Landslide Reconnaissance Following the December 3, 2007 Storm - Chehalis Headwaters, Boistfort Valley Area
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Landslide Reconnaissance Following the December 3, 2007 Storm - Chehalis Headwaters, Boistfort Valley Area 
 

Keller Creek Area

On December 3rd, an intense rainstorm blew in from the south, stalling over the Willapa Hills. Rain gages operated by Weyerhaeuser in the Willapa Hills recorded 14 to 20 inches of rain in a 48 hour period. This intense rainfall quickly saturated soils and flooded creeks and rivers, sending a surge of water downstream. In areas with shallow soils, water penetrating into the subsurface accumulated on bedrock or impenetrable substrates. At some critical point, the accumulated water reduced the pore pressure and resistive forces of the soil enough for it to initiate downhill, leaving the bedrock or impenetrable substrate relatively unscathed. The landslides moved everything above the bedrock or impenetrable substrate, carrying trees, rock, and mud downhill, often into creeks or rivers. These types of landslides we define as debris slides and debris flows, which made up the majority of the landslides recorded during this event.

Figure 1: A view of a small stream channel that connects to Keller Creek (outside of photo). A debris avalanche at the road had formed into a debris flow, moving off the edge of the photo. Another debris slide is visible in the adjacent drainage to the left on the photo. (Click on photo for larger image)

Figure 2: A view into the headwaters for Keller Creek. A debris slide sits near the center of the photo, probably flowing into the headwaters of Keller Creek. Another landslide at the very top of that same stream transformed into a debris flow, flowing into the main channel of Keller Creek, which also contains a debris flow (far left of photo). (Click on photo for larger image)

Figure 3: A view up into the headwaters of Keller Creek. A large debris flow came down this channel, but its source is unknown. (Click on photo for larger image)

Figure 4: A view of the northern valley wall of Keller Creek. Three debris slides flowed down the edge of this clearcut. (Click on photo for larger image)

Figure 5: A debris slide on the northern valley wall of Keller Creek. The timber is probably near submature timber in age (15-50 years). (Click on photo for larger image)

Figure 6: A view of a clearcut on the northern valley wall of Keller Creek. Two small landslides moved on the hillside, although neither appears to have flowed into a stream. (Click on photo for larger image)

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 Contacts

Stephen Slaughter
Geology & Earth Resources Division, Hazards Geologist
Washington State Department of Natural Resources
360-902-1498
Fax 360-902-1785
stephen.slaughter@dnr.wa.gov

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