Ten years after the Oso landslide
Ten years ago this week, on a clear and sunny Saturday morning in western Washington State, the hillside above the community of Steelhead Haven gave way.
A torrent of mud and debris tore across the valley, destroying homes and taking the lives of 43 people on March 22, 2014. The Oso landslide devastated a rural community and brought landslide hazards into the public conscience as the nation watched families, neighbors and first responders search through the debris for signs of life or closure. The Oso landslide and the immediate national understanding of landslide hazards set in motion a wide-ranging response at all levels of government. The scientific understanding of these types of landslides has significantly advanced, driven by the Oso landslide.
Landslides are commonplace in mountainous and hilly areas of Washington, the Pacific Northwest, and the nation. The Oso landslide occurred on a sunny day; there wasn’t an earthquake or any obvious trigger. What made the landslide so devastating was its exceptional mobility that allowed it to travel much further and faster than a similar landslide the community experienced in 2006.
The mobility of the landslide spurred several scientific investigations, including some by the USGS. Scientists now have a firm understanding that the exceptional mobility of the landslide was generated by liquefaction of the river valley’s saturated soil as the landslide traveled over it, similar to a car hydroplaning over wet pavement.
Examination of high-resolution topographic data for the region revealed significant evidence of past landslides in the valley, with some landslide deposits displaying similar mobility to Oso. The conditions of this landslides in this region are not that uncommon over the recent geologic past; those landslides are restricted to a special set of geologic conditions left by the retreat of continental and alpine glaciers more than 10,000 years ago.
So, how have the science advances over the last ten years since the Oso landslide been used to reduce risk?
The specific answer, for communities like Steelhead Haven that are built in narrow river valleys, is the new understanding has not yet appreciably reduced risk. Avoidance, permanently getting out of the way, is not always a practical landslide risk reduction strategy. And for many communities, particularly rural and isolated ones like those in southeast Alaska, the mountainous interior of Puerto Rico, and in Appalachia, that is often the case.
The new knowledge gained about landslide behavior, that some landslides can move fast and travel far, and the geologic and topographic settings where such landslides occur, can be useful for planning new development, but it is an open question as to how that understanding translates to reducing losses for existing building stock and infrastructure. However, science and technological advances are driving improvements to existing landslide models and monitoring methods that can be applied to other risk reduction strategies, such as supporting warning and evacuation planning where and when that risk-reduction strategy is appropriate and cost-effective.
New attention to the risks and hazards associated with landslides came in the aftermath of Oso. This led to the passage of Public Law 116-323, the National Landslide Preparedness Act, which was signed into law on January 5, 2021 and expanded USGS capabilities within the Landslide Hazards Program. As part of Act, the USGS established a national landslide inventory, a compilation of landslide inventories mapped by state geologic surveys, academics, and other landslide scientists.
The national inventory helps users understand where landslides like Oso have occurred in the past. The Act also authorized the USGS to provide local, state, Tribal, and territorial government grants to improve landslide hazard mapping, communication, outreach, education, and planning. The first of these grants will be awarded later this year. Congress is considering reauthorization of the National Landslide Preparedness Act and held a hearing on it in January of 2024. You can read the USGS's statement on for the hearing here.
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