CAVE FORMATION AND GEOLOGY

Basic Cave Geology for Elementary

Where Do Caves Come From?
In Caves are found a kind of rock called dolomite. It is similar to limestone. Like limestone, dolomite is formed at the bottom of the sea. Later on, forces from inside the earth pushed up the sea bottom to make the mountains. These forces, pushing up on the rock layers, cracked the dolomite, much like a baseball hitting a window cracks the glass. These cracks are called joints. This was the very start of cave forming, and it happened just as the dinosaurs started to roam the Earth.
As rainwater fell on the ground, it picked up a small amount of acid from the rotting leaves. This acid, called carbonic acid, is the same thing that gives soda pop its fizz. This acidic water can dissolve holes in dolomite. Below the water table, the rock was filled with this acidic water. Between the layers of rock and inside the joints, the water slowly dissolved away the rock. This made a large water-filled space. As the Current River cut its river valley, it cut down through the rock layers until it opened up the cave. This let the water out and gave us an air-filled cave.
How Does Water Move Underground?
Water from rainfall still moves into the cave today. A small amount seeps through the rock. This seepage gets filtered as it comes down. It is clear, but not always pure water. Most water that enters the cave comes down through the joints, which connect the cave with the surface. Where there are many joints, sinkholes can form on the surface. Sinkholes act like funnels, collecting rain water from the surface and funneling it into the cave. At some caves, joints leading down from sinkholes have become so big that people can enter the cave through the sinkholes.
Sometimes, a cave can pirate water from a surface stream. Just as a pirate took treasure away from someone else, a cave may take water away from a surface stream. If a stream crosses a joint, water may flow down the joint and into the cave. On the surface, water may be flowing down the stream, and then just disappear. This is called a losing stream. Like sinkholes, a losing stream usually means that there is a cave nearby.
All of this water that enters the cave has to go somewhere. It is no surprise that many caves have springs flowing out of them. Caves are not cut off from the rest of the world. Many have a constant flow of water moving in and out of the cave all of the time. This water carries the clay, which becomes cave mud. This is natural. Unfortunately, people have often used sinkholes for trash dumps. This means that some caves get lots of junk in them. This is bad for the people and animals that depend on the caves for their water.
1. Do you drink spring water or well water that comes from caves?

2. Do you think it is a good idea to fill sinkholes with garbage?

3. What can happen if you do?

4. How many ways can water get into caves?

Calcite Deposits or Speleothems
Remember that all this water moving into the cave carries carbonic acid. Just like sugar dissolves in water, the mineral calcite is dissolved out of the rock by the acidic water and carried down into the cave. When the water drips down into the cave, it deposits calcite on the ceiling. Each drop deposits a little ring of calcite, building a long hollow tube. These are called soda straws, because they look like the straws through which you sip a soda. This happens very slowly, often taking 100 years for a straw to grow only one inch. Once one is broken, it takes a long time to grow back.
A soda straw is the beginning of a stalactite. "Stalactite" has a "c" in it, and a stalactite is a calcite deposit that sticks tightly to the ceiling. A soda straw becomes a stalactite when the inside of the tube becomes blocked. Unable to run down the inside, water runs down the outside, depositing calcite and thickening the soda straw. The stalactite continues to grow as long as the water keeps dripping. Water that drips onto the floor of the cave also leaves calcite behind. This builds up into a stalagmite. Stalagmite" has a "g" in it, and a stalagmite is a calcite deposit that grows up from the ground. If a stalagmite gets tall enough, it might reach a stalactite. When a stalactite and a stalagmite grow together, they form a column from floor to ceiling. Stalactites, stalagmites, and columns are called dripstone because they are deposited by dripping water. Flowing water also deposits calcite, making flowstone. A flowing stream of water can even build dams of flowstone across itself. These are called rimstone dams. Scientists call all of these calcite deposits "speleothems" from Greek words meaning cave rock.

