Green River at St. Louis EarthCache
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The Geen River at Mammoth Cave National Park
NOTE: These geological features of the Green River were observed and documented during a float trip which launched at Dennison Ferry (parking coordinates below) and terminated at the Green River Ferry 7.5 river miles downstream. While these areas may be reached on foot, they would easily be rated a 4.5 terrain. A canoe or other floatable is highly recommended. This Earthcache listed with permission from Mammoth Cave National Park management and staff.
Please read and follow MCNP Boating/Camping Rules and Regulations HERE!
White Nose Syndrome (WNS) is killing the bats. Be aware of it by reading THIS!
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St. Louis Limestone, 300 Million Years Old
The posted coordinates will bring you to an exposed St. Louis limestone strata. This is the deepest and oldest of the limestones found at Mammoth Cave National Park.
Limestone labyrinth
Mammoth Cave developed in thick Mississippian-aged limestone strata capped by a layer of sandstone, making the system remarkably stable. It is known to include more than 360 miles of passageway. Mammoth Cave National Park was established to preserve the cave system.
The upper sandstone member is known as the Big Clifty Sandstone: thin, sparse layers of limestone interspersed within the sandstones give rise to an epikarstic zone, in which tiny conduits (cave passages too small to enter) are dissolved by the natural acidity of groundwater. The epikarstic zone concentrates local flows of runoff into high-elevation springs which emerge at the edges of ridges. The resurgent water from these springs typically flows briefly on the surface before sinking underground again at elevation of the contact between the sandstone caprock and the underlying massive limestones. It is in these underlying massive limestone layers that the human-explorable caves of the region have naturally developed.
The limestone layers of the stratigraphic column beneath the Big Clifty, in increasing order of depth below the ridgetops, are the Girkin Formation, the St. Genevieve Limestone, and the St. Louis Limestone.
The upper sandstone caprock is relatively hard for water to penetrate: the exceptions are where vertical cracks occur. This protective role means that many of the older, upper passages of the cave system are very dry, with no stalactites, stalagmites, or other formations which require flowing or dripping water to develop.
However, the sandstone caprock layer has been dissolved and eroded at many locations within the park, such as the Frozen Niagara room. The "contact" between limestone and sandstone can be found by hiking from the valley bottoms to the ridgetops: typically, as one approaches the top of a ridge, one sees the outcrops of exposed rock change in composition from limestone to sandstone at a well-defined elevation.
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LEFT: ARF! St. Louis strata CENTER: Limestone Close-up RIGHT:Locationless Shot
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Post a photo and share your visit!
Additionally, to demonstrate the educational value of this site, please email the answers to the following questions to ARF!.
1. What are the three layers of limestone named?
2. How old is the St. Louis limestone layer?
3. How thick is the visible layer of limestone seen at the posted coordinates?
Please email your answers first, then LOG THE FIND. Do not wait on a reply from me. FINDs which do not meet logging requirements will be removed.
Earthcaching: Leave No Trace!
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This Earthcache listed with permission of Mammoth Cave and The National Park Service.
Please read and follow MCNP Boating/Camping Rules and Regulations HERE!
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