Rocky Mountain Section - 69th Annual Meeting - 2017

Paper No. 20-6
Presentation Time: 3:40 PM


THAPA, Prasamsa, Department of Geography, University of Calgary, 2500 University Drive, Calgary, AB T2N 1N4, Canada,

Despite the importance of low-magnitude high-frequency rockfalls (<100 m3) in landscape development, few studies have documented rockfall rates over extended spatiotemporal scales. Herein, the contribution of rockfall activity to the sediment cascade in Kananaskis, Canadian Rockies is calculated by creating an inventory of talus slopes derived from aerial photography, covering ~500 km2. Factors controlling rockfall-talus processes in alpine environments include (i) steep slopes (often associated with structural geology and/or glacial erosion); (ii) frost weathering. Each talus slope identified is examined to access its association with structural geology (e.g., folds, faults), glacial erosional features (i.e. cirques, oversteepened slopes) leading to increased paraglacial activity, and periglacial-driven processes (frost-cracking leading to rockfall susceptibility). Approximately, 69% of talus slopes in Kananaskis are associated with cirques and U-shaped valleys. Statistical analysis indicates that the magnitude of talus polygons is significantly different for those located in cirques vs. other steep cliffs. Since frost-induced rockfall is more effective at the frost-cracking window (FCW) (-3 to -8 ˚C), climatic control was analyzed using a paleoclimate model to reconstruct climate at 12, 10, 8, 6, 4, 2, 0 ka BP. Reconstructed daily temperature data indicate that at valley bottoms (1391 masl), a large number of days (60-100) in the year fall in the FCW, whereas at higher elevations, < 50 days fall in the FCW. Because the longest FCW is at low elevations and talus is found at higher elevations, FCW may not be the dominant controlling factor for our study location. Based on talus volumes, long-term estimates (~12 ka BP) of erosion rates for rockwalls range from 0.01-0.79 mm yr-1. Our findings provide important information on the contribution and controls of rockfall activity in landscape development for previously glaciated drainage basins in the Canadian Rockies.