AN UNUSUAL EARLY-WINTER FLOOD AND ITS VARYING GEOMORPHIC IMPACT ALONGA SUB-ALPINE RIVER IN THE ROCKY-MOUNTAINS OF MONTANA, USA

An unusual early-winter flood in 1989 caused widespread flooding along the Middle Fork of the Flathead River, Montana. Repeat photography wa s used to assess the geomorphic nature of the flood damage and to dete rmine the relative contributions to the flood from tributaries from op posite sides of the river. Tributaries from the Flathead Range are sho rt and traverse steep channels frequently incised into bedrock; these streams caused flooding and extensive geomorphic change immediately do wnstream of their junctures with the Middle Fork. Streams from the Lew is Range are long, have relatively gentle slopes, and flow in alluvial channels in their lower reaches. Those streams experienced little flo oding and caused few changes in the Middle Fork downstream.