RN-02 Glacial outburst floods on the Animas River, Colorado and New Mexico

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This report covers mapping of glacial and flood deposits in southwestern Colorado and northwestern New Mexico along the Animas River valley. The author outlines a framework of four “catastrophic floods,” three of them associated with Colorado glaciations (Durango, Bull Lake, and Pinedale). The source area for these floods is proglacial Lake Durango. The origins of the fourth, and oldest, outburst flood are less well constrained, though here this flood is associated with early Pleistocene time.

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-03 Glacial outburst floods on the Uncompahgre River, Colorado, and RN-04 Glacial outburst floods on the Lake Fork of the Gunnison River, Colorado.

From the overview:

Four catastrophic floods ran down the Animas River valley of southwest Colorado during the Pleistocene. Outlet valley glaciers from the San Juan icefield flowed southward down the Animas River valley and reached Durango during the last three glacial advances. Each of these glacial advances caused glacial outburst floods, and the earliest flood probably had a similar origin. Nested end moraines at Durango show each glacier reached the same end point, with less than a mile separating the three moraines. Upstream from these moraines is a long, flat-floored valley with extremely low gradient that represents the infilled proglacial lake that formed behind the end moraines as the glaciers receded. Failure of the morainal dams led to catastrophic draining of the proglacial lakes. The floods ran the length of the Animas River, carrying flood deposits more than 50 miles downstream to the confluence of the Animas River with the San Juan River at Farmington, New Mexico.