Geology For Kids
Caves don’t start as caves; they form in rocks over millions of years. Most caves are in “soluble” rock—that is, rock that can be dissolved by a weak, natural acid. These soluble rocks include limestone, dolomite, gypsum, and marble. Most of the caves all over the world that form through this natural acid are made of limestone, just like Cave of the Winds.
A cave begins to form when water seeps through cracks in the soluble rock. Rainwater absorbs carbon dioxide in the ground and forms a weak acid called carbonic acid. As this acidic water moves through the limestone toward the water table, it dissolves the limestone and, in time, it develops an underground channel, kind of like an underground river. Water begins to fill every open crack in the rocks below the water table.
If the water table drops, which it can do for many reasons over the years, the upper level passages of the underground channel become filled with air. Limestone now dissolves very quickly due to the large amounts of carbonic acid in the cave.
Now the fun begins—cave decorations or “speleothems” begin to form. These speleothems are the shapes you see in caves: stalactites, stalagmites, and more. Speleothems form as the minerals in the water build up, one on top of the other, as the water drips and drizzles throughout the cave. Although the time can vary, it takes anywhere from 1—1000 years for one cubic inch of a speleothem to form!
The color of speleothems is determined by the mineral content. Pure calcite (crystallized limestone) is white or almost colorless. In Cave of the Winds, other minerals such as iron combine with the calcite, and the color can go to red, orange, and even black.
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