The geology of caves
How did that hole get in the ground anyway?
Karst is an area characterized by soluble rocks, resulting in sink holes, ravines and underground streams. Major karst regions are found in China, states like Pennsylvania, Kentucky, Florida, and Texas in the United States, Puerto Rico, and the Dalmatian Coast along the Adriatic Sea in Italy and Slovenia. The Dalmatian Coast is where we get the name Karst, the area of a limestone plateau north of Trieste. The Plateau normally marks the boundary between ethnic Italians and Slovenes.
Caves have appealed to explorers since the dawn of man. For example, the caves near Lascaux, France are renowned for the Stone Age art that graces their walls. Limestone, marble (which is really metamorphized limestone), gypsum, and salt are all soluble rocks. When they dissolve and slowly waste away because of groundwater or underground rivers, caves form. Carlsbad Caverns in New Mexico, Mammoth Cave in Kentucky, and the Lascaux caves are just a few examples of the many caves tht dot the landscape of Earth.
Photo credit: NeilsPhotography on Flickr
Duino, Karst Plateau, Italy
Stalactites and stalagmites
What's the difference anyway?
According to experts, a stalactite, not the common form stalagmite, is generally made of calcite and formed by dripping water and hangs from the roof of a cave. They form when water (from rain or snow or melting ice) drips through the cave ceiling, becomes slightly acidic and reacts with the limestone to form calcite drips. Stalactite is derived from the Greek word for dripping, stalaktos. They are the most common form of speleotherm. Wait, speleotherm, what's that? That's the general term for all cave mineral deposits.
A stalagmite is the speleotherm that forms upward from the cave floor, the complement of a stalactite. They form when drip water that is still saturated with calcite hits the floor. Especially massive stalagmites are found in Carlsbad Caverns, New Mexico. The word stalagmite also comes from Greek - drip, stalagma.
A third kind of speleotherm you may have seen are cave flowers. They are usually made of gypsum, a soft mineral. A good analogy is squeezing cake icing through a decorator's tip to make flowers or lines or leaves. Gypsum is thought to be squeezed through holes in the cave walls and ceilings to form spectacular flowers. Excellent examples of cave flowers are found in Mammoth Cave in Kentucky.
Photo credit: Kurt Thomas Hunt on Flickr
Make your own cave
Ok, just a model of one
This is adapted from Making Connections: a Curriculum and Activity Guide to Mammoth Cave National Park.
What you need:
- modeling clay
- small clear plastic container
- 3-8 sugar cubes
- an eyedropper
- a toothpick
- some water
What you do:
- Form a flat pancake shape with the clay
- Carefull lay the clay in the container so that part of your pancake fills the bottom. Drape the extra clay up the side and over the edge of the container.
- Place 3-8 sugar cubes on the clay in the bottom of the container. The sugar cubes represent the soluble rocks, like limestone.
- Fold the excess clay over the top of the sugar cubes, pressing to seal the edges in a few places.
- Poke a few holes in the top layer of clay. These are equivalent to the places where rain or snow can drip through to the ceiling of the cave.
- Using the eyedropper, drip a little water onto the cave. This is the rainwater.
- Watch what happens to your "cave" through the side of your clear container. Some of the sugar cubes will dissolve and form an interesting internal structure in your "cave".
Caves are fragile
Please protect them
Caves and other karst environments are extremely fragile places. Agriculture, urban development, waste disposal, and even tourism can destroy caves and the fragile lifeforms that live in them.
For example, since 2006 white nose syndrome has been seen in bats in the eastern US. The fungus Geomyces destructans infects muzzles, noses, ears, and wings. When bat colonies are infected with this fungus, death increases dramatically. Research suggests that the fungus may be transmitted from bat to bat, and as an unwanted hitchhiker upon people, their clothing, and gear. As a result of WNS, many caves, including Mammoth Cave in KY, are trying to protect bats from this nasty fungus. People are asked to wear different shoes than they've worn exploring other caves, so they don't accidentally bring Geomyces destructans to the bats who call Mammoth Cave home. Visitors also walk across disenfectant solution when leaving the cave. Hopefully, these measures will help stop the spread of WNS!
The first step in preserving karst landscapes is education. If you have the opportunity to visit a tourist cave, go and learn more about caves and karst firsthand. You'll already know about cave formation, stalactites, stalagmites, cave flowers, and some of the interesting creatures that live in caves.
Photo credit: U.S. Fish and Wildlife Service - Northeast Region