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.
|October 30, 1994|
|Successive prehistoric lahar deposits at Coal Creek bridge.|
|Left and below: 1980 lahar deposits along the Toutle River.|
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
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.
|Looking down the Toutle River. Large landslide blocks are silhouetted in the middle distance.|
|Looking toward Mount St. Helens.|
|Fragment of glacially polished rock in the landslide debris.|
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.
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.
|Looking down the Toutle River. The river incised about 10 meters since 1980.|
|Braided channel of the upper Toutle River.|
|Distant view of the landslide.|
|Coldwater Lake visitor Center. The road to Johnston Ridge was not yet open in 1994.|
|Coldwater Lake from the visitor center.|
|The Coldwater Lake landslide dam|
|Coldwater Lake looking east|
Created 7 April 2003, Last Update 01 July 2012
Not an official UW Green Bay site