Cave Formation: How Solution Caves Form

A Gateway to Another World Beckons Adventurers

A Fascination With Caves

Humans have long been fascinated with caves and wherever they discover them, have sought out to explore these chambers and uncover their secrets. Caves exist all around the world and for those adventurous enough to enter in or descend into their depths, many wonders await.

We tend to think of the ground beneath our feet as being solid but this isn't necessarily so. While it may be stable enough to walk on, deep below, other processes are at work that in certain areas have created a subterranean world. It seems hard to believe that vast cave systems could and do exist underground.

This begs the question: how do caves actually form?

It all starts with dissolution of soluble materials. This is a natural process and it occurs in karst environments. Continue reading to learn more about what at first may seem a somewhat mysterious process.

Some Caves Form Through Wave Action

What Forces Shape Formation of Caves?

The earth is in a constant state of flux and different forces contribute to cave formation, such as wave and volcanic action, glacial action or geological movement; however, many caves form in soluble rock, such as chalk, dolomite and gypsum, limestone, marble and salt. Caves that form out of soluble materials are called solution caves.

The largest caves, in fact, are formed in limestone, which dissolves through the action of both rainwater and groundwater charged with carbonic acid and other naturally occurring organic acids. This produces an environment scientists call karst, characterized by underground drainage systems.

Rainwater (containing carbon dioxide) trickles down through the soil layer to limestone beds. It picks up even more carbon dioxide as it works its way through the soil, which is rich in carbon dioxide by means of decaying organic matter. By a natural chemical process, the water and carbon dioxide form carbonic acid, which is a weak acid solution.

As this acidic water passes through hairline fractures and crevices in the ground and comes into contact with soluble minerals, rock, or more commonly, limestone bedrock, it dissolves these materials. Wherever the water runs, dissolution takes place, and as time passes, the cracks widen and form paths and eventually, a network forms that then allows even more water in.

Rainwater Works on Soluble Materials and Aids in Cave Formation

A Process of Dissolution That Creates an Underground Labyrinth

A Closer Look at Formation of a Cave at the Water Table

Solution cave formation takes place at the water table. The water works its way downwards to where the ground is saturated. Once there, water collects and soon, channels and paths begin to form. This contributes to a faster rate of dissolution of surrounding soluble materials.

As this process continues and more rock dissolves, crevices form, and over time, these widen. The water continues dissolving soluble material it comes into contact with and as centuries pass, so much material dissolves that openings form, which develop into tunnels, and in some cases caves and chambers. If this process continues uninterrupted, actual cave systems develop, which can span across miles. (If the water table drops, the active area of cave formation shows a corresponding drop.)

As can be seen, solution caves eventually become large enough for humans to enter. Some of these caves are mammoth in size, with numerous chambers and galleries.

Mammoth Cave Entrance

A Massive Cave System in Kentucky

Mammoth Cave in Kentucky is a perfect example of this process. It is the longest cave system the world, with approximately 405 miles of surveyed passageways. Each year more areas are discovered, so this figure changes. The cave system formed in limestone strata capped by a layer of sandstone. Mammoth Cave National Park was established to preserve this impressive cave system.

Mammoth Cave

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Caves Used for Shelter, Habitation, and Storage

Solution caves have been used for centuries by both animals and humans, not only as temporary places to "hole up" but even as places to take up permanent residence.

A cave offered shelter out of the elements and animals frequented them and still do to take refuge from blazing sun or to escape rain and snow. Caves also offered a spot to hide and a place to sleep.

It wasn't much different for humans. Natural forces had already done much of the building work already and primitive humans made use of caves for shelter and in some cases to live in. Large arches and caves were also used to build dwellings in. And In some places, monasteries and temples were built into cave openings.

Caves have been used historically to stash items and in modern times, with their relatively constant temperature, they are used to store cheese and wine.

Caves Offer a Cool Place Out of the Heat

A Cave Offers Shelter Out of the Cold

Used by Hunter-Gatherers

Caves as Permanent Dwellings

In Modern Times

Caves and their potential as places for habitation haven't been overlooked in modern times. Some existing caves have been refurbished and others dug out intentionally to serve as dwellings. These may include modern innovations, such as electricity and running water, and clever use of light portals to concentrate and direct light below. Temperature is fairly constant and a cave home can be energy efficient. Some are used as vacation get-aways and others as permanent residences. Cave homes are in use in various places around the world, most notably in Spain, China, and Turkey.

What forms Below Over Thousands of Years is Truly Awe-Inspiring

This article wouldn't be complete without touching on one of the all-time favorite human activities: that of exploring the incredible formations that result as part of cave formation.

