Abstract

An air photo survey along some rivers in Central Alberta revealed the frequent occurrence of a raised valley rim in the ground surface adjacent to valleys where postglacial channels were incised through a region of low topographic relief. Subsequent more detailed studies lead to the conclusion that, in large part, these features are due to elastic rebound of the rock into which the valley has been eroded. Rebound of the valley floor occurs due to vertical stress relief and gives rise to a gentle anticlinal structure. This structure and the upwarping of the beds in the valley walls can be predicted by a mathematical model based on elastic behavior and incorporating modifications to deal with stratified rock masses.Evidence of valley rebound was noted at the sites investigated and typical cases are presented. The amount of rebound varies with the modulus of elasticity of the rock and may be as much as 10% of the valley depth.The upwarping of the beds will locally influence the dip of the beds. The rebound should be accompanied by interbed slip which would give rise to gouge zones. If these gouge zones occur near the base of the valley walls, they will have an important bearing on landslide activity. The raised valley rim has other geomorphological implications.

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