National Geographic: Scientists hoping to better understand what triggered the tragic landslide in western Washington are eyeing two prime suspects: rising groundwater that weakened slide-prone soils, perhaps exacerbated by logging; and the Stillaguamish River, which persistently chewed away at the bottom of the hillside. The March 22 landslide wiped out an entire neighborhood near the small town of Oso, leaving at least 27 dead and another 22 missing. But answers to what caused the hillside to come thundering down...