An article in Science magazine describes how geology and heavy rains contributed to the huge Oso landslide that flowed much farther than other slides of similar size.
Even for Slide-Prone Region, Landslide Was Off the Chart (Subscription only)
As Science went to press, 27 people in that community of Oso, an hour’s drive north of Seattle, were confirmed dead and 22 were still listed as missing. Although a flurry of critical media accounts have cited expert predictions of landslides for the area that were seemingly ignored, Iverson contends that the distance traveled by the Oso landslide was far beyond the norm for slides of its size falling from less than 200 meters. “I would not have anticipated this,”he says. In the annals of landslide science, he says, last week’s catastrophe was “an extreme event.”
Yet the latest Oso landslide stands out as an anomaly. USGS maintains a database of slides that includes data such as debris volume, height of the hillside that produced the slide, and length of runout. Last week, Iverson crunched the numbers for the Oso slide, which had an estimated volume of 8 million cubic meters and fl owed about 1.13 kilometers from the toe of the slope. “It ran out three times longer than would have been expected by looking at other slides of this height and volume,” Iverson says. If the landslide had been in the normal range, it would have blocked the river and possibly destroyed a few houses, he says. “But nothing like what happened.” Iverson suspects that geology and bad weather conspired to create conditions for the monster slide.
The death toll is now 35. It is the deadliest landslide in U.S. history. Could it have been prevented? No. Could loss of lives could have been prevented? Yes. Sadly, people can be oblivious to hazards or ignore warnings and still wish to live there regardless of the risk.
For more on the controversy over the warnings in this area and even a connection to the “Sovereign Citizen” movement, see this piece by Don Prothero.