Comparison of Landslides and their Related Outburst Flood Deposits, Owyhee River, Southeastern Oregon

Shannon Marian Othus
May 2008

Abstract

Numerous landslides have entered the Owyhee River canyon north of Rome, Oregon. As the river flows through different lithologic units, the style of mass wasting changes from large slump events and small rock falls to large earthflows. The change in mechanism of mass wasting from upstream to downstream seems to depend on several factors: (1) the ratio of the basalt cap to the exposed underlying sediments, (2) the composition of underlying sediments, (3) the canyon geometry, and (4) the extent and frequency of mass wasting. All three mechanisms of mass wasting have the ability to block the river channel and display associated flood deposits downstream. Only earthflows show aggradation deposits upstream, suggesting greater longevity than other types of mass wasting. Also, based on the frequency and size of related outburst flood deposits, smaller rock falls could possibly have the greatest cumulative effect on river channel evolution.

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