Photo of the Week: September 3, 2012

Inside the Big Ice Cave in Montana’s Pryor Mountains, a rainbow of color paints the limestone walls in spectacular hues of tuquoise, yellow, and orange. Concealed by the darkness of the cave, these colors can be difficult to see with the naked eye. Lucky for us, the camera can detect features that the eye cannot perceive in low light conditions, and by using a long exposure technique, the colors of the cave are revealed here in all their splendor.

Caves form in limestone when calcite, which makes up the rock, is dissolved by acidic fluids. Rain water becomes naturally acidic from mixing with carbon dioxide in the atmosphere, creating carbonic acid. As the slightly acidic water percolates below the surface, limestone is dissolved to form caves. The Pryor Mountains contain the 350 million year old Madison Limestone, which contains high amounts of calcite, making it ideal for cave formation.

Here you can see ice present on the floor of the cave, giving the Big Ice Cave its name. Deep inside, dripping water can be heard echoing out of fractures from the cave walls and ceiling. This water collects on the floor and eventually forms ice speleothems (stalagmites and stalactites).

At an altitude of 7,350 feet above sea level and insulated by its thick limestone walls, The Big Ice Cave remains approximately 32 degrees fahrenheit year-round, a cool reprieve from the 80+ degree summer temps just a few steps away from the cave’s entrance!


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