RN-03 Glacial outburst floods on the Uncompahgre River, Colorado

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This report covers mapping of glacial and flood deposits in southwestern Colorado along the Uncompahgre River valley. Multiple glacial advances are recorded by the deposits in this area, and the author discusses glacial outburst floods from two proglacial lakes (“Lake Uncompahgre 1” and “Lake Uncompahgre 2”). Examination of lacustrine sediments and fossils assemblages aided in characterizing these two lakes, and their relationships to the different periods of glaciation.

For more information on glacial outburst floods in Colorado, please see related Research Notes publications: RN-01 The Vallecito flood— a catastrophic flood on Los Pinos River, southern San Juan Mountains, Colorado and New Mexico, RN-02 Glacial outburst floods on the Animas River, Colorado and New Mexico, and RN-04 Glacial outburst floods on the Lake Fork of the Gunnison River, Colorado.

From the abstract:

Outlet glaciers from the San Juan icefield flowed down the Uncompahgre River valley 23 miles to Ridgway, Colorado. Three major glacial advances are recognized, with each glacier reaching a maximum extent within a half-mile of each other. Ages have not been determined, but suggested ages are Durango, Bull Lake, and Pinedale (Last Glacial Maximum). The Bull Lake and Pinedale glaciers created lakes that ultimately failed catastrophically to produce outburst floods. The Bull Lake flood carried many large flood boulders to Montrose, Colorado, 23 miles down valley. The Pinedale flood occurred when the distal proglacial lake’s morainal dam was breached at two places, perhaps from overtopping. This flood was smaller than the first, but it carried flood boulders nine miles downriver and diverted the river’s course both at Ridgway and at Montrose.