Geographia Polonica (2008) vol. 81, iss. 1

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Forty Years of Rockfall Accumulation at the Mount Wilcox Site, Jasper National Park, Alberta, Canada

Brian H. Luckman

Geographia Polonica (2008) vol. 81, iss. 1, pp. 79-92

Abstract

Rockfall accumulation was measured in 1981 and 2000 along ca. 850 m of the formerBanff-Jasper highway that skirts a large talus cone from Mount Wilcox in Jasper National Park,Alberta. Approximately 34.5 m3 of rockfall debris has accumulated on the roadbed since it wasabandoned in 1961. The largest boulder was 4.65 m3 and 5 others were >0.95 m3. Estimatedminimum accumulation rates from 20–30 m sections of highway adjacent to the base of the coneare mainly between 0.1–0.3 mm yr -1, with rates >0.4 mm yr -1 reflecting the presence of individuallarge boulders. These rates correspond to a thickness of 1–5 m over the Holocene and may bereasonable estimates for deposition at the outer talus fringe of such large cones. Over the observationperiod, approximately 10 rockfalls > 0.25 m “a” axis were deposited on the road eachyear, but only one every two years was > 0.5 m. Much larger rockfalls (up to 6–10 m3) havetraveled across the road, creating bumpholes, and been deposited on the outwash. These resultsindicate some of the problems with trying to estimate rates of contemporary rockfall activity fromsampling programmes based on relatively short periods of time and limited depositional areasbecause of the magnitude frequency distribution of the rockfall events.

Keywords: rockfall accumulation, lichenometry, the Canadian Rockies

Brian H. Luckman, Department of Geography, University of Western Ontario London, Ontario, Canada N6A 3K1