ABSTRACT
Forest operations in mountainous regions of the Pacific Northwest have a major impact on soil-erosion processes. The principal mass erosion processes are slow, downslope movement involving subtle deformation of the soil mantle and discrete failures, including slow-moving, deep-seated slump-earthflows; rapid, shallow soil and organic debris movement from hillslopes; and rapid debris movement along downstream channels. In many areas, forest vegetation plays an important role in stabilizing slopes and reducing the movement rate and occurrence of these mass erosion processes. The combined term slump-earthflow is used because many deep-seated mass movements in the Pacific Northwest have slump characteristics in the headwall area and develop earthflow features downslope. Geologic, vegetative, and hydrologic factors have primary control over slump-earthflow occurrence. The areal occurrence of slump-earthflows in volcanic terranes of the Pacific Northwest is also closely linked to bedrock type. Creep, slump-earthflows, debris avalanches, and debris torrents function as primary links in the natural transport of soil material to streams in the Pacific Northwest.
