| Summary: | The fact of the diversion of the Souris River from the Pembina Trench across the Tiger Hills is well known, but when and why this happened has not been clarified. The main objective of this essay is to answer these two questions. A brief survey of the surficial deposits, especially their relation to the preglacial bedrock topography, and a review of the evidence for the diversion are made. Two means of diversion, other than the process of capture, are considered. A critical line of enquiry as to the time and cause of the diversion proved to be the chronology of events in that section of the Souris Valley north of the Tiger Hills. It was found that diversion occurred earlier than was formerly believed, perhaps as early as glacial Lake Brandon, but, in any case, very early in the history of glacial Lake Agassiz I. A lowering of the level of the latter was evidently not required in order to initiate headward erosion of a tributary of the Assiniboine, if capture were the process involved. Circumstances were such that capture was distinctly possible and in the writer's opinion the balance of evidence actually swings slightly in its favour. The chronology of the Souris Valley also has application to post-glacial variations in discharge and present underfitness, as well as rates of river cliff recession and the operation of geomorphological processes.
|
|---|
