Figure 2 (IMAGE)
Caption
The 2014 State Route 530 (Oso) landslide in northwest Washington overran the entire North Fork Stillaguamish River valley. Here, U.S. Geological Survey civil engineer Brian Collins examines grey clay deposits overlying the brown sand that forms the underlying alluvial river valley. The clay was initially high up on the slope hundreds of meters uphill (to the left of the image) and destroyed the Steelhead Haven neighborhood where 43 people perished. The landslide was rafted across the valley by water pressures caused by liquefaction (fluidization and loss of strength) of the alluvium, and ripped trees from the ground, leaving only root pieces sticking out of the alluvium. Photo by Mark Reid (USGS).
Credit
Mark Reid (USGS)
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Photo by Mark Reid (USGS).
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