MAMMOTH CAVE
Western Kentucky’s Mammoth Cave is the longest known cave
on Earth, with over 412 miles of passages currently explored &
mapped. If the 2nd & 3rd longest caves in the world were put together
(= Mexico’s White Cave-Two Eyes System & South Dakota’s Jewel Cave),
Mammoth Cave would still beat them out by about 50 miles. In a good year,
5 to 6 miles worth of new Mammoth Cave passages are found and mapped.
Cave mapping has shown that Mammoth Cave passages are less than 1200 feet away
from caves at Fisher Ridge, where 119 miles worth of passages are known.
Mammoth Cave’s total known length will jump to >500 miles if a connection is
made (both sides have “agreed” to not look for a connection, despite what the
Fisher Ridge Cave people and website say). It’s been estimated that, in
total, Mammoth Cave may have between 600 to 1000 miles of passages.
Casual visitors are only allowed access to about 12 miles worth of Mammoth
Cave’s passages.
The name “Mammoth Cave” refers to the immense size of
many of the rooms and passages. The name does not refer to its
world-record length, nor to the early discovery of mammoth fossils here
(actually, fossil proboscidean skeletal remains have been reported from
this locality).
The cave is developed in Middle & Upper
Mississippian limestones. Partial dissolution of these limestones appears
to have started during the late Cenozoic, since at least the Pliocene (the last
~5 million years). Limestone dissolution results from the presence of
slightly acidic groundwater. Groundwater originates as rain, snowmelt, or
runoff. It percolates through joints and bedding planes of the limestones
and slowly dissolves them.
Why is the groundwater slightly acidic?
Rainwater is slightly acidic due to the presence of carbonic acid (H2CO3),
the result of water-atmosphere interactions (H2O + CO2 -->
H2CO3). Once in the ground, water becomes more
acidic by picking up complex organic acids from soils and additional carbonic
acid. Air occupying spaces in soil is enriched in carbon dioxide gas, so
groundwater will end up having more carbonic acid than it did as rain.
Groundwater dissolution has produced
a vast network of passages in Mammoth Cave that vary in height, width, and
cross-section shape. Horizontal cave passages that are wider than they
are tall and have an ~elliptical shape in cross-section view are called tubular
passages. They originally dissolved out at or below the water
table (in the phreatic zone).
Tubular passage showing the classic,
elliptical cross-section shape. This is Cleaveland Avenue in Mammoth
Cave.
Vertical passages, steeply
tilted passages, and tall & narrow, subhorizontal passages generally
dissolved out above the water table. These are known as vadose
passages. One type of vadose passage is the canyon passage, which
is taller than it is wide. Canyon passages form as water downcuts through
limestone while draining toward the water table.
Canyon passage showing the classic,
irregularly narrow & high cross-section shape. This is Boone Avenue
in Mammoth Cave.
The elevation of the water
table in the Mammoth Cave area has been dropping over the past 5 million
years. Currently, the water table in the cave is almost at the same level
as the Green River, the main drainage in the area. So, the lowest
passages of Mammoth Cave are partially to fully flooded. All the passages
above that are dry to mostly dry. The upper dry levels indicate where the
water table used to be. Depending on how one counts “levels”,
Mammoth Cave has 6 or 7 levels (named Levels A to F).
Mammoth Cave, Historic
Entrance (looking SE) - many of the currently-offered cave tours enter
here. The rocks here represent the Beaver Bend Member of the Girkin
Limestone (lower Chesterian Series, lower Upper Mississippian).
Reported lithologies in the Beaver Bend include lime mudstones (micrites;
micritic limestones), some fossiliferous to oolitic wackestones, and lime
mudstones having patches of coarsely-crystalline calcite spar.
It is not certain exactly
when Mammoth Cave was discovered. A story about its 1797 discovery by a
man named Houchins (or Hutchins) is fictional (the park service knows this, but
still tells the story during cave tours). However, Mammoth Cave’s
earliest acknowledgement in available historical records dates to 1797.
Entrance dale to Mammoth
Cave’s Historic Entrance (looking NW) - the cave mouth shown above is
downhill from the park’s visitor center, accessed via this paved path. A
small creek (left side of photo) has carved this little valley. This
creek valley intersected & breached level B of Mammoth Cave (= the 2nd
highest level in the cave system), resulting in the Historic Entrance.
The Green River is ~0.3-0.4 miles further downhill.
Big Clifty Sandstone (looking SW) - the rocks
along the entrance dale (see above photo) are quartzose sandstones of the Big
Clifty Sandstone (Chesterian Stage, lower Upper Mississippian). This is
the “insoluble caprock” unit on Mammoth Cave Ridge. The sandstone has
obvious, well-developed cross-bedding, indicating deposition by a
one-directional current. Large talus blocks of Big Clifty Ss. line most
of the paved path from the visitor center down to the Mammoth Cave Historic
Entrance.
