Cave Features

The decorative dripstone features are called speleothems (from the Greek spelaion for cave and thema for deposit). When these structures are highlighted by lanterns or electric lights, they transform a cave into a natural wonderland.

The most familiar speleothems are stalactites and stalagmites. Stalactites hang downward from the ceiling and are formed as drop after drop of water slowly trickles through the cracks in the cave roof. As each drop of water hangs from the ceiling, it loses carbon dioxide and deposits a flim of calcite. Successive drops add ring on top of ring, the water dripping through the hollow center of the rings, until a pendant cylinder forms. Tubular or "soda straw" stalactites grow in this way; most are fragile and have the diameter of a drop of water, but some reach a length of a yard or more. The large cone-shaped stalactites begin as these fragile tubes and then enlarge to cones when enough water accumulates to flow along the outside of the soda straws. Deposition of calcite on the outside of the tubes, most of which occurs near the ceiling and tapers downward, results in the familiar cone shapes.

Stalagmites grow upward from the floor of the cave generally as a result of water dripping from overhanging stalactites. A column forms when a stalactite and a stalagmite grow unitl they join. A curtain or drapery begins to form on an inclined ceiling when drops of water trickle along a slope. Gradually a thin sheet of calcite grows downward from the ceiling and hangs in decorative folds like a drape. Sheets of calcite that are deposited on the wall or floor by flowing are called flowstone. Rimstone dams are raised fencelike deposits of calcite on the cave floor that forms around pools of water.

Helictites are curious twisted or spiraling cylinders or needles. They apparently develop when water seeps through the ceiling so slowly that slight chemical or physical changes can cause reorientation of the crysal structure of the calcite or gypsum. Cave corals, also are formed by slowly seeping water, are small clusters of individual knobs.

Most cave passages contain deposits of material that have been washed into the cave. This material, know as cave fill, varies from sand and clay to stratified gravel. The pebbles in these deposits often are highly polished or frosted and sometimes are as large as 6 inches in diameter. Cave fills are particularly noteworthy because they contain materials that reflect a geologic history and a record of past climates surrounding the area.

Rock material produced by the collapse of the ceiling or walls of a cave is called breakdown and may range in size from plates and chips to massive blocks. Most breakdown present in caves today appears to have occured thousands of years ago. It is generally associated with the early history of cave development.

Source material quoted from:
U.S. Department of the Interior / U.S. Geological Survey publication Geology of Caves ISBN 0-16-036026-9 Written by: W. E. Davies and I. M. Morgan