Glacial Lake Souris

Glacial Lake Agassiz seems to get all the press. Most North Dakotans are aware that the Red River Valley is glacial Lake Agassiz, but I suspect that few North Dakotans have heard much about glacial Lake Souris.

At the end of the last ice age, glacial Lake Souris formed in front of the receding glacier and covered much of Bottineau and McHenry counties as well as portions of Rolette and Pierce counties. During the course of a few thousand years, it changed in size and elevation, and because it was a rather shallow lake, the lake margin is often not apparent to the casual observer.

Between the Turtle Mountains and the Souris River, the lakebed occupies a wide band of land from north of the Canadian border, then angling southeast to Rugby. On the west side of the river, the lakebed parallels the river for a few miles from just south of Westhope to just north of Denbigh. One of the more noticeable approaches to the lakebed is west of Bottineau on highway 5.

Heading west from Bottineau you’re traversing a glaciated landscape. About three miles past the highway 14 turnoff to Carbury, the highway drops onto a level expansive plain. That’s glacial Lake Souris. As you might expect, much of lakebed is flat, contains deep rich soils, and as a result is some of the most productive farmland in the state.

The near-shore and off-shore regions of glacial Lake Souris formed the sandy soils and sand dunes around Towner, Bantry, and Denbigh. The dunes in the Denbigh area can reach heights of over fifty feet and support some rather unique sand prairie.

The beginning of the end for glacial Lake Souris came after most of the glacier had retreated northward around 11,000 years ago. Drainage of glacial Lake Regina in southeastern Saskatchewan released a flood of water southeastward, which cut the Souris and Des Lacs River valleys. Now, of course, the lake has drained, and the Souris River makes a U-turn near Velva and flows back into Canada near Westhope.

The next time you’re out traveling that part of the state, take a closer look at that glacial Lake Souris. It’s an interesting piece of North Dakota’s geological heritage.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.