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Become an Earthcache Master:
Sinkholes are geological features. They are natural depressions on the land surface that occur in regions containing underground deposits of limestone.
The area of South Carolina where you are currently standing was covered with a shallow, subtropical sea approximately 40 to 50 million years ago. In this sea millions of shelled microscopic and macroscopic animal thrived. When these animals died, their shells and skeletons, which were rich with calcium, settled to the ocean floor forming layers of sediment composed of clays, silt and minerals. Then for millions more years, additional layers of sediment and plant materials were accumulated. Pressure and chemical reactions transformed the sediment into limestone. Later, some of these limestone deposits eroded resulting in the natural occurrence of sinkholes.
A sinkhole typically begins to form when seeping groundwater (which is naturally mildly acidic) or an underground stream very slowly and steadily dissolves the calcium carbonate of limestone, which creates a crevice that expands as time passes. As the limestone continues to be dissolved by the action of the mildly acidic groundwater, these channels eventually expand to form submerged caves and large cavities are formed in the rock. As years pass, the groundwater level may drop, either by human consumption or by natural reasons such as drought, causing the cave to become filled with air. If sufficiently enlarged, the roof of the subterranean cavern may be unable to support the weight of the overlying rock and thin soil causing the roof of the cavern to collapse, thus forming a sinkhole. Limestone deposits are generally covered by layers or sand and clay, but natural outcrops above the surface occasionally occur along river and lake shores, such as the banks of Lake Marion. Sinkholes typically occur in areas where the overlying soil layer is thin. Other factors that determine sinkhole development include the permeability of the limestone, which affects the water table depth and solubility of groundwater, and the depth and thickness of the limestone deposit.
At Santee State Park sinkholes are present and occur in various stages of development, ranging from small underground caves to large open depressions. The Santee Limestone sinks Heritage Trust Site contains an extensive system of sinkholes and underground passages. This site represents one of the most outstanding examples of a sinkhole complex in South Carolina.
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In order to log this earthcache as found you will need to explore both the Santee State Park visitor center and the Sinkhole Pond Nature Trail and answer the following questions.
Your journey for this earthcache begins at the Santee State Park Visitor Center, N 33 33.119, W 80 30.175.
1. Inside the visitor center, you will find a wealth of information about Santee State Park, including information on the limestone and sinkholes. There is a map that shows the Karst areas of the United States. Karst refers to irregular deposits of limestone in which erosion has produced sinkholes, fissures, underground streams and caverns. According to this map, are more karst areas found in the eastern or the western portion of the United States?
2. The visitor center also has information on Life at the Santee Limestone Sinks. The large complex of sinkholes and surrounding hardwoods contain habitat for several unique plant and animal species. Certain plants, called calciphiles, find calcium-bearing limestone soils quite favorable and grow specifically on exposed outcrops of limestone or marl (a friable earthy deposit consisting of clay and calcium carbonate.) The sinks also provide shelter and breeding sites for a variety of animal species such as snakes, frogs and salamanders which play an important part in the environment. Name one mammal and one specific plant species (found on the display inside the visitor center) that are associated with the Santee State Park limestone sinks and limestone outcrops.
3. Limestone was first mined in South Carolina in the 1820s and since that time it has been used in a variety of ways. According to the display inside the visitor center, what are two ways in which limestone is currently utilized? After limestone is removed, along with layers of soil and other rock, by surface mining, what often happens to the previously mined area?
4. On your way into the visitor center, you may have noticed a few large boulders as you walked down the entry path. Did you notice anything unusual about these boulders? Probably not. But, after viewing the displays inside, you should now be able to notice something very special about these boulders. Go back outside and examine them again and tell me what type of what type of rock these boulders consist. Look closely, you should be able to see some evidence of the past. What evidence of the past do you see? (You don’t have to be specific, just a basic answer is all that is required.)
Now it is time to get onto the trail to examine some Santee sinkholes for yourself. Many people could walk near a sinkhole and have no idea that it is more than a hole in the ground. But, not you. Using what you’ve learned already, you should quickly spot sinkholes along the trail. You will find that even though sinkholes are formed in the same manner, that the resulting depression can vary greatly in size, shape and appearance. Your next stop is the Sinkhole Pond Nature Trail. (Remember that the ground in some areas of the trail can be unstable. For your safety, obey the posted signs and do not enter any fenced areas. The fences are there for a reason to protect your safety and preserve the natural sinkholes.) The trail is an easy .5 mile loop trail. The trail begins at N 33° 30.970 W 080° 29.241.
5. Just to the right of the trail head for the Sinkhole Pond Nature Trail you will find a sinkhole within a fenced area. What shape is this sinkhole?
6. In researching sinkholes, I came upon an excerpt from a book, Travels in North America, by Charles Lyell. Lyell was considered the foremost geologist of his day in the 1800s and was an influence on a young Charles Darwin. In this book, Lyell wrote that he was told of a limesink near the Santee River that suddenly opened and into it fell a plough (plow) and the mule pulling it. (Lyell C, Travels in North America.) Near the trail at N 33 30.836, W 80 29.275, you will find a sinkhole. Do you think this sinkhole could have brought down and contained a mule and plough?
7. At the end of the trail (N 33 30.733. W 80 29.423) you will find a Sinkhole Pond. At the time of your visit there should be some water present. Water most often pools only in the lowest portion of the depression. However, during dry periods you may not see a defined pond and during particularly wet periods you may see two ponds. What is the length of this pond? (Just an estimate is fine. You can easily walk along one side of the pond (side closest to the trail) and let your GPSr estimate the footage for you.)
8. Near the end of the trail loop, at N 33 30.956, W 80 29.286, you will discover another sinkhole. You will notice that this sinkhole has been fenced as well. Look closely at the position of the sinkhole compared to the boundary of the fence. Based upon these positions what do you think may have happened to the sinkhole since the fence was erected?
9. Just before you exit the trail, you will see a sign that will summarize all that you have learned. This sign gives diagrams and descriptions of how sinkholes are formed in six simple steps. On this sign you will learn how rainwater becomes acidic. Tell me with what rainwater contacts that makes it become acidic?
A photo of you and your GPSr is always appreciated as added proof of your visit. If you have the ability to take and upload a photo, please do so. If you do not have that ability, please don’t let that keep you from exploring the Santee sinkholes, learning a bit about earth science or logging this earthcache.
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This earthcache is located at Santee State Park and does require an admission fee to enter the park. Currently the fee is $2 adults, $ 1.25 SC seniors and free for age 15 & younger.
The park’s office hours are Monday through Sunday 8:00am to 5:00pm and the days of operation are Monday through Sunday from 6:00am to 10:00pm. For more information on the park, visit the park website at http://www.southcarolinaparks.com/park-finder/state-park/535.asp
I hope you have enjoyed learning about the sinkholes of Santee State Park. Remember to Leave No Trace of your visit, take only memories, knowledge and photos and practice outdoor ethics.
Lyell, Charles. Travels in North America 2 volumes, 1845 (John Murray, London)
Congratulations to mopar73mopar and aw2008 for being FTF.
As of April 11, 2009, I am adding this note to all of my earthcache listings. I request that you email the answers to me on the same day that you log your “found it” log. (This does not have to be the day you visit, just the day you log the find on the computer.) I also request that you do not log a “found it” log unless you have actually visited the site of the earthcache and sent the answers to me. As much as I hate to do so, I will delete logs of finders who have not provided the appropriate answers.
Additional Hints
(Decrypt)
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