EARTH Magazine: Dating of Landslides Around Oso Reveals Recurring Patterns
From EARTH Magazine, June 21, 2016 -- In March 2014, 43 people were killed when 7.6 million cubic meters of mud and debris violently engulfed a portion of Oso, Wash., after a period of heavy rain. The region where this occurred is characterized by impermeable clay and silt deposits, sometimes measuring more than 200 meters thick, which formed 16,000 years ago when an ice sheet covered the region. These deposits and the addition of a wet, rainy climate makes the Stillaguamish River Valley ripe for more landslides.