Belt Meteor Crater - Actually A Sinkhole

December 14, 2021


Photographer: Rod Benson

Summary Author: Rod Benson

This photo features the Belt Meteor Crater, which is located on private land in central Montana. Contrary to its name, this landform was NOT made by a meteorite slamming into the prairie. Instead, this landform is a sinkhole that was caused by the dissolution of limestone beneath the surface. The rim of the crater is made of sandstone, but a thick (up to 1,700 feet / 520 m) formation called the Madison limestone underlies the area. As water soaks down through soils above, it becomes slightly acidic. While this water works its way down through cracks, it dissolves away the limestone and forms caves. The sinkhole is 100 feet (30 m) across and 40 feet (12 m) deep, so a fairly large cave must have formed in the limestone here not far beneath the surface. Eventually the layers of sandstone above the cave collapsed onto the cavern floor to form the sinkhole.

The Belt Meteor Crater once served as a buffalo jump, or "pishkun", for Native Americans as evidenced by bison bones and arrowheads on the floor of the hole. "Pishkun" is a word from the Blackfeet meaning "deep blood kettle." Scientists visited the sinkhole to collect bison bones that can be carbon-dated to determine when Native Americans used it. They also found an arrowhead(s) made of obsidian. Experts can determine where the obsidian came from by comparing its mineral composition with obsidian outcrops in the region. This can also help provide insights about Native American trade routes.

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