Just before 11 a.m. on March 22, 2014, an ominous rumble startled the residents of the little town of Oso, Washington, about an hour’s drive from Seattle. It was the terrifying sound of the United States’ deadliest landslide in decades. In less than two minutes, a 250 acre field of debris 20 feet deep slammed into a neighborhood of 35 homes. In the wake of the tragedy, geomorphologists are tracing the geological history of Oso to explain why the site was so unstable. But Oso isn't alone. Globally, landslides and other ground failures cost more lives and money each year than all other natural disasters combined. The threat of bigger, more frequent landslides is growing as climate change increases intense precipitation events. As NOVA follows scientists surveying landslide danger zones, discover how and why landslides happen and how new laser monitoring technologies may help predict landslides before disaster strikes.