DESCRIPTION:
South Fork Toutle River Drainage, Mount St. Helens, Washington

[MAP,18K,InlineGIF)
Major Hydrologic Features in the Mount St. Helens Region
-- Modified from: Crandell and Mullineaux, 1978, USGS Bulletin 1383-C

The South Fork Toutle River heads on the west flank of Mount St. Helens, and flows west-northwest to its confluence with the North Fork Toutle River. A small area in the headwater of the drainage was affected by the blast of May 18, 1980. Tephra deposits in most of the South Fork Toutle drainage are negligible, but are up to 5 centimeters thick on the flanks of Mount St. Helens. A lahar, generated from water-saturated volcanic ejecta during the initial stages of the May 18, 1980, eruption flowed the length of the channel. A second, smaller lahar generated during the afternoon of May 18 also flowed the length of South Fork Toutle River.

In February 1981, a gaging station was established near the town of Toutle, 8 kilometers upstream from the confluence of South Fork Toutle and North Fork Toutle Rivers (TOSW). Water and suspended-sediment discharge data are collected at that site.

Twenty-five cross sections were established between 1980 and the end of WY 1982; all but one of the cross sections are grouped into three clusters ... -- (Web note: Spotted Buck, Above S-1, and Mouth reaches) -- . Four of these cross sections are considered indicator sections and are surveyed monthly or after large storms. During WY 1983, seven cross sections were established near the base of Mount St. Helens (Sheep Canyon and Disappointment Creek reaches).

May 18, 1980 Eruption

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