CAVE ECOLOGY

Surface / Subsurface Relationships:
Caves and the land in which they are located are closely tied together. What happens on the surface can affect the subsurface including groundwater and caves.
Groundwater pollution in cave country is a serious problem. It is often more serious than surface water pollution.
Several types of groundwater pollution occur frequently. The most common form of groundwater pollution is human waste (sewage), followed by industrial and hazardous waste. All too commonly, poorly planned sewage systems (such as septic field systems) contaminate nearby wells and springs. Entire towns may contaminate karst groundwater systems if they discharge waste water to surface streams which sink into the ground and feed groundwater supplies. Whatever the source, groundwater pollution is the result. The key to preventing these problems is sound planning which places major emphasis on the protection of groundwater quality.
If sewage enters karst groundwater systems, it can seriously deplete the amount of oxygen dissolved in the water. Without this oxygen, aquatic life will die of suffocation. When serious oxygen depletion occurs, the underground waters exude offensive odors.
Industrial waste includes everything from chemical and gasoline spills to landfills to the disposal of hazardous and radioactive wastes. The location of industrial plants is important since many factories use chemicals and other materials which can seriously degrade water quality. Factories must have good waste disposal facilities.
Gasoline and other petroleum products are very familiar to all of us. However, many of these products are very serious water pollutants. Leaking underground fuel storage tanks have ruined thousands of wells. Gasoline can readily follow the same underground routes as water. Imagine what would happen if gasoline were spilled in a sinkhole. Unfortunately, it is almost impossible to remove all of the gasoline once it enters the groundwater system.
With the nation's growth and with changes in technology have come exotic wastes. Many of these wastes are hazardous, and many of the wastes present extremely difficult disposal problems. Hazardous wastes can create particularly serious groundwater pollution problems in karst areas.
Even the disposal of common trash and garbage creates serious problems in karst areas. We generate about 1 kilo of solid waste per person per day. At present, much of this waste goes to landfills. In karst areas, substantial volumes of water commonly move through the trash and create a liquid called landfill leachate. These leachates routinely contain large concentrations of heavy metals, chemicals and toxic materials. Furthermore, landfill leachates have a tremendous demand for oxygen. When landfill leachates mix with clean groundwater supplies, they often produce septic springs and wells. Septic waters kill aquatic life and cause terrible odors.
City sewers can also cause problems for groundwater in karst areas if the sewers leak. (and they often do leak!) Sinkhole development and land subsidence are common processes in karst areas, and these processes can crack sewer lines or separate connections in the lines. Much of the sewage from the sewer lines discharges into springs.
What can we do about all of these problems? First, everyone needs to understand that wastes from our use on the surface can easily enter karst groundwater systems. Creating pollution problems is not a benefit for anyone.
Factories must be located where they are not likely to cause serious groundwater pollution problems. For example, we should avoid locations in areas with numerous sinkholes.
The storage of gasoline and other fuels must be done very carefully. Many of the newer fuel storage tanks are designed so that they are less likely to leak and so that leaks can be more easily detected. When leaks and spills do occur, clean-up efforts must begin quickly.
Many city sewers are very old and have leakage problems. These sewers need to be replaced. Sometimes old sewers can be repaired by inserting new plastic pipes inside the old sewer lines. New sewers need to be constructed of materials which can better withstand the effects of sinkhole collapse and land subsidence. When new sinkholes develop along this sewer line, this new pipe will stretch across the holes rather than break and dump sewage into the groundwater system.
Sinkholes
A good way to understand some of the relationships between the surface and the subsurface in cave areas is to discuss sinkholes. A sinkhole is a depression in the earth's surface with subsurface drainage. Sinkholes occur because solution has dissolved out a drainage network in the rock through which substantial quantities of water can pass from the surface into the subsurface.
Sinkholes connect with the underground stream system in the area. Soil, organic debris, and pollutants move underground from sinkholes during rainstorms. These materials are transported through the underground stream system (which of course passes through caves), and finally reappear on the surface again at springs.
A sinkhole is a portion of the underground stream system. A sinkhole relates to the underground stream in much the same way as a surface gully relates to a surface stream system. If we are to protect the quality of water in surface streams, we must protect the quality of water in gullies. Similarly, if we are to protect the quality of water in underground streams and springs, we must protect the quality of water entering sinkholes.
Some people even dump garbage in sinkholes! Can you think of a worse place to put your garbage?