Carlsbad Caverns National Park

Giant and Two Domes, Carlsbad Caverns National Park.
Giant and Two Domes, Carlsbad Caverns National Park. (courtesy, NPS)

Carlsbad Caverns National Park preserves a portion of the Capitan Reef—one of the best-preserved, exposed Permian-age fossil reefs in the world. Water, geologic forces, climactic changes, and vast spans of time have produced and changed the fossil reef and its spectacular caves—a process that continues to the present day.

One Theory
None of us witnessed the formation of Carlsbad Cavern. And since time and conditions don't allow us to duplicate the process in a laboratory, we are left with theories based on puzzle pieces. One theory, simplistically stated is...

A very long time ago, a shallow sea covered Carlsbad Cavern. Plants and animals lived and died in the sea. Their shells and skeletons piled on top of each other, making a reef. Over time, many layers piled up, squashing the shells and making the layers hard, compact, and thick.

The sea dried up, causing the reef to be exposed to the air. Movements in the earth's crust pushed the reef upwards, forming a limestone mountain. Trees and other plants grew on the mountain, covering the old reef and causing cracks to develop in the limestone.

Rainwater sank into the soil and went down through the plants' roots and finally down through the cracks in the limestone. On its way through the atmosphere and the soil, the water absorbed carbon dioxide. A weak acid was chemically formed when the water mixed with the carbon dioxide. The resulting carbonic acid dissolved the calcite in the limestone.

At some point, large rocks in the cave ceiling fell. This opened up chambers, like the Cavern's Big Room—25 stories high and a third of a mile wide. As water seeped and dripped its way into the Cavern, beautiful formations decorated the cave.

Soluble Rock
The largest and vast majority of caves are formed in soluble rocks—those that can be dissolved by a weak, natural acid. Limestone, dolomite, gypsum, and marble are soluble rocks. Carlsbad Cavern, Lechuguilla Cave, Slaughter Canyon Cave, and Mammoth Cave are all solutional caves.

Cave Formations
A cave formation is a speleothem. The word comes from two Greek words—spelaion, meaning cave and thema, meaning deposit. Speleothems are mostly calcite, the same mineral that makes up limestone. When the water table lowers and air enters the cave conditions are right for the process of cave formations to begin. Slightly acidic water percolates through the limestone above the cave dissolving the calcite. When the water reaches the cave, calcite is redeposited.

Two factors that influence the growth rate of the cave formations:

1. Temperature
The outside temperature affects the rate of decay of plants and animals. The higher the temperature, the faster the decay. As the decay rate increases, so does the carbon dioxide in the soil. When high levels of carbon dioxide are present, the water flowing through the soil is more acidic.

2. Water
The more rainfall, the faster the growth.

Two factors determine the shape of cave formations:

1. How the Water Enters
Does the acidic water enter the cave by dripping, seeping, or splashing?

2. Whether the Water Stands or Flows

Mineral content determines the color of a cave formation. Pure calcite is white, almost colorless. Iron and other minerals combine with calcite crystals to add red, orange, and black.

What's in a Name?
In the case of a speleothem, it's as good as a picture.

Soda Straw
A soda straw is hollow on the inside and has water dripping through it. Over time the inside clogs with calcite, causing the stalactite to grow larger.

Water in a cave does not always drip. It may seep along a slanted ceiling, forming thin draperies that hang in folds. They are also known as curtains and ribbons.

Flowstone is a cave formation that looks like a flowing stone waterfall. It forms when water seeps down cave walls, over rocks, and onto the floor.

A flat shelf of stone can form around the edges of cave pools and around stalagmites in a cave pool. Even if a pool dries up, the shelfstone remains.

Cave Pearls
Cave pearls are stone balls and can be as large as ping-pong balls. A pearl forms around grains of sand. Layers of calcite are added to the grain over time. Dripping water keeps the pearl moving round and round in the pool.

Popcorn are clusters of calcite balls that build upon the walls of a flooded cave.

An helictite is similar to a soda straw, except it curls and twists in every direction, even against gravity. No one is certain how helictites forms.

Totem Poles
A totem pole is as skinny as the stalactite above it. However, some are taller than skyscrapers and bigger than a giant redwood.

Published: 29 Apr 2002 | Last Updated: 15 Sep 2010
Details mentioned in this article were accurate at the time of publication


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