Lake Cut Bank was a

glacial lake A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land and then melts, filling the depression created by the glacier. Formation Near the end of the last glacial period, roughly 10,0 ...

formed during the late

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

along the

Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...

and Sun Rivers. After the

Laurentide Ice Sheet The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million years a ...

retreated, water melting off the glacier accumulated between the Rocky Mountinas and the ice sheet. The lake drained along the front of the ice sheet, eastward towards the

Judith River The Judith River is a tributary of the Missouri River, approximately 124 mi (200 km) long, running through central Montana in the United States. It rises in the Little Belt Mountains and flows northeast past Utica and Hobson. It is ...

and the Missouri River. The front of the

Keewatin ice sheet Keewatin is a Cree word meaning "Blizzard of the North" and can refer to the following: __NOTOC__ Places Canada * Keewatin, Ontario, a town amalgamated with the towns of Kenora and Jaffray Melick to form Kenora * District of Keewatin, Northwest T ...

completely blocked the valley of Cut Bank Creek so that for the ice dam was bordered by the water of an extensive lake, which has been designated glacial Lake Cut Bank. It is defined by the granitic pebbles and boulders on top of the hills southeast of

Cut Bank A cut bank, also known as a river cliff or river-cut cliff, is the outside bank of a curve or meander in a water channel (stream), which is continually undergoing erosion.Essentials of Geology, 3rd Ed, Stephen Marshak Cut banks are found in abu ...

and are present at several places in the basin farther north and west all below . The pebbles were deposited from icebergs floating on the lake. The lake bottom is identified by the laminated silts over the flatter parts of the basin. The silts are up to as seen in some of the coulees. Additionally, stratified sand and gravel are visible in the basin. There is no defined shoreline. The lake has been mapped below contour, with shore like slopes between . The Carlow Flat shows evidence of being submerged part of the time. About southwest of Cut Bank the same granite pebbles are found at . This is taken as the maximum and first lake level. The lake drained southward along the ice front. Later the water fell to and flowed through the sag occupied by ponds. The inner gorge of

Cut Bank Creek The Cut Bank Creek is a tributary of the Marias River in the Missouri river basin watershed, approximately 75 mi (123 km) long, in northwestern Montana in the United States, which having deeply eroded steep cliff banks eponymously gives ...

formed after the glacial lake drained. The lake received runoff from the adjacent land area and from the north front of the

Two Medicine Two Medicine is the collective name of a region located in the southeastern section of Glacier National Park, in the U.S. state of Montana. It has a campground alongside Two Medicine Lake. From the period starting in the late 1890s until the com ...

Glacier for over (Squaw Buttes, southwest of Cut Bank, westward to the mountains). Cut Bank Glacier and the South Fork of the Milk River drained into Lake Cut Bank. Water from the St. Mary Glacier and from both the mountain glaciers and the Keewatin ice sheet, north of the international boundary drained into the South Fork of the Milk River and then into glacial Lake Cut Bank. The glacial river channel is not abandoned. It runs form the Milk River northeast of Landslide Butte to the head of Rocky Coulee. By assuming that each layer of the laminated clay deposited in this lake is a

varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (var ...

, representing one season's deposition, the longevity of the lake could be counted. Glacial lakes in Montana

References

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See also