Cave Geology

CAVE GEOLOGY
Caves are formed when rain water, acidified by carbon dioxide in the soil, seeped downward through millions of tiny cracks and crevices in the limestone layers. This weak carbonic acid (the same acid as in soda pop) dissolved a network of tiny microcaverns along cracks. If the bedrock is lifted, the erosion will create deeper channels. Just as rivulets converged into streams above ground, water flow paths through the limestone also converged into incrementally larger flow paths.

As rainwater continued to enter the system and more limestone was dissolved, the microcaverns enlarged. Because the major drains carried the most water, they enlarged the most. Caves were forming. If the water table continues dropping new underground drains formed at levels lower than the older ones, and the older channels empty. Thus the oldest cave passages are the closest to the surface, and the youngest horizontal passages are the deepest underground.

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CAVE FORMATIONS
Stalactites: As water and time enables the removal of limestone and the formation of cave passages, so too, they enable the deposition of "cave decorations" called speleothems. These decorations include both the familiar gypsum flowers and needles. Although these speleothems seem to grow magically from the walls, ceiling, and floors, they are actually formed by the processes of dissolutoin and precipitation. The two most common types are composed of the major mineral in limestone, calcium carbonate (CaCo3) and by salts of a minor component, sulfates (SO4). Carbonate speleothems, such as stalactites, are deposited in passages where there is no sandstone caprock above. Here, vertically seeping water dissolves calcium carbonate and can redeposit it if the water drips into an air-filled passage. The water loses carbon dioxide (CO2) to the cave air, much like a soda pop loses CO2 bubbles when opened. The loss makes the water less acidic, so it is unable to hold as much calcium carbonate in solution. The calcium carbonate is then precipitated as travertine speleothems. The shape of the speleothems depends on where and how fast water enters a cave passage.

Soda straw stalactites form on the ceiling by slowly dripping water. As each droplet falls it leaves behind a minute deposit around its border and a thin, hollow tube slowly grows toward the floor. If the tube closes and if the water drips quickly, a more conical stalactite forms. Fast-dripping water loses still more cabon dioxide as it falls and deposits a tiny bit of calcium carbonate on the floor to accumulate as a stalagmite growing upward. Because the drops splash when they hit, stalagmites tend to be broader than their "partner" stalactites directly above. If a stalactite and a stalagmite eventually meet, the result is a column.

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Draperies: Water seeping along cracks on a sloping ceiling deposits draperies that are often translucent enough to show banding of colors due to traces of different minerals. Iron, the most common element, tints speleothems hues of brown and orange. If water is sufficient, it spreads into thin sheets on the walls and over ledges and deposits flowstone.

<Back Gypsum Flowers: Sulfate speleothems, like gypsum flowers, are deposited in dry passages beneath the sandstone caprock. Calcium sulfate (gypsum) is much more soluble than calcium carbonate and can be carried toward cave passages by the slight amount of water that seeps through the sandstone caprock. The water in the damp limestone is slowly drawn by capillary action into dry passages (85%-95% relative humidity) from all directions. As the water evaporates gypsum is deposited. At its most spectaclar, this mineral (CaSO4) *2(H2O) forms white to gold flower-like structures that seem to ooze and curl from the wall, ceiling, and floor much like icing from a cake decorator's nozzle. In fact, gypsum speleothems grow from the base. This phenomenon helps explain why they can form loose crusts or blisters and how gypsum growing in limestone cracks can force off bits of limestone and gypsum from the ceiling and wall. This process is extremely slow, however, and passages that appear to be unstable are usually held together by the shining crystals of gypsum in all the cracks and crevices.

		CAVE GEOLOGY Caves are formed when rain water, acidified by carbon dioxide in the soil, seeped downward through millions of tiny cracks and crevices in the limestone layers. This weak carbonic acid (the same acid as in soda pop) dissolved a network of tiny microcaverns along cracks. If the bedrock is lifted, the erosion will create deeper channels. Just as rivulets converged into streams above ground, water flow paths through the limestone also converged into incrementally larger flow paths. As rainwater continued to enter the system and more limestone was dissolved, the microcaverns enlarged. Because the major drains carried the most water, they enlarged the most. Caves were forming. If the water table continues dropping new underground drains formed at levels lower than the older ones, and the older channels empty. Thus the oldest cave passages are the closest to the surface, and the youngest horizontal passages are the deepest underground.
<Back
		CAVE FORMATIONS Stalactites: As water and time enables the removal of limestone and the formation of cave passages, so too, they enable the deposition of "cave decorations" called speleothems. These decorations include both the familiar gypsum flowers and needles. Although these speleothems seem to grow magically from the walls, ceiling, and floors, they are actually formed by the processes of dissolutoin and precipitation. The two most common types are composed of the major mineral in limestone, calcium carbonate (CaCo3) and by salts of a minor component, sulfates (SO4). Carbonate speleothems, such as stalactites, are deposited in passages where there is no sandstone caprock above. Here, vertically seeping water dissolves calcium carbonate and can redeposit it if the water drips into an air-filled passage. The water loses carbon dioxide (CO2) to the cave air, much like a soda pop loses CO2 bubbles when opened. The loss makes the water less acidic, so it is unable to hold as much calcium carbonate in solution. The calcium carbonate is then precipitated as travertine speleothems. The shape of the speleothems depends on where and how fast water enters a cave passage. Soda straw stalactites form on the ceiling by slowly dripping water. As each droplet falls it leaves behind a minute deposit around its border and a thin, hollow tube slowly grows toward the floor. If the tube closes and if the water drips quickly, a more conical stalactite forms. Fast-dripping water loses still more cabon dioxide as it falls and deposits a tiny bit of calcium carbonate on the floor to accumulate as a stalagmite growing upward. Because the drops splash when they hit, stalagmites tend to be broader than their "partner" stalactites directly above. If a stalactite and a stalagmite eventually meet, the result is a column.
<Back
		Draperies: Water seeping along cracks on a sloping ceiling deposits draperies that are often translucent enough to show banding of colors due to traces of different minerals. Iron, the most common element, tints speleothems hues of brown and orange. If water is sufficient, it spreads into thin sheets on the walls and over ledges and deposits flowstone.

<Back		Gypsum Flowers: Sulfate speleothems, like gypsum flowers, are deposited in dry passages beneath the sandstone caprock. Calcium sulfate (gypsum) is much more soluble than calcium carbonate and can be carried toward cave passages by the slight amount of water that seeps through the sandstone caprock. The water in the damp limestone is slowly drawn by capillary action into dry passages (85%-95% relative humidity) from all directions. As the water evaporates gypsum is deposited. At its most spectaclar, this mineral (CaSO4) *2(H2O) forms white to gold flower-like structures that seem to ooze and curl from the wall, ceiling, and floor much like icing from a cake decorator's nozzle. In fact, gypsum speleothems grow from the base. This phenomenon helps explain why they can form loose crusts or blisters and how gypsum growing in limestone cracks can force off bits of limestone and gypsum from the ceiling and wall. This process is extremely slow, however, and passages that appear to be unstable are usually held together by the shining crystals of gypsum in all the cracks and crevices.