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An investigation of talus slope development in the Similkameen Valley near Keremeos, B.C. Worobey , George A.

Abstract

Talus form and development in the Similkameen Valley near Keremeos, British Columbia was investigated. Initial observations suggested that talus formation in the region was entering a passive stage and subsequent analysis has confirmed that the talus slopes are tending towards stability. Volcanic ash exposed on one talus slope allowed the calculation of relative rates of past and recent talus accumulation which supported a 'diminishing sediment yield' concept. Analysis of climate data recorded at Keremeos since 1930 revealed a high frequency of frost cycles. This suggests the importance of frost action as a mechanism of weathering along the exposed headwalls and it is thought that the occurrence of abundant and massive talus forms in the region is basically the result of frost weathering in association with lithologic controls. A fence structure designed to capture rockfall debris yielded fair results and substantiated the validity of using vegetation as an index of stability on talus slopes. A weak but not monotonic increase in sediment size down slope was detected on a number of slopes, contradicting an initial visual impression. Debris sampled along lateral profiles on one talus cone is significantly larger at the 1% level than debris sampled along the central profile. Some correlation between size and angle is implied, since the lateral profiles are also steeper; it is hypothesized that transport mechanisms down the sides are different from those along the center of the cone. Readily observable cross-slope sorting, resulting in the development of longitudinal strips of fine and coarse debris, is explained in terms of differential mass movement mechanisms. It is concluded that the talus slopes studied are complex and influenced by a variety of processes in addition to primary deposition. The mapping of one talus cone at a five foot contour interval provided the basis for a detailed analysis of talus form. A sample of the debris size taken simultaneously with the mapping of the surface allowed for the calculation and establishment of a fourth degree trend surface, an examination of which is made in conjunction with the map and photos of the cone. Practical implications of the development of talus as applied to this region are discussed.

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