. Mass wasting in coastal Alaska. Mass-wasting Alaska. If the amounts of material are suf- ficient, they may become debris flows upon reaching the streams as a result of increased water content. More frequently, the debris is simply carried away as increased sediment load in the stream. Rapp (1 96l) in Scandinavia and Bishop and Stevens (1964) in southeast Alaska describe a phenomenon associated with this kind of flow resulting from debris avalanche accumulations in the bot- toms of steep-sided channels. Debris Figure 10.—Torrent flow deposit (center foreground) produced by failure of debris d
. Mass wasting in coastal Alaska. Mass-wasting Alaska. If the amounts of material are suf- ficient, they may become debris flows upon reaching the streams as a result of increased water content. More frequently, the debris is simply carried away as increased sediment load in the stream. Rapp (1 96l) in Scandinavia and Bishop and Stevens (1964) in southeast Alaska describe a phenomenon associated with this kind of flow resulting from debris avalanche accumulations in the bot- toms of steep-sided channels. Debris Figure 10.—Torrent flow deposit (center foreground) produced by failure of debris dam within the timber in center V-notch. CONCLUSIONS AND RECOMMENDATIONS forms a dam across a stream at the base of an avalanche. Subsequent material from upstream avalanches accumulates behind this barricade (fig. 9). When the dam gives way, a large volume debris flow or debris torrent occurs (fig. 10).. Figure 9.—Natural dam across V-notch drainage pro- duced by accumulation of forest debris. Upstream debris-avalanching produces a buildup of soil and organic debris behind the dam which, when released, produces a large-scale debris torrent. Mass wastage is the dominant process of natural erosion and slope reduction in geologically youthful southeast Alaska. Steep slopes and excessive soil-water content are the principal causes of slide occurrence; destruction of natural slope equilib- rium and stabilizing root systems are secondary factors. Slope gradient alone characterizes the region as primed for mass move- ments of all types. Sections of almost every timbered slope exceed the natural angle of stability of the soil on them. With the high rainfall of the region and resultant, almost continuous, saturation of the soils, these over- steepened slopes become particularly sensitive to events tending to disrupt their delicately balanced stability. Excess soil water, directly related 13. Please note that these images are extracted from scanned page images that may have been digi
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