Killer Landslides

In March 2014, following several months of heavy rain, the hillside above the town of Oso, in western Washington state, suddenly gave way, inundating the area with up to 75 feet of liquefied mud. Homes were wiped off the map, cars and drivers swept off the road, and dozens of people were killed. Could the disaster have been prevented and were warning signs missed? Filmmaker Liesl Clark's PBS-aired NOVA documentary offers an anatomy of this headline-making tragic landslide, which rushed through the valley at speeds of up to 60 miles per hour, carrying people, houses, and deadly debris in its destructive path. Landslides occur when gravity, aided by rain or water soaked soil, simply overcomes the binding material that makes up the slope, and Oso's soil of sand and clay turns out to be the perfect recipe for instability. Rescue efforts, using helicopters, was a time-consuming, uncertain, and deadly process, risky for the would-be rescuers as well as the victims. Geologists and soil experts conduct what amounts to a crime scene investigation, searching for cracks in the upper reaches of the slope—telltale signs of a looming disaster. Early warning is particularly important, because once a slide begins, it's already too late to save many victims. In the U.S., researchers use outdoor laboratories and slide flumes, creating artificial landscapes to mimic real landslide conditions (the documentary also examines conditions in slide-prone areas such as the Himalayas and Switzerland). The bottom line here is that climate change and a growing population portends more frequent, larger, and deadlier landslides. Combining vivid testimony with disaster footage, this is recommended. Aud: P. (S. Rees)