The landslide occurring early Saturday morning on March 22nd, near Arlington WA, came as a result of a period of heavy rain in the Snohomish County, which climbed up to 7.14inches, only a couple of inches lower than the wettest March ever recorded. The photograph on the left, is taken before the disaster, and shows traces of an older landslide on the top of the hill, proving that the area has experienced similar events in the past. The photograph on the right is taken shortly after the mudslide, showing the massive volume of soil that was mobilized. Namely, nearly one square mile of debris and mud went through the Stillaguamish river into the Highway 530 and the developed area, located opposite to the slope, destroying 30 or more homes. So far, 25 people lost their lives under the mud and debris in the largest landslide ever recorded in the US history and 90 are still missing.
The hillside that collapsed is located in an area prone to landslides and floods, with a partial collapse of the same slope occurring back in 2006. That year, a mudslide blocked river's North Fork and the river changed course through a new channel threatening the Steekhead Drive area, the exact same neighborhood destroyed now. This time, the blocked river water is releasing some flow downstream but at a flow rate which does not raises concerns for a devastating rupture.
The state has previously taken measures to deal with the unstable slopes in the area, with the most recent major project called the Skaglund Hill Permanent Slide Repair costing the Washington State Department of Transportation (WSDOT) $13.3 million. The project secured a half-mile long part of Highway 530, west of Saturday's slide and according to WSDOT, it was initiated after a state maintenance crew discovered a "rapidly growing crack" caused by slope movement. The project included the installation of drainage pipes and the planting of trees along the slope, as well as a rock buttress between the Highway and the river.
View pictures from the site in the photo gallery below!
Source: Seattletimes
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