A team of scientists says intense rainfall likely played a major role in triggering the Oso landslide in March.
The report released Tuesday says many other factors such as previous landslide activity also weakened the slope that collapsed on March 22, killing 43 people in Oso about 55 miles northeast of Seattle.
The team says the slide, the deadliest in U.S. history, occurred in two major stages. A fast-moving mudflow remobilized a 2006 slide, bringing down old slide deposits across the valley. Another slide followed a few minutes later.
The report makes several broad recommendations that include doing an examination of landslide risks and communicating the information to the public.