Lake Great Falls was a prehistoric proglacial lake which existed in what is now central Montana in the United States between 15,000 BCE and 11,000 BCE.[3][4][5] Centered on the modern city of Great Falls, Montana, Glacial Lake Great Falls extended as far north as Cut Bank, Montana, and as far south as Holter Lake.[6] At present-day Great Falls, the Glacial Lake Great Falls reached a depth of 600 feet (183 metres).[7]
Lake Great Falls | |
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Lake Great Falls | |
Location | Cascade, Montana |
Coordinates | 47°30′14″N 111°17′11″W / 47.503784°N 111.286353°W[1] |
Lake type | Glacial lake (former) |
Primary inflows | Laurentide Ice Sheet |
Primary outflows | Along the face of the Ice sheet. |
Basin countries | United States |
Max. length | about 26 miles (42 km) |
Max. width | about 7.8 miles (12.6 km) |
Surface area | varied |
Surface elevation | 3,500 m (11,500 ft) |
References | [2] |
Approximately 1.5 million years ago, the Missouri River, the Yellowstone River and Musselshell River all flowed northward into a terminal lake.[8][9] During the last glacial period, the Laurentide and Cordilleran ice sheets pushed these lakes and rivers southward.[3][8] Between 15,000 BCE and 11,000 BCE, the Laurentide Ice Sheet blocked the Missouri River and created Glacial Lake Great Falls.[3][4][5]
About 13,000 BCE, as the glacier retreated, Glacial Lake Great Falls emptied catastrophically in a glacial lake outburst flood.[5] The meltwater poured through the Highwood Mountains and eroded the hundred mile-long, 500-foot-deep (150 m) Shonkin Sag—one of the most famous prehistoric meltwater channels in the world.[10]