Mammoth Cave, Historic
Entrance (looking NW) - the rocks here are Beaver Bend Member limestones
(Girkin Ls.).
A small waterfall occurs at Mammoth
Cave's Historic Entrance. Water flow is minimal to nonexistant during dry
spells. A mixture of limestone rubble and tree branches litter the floor
of the cave mouth directly below this waterfall (see photo below). Water
does not pond here, but trickles into the cave for a very short distance, then
disappears by downward percolation, helping to enlarge one or more inaccessible
vadose passages.
It is customary to use
fanciful (& sometimes silly or nonsensical) place names in caves. Of
course, none of these names have real meaning in a geologic sense. The
names are still useful, however. The human mind processes information
about objects or places more readily if a name is available. This
phenomenon is referred to by some as “name magic”.
Audubon Avenue &
Rafinesque Hall
Sparks
Avenue & Mammoth Dome
Cleaveland
Avenue
Kentucky
Avenue (= Grand Avenue)
Frozen
Niagara
Echo
River Spring
Sand
Cave
Dripping
Springs Escarpment
Much
of the info. presented here & in the following pages is synthesized from
the following:
Lee, E.F. 1835. Map of the Mammoth Cave,
Accompanied with Notes. 1 sheet.
Bishop, S. 1845. Map of the Explored
Parts of the Mammoth Cave of KY. Louisville. Morton &
Griswold. 1 sheet. [facsimile published 1985]
Bullitt, A.C. 1845. Rambles in the Mammoth Cave
During the Year 1844, by a Visiter. Lousville. Morton &
Griswold. 101 pp. 1 fold-out map. [facsimile published 1985]
Richards, C. 1868. The Mammoth Cave,
pleasures and pains of western travel, uncertainties of railways and
steamboats, a woman's experience under ground, the Mammoth Cave from an
unromantic point of view. The New York Times September 7, 1868. [warning:
article contains anti-male sexist commentary and anti-nature commentary]
Hovey, H.C. 1880. One hundred miles in
Mammoth Cave. Scribner's Monthly Magazine 20: 914-924. [facsimile
published 2000]
Kämper, M. 1908. Map of the Mammoth
Cave, Kentucky. 1 sheet. [facsimile published 1981]
Hovey, H.C. & R.E. Call. 1912. Mammoth
Cave of Kentucky, with an Account of Colossal Cavern, Revised Edition.
Louisville. John P. Morton & Company. 131 pp.
Watson, P.J. (ed.) 1974. Archeology of
the Mammoth Cave Area. New York. Academic Press. 255 pp.
Palmer, A.N. 1981. A Geological Guide
to Mammoth Cave National Park. Teaneck, New Jersey, USA.
Zephyrus Press. 196 pp.
George, A.I. 1990. Effects of the New
Madrid Earthquake (1811-1812) damage to the Mammoth Cave saltpeter works,
Kentucky. Journal of Spelean History 24: 10-12.
George, A.I. & G.A. O'Dell. 1992. The
saltpeter works at Mammoth Cave and the New Madrid Earthquake. The
Filson Club History Quaterly 66: 5-22.
Cave Research Foundation. 1993. Mammoth
Cave System. Dayton. Cave Research Foundation. 1 sheet.
Kennedy, M.C. & P.J. Watson. 1997. The
chronology of early agriculture and intensive mineral mining in the Salts Cave
and Mammoth Cave region, Mammoth Cave National Park, Kentucky. Journal
of Cave and Karst Studies 59: 5-9
Granger, D.E., D. Fabel & A.N. Palmer.
2001. Pliocene-Pleistocene incision of the Green River, Kentucky,
determined from radioactive decay of cosmogenic 26Al and 10Be
in Mammoth Cave sediments. Geological Society of America Bulletin
113: 825-836.
Santucci, V.L., J. Kenworthy & R. Kerbo.
2001. An Inventory of Paleontological Resources Associated with
National Park Service Caves. National Park Service. 50 pp.
Thompson, B. & J. Thompson.
2003. Images of America, Mammoth Cave and the Kentucky Cave
Region. Charleston. Arcadia Publishing. 128 pp.
White, W.B. & E.L. White. 2003. Gypsum
wedging and cavern breakdown: studies in the Mammoth Cave System,
Kentucky. Journal of Cave and Karst Studies 65: 43-52.
Palmer, A.N. 2007. Cave Geology.
Dayton. Cave Research Foundation. 454 pp.
Arthur N. Palmer, pers. comm., 2009 & 2010 &
2011.