Landslide Reconnaissance Following the December 3, 2007 Storm - Thurston County
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Landslide Reconnaissance Following the December 3, 2007 Storm - Thurston County 
 

Rock Candy Mountain Debris Flow / Ranch House BBQ

On December 3rd, 2007, two debris flows were triggered at the top of two tributaries of Kennedy Creek. These debris flows flowed down the two creeks, merging into a single channel. The debris flows heavily scoured the stream channels, bulking large amounts of soil, rock, and debris before flowing into the Ranch House BBQ and depositing debris across Highway 8. The debris flow damaged or destroyed a cabin, outbuilding, two storage buildings, and the main restaurant, causing a minimum of $1 million in damage. Of the two channels that debris flows occurred in, however, we only investigated the eastern channel debris flow to the initiation point.

Highway 8 and the Ranch House BBQ

 

Map 1: The location of the initiation landslides and debris flow. The main debris flow probably continued as a hyperconcentrated flow west of the Ranch House BBQ and along Kennedy Creek. The deposit area and debris flow is an approximate representation of where the debris flow initiated, moved, and deposited. Click on map to view larger image.

 

Figure 1: The main building of the Ranch House BBQ. The debris flow moved across the property, destroying numerous buildings and coating the property in mud. Click on the photo to view larger image. (photo by Kelsay Davis)

 

Figure 2: A view of debris along Highway 8 and the storage unit of the Ranch House BBQ, which was almost pushed onto Highway 8. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

 

Figure 3: A view of the median along Highway 8. As the debris flow moved across the highway, it deposited mud, woody debris, and restaurant items on and along Highway 8. Much of this debris was probably pushed here during the initial clearing of Highway 8. This debris continued west (downhill) along Highway 8 and probably Kennedy Creek for a considerable distance. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

 

Figure 4: Looking south towards the Ranch House BBQ and Highway 8. The brown building in the distance was attached to the foundation on the lower left side of the photo. Click on the photo to view larger image. (photo by Kelsay Davis)

 

Figure 5: A closer view of the brown building in Figure 4. The building was thickly covered with mud inside and debris was piled up on the building. The building probably floated on the debris flow and was stopped by a wooded fence. Click on the photo to view larger image. (photo by Kelsay Davis)

B-Line Road
Approximately 3,000 feet south of the Ranch House BBQ on the B-Line road.

 

Figure 6: A view of the washed out bridge along the B-Line road. Note that DNR geologist Kelsay Davis is standing at the debris line for the debris flow. The bridge was relatively undamaged downstream and appeared to flow on top of the landslide. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

 

Figure 7: Looking downstream towards the Ranch House BBQ from the bridge site; note the scouring on the channel sides and woody debris scattered throughout the channel. Click on the photo to view larger image. (photo by Kelsay Davis)

 

Figure 8: Looking south at the bridge site from the upstream side. The bridge site acted as a blockade or temporary dam when the debris flow traveled through here, entrapping timber and debris. It probably was quickly lifted by the massive force of the landslide. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

B-530 Road
The two debris flows intersecting at the B-530 road, located about 1,500 feet south of the B-Line road; we followed the eastern channel and did not follow the western (main) channel to the initiation point.

 

Figure 9: The western debris flow as it intersects the B-0700 road. Most of the energy appeared to be dissipated as the debris flow moved across the road. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

 

Figure 10: The western debris flow upstream of the B-0700 road.  The debris flow was powerful enough to scour the channel sides and remove debris from the channel. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

 

Figure 11: A view of the western debris flow downstream. The landslide scarred the trees, probably with woody debris and rock as it travelled downhill. This also gives a minimum height of the debris flow. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

 

Figure 12: A view of the initiation slide for the debris flow. The landslide failed out of a hollow at the top of the stream. It was composed of shallow soils above impermeable and unaffected substrate. Cracks were also located just east of this landslide, indicating another landslide. This landslide moved less than 1 foot before stabilizing. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

 

Figure 13: A view of the main channel (western) debris flow as it crosses the B-700 road; note the size of the old growth trees lodged at the bridge site. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

 

Figure 14: Looking upstream from the bridge site at the main (western) channel of the debris flow. Click on the photo to view larger image. (photo by Kelsay Davis)

 

Figure 15: Looking downstream from the B-0700 road at the main (western) channel of the debris flow. Click on the photo to view larger image. (photo by Isabelle Sarikhan)

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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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