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 b