Mount Saint Helens: Toutle River Valley

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Data for Mount Saint Helens is somewhat ambivalent. The topography available online from the U.S. Geological Survey dates from 1981 and shows changes due to the eruption. But all the other data layers - hydrography, roads, and so, date from 1978! Thus the data show the pre-eruption glaciers, outline of Spirit Lake, and the now-buried course of old state highway 504. On the maps above, the buried highway is dark purple, new lakes are light blue and the debris flow is light brown. Post-eruption data from U.S. Forest Service maps.

Mt. St. Helens 1994 October 30, 1994
Mt. St. Helens 1994
Mt. St. Helens 1994
Mt. St. Helens 1994Successive prehistoric lahar deposits at Coal Creek bridge.
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Mt. St. Helens 1994Left and below: 1980 lahar deposits along the Toutle River.
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Mt. St. Helens 1994Sediment Retention Structure. Built 1986-1989 by the Army Corps of Engineers to trap sediment and prevent clogging of the lower Toutle and Cowlitz River channels. It is 550 meters long, 56 meters high and is expected to fill by 2035.

The dam is mostly to catch sediment, not water. It has a series of outlets at different elevations to pass water, and is designed so that upper outlets will drain water as lower ones are clogged by sediment.

Upper Toutle River Valley

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Mt. St. Helens 1994Mt. St. Helens 1994

The Debris Flow

Mt. St. Helens 1994Looking down the Toutle River. Large landslide blocks are silhouetted in the middle distance.
Mt. St. Helens 1994Looking toward Mount St. Helens.
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Mt. St. Helens 1994Fragment of glacially polished rock in the landslide debris.
Mt. St. Helens 1994Tree trunks in the landslide rubble.

Below: the large hills are landslide blocks that were literally shaken to pieces by the landslide. Originally solid rock, they are now mostly disaggregated.

Mt. St. Helens 1994Mt. St. Helens 1994
Mt. St. Helens 1994Note the color boundary on the left side of the hill across the pond. This is a former lithologic contact, although the blocks have been shaken so thoroughly they can be dug with a shovel.

Below: looking toward Mount St. Helens.

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Mt. St. Helens 1994Looking down the Toutle River. The river incised about 10 meters since 1980.
Mt. St. Helens 1994Braided channel of the upper Toutle River.
Mt. St. Helens 1994Distant view of the landslide.

Coldwater Lake

Mt. St. Helens 1994Coldwater Lake visitor Center. The road to Johnston Ridge was not yet open in 1994. 
Mt. St. Helens 1994Coldwater Lake from the visitor center.
Mt. St. Helens 1994The Coldwater Lake landslide dam
Mt. St. Helens 1994Coldwater Lake looking east

Mount Saint Helens

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Mt. St. Helens 1994Mt. St. Helens 1994

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Created 7 April 2003, Last Update 01 July 2012

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