Toutle River - Volcanic Sediment

Volcanic Sediment

The eruption of Mount St. Helens and subsequent lahars poured vast amounts of sediment into the Toutle. The United States Army Corps of Engineers dredged sediment from the river and built the $65 million Sediment Retention Structure on the North Fork Toutle River to prevent debris from continuing downstream. Part of the same engineering works is a tunnel to drain Spirit Lake, on the north side of the volcano, after the eruption blocked the lake's natural outlet.