Abstract

The mudflows described formed in August 1941 in the Teton Range, Wyoming, and are of the little-known alpine type. Most of them occur in the larger canyons at 7500 to 8500 feet altitude, beneath talus slopes at the base of couloirs in the canyon walls. Individual mudflows vary in pattern due to differences in volume, gradient, and topography. They are distinguished by sandy matrix and a profusion of relatively small boulders. Where mudflows invaded steep sections of the canyons their lower portions were reworked by flood waters of the main streams, and consequently typical mudflows grade downward into roughly sorted deposits somewhat like torrent fans.

Factors responsible for the formation of these mudflows include (1) development of unstable talus slopes as they approached saturation following prolonged rainy and cloudy weather; and (2) exceptionally heavy and sudden rain which caused shortlived torrents to descend the steep couloirs of the canyon walls onto unstable talus beneath.

The Teton mudflows demonstrate that in alpine regions, as in semiarid, unusual weather conditions may initiate mudflows in numbers so large as locally to overshadow many other geomorphic agencies. They then play a significant role in moving rock debris out into the zones of stream attack, in the central parts of the canyons. Here they ultimately lose their characteristic mudflow form as the fine matrix is swept away and the boulders are distributed downstream.

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