SECONDARY PERMEABILITY AS A POSSIBLE FACTOR IN THE ORIGIN OF DEBRIS AVALANCHES ASSOCIATED WITH HEAVY RAINFALL

Throughout much of the Appalachian region, heavy rainfall leads not only to flooding but also to extensive erosion and landsliding. Such a heavy rainfall occurred on August 18, 1972, in southwestern West Virginia with the heaviest rainfall and resultant damage centered over the Gilbert and Bens Creek drainages. Landslides, in the form of debris avalanches, were the principal form of mass movement during the storm. A number of these landslides appear to have resulted from soil zone saturation associated with temporary spring flows issuing from bedrock to the soil mantle where joints in highly fractured shales and coal beds intersected underlying, relatively unjointed, sandstones. Thus, it appears that, in this case, increased pore-water pressures as an effect of concentration of flow through secondary permeability played a substantial role in the localization and formation of slide masses. How widespread this phenomenon may be is not known. © 1979.