Abstract

Widespread clastic deposits, 80-1800 m long, on the eastern side of the Sawtooth Range are the result of debris flow and slushflow. Small hillslope debris flows (10-103 m3), originating on talus slopes at the mountain front and not associated with preexisting gullies, and large channelized debris flows (103-104 m3), debouching from basins within the mountains, are comparable morphologically to those in other high-latitude and high-altitude environments. Channelized deposits are often modified by the effects of slushflow and fluvial activity. Provisional lichen growth curves for the area were produced by correlation of thallus size with the enlargement of ice-wedge polygon troughs. Lichenometry and aerial photograph interpretation were used to estimate the age of deposits so that event frequencies and rates of geomorphic work could be calculated. Vertical transport by rapid mass movements during the 20th Century averaged 17 x 103 Mg ·m ·a-1 ·km-2 ( ± half an order of magnitude), corresponding to a rock denudation rate of 0.05 mm ·a-1 for the basins and peaks feeding the east-facing slopes. Channelized debris flow produced more than 70% of this transport. Several of these large flows occurred in each of the three periods of 30-35 years examined, so their recurrence intervals are substantially shorter than values reported from locations in northern Scandinavia and Spitzbergen.

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