J. H. Hardison | USGS Science

USGS2018

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.

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USGS2005

Geomorphic change and vegetation development on the Muddy River Mudflow Deposit

Geomorphic disturbances are widely recognized as important processes that influence plant-community development and landscape-scale vegetation patterns [e.g., Veblen and Ashton (1978), Garwood et al. (1979), Swanson et al. (1988), and Malanson (1993)]. In volcanically active areas such as the Pacific Northwest, mudflows are locally important geomorphic disturbance events governing short- and long-term ecological conditions. Volcanic mudflows can scour and inundate river valleys with large volumes of debris (Janda et al. 1981; Pierson 1985; Vallance and Scott 1997; Scott 1988; Vallance 2000; Kovanen et al. 2001) and influence plant succession tens of kilometers downstream from their points of origin (Halpern and Harmon 1983; Adams and Dale 1987;Wood and del Moral 1987; Frenzen et al. 1988). In addition to altering plant succession, large volcanic mudflows can initiate a cascading chain of secondary disturbances that further modify the landscape and affect subsequent ecological responses (see Swanson and Major, Chapter 3, this volume).

Book chapter↗