Geology:
Sinkholes/Karst Caves are common in Tennessee & Georgia where the rock below much of the surface of the land is limestone. As rainwater seeps down into the earth's surface and comes into contact with limestone, chemical reactions cause the limestone to slowly dissolve. As water continues to flow through holes that were created as the limestone dissolved, the holes become larger. Some small holes eventually become caves.
Generally, there are three ways caves are made.
1) Some caves are found in coastline cliffs and have been chipped away by the relentless pounding of waves.
2) Other caves have formed where the outer surface of a lava tube has cooled and hardened and the inside of the molten rock has drained away. Caves can even form inside glaciers where the meltwater carves tunnels to start its long journey to the sea.
3) Most caves form in karst, which is composed of limestone, dolomite, and gypsum rocks which slowly dissolve in presence of water that is slightly acidic. As it falls to the ground, rain mixes with carbon dioxide (CO2)in the atmosphere, then picks up more CO2 while seeping into the soil. This resulting weak acidic solution dissolves calcite, the main mineral of karst rocks. As the acidic water percolates down into the Earth through fractures and cracks in the rock, it creates a network of passages much like an underground plumbing system. As more water seeps down, the passages widen. This allows even more water to flow through the passages, and eventually some of them become large enough to earn the distinction of cave. It takes vast numbers of years for these so-called “solutional caves” to widen large enough to hold a human. The water continues its downward/inward journey through the Earth until it reaches a level at which the rocks are completely saturated with water. In these areas, masses of water slosh to and fro on a continual basis, which explains why many underground caverns are nearly horizontal.
So what makes this Karst unique?
First, its size. We are on the very edge of the area where karst topography tends to be.
Second, the volume of water in the ponds shows that the sinkhole has been in existance for a long time and that sinkholes across the Cohutta Fish Hatchery Park have contributed to the size of the ponds and thus the success of the hatchery program.
Finally, the clarity of the water (thanks to the GIANT FILTER that this karst is, has allowed Lake Sturgeon to be reintroduced to Northeast Georgia.
The Experiment (for logging requirements 4, 5)
MATERIALS: balance plastic cup (clear) - 9 oz size, one egg in shell (raw) vinegar paper cup (unwaxed), one water (distilled)
PROCEDURE: 1. Label the plastic cup “vinegar” and the unwaxed paper cup “water.”
2. Place the egg carefully into the plastic cup. (The results will be even more dramatic if you "blow out the contents of the egg" then reseal the ends)
3. Pour vinegar over the egg until the egg is covered.
4. Fill the paper cup about half full with water and place it on top of the egg to keep the egg submerged under the vinegar for five days, then make observations (logging req #4, 5).
DEFINITIONS:
KARST -- "An area of irregular limestone in which erosion has produced fissures, sinkholes, underground streams, and caverns." In this region it often refers to a geographic area with soluble rock, like limestone, underneath it. Karst is characterized by sinkholes, caves and an underground drainage system. The region that extends from It is interesting to note that "Karst" is a German term and refers originally to a location in Germany called "Karst", a limestone plateau near Trieste.
SINKHOLES -- (also called "sinks"), are the characteristic landform of karst. Most sinks, known as "solution sinkholes," form as the limestone dissolves, creating sunken areas in the land surface. Other sinks, known as "collapse sinkholes," form when caves collapse and suddenly drop a portion of the land surface above. The outer edges of sinkholes are normally round or oval, and their bottoms are either bowl or funnel shaped. When water drains into a sinkhole, it works like a funnel to feed the water into caves and underground streams below. Litter and pollutants that are in the water are also carried underground.
LOGGING REQUIREMENTS
1. Please list the GC39TQZ and earthcache name as well as the # of people in your group.
2. Estimate the size of the sinkhole karst that you are standing in. You may be precise by defining some waypoints on the edge of the sinkhole.
3. Identify what is causing the sinkhole. Approximately how far away is the sink from the causative feature?
4. (From home science experiment below) --
a. What was the overall change to the egg? to the cup?
b. what "geological" (aka chemical) changes did you observe?
c. What acted as the calcium carbonate? As the 'weak acid' in your experiement?
5. Compare/contrast the similarities and differences you observed with the experiment and the KARST CAVE you observed at GZ.
REFERENCES:
- The Free Dictionary -- http://www.thefreedictionary.com/karst http://www.southeastwaterforum.org/files/nega2007web.pdf
- Geology of Eastern North America. David . Roberts. Peterson Field Guides series. Science Textbooks 7th grade.