Red River of The North - Geology

Geology

The Red River flows across the flat lakebed of the ancient glacial Lake Agassiz, an enormous glacial lake created at the end of the Wisconsin glaciation from meltwaters of the Laurentide ice sheet. As this continental glacier decayed, its meltwaters formed the lake, and over thousands of years sediments precipitated to the bottom of the lakebed. These lacustrine soils are the parent soils of today's Red River Valley. The river itself is very young; it began only after Lake Agassiz drained, about 9,500 years ago.

The word "valley" is a misnomer. While the Red River drains the region, it did not create a valley wider than a few hundred feet, and the much-wider floodplain is the lakebed of the glacial lake. It is remarkably flat; from its origin near Breckenridge, Minnesota to the international border near Emerson, Manitoba, its gradient is only about 1:5000 (1 metre per 5 kilometres), or approximately 1 foot per mile. The river, slow and small in most seasons, does not have the energy to cut a gorge. Instead it meanders across the silty bottomlands in its progress north. In consequence, high water has nowhere to go, except to spread across the old lakebed in "overland flooding". Heavy snows or rains, on saturated or frozen soil, have caused a number of catastophic floods, which often are made worse by the fact that snowmelt starts in the warmer south, and waters flowing northward are often dammed or slowed by ice. These periodic floods have the effect of refilling, in part, the ancient lake.