Although Snohomish County, Washington officials insisted they couldn’t have anticipated the March 22nd massive Oso, Washington landslide that took down the hillside, destroyed homes, and cost the lives of over 30, records dating as far back as the 1950s show that the hillside in Oso has been unstable and prone to landslides.

The area affected by the most recent disaster has been hit before in 1951, 1967, 1988 and 2006. Fifteen years ago, Geomorphologist Daniel J. Miller studied the hillside above Oso, Washington and filed a report with the Army Corp of Engineers warning of “the potential for a large catastrophic failure.” Snohomish County Executive John Lovick and Public Works Director Steve Thomsen said they were not aware of the 1999 report.

Multiple Factors Involved in the Oso Slide

Although authorities believe the slide was caused by ground made unstable by recent heavy rainfall, several other factors were also involved.

The Ice Age glacier that covered the top half of North America left a layer of packed silt covered with soft sand in the area of the Oso landslide. With lack of trees to take up rain water in the sandy soil due to repeated logging in the area, and inability of water to filter through the packed earth beneath, the stage was set for disaster. At the same time, the nearby river engorged with rainwater continued to undercut the base of the slope. A small earthquake in the area just before may have been the event that triggered the slide.

Snohomish County Cuts Costs at a Price

Ten years before the March 22nd slide, county officials considered purchasing homes in the area to protect people from the possibility of such a disaster – at a cost of $3 million. Instead, even after a 2006 landslide rushed over the area, authorities chose the cheaper option of trying to stabilize the base of the slope. Perhaps, after decades of ignoring the inevitable, county officials will finally realize that the only sensible thing to do is restrict development in this unstable area.