Background for Teachers - Cave or Cavern?
Cave or Cavern?
Caverns are just one type of cave. There are five main types of caves:
- SOLUTION CAVES –
- Solution caves are formed in carbonate and sulfate rocks such as limestone, gypsum, dolomite, and marble. These caves are formed by the effects of slow-moving groundwater. Most of the caves in the world are solution caves. EVERYTHING WE'VE TAUGHT THIS MONTH IS BASED ON SOLUTION CAVES.
- LAVA CAVES –
- Lava caves are tubes or tunnels created when exterior lava cools while interior molten lavas continues to flow through.
- SEA CAVES –
- Sea caves are created by the constant pounding action of the water and sand against rocks along the shore.
- GLACIER CAVES –
- Glacier caves are tunnels created through glaciers by melt water excavating through the glacier’s ice. (Ice caves are different – they are found inside lava or solution caves where conditions are such that ice forms and persists year-round.)
- EOLIAN CAVES –
- Eolian caves are found in the desert where it is very dry and are formed when the wind blows sand or silt against rocks over time.
In Texas, we have mostly solution caves. In central-Texas you will find a large number of limestone caves, while in the northern part of Texas you will find gypsum caves.
Check out this image showing the types of caves across the United States. Take note of where the limestone and gypsum caves are in Texas:
When explaining "speleothems" to your students, you'll want to make sure they understand that WATER is a necessary ingredient in their creation. Stress that, without water, a cave could not receive "cavern" designation.
In solution caves the air is often heavy with carbon-dioxide allowing for concentrations of calcite. Calcite is a major constituent of sedimentary rocks such as limestone. When calcite-rich earth and water mixtures cling to the sides of overhangs they create "drapery." Sometimes other minerals make their way into the mix and the resulting formation looks like bacon, hence, these formations can be called...well...you guessed it, "Bacon!"
For some magnificent photos of drapery visit: http://www.goodearthgraphics.com/virtcave/drapery/drapery.html
Stalactites hang from the tops of caves or from other formations and are created by deposits left from slowly dripping water. Those deposits are largely calcium carbonate. It takes hundreds of years for a single stalactite to form since a typical one grows at a rate of only about .0013 inches per year!
Generally speaking, stalactites will be thinner at the tip than stalagmites because of gravity.
Like stalactites, stalagmites are also formed from deposits left by slowly dripping water. The difference is that stalagmites are formed on the floor of the cave. Those deposits are also largely calcium carbonate, but rather than dripping to the tip-top slowly over time, they pile up from the bottom up. They grow at about the same rate as stalactites – about 1 centimeter per 100 years!
Generally speaking, stalagmites will be thicker at the tip than stalactites because of the "piling up" effect and gravity that has the wet deposits rolling down the stalagmite's sides. Stalagmites are usually rounded at the tip.
TRICK FOR REMEMBERING!
The difference between Stalactites and Stalagmites
It can be tough to remember which is which so help your students by teaching them this trick:
Stalactite has 3 "T's" and Stalagmite has 2 "T's"
*** StalacatiTe – has one extra "T" and that stands for TOP
*** That "T" sound sounds for TOP, too!
When a stalactite going down and a stalagmite going up join one another, a column is born. Usually, the dripping continues and thickens the column over time.