Stalactite, stalagmite and columns
Stalactites, stalagmites, and columns are formed when water, saturated with calcium carbonate and other minerals drips from a cave ceiling. The calcium carbonate precipitates out as calcite. (When the saturated water does not drip from a cave ceiling, but flows on the floor or a wall, it creates drip stone and drip curtains).
A stalactite begins with a single mineral-laden drop of water. When the drop falls, it leaves behind a tiny deposit of calcite. Each subsequent drop that forms and falls deposits another calcite deposit. Eventually, these rings form a very narrow (0.5 mm), hollow tube commonly known as a "soda straw" stalactite. Soda straws can grow quite long, but are very fragile. If they become plugged by debris, water begins flowing over the outside, depositing more calcite and creating the more familiar cone-shaped stalactite.
The corresponding formation on the floor underneath a stalactite is known as a stalagmite. These are formed as calcite-laden drips land on the floor of a cave, and calcite is precipitated out.
Given enough time, these formations can meet and fuse to create columns.
In the progression of pictures from the Oregon Caves (near Grants Pass, Oregon, USA) below:
The first pictures shows soda straws -- thin, hollow calcite tubes that will become stalactites.
The second picture shows stalactites (roof) and a stalagmite (floor), much more developed.
The third picture demonstrates how a stalactite and stalagmite may eventually merge, to create a column.
The fourth picture shows a fully developed column.
Text and photos © Bruce Martin
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