Lake Jackson Earthcache EarthCache
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The Lake Jackson Earthcache is located in Florala State Park. The park’s hours are 7 a.m. to sundown daily. The park offers many activities such as swimming, paddleboat rentals, fishing and picnicking. A modern lakeside campground is available. Water skiing and personal watercraft are also allowed. Posted coordinates are for the lake itself. Several parking coordinates are provided and the earthcache can be viewed anywhere around the shore of the lake. 
Lake Jackson is a 408 acre natural lake. The lake straddles the Alabama-Florida line with 51% lying in Alabama and 49% lying in Florida. It contains about 1.58 billion gallons of water. Most of the lake bottom lies 12-14 feet below the surface but depths reach up to 28 feet in areas. Lake Jackson is unique in the State of Alabama and it is thought to be the largest natural sinkhole in the state. The stratigraphic and structural character of the geology underlying Lake Jackson gives us clues to its formation (fig. 2). Normal faulting of the Chickasawhay and Marianna Limestone found in this area, created conduits for the infiltration of water (fig. 2 frame 2). This water dissolved the limestone forming a solution cavity. Over time a large cavity system developed underneath residuum overburden (fig. 2 frame 3). Eventually, the overburden collapsed forming a sinkhole at least 1 mile in diameter (fig. 2 frame 4). As surface water drained into the sinkhole it transported large volumes of sand, silt and clay. Over time the sinkhole filled with sediment and eventually held water to form the configuration of Lake Jackson (fig.2 frame 5). 
Lake Jackson is primarily recharged from rainfall. Some recharge comes from overland or sheet runoff from the surrounding land area. There are no streams or springs recharging the lake. This area of the state receives about 60 inches of rainfall annually. Of this value about 23 inches is lost to evaporation. This leaves a potential rainfall recharge value of 37 inches. About 21.6 inches of rainfall is thought to runoff into the lake. An acre inch of water is equal to about 27,154 gallons of water. Due to its small surface recharge area, the lake is in a delicate balance. It remains stable during periods of near normal rainfall. During periods of extended drought, or if water were to be withdrawn from the lake for off-site uses, the water level would decline rapidly. For this reason, the lake is used for recreation and not as a suitable source of water for off-site use.
To receive credit for this earthcache email me the following:
1. Send me the coordinates from where you viewed the lake and estimate the distance to the opposite side of the lake.
2. Given the delicate balance in which this lake exists, did you see signs that the lake was in a period of adequate recharge or not.
3. Using the values in the cache description calculate the recharge value due to rainfall (multiplying inches of rainfall x gallons per inch x acres of lake surface). You may ignore the runoff value. You may express your answer in either gallons per year or gallons per day.
source: http://portal.gsa.state.al.us/download/SGAP/Choc%20Pea/Lake%20Jackson/Lake%20Jackson%20Report%20PDF.pdf
Additional Hints
(Decrypt)
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