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Stalactites and Stalagmites

© Copyright 2002, Jim Loy

Of course, you know the difference between a stalactite and a stalagmite. They occur in limestone caves. The stalactite is above, and hangs downward like an icicle; the stalagmite is below and sticks up. They grow in pairs, the slightly acidic water dissolves some of the limestone, carrying it downward. When the water evaporates, the limestone appears to have flowed downward. Some of the water does not evaporate until it has fallen through the air, and landed on the floor, the remaining limestone building the stalagmite. Sometimes the stalactite is missing, as they sometimes break off and fall; you will often see their pieces on the floor. Or human visitors may break them off, and take them away. Often, the stalactite and stalagmite will connect, and become a column.

This flow of water, slightly acidic from acid rain or from passing through something acidic, is what digs out the caves. It essentially widens cracks in the rock. And the ceiling may also collapse, making a mound of limestone on the floor, and a concave dome above.

There are other types of caves. Lava tubes are created when lava flows as a river; the lava at the edges often solidifies into a hollow tube, or it may be open at the top. When the lava quits flowing, sometimes an empty tube is left, perhaps going on for miles.

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