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stalactites and stalagmites


stalactite and stalagmite
A stalactite and stalagmite just beginning to meet and form a column. Credit: U.S. National Park Service
Rocky structures found growing downward from the roof (stalactites) and upward from the floor (stalagmites) of caves formed in limestone. (Remember, stalaCtites hang from the Ceiling and stalaGmites grow up from the Ground.) Rainwater percolates through the rocks above the cave and, as it contains atmospheric carbon dioxide, can dissolve calcium carbonate en route. On reaching the cave, the water drips from the roof to the floor; as a drop hangs, some water evaporates, leaving a little calcium carbonate as calcite on the roof. Repetition forms a stalactite; and evaporation of the fallen water on the floor forms a stalagmite. On occasion, the rising stalagmite and descending stalactite fuse to form a column. Stalactites, stalagmites, and columns are called dripstone because they are deposited by dripping water.


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