A high-magnitude debris flow occurred in late summer 2000 from tightly folded sedimentary rocks in a steep 2.66 km2 basin in the remote Donjek River valley of southwest Yukon. The debris flow deposited at least 206 344 m3 of material, with a peak discharge on the order of 1000 m3/s. No evidence of any previous events of this magnitude was found at the site. The headscarp is aligned with the strike of a west-plunging overturned syncline in heavily weathered Upper Paleozoic to Upper Triassic argillite, interbedded siltstone and argillite, and thinly bedded limestone. Tree-ring analysis on two white spruce killed by the debris flow indicate that the debris flow occurred in July to early-mid August 2000. The heaviest monthly total precipitation on record (1967-2003) for August occurred in 2000 and most likely played a role in slope failure. The volume and peak discharge estimated are the largest reported from a debris flow occurring in the last 100 years in the St. Elias Mountains.
