A portion of the Mount St. Helen's Sediment Retention Structure is shown here on May 21, 2025. After Mount St. Helen's eruption in 1980, the U.S. Army Corps of Engineers worked to offset the impacts of the flow of debris into the Toutle, Cowlitz and Columbia rivers. The Sediment Retention Structure, completed in 1989, keeps hundreds of millions of cubic yards of sediment from rushing down the Toutle River, preventing significant flooding and navigation problems.