ABSTRACT: The 1903 Frank Slide, Alberta, Canada : a review of one hundred years of investigation.

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Abstract

The Frank Slide occurred without warning at 0410h on April 29th, 1903. It involved 30 M m 3 of Paleozoic limestone, which travelled down Turtle Mountain and swept across the Crowsnest Valley, climbing 145 m up the opposite slope. H/L is 0.22. The movement lasted ca. 100 seconds suggesting an average velocity of ca. 30 m/s. The landslide was immediately investigated by R.G. McConnell and R.W. Brock, who, in their famous report, introduced the term "rock avalanche" to describe the event. No weather or seismic trigger is associated with the landslide. However, McConnell andBrock pointed to the role of coal mining in overthrust Mesozoic rocks at the base of Turtle Mountain as one of the causes of the catastrophe. A subsequent investigation in 1912, led by R.A. Daly, further documented the geology and found that the coal mining was instrumental in triggering the event. In the 1970s, D.M. Cruden and J. Krahn undertook an important re-examination of the geology of the Frank Slide, which produced a geological interpretation significantly different from earlier work. Krahn and N.R. Morgenstern applied numerical methods to assess the role of mining in the failure and carried out direct shear tests on the limestone. In the 1980s, Cruden and O.Hungr initiated the study of the debris with reference to emplacement mechanisms and D.K. Norris produced the definitive geological cross-section of Turtle Mountain. In the 1990s, a numerical analysis by B. Benko and D. Stead found that, with the slope at or near the limit equilibrium, mining-induced deformation may havebeen a contributory factor in the failure. Hungr and S.G. Evans undertook a dynamic simulation of the rock avalanche. K. Sassa et al. analysed the interaction between the debris and the valley floor sediments and its effect on run-out. Most recently, R. Couture studied the geomechanics of initial failure, and the fragmentation characteristics of the debris. Six key issues have thus emerged in the 100 year investigation of the Frank Slide; a) the precise geological structure of the source area and its relation to initial failure, b) the geomechanics of initial failure, c) the role of coal mining in loosening the slope, d) the present stability of the flanks of the slide and the hazard thatthey pose, e) the run-out mechanism, and f) the structure and sedimentology of the debris. The understanding of these issues has undergone a significant evolution since 1903; the extent to which they have been resolved has major implications for rock slope hazard assessment in the Rocky Mountains and the thematic understanding of rock avalanche initiation and subsequent motion.

Bibliography of Canadian Geomorphology