Abstract

We studied 30 large debris fans along the Alaska Highway between the Alaska-Yukon boundary near Beaver Creek and the south end of Kluane Lake to document late Holocene and historic debris flow activity and to evaluate the hazard that debris flows pose to the highway and other infrastructure. We used dendrochronology and tephrochronology to date surfaces on the fans and to estimate debris flow recurrence. All of the fans are paraglacial landforms of largely latest Pleistocene and early Holocene age. Debris flows continued to occur, probably at a diminishing rate, during the middle and late Holocene, but have only left an irregular carapace of deposits on the early Holocene fans. The White River tephra, which is about 1,200 years old, occurs across the surface of most of the fans, indicating that few debris flows and floods have escaped existing channels of streams on the fans. We conclude that future debris flows, like those that have occurred on nine fans in the past few decades, will mostly be restricted to present stream crossings.

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