Abstract: Numerous active-layer detachments occurred in watersheds surrounding Dawson City following forest fires that burned the area during the summer of 2004. The distribution of these shallow landslides was mapped in the Mickey Creek, Steele Creek and Fifty Mile Creek watersheds. Selected slope failures were surveyed in detail to describe their geometry and geomorphological settings in order to investigate the mechanisms of failure, and to assess the effects of the forest fires on local permafrost conditions. The failures generally initiated on moderate convex slopes at shallow depths (< 65 cm ) in silty colluvium; frost tables were close to 1 m in depth. Most active-layer detachments
were on the order of 5-20 m wide and 10-100 m long and occurred on slopes with a variety of aspects; however, the detachments occurred only where permafrost was present. In some cases, they developed on gentle slopes (as low as 10°) and traveled several hundred metres, depositing sediment directly into creeks, or across access trails. Their cumulative effects may significantly impact sediment transport within the watersheds. Potential concerns for fish habitat and implications for placer mining water quality regulations have consequently been raised.

Authors: Lipovsky, P.S., Coates, J., Lewkowicz, A.G. and Trochim, E.

Keywords: Geomorphology, Permafrost, Placer Mining, Surficial Geology

NTS Mapsheet(s): 115N, 115O, 116C

Citation: Lipovsky, P.S., Coates, J., Lewkowicz, A.G. and Trochim, E., 2006. Active-layer detachments following the summer 2004 forest fires near Dawson City, Yukon. In: Yukon Exploration and Geology 2005, Emond, D.S., Bradshaw, G.D., Lewis, L.L., and Weston, L.H. (eds.), Yukon Geological Survey, p. 175-194 .

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