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USGS CMG InfoBank: Stalactites and Stalagmites

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Comment: 05:53 - 07:15 (01:22)
Source: Annenberg/CPB Resources - Earth Revealed - 21. Groundwater
Keywords: cave, groundwater, "carbon dioxide", "carbonic acid", limestone, precipitation, evaporation, "calcium carbonate", stalactite, stalagmite

Our transcription: The most vivid example of this is the formation of caves.
Infiltrating groundwater is always slightly acidic because it has reacted with carbon dioxide in the air, thus forming carbonic acid.
This acid gradually dissolves limestone, especially along joints.
If the groundwater eventually drains off, it will leave behind air-filled caverns.
Columns of rock build up inside these caverns.
These formations are created by droplets of groundwater seeping into the caves.
As each drop clings to the ceiling for a brief moment, enough evaporation takes place to precipitate a minute amount of calcium carbonate.
Over centuries, untold millions of such microscopic grains of rock will form "stalactites" above, and from the buildup of droplets that reach the floor below, "stalagmites" will form.

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