One decade ago this week, 18 million tons of clay and sand enveloped part of the Stillaguamish Valley in northern Washington, burying a neighborhood and killing 43 people in what is known as the Oso Landslide. The deadly event led to measures at both the state and federal level to better detect potential slides, and it provides a reminder of the need for continued diligence.
In 2021, Congress passed the National Landslide Preparedness Act, which has helped identify and analyze hazards across the country. The legislation also has helped coordinate response between federal and local agencies and tribes. But money is scheduled to run out, and a bill to reauthorize funding is under consideration.
“Since we passed this bill, federal agencies have improved mapping technologies and gained a better understanding of the landslide risks facing our communities,” said Sen. Maria Cantwell, a primary proponent of the legislation. “Now, nearly a decade since the devastating Oso landslide, and as more wildfires and atmospheric river events make landslides more likely, we must reauthorize and update these federal programs.”
While preventing landslides is impossible, improved knowledge can help keep people out of harm’s way. As Hilary Franz, the state’s commissioner of public lands, told The Seattle Times: “We live in a steep, wet state, so landslides are an inevitability, but I don’t think many people really know how significant the risk is and where those risks lie. Oso served as the major wake-up call to everyone.”
Thanks to funding from the Legislature, the Department of Natural Resources that Franz oversees has used lidar — Light Detection and Ranging — to create intricate topographical maps. The process employs lasers mounted on aircraft that aim light toward the ground and measure the reflected light. The benefit is that the lasers can make it through tree cover to reach the ground, providing a more complete picture than previously possible.
The work allows for the mapping of previous landslides — even those before recorded history. Geologists have identified 34,683 slides in Washington, and experts say that previous events are the best predictor of future slides. Yet, as The Seattle Times reports: “They haven’t taken the next step, recommended by a number of outside experts, of plugging that data into models to try to map the potential hazard zones of future landslides, and then highlighting where a landslide would have the gravest consequences.”
Meanwhile, the Department of Natural Resources has five full-time geologists analyzing landslide risks. Before Oso, there was one employee who spent half their time on landslides.
The efforts are particularly urgent as climate change alters the landscape. Hotter, drier summers kill trees and weaken hillsides; heavier rains then saturate and soften those hills. As Joseph Wartman, a University of Washington engineer, said: “One of my grave concerns is that we are going in the right direction and making progress, but I’m afraid that we are being outpaced by the changing climate. We’re really beginning to see the practical implications, which leads to these cascading, devastating effects.”
While humans cannot prevent landslides, we can avoid building, living and working in dangerous areas — if we can identify them.
As Rep. Kim Schrier, D-Sammamish, said of the bill before Congress: “This bill will make crucial investments to further our understanding of landslides, improve our preparation for these natural disasters, and ultimately safeguard our communities.”