In the darkness and depths of caves around the world, cavers have discovered incredible stone formations known as stalactites, mineral treasures hidden away in an underground world.

In what scientists call a karst environment, caves and subterranean chambers form through the action of moving water and other natural forces, generated by solution of bedrock. This action also contributes to formation of stalactites, cave deposits or cave "decorations" that form over thousands of years.

These cave formations assume fantastical shapes and sizes and have long fired the imagination of cavers and adventurers, eager to explore and answer the question: what treasures are hidden below? These can be truly amazing and are well-worth seeing at least once in a lifetime.

What Are Stalactites and How Do They Form?

Stalactites are secondary mineral deposits known as speleothems. They are jagged cone-shaped formations, assuming varied lengths and sometimes incredible sizes, hanging from the ceilings and walls of limestone caves.

Stalactites form through a chemical reaction between water and limestone. Carbon dioxide in water acts to dissolve limestone.

When a droplet of mineral-laden water falls from the ceiling or walls of a cave, a thin ring of calcite is left in its wake. As each droplet falls, this process is repeated. Over time, as deposits build up, a narrow tube forms. These tubes are known as soda straw stalactites. Soda straws can grow to a good length but they remain narrow, hollow tubes.

When one of these tubes becomes plugged, this opens the way for a larger stalactite to form. How so? Water is forced to run on the outside of the tube, which leads to a build up of deposits on the area of the soda straw. As more calcite is deposited, a larger stalactite forms and assumes the typical conical shape.

Massive Stalactite in Doolin Cave, Ireland

How Long Does it Take and How Big Can Stalactites Get?

The growth rate of a stalactite is estimated to be about 1" (2.5 cm) for every 4000-5000 years.Many years must pass for formation of larger stalactites.

Over time, stalactites may reach impressive lengths, such as the large 20' stalactite hanging in Doolin Cave in Ireland or--what is considered one of the largest stalactites discovered to date--the 27' foot specimen in Jeita's Grotto in Lebanon.

Exploring Doolin Cave

Preserving Ancient Cave Formations for Future Generations

Because these remarkable speleothems take so long to form, efforts are underway in some karst areas to protect stalactite cave formations for future generations

An Amazing Underground World

A Remarkable Display

Limestone caves are solutional and are more likely to contain remarkable displays, formations that hang down like icicles or rise up in ghostly spires or that form into huge rippling sheets resembling strips of bacon. The same water that dissolves the calcite in limestone can deposit the calcite in other areas, creating formations known as speleothems. Cavers who explore limestone caves are treated to soda straws, stalagmites, stalactites, draperies, boxwork formations and more, and in varying hues and shades.

* In some cases, oil-eating microorganisms have produced hydrogen sulfide that rises up and mixes with ground water producing sulfuric acid. This sulfuric acid dissolves the limestone and forms caves.

Just Made for Exploring

Caves Appeal to Modern Adventurers

Modern-day cavers enjoy testing their skills and strengths in caves and caverns around the world. Whether found along a seashore, or discovered in the desert, or in a mountainous karst environment, caves hold intrigue and mystery and beg exploration with so much waiting below the surface.

Sources

Sources:

1. P. M. Pedley, M. Rogerson, Tufas and Speleothems: Unravelling the Microbial and Physical Controls, Geological Society of London, 2010
2. Tony Waltham, Great Caves of the World, Firefly Books, 2008
3. Emil Silvestru, The Cave Book, Master Books, 2008
4. Arthur N. Palmer, Cave Geology, Cave Books, 2007
5. Ford, D, Trevor, Limestones and Caves of Whales, Cambridge University Press, June 2, 2011
6. Silvestru, Emil, The Cave Book, Master Books, April 30, 2008
7. Waltham Tony, Great Caves of the World, Firefly Books, October 10, 2008
8. Palmer, Arthur N., Cave Geology, CAVE BOOKS, July 1, 2007
9. Davis, R.V., Limestone Caves, Dalesman Publishing Co Ltd, July 1978

Further Reading:

Burnham, Robert, Caves, Cliffs and Canyons, Discovery Communications

• Cody Caves – One of B.C.s Best-Known Cave Systems
  Ancient calcite formations and a network of limestone tunnels make Cody Caves one the best caving sites in the B.C. back country.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2013 Athlyn Green

Have you ever gone caving?

Athlyn Green (author) from West Kootenays on May 03, 2017:

Yes, they are very intriguing. We have no idea, up on the surface, what may be below our feet.

Devika Primić from Dubrovnik, Croatia on March 22, 2013:

When I see a cave I ma always curious about what its like on the inside so mysterious Most interesting facts here about cave formation..