Geomorphic response of the Muddy River Basin to the 1980 eruptions of Mount St. Helens, 1980–2000

The 18 May 1980 eruption of Mount St. Helens produced a mosaic of primary landscape disturbances that decreased in intensity with distance from the volcano across the headwaters of Muddy River and its tributaries. Subsequent geomorphic responses were influenced by evolving hillslope and channel conditions that affected fluxes of water, sediment, and wood, as well as by an exceptional storm in February 1996. Sediment fluxes have generally decreased, but downed wood in channels remains episodically mobile. Geomorphic change and biotic activity in the basin continue to interact in terrestrial, riparian, and aquatic ecosystems and in many cases diversify ecosystem conditions.