Influence of Debris Avalanche Block Faces and Mixed Facies on the Evolution of the North Fork of the Toutle River Drainage (1980-Present), Mount St. Helens, WA

An integrated field and laboratory-based study is outlined that proposes the role that sedimentary, geomorphic, and vegetative variables have played in the recovery on the North Fork of the Toutle River (NFTR) following the May 18, 1980 eruption of Mount St. Helens. The abundant volcaniclastic detritus produced by this eruption temporarily overwhelmed drainage systems flowing from the crater including the NFTR. The sedimentary detritus delivered to the upper reaches of the NFTR including debris avalanche facies has had a profound effect on the Morpho-sedimentary character of this drainage system. Planning and hazard evaluation along the North and South Forks of the Toutle River as well as the main Toutle River depend upon a clear understanding of sediment balance within the stream system. Data gathered during the duration of this project will extend understanding of that balance by quantifying the relative contributions of volcanogenic sedimentary detritus from prominent source deposits.


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