The tour proceeds through Broadway in what was originally the upstream direction for the underground water (Figure 16). Here the sediment has been partly removed through lower-level passages by stream action, so the floor descends into the Ste. Genevieve Limestone as far as the Joppa Member, while the ceiling remains at the same level as in the Rotunda. Some sediment has also been moved around by saltpeter miners.

Figure 16: Part of the Main Cave beyond the Historic Route (see Figure 15). This is the upstream end of Broadway (more specifically, the lower half of Broadway).

At point #3, at the "Methodist Church," about 1000 feet (300 m) beyond the Rotunda, the passage branches into two separate levels, each only half as high as Broadway. The upper level disappears into a pile of breakdown (collapse material), and the lower one continues straight ahead as the "Main Cave."

What is the relationship between the two levels? Continuing on to point #4, we see the upper level come in again, cross over the Main Cave, and disappear in the former upstream direction as Gothic Avenue, a tube about 15-20 feet (4.66 m) high. The great ceiling height of Broadway represents the combined height of the two branches.

The trail continues through the Main Cave for a short distance to the Giant's Coffin, an enormous breakdown block. It then exits to the right through a narrow canyon (Dante's Gateway), which once drained water from the Main Cave to the lower levels. The canyon descends through the light-gray Joppa and Karnak Members to the Wooden Bowl Room. Named for one of the prehistoric Indian artifacts found here, the Wooden Bowl Room is located at level C, (550 feet = 168 m; see Figure 3) where several passages intersect one another. The thick-bedded Karnak Member forms the flat ceiling of this wide, low room.

A steep descent through the upper Fredonia Member leads to the tour's first tubular passage, a lower loop of level C called Black Snake Avenue (location #5 on the map; see Figure 17). This passage is located in the thick, crystalline F3 unit. In this part of the cave the F3 unit contains a yellow dolomite bed, which forms the smooth passage floor.

At one point there are fissures extending into the ceiling. Many geologists consider such features to have formed when water descending through the fissure mixed with water in Black Snake Avenue. Groundwater is able to dissolve more limestone if it has a high level of carbon dioxide. Most carbon dioxide is contributed by the soil as the water seeps through it. The mixture of two saturated solutions having different carbon dioxide contents can produce an undersaturated solution capable of dissolving more limestone.

Figure 17: Black Snake Avenue, a tube at level C. This is the upstream end of Pensico Avenue, shown in Figure 10. Here it occupies two closely spaced tiers.

Is this a feasible explanation for the ceiling fissures? What are a few flaws in this argument? It is more likely that the fissures were formed by periodic flooding, back when the passage was at or near the water table. Each flood would deliver water rapidly from the surface, water that was highly capable of dissolving limestone. Filling of the passage under hydraulic pressure would force this aggressive water into all cracks in the surrounding cave walls and ceilings, enlarging the cracks into fissures. The water would then drain out as the flood subsided.

Just beyond the fissures, the contacts between several limestone beds have been dissolved inward into the passage walls to form a tiny maze of tubes. Below these tubes the walls are deeply grooved by water that apparently flowed out of the tubes. Do these features clarify the origin of the fissures in the ceiling?

Note the excellent solutional hollows (scallops) in the nearby floors of the passage. The direction of flow is shown by their asymmetry (as in sand dunes). The steep side of each hollow is on the former upstream side. Our tour is moving in the direction of former flow. Also, the average length of the scallops can be used to estimate the former flow velocity. Measure the average length of the well-developed scallops in centimeters and divide that number into 275 to get the former flow velocity in centimeters per second. For example, scallops 5 cm in length would indicate a local flow velocity of about 55 cm/sec. Obviously this is approximate, because the flow velocities vary with time. These probably represent the high-flow velocities that last enlarged the passage.

Black Snake Avenue passes beneath the Main Cave and extends along the northeastern edge of Mammoth Cave Ridge, where a great deal of water enters from the nearby limestone-floored valley. This water forms many impressive vertical shafts that intersect the otherwise dry passages in this part of the cave. While the tubes at this level were forming, they lay close to the level of the Green river, but they are now located far above the river. Water drains from the surface through narrow canyons into the tops of vertical shafts and flows out through the shaft drains to the lowest and still active passages near the level of the Green River.

A typical shaft is Bottomless Pit, which yawns to a depth of about 100 feet (30 m) below the level of the trail and rises 60 feet (18 m) above. A bridge now spans the chasm, but before this addition, in order to pass this point, early explorers were treated to the unforgettable experience of crawling around the pit on a narrow ledge.

The tube continues as Pensico Avenue, but the tour follows a branch to the left and descends a short flight of stairs through an opening called Scotchman's Trap. This opening leads to several low, wide passages in the dolomitic limestone of unit F2, at level D (500 feet = 152 m). The trail branches into a narrow canyon called Fat Man's Misery. This passage is shaped like a keyhole, wide at