On March 22, 2014, an ominous rumble startled the residents of Oso, Washington. It was the terrifying sound of what would become the United States' deadliest landslide in decades. While a massive search and rescue effort continues at the site, geologists are tracing the geological history of Oso to explain why the site was so unstable. But all around the world, scientists have reason to fear that the worst is yet to come.

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Tags: PBS, Nova, Killer, Landslides, 2014