ABSTRACT: Before the Frank Slide: preparatory and triggering causes from maps and photographs.

CGRG Bibliography of Canadian Geomorphology
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Abstract

The Frank Slide was prepared by deformation during the Rocky Mountain Orogeny which thrust the Turtle Mountain Anticline up along the folded and splayed Turtle Mountain Fault. Easterly dipping, stronger, Palaeozoic limestones and dolomites then rested on sheared, weaker, Mesozoic clastics and coals. Fluvial erosion along the strike of the Anticline created Jurassian relief which was then emphasized by Pleistocene glacial erosion. Cordilleran valley glaciers steepened the eastern flank of Turtle Mountain but left buttressing kame moraines. These were eroded postglacially by the Crowsnest River which was pushed against Turtle Mountain between its North and South Peaks by the growth of the alluvial fan of Gold Creek. The Blairmore Group mudstones and shales beneath the kame moraines were susceptible to toppling. So the slope between the Peaks was steepened by fluvial erosion of its toe. Photographs of the east slope of Turtle Mountain before the Slide show disturbed vegetation, uneven topography, steep slopes and rock fall deposits. Coal mining between the Peaks was the penultimate preparation for the Slide which was triggered by rapid spring snow melt. Terzaghi's concept of the reduction of the factor of safety of the east slope from 2.5 to below 1 by less than 2 years of coal mining was based on an imprecise contemporary report of the Slide. Our more detailed studies have lessened the emphasis on human activity as the Slide trigger and contributed to a reassessment of the rock slide hazard in the deformed sedimentary rocks of the Canadian Cordillera. However coal mining subsequent to the Slide, which was then abandoned as the Frank Mine caught fire, raised concerns about the stability of the South Peak. These have yet to be fully allayed.

Bibliography of Canadian Geomorphology