Mount Saint Helens: Toutle River Valley

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

Data for Mount Saint Helens is somewhat ambivalent. The topography availableonline from the U.S. Geological Survey dates from 1981 and shows changes due tothe eruption. But all the other data layers - hydrography, roads, and so, datefrom 1978! Thus the data show the pre-eruption glaciers, outline ofSpirit Lake, and the now-buried course of old state highway 504. On the mapsabove, the buried highway is dark purple, new lakes are light blue and thedebris 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 1994 Successive prehistoric lahar deposits at Coal Creek bridge.
Mt. St. Helens 1994
Mt. St. Helens 1994 Left and below: 1980 lahar deposits along the Toutle River.
Mt. St. Helens 1994 Mt. St. Helens 1994
Mt. St. Helens 1994 Sediment 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

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

The Debris Flow

Mt. St. Helens 1994 Looking down the Toutle River. Large landslide blocks are silhouetted in the middle distance.
Mt. St. Helens 1994 Looking toward Mount St. Helens.
Mt. St. Helens 1994 Mt. St. Helens 1994
Mt. St. Helens 1994 Fragment of glacially polished rock in the landslide debris.
Mt. St. Helens 1994 Tree 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 1994 Mt. St. Helens 1994
Mt. St. Helens 1994 Note 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.
Mt. St. Helens 1994 Mt. St. Helens 1994
Mt. St. Helens 1994 Looking down the Toutle River. The river incised about 10 meters since 1980.
Mt. St. Helens 1994 Braided channel of the upper Toutle River.
Mt. St. Helens 1994 Distant view of the landslide.

Coldwater Lake

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

Mount Saint Helens

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

Return to Historic Sites Index
Return to Virtual FieldTrips Index
Return to Professor Dutch's Home Page

Created 7 April 2003, Last Update 08 June 2020