seated unstable area got missed. It would be interesting to see how this landform looks with a better digital elevation model or on the ground.  

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