This Earthcache is located in Charleston Falls Preserve. Parking location is included as waypoint. The initial path is hard packed gravel, about 0.4 miles long and mostly flat if you take the most direct route. There are plenty of other trails that will get you there eventually if you want to find some of the physical geocaches hidden throughout the Preserve. Once you get to the top of the falls there is more than one path to the cave. You can go down the stairs and follow that path or go around the rim of the ravine and come at the cache from the north. While you can take either path, you MUST stay on the trails. The park is open from 8 a.m. to sunset every day of the year. The sunset time can be found posted on the sign as you enter the trails as well as on the Park Hours Page. You are not allowed to enter the trails within 25 minutes of sunset. If you bring a flashlight you are allowed to go as far into the cave as far as you can make it. (One of the park district employees told me you can make it 33 feet.)
Charleston Falls is a great example of the kind of erosion you probably think of when you hear that word. Flowing water is a type of physical erosion which we can frequently observe. The effects of another kind of physical erosion (glaciers) can also be observed throughout this part of the country. However, that is not the main kind of erosion you'll be thinking about today.
This cache is all about chemical erosion. To be more specific, it is about the chemical reaction between limestone (calcium carbonate, a base) and carbonic acid. The calcite that makes up this limestone generally comes from long dead marine organisms (such as coral). There is a layer of shale under the limestone which is composed of compacted clays or silts and is less permeable than the limestone. When water absorbs carbon dioxide it increases the acidity by creating more carbonic acid. When the acidic water passes through the limestone it dissolves the calcium carbonate and carries it away. More water, or more acidic water, will increase the rate of dissolution. Eventually enough limestone can be removed from one area and that will result in a cave. Many caves are still filled with water, but this one is above the water table so we can observe it without special gear.
So where does that CO2 come from? Carbon dioxide is released by many natural processes, including you. You are producing CO2 and breathing it out (I hope) while reading this cache listing. In fact, anything that uses aerobic respiration to generate energy produces CO2 as a byproduct. Plants use photosynthesis to convert CO2 into carbohydrates (and release oxygen as a byproduct). After the plants die the decomposition process generally relies on organisms using aerobic respiration to break those carbohydrates back down in to CO2 and water.
To log this cache, e-mail me the answers to the following questions (please do not post answers online):
1. How does the water become acidic? Why does this matter?
2. Compare the floor of the cave with the walls and ceiling. How are they different? Why are they different?
3. (optional) Include a picture of yourself in Charleston Cave in your online log. Try to not show the cave mouth since that would give people the answer to #2.
Bibliography:
1. http://en.wikipedia.org/wiki/Erosion
2. http://www.esi.utexas.edu/outreach/caves/caves.php
3. http://www.miamicountyparks.com/Park.aspx?c=CFP
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