Mount St. Helens, Washington: Toutle River and Johnston Ridge

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.

	In Castle Rock there is now a commercial visitor center.
	Left and below: Views of the lower Toutle River Valley showing the lahar deposits.
	The former route was obliterated by the eruption and rebuilt at a much higher elevation.
	Left and below: Elk herd on the valley floor.

Coldwater Ridge

	Left and below: Coldwater Lake was dammed by the landslide.
	Hummocky landslide deposits.
	Looking at the main mass of the slide, with the flank of Mount Saint Helens in the distance.

Johnston Ridge

	The western part of the monument is not a good place to see blast effects because in the 1950's and 1960's it had been clear cut in a checkerboard fashion. Here we can clearly see a section boundary with stumps to the left of center and blast-downed trees to the right. Below: more views of the clear-cut boundary.
	Mt. St. Helens ejecta on display.
	When my wife can lift a rock that size, you know it's light!
	Coldwater Peak east of Johnston Ridge. Note the standing trees to the left of the peak, which were probably sheltered from the blast (although not the thermal effects of the ash cloud).
	Looking toward the head of the valley north of Johnston Ridge.
	A thick debris flow in the valley slopes west toward the Toutle River valley and thins down-valley. It is not run-up from the main debris flow. It can only have come from uphill over the top of Johnston Ridge. The top of Johnston Ridge is some 380 meters above the pre-1980 topography to the south. Being able to climb that height implies a velocity of about 250 km/hour.
	Bridge over Hoffstadt Creek.

Buried A-Frame

It only took me 23 years and three trips here to get pictures of this place. I first saw it in December 1980 but was unable to get a picture then or in my trip in 1994.

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Created 14 July 2003, Last Update 20 December 2005

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