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Warm Mineral Springs (spring)
The Warm Mineral Springs is a water-filled sinkhole located in North Port, Florida, a mile north of U.S. 41. The primary water supply is a spring vent deep beneath the pool's water surface. Warm Mineral Springs is the only warm water mineral spring in the State of Florida. It is an important geological and archaeological site containing Native American remnants. It functioned as a small natural spa since the 1960s. People travel from all over the world to soak in the mineral-rich waters. The waters are believed to have extraordinary healing powers and some believe it was the fountain of youth sought by Ponce de Leon. It was added to the U.S. National Register of Historic Places on November 28, 1977. The springs re-opened for swimming only on April 12, 2014.
==Geology==
Warm Mineral Springs is a sinkhole formed in carbonate rock by the collapse of the roof of a cavern 30,000 years ago. The land surrounding the sinkhole is flat, and about above mean sea level. The circular opening of the sinkhole at the current water level is across. The sinkhole is deep, and is shaped roughly like an hourglass. The opening narrows to across a few meters below the surface of the water. About below the surface the opening widens for a short space, forming a ledge under an overhang. The opening narrows to across at below the surface, and then opens up again, reaching across at the bottom of the sinkhole. Debris from the collapsed roof and sides of the sink, and other material that has fallen into the sink, forms a large cone at the bottom, rising to below the surface of the water.〔Rupert:1〕
The environment in Florida during the Pleistocene period was much different than today. Due to the enormous amount of water frozen in ice sheets during the last glacial period, the sea level was at least lower than it is today. Florida had about twice the land area of today, its water table was much lower, and its climate was cooler and much drier. There were few running rivers or springs in the part of Florida that is now above sea level. The few water sources in the interior of Florida were rain-fed lakes and water holes perched on relatively impervious deposits of marl and deep sinkholes partially filled by springs, such as Warm Mineral Springs. The water level in the sinkhole 12,000 years ago was about lower that it is today. Dripstone (stalactites and stalagmites) has formed on the walls of Warm Mineral Springs down to about below the present level of the water, indicating that the water level in the sinkhole was at least low long enough for the dripstone to form.〔Milanich:38-40〕〔Rupert:2〕〔Cockrell:64〕
Although there are many small freshwater springs in the walls of the sinkhole, the primary source is a vent below the surface of the water which discharges an estimated a day of warm [] mineralized water. The water has a high content of dissolved chloride (1,600 to 1,700 milligrams per liter [mg/l]) and hydrogen sulfide (9,200 to 9,600 mg/l), and essentially no dissolved oxygen. The source of the water is uncertain. The water enters the sinkhole at the level from a conduit that extends with several turns to a point from the entrance and below the surface of the water. The conduit has an elliptical shape, about high by wide, for much of its length. At the far end the conduit opens up into two small caverns. Most of the flow appears to enter through the floor of the last cavern. Between and a day overflows from the sinkhole.〔Rupert:3-5〕〔Cockrell:63〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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