A large landslide occurred in northwest Washington at about 10:37 am PDT on Saturday, March 22, 2014. Multiple casualties are confirmed as a direct result of the landslide and many people remain missing. Landslide debris covered about 30 houses and 0.8 miles of State Route 530.
The landslide occurred in an area of known landslide activity, but this time the slide was much larger, traveled much further, and had greater destructive force than previously experienced. Precipitation in the area in February and March was 150 to 200% of the long-term average, and likely contributed to landslide initiation.
The slide took place along the edge of a plateau about 600 feet high composed of glacial sediments. The volume of the slide is estimated to be about 10 million cubic yards, and it traveled about 0.7 miles from the toe of the slope. This travel distance is about three times longer than expected based on published information regarding previous slides of this height and volume worldwide. If the landslide had behaved in the expected range, it would have likely blocked the river and possibly destroyed a few houses. Instead it led to tragic loss of life and destruction of property.
Flow also dammed and temporarily blocked the upper part of the North Fork Stillaguamish River. A pool of water formed behind the debris dam, which flooded houses and other structures. There were initial fears that the debris dam would […]