Lessons from the Oso Landslide

On March 22nd, a forested hillside northeast of Seattle broke away and sent a  mile of mud towards the rural community of Oso. The results were utterly devastating. 41 are confirmed dead and two remain missing, 49 homes were completely destroyed, and the town of Darrington was cutoff as Highway 530 became impassible and the Stillaguamush River backed up. It is the second-worst natural disaster in Washington state history (the worst being a volcanic eruption in 1980). The recovery effort has been massive, with volunteer and professional response teams from local, state, and federal agencies working around the clock for a month. At the same time, investigative reporting has revealed that this disaster may have been preventable with proper planning.

The 600-foot cliff left behind afterwards. (The Seattle Times)

At 10:37 a.m., the hillside broke away and ripped across the landscape at an incredible 60 m.p.h. Witnesses described a wall of mud like a tsunami carrying rocks, trees, and houses. It surged across the river at the bottom of hill and into the Steelhead neighborhood, eventually stopping after burying Highway 530. The resulting pile of debris is 1,500 feet long, 4,400 feet wide, and 30 to 70 feet deep. Eight people were rescued on the day of slide by helicopter crews and first responders.

There were initial concerns that the backed-up river would break through the mud dam in a flash flood, but eventually the river formed a new channel. An alternate route to Darrington, a small town a few miles away from the slide, was opened when the county cleared snow from a one-lane gravel road. The tragedy has brought together local residents and outpouring of support in the form of donations and volunteer work.

The extent of the damage is evident from the air. (The Seattle Times) For a detailed view of the affected area, click here.

The first legal claim against Snohomish County and the state Department of Natural Resources (DNR) has already been filed, with more likely to follow. It alleges that the County and DNR increased the risk of a landslide when they allowed timber clear-cutting on the hill in 2004. However, the hillside has a history of unstable geology going back to at least 1937. Multiple smaller slides have been recorded, and subsequent reports published, in the decades since. Snohomish County’s John Pennington, director the Department of Emergency Management, sparked controversy when he claimed, “It was considered very safe. This was a completely unforeseen slide. This came out of nowhere.”

The exact cause of the slide was likely a multitude of factors, one of them being weeks of heavy rain beforehand. But the fact is that the hillside was a known risk and the County allowed people to live there without forewarning. In 2004, the County considered buying out the at-risk properties but decided not to. In the winter of 2006, another small slide shifted the Stillaguamush River. As a geomorphologist inspected the results of that slide, he was shocked to find new homes being built across the river. That summer, crews built a retaining wall along the river to prevent it from cutting into the hillside, but it was no match for the latest slide. Surviving and neighboring residents claim they were never notified of the risk to their homes, or that the County was considering moving them.

Workers create ditches to drain the debris area. (The Seattle Times)

But this event highlights how many other communities don’t know or care about the risk of their land use decisions in hazardous areas. Regulations on building in these “critical areas”, like steep slopes, floodplains, and wetlands, vary from state to state and can be nonexistent or unenforced in rural areas. The Oso landslide should spur adoption of improved surveying and mapping technology, which we already have, to identify hazards. Cities and counties can also be more aggressive in preventing construction in these areas or asking people to leave; the latter is regularly done by King County in flood-prone areas, and the state of New York is buying out coastal properties in the wake of Hurricane Sandy. And with infrastructure and at the societal level, we must become more resilient to the calamities that will increase with climate change.

Today, one month after the mudslide, President Obama will visit the area and meet with residents, emergency workers, and government officials. Hopefully, we can begin a national conversation about disaster preparedness and responsible hazard planning.

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One Response to Lessons from the Oso Landslide

  1. Pingback: On Growth, Transit, and Bikes in Vancouver B.C. | The Northwest Urbanist

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