Landslide of the Week – Piper Road Landslide
June 1, 2009
Each week we will feature a new landslide in Washington State. Washington State is covered with dynamic and sometimes quirky landslides.
Piper Road Landslide
The Rock Creek Landslide (also known as the Skamania, Stevenson, or Piper Road Landslide) started in 2007 probably after heavy rains hit the area in November of 2006. Movement started to accelerate in February of 2007 and continues to today.
This photo was taken shortly after the landslide started to become more active. The landslide itself has started to cut back into the bluff. DNR Division of Geology and Earth Resources Geologists investigated the landslide at this time to determine clues to the landslide and possibly mitigation to help reduce or stop the landslide movement.
By November of 2007, the landslide had progressed significantly upslope:
At this point, the landslide had destroyed one house (in July of 2007) and the town of Stevenson was desperate for aid and help to mitigate the landslide. The landslide was no longer threatening only houses, but now threatened to destroy a road (with utilities below) and inundate a sewage treatment plant. If left unchecked, sediment would continue to aggregate and threaten to take out the bridge of State Route 14, which is one of the few points that connect major utility lines between eastern and western Washington (such as a natural gas pipeline). Unfortunately, no aid was forthcoming and Stevenson was left to deal with the landslide on its own. I think the quote was (in a conference call regarding the landslide) something akin to “larger towns have been destroyed or abandoned by landslides”. It is, perhaps, the unfortunate result of building in unstable areas.
The long term problems might be bigger than losing a couple of bridges and a sewage plant. The Bonneville Dam is located just downstream of Stevenson and Rock Creek drains into Lake Bonneville. Sediment from the landslide is flowing into Lake Bonneville, which can impact fish populations and slowly inundate the lake and create a sediment headache down the road (of course, this could be dredged out). If the sewage plant is impacted, raw sewage could flow into Lake Bonneville (as far as I know, it isn’t used for drinking water), which could lead to things like an algae bloom or dead zones, anoxia, or just misery and destruction. Granted, probably not enough sewage to do that in such a big lake, but worst case scenario.
The landslide is located on the Bonneville/Cascade Landslide complex and is probably the result of continued movement and activity of the landslide.
As in the Greenleaf Basin Landslide, a combination of higher rainfall and geologic setting probably resulted in the landslide movement. Erosion of the toe of the landslide by Rock Creek, overtime, probably reduced the lateral strength of the landslide and eventually resulted in a breakdown in resistive forces.
The geology of the landslide is well covered in this report by Mark Yinger Associates.
The Rock Creek Landslide Website has been established for the Piper Road landslide (with webcams fixed on the landslide) and additional images.