Date of Award:

5-2000

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

John C. Schmidt

Committee

John C. Schmidt

Committee

Darrell Kaufman

Committee

Jim Evans

Abstract

Large-scale characteristics of Ladore Canyon debris fans are dependent upon the bedrock and lithology of the mainstem and tributary canyons. The largest fans occur in the widest section of the mainstem canyon, which typically correlates with the location of large faults. The steepest fans are found at the mouths of tributaries where cliffs are formed by resistant lithologies. Smaller-scale fan characteristics are dependent upon the magnitude and frequency of events from the respective drainage basin, which is controlled primarily by climate. Three distinct deposit ages (oldest, intermediate, youngest) were distinguished on individual fans and were tentatively correlated throughout the canyon based on observations of boulder weathering, boulder concentration, soil development, vegetation, and topography.

During fall 1997 and late spring 1998, four debris flows aggraded fans in Ladore Canyon. The largest of the four events, Wild Mountain, deposited a 3,800-m² fan in the mainstem canyon, significantly constricting the Green River. Three of the four debris flows occurred in drainages that had been burned by forest fires during summer 1996. The debris flows were initiated during rainfall events with precipitation totaling more than 3 cm. Events of this magnitude have rarely been recorded in the region during the period of record.

Measurements from the Wild Mountain debris fan indicate that under current operating conditions of Flaming Gorge Dam, the Green River has a limited capacity to mobilize newly deposited debris-flow material; therefore, particles eroded from the fan face cannot replenish downstream gravel bars. High release discharges equivalent to the 1997 high releases from Flaming Gorge Dam have a greater potential to rework newly deposited debris fans.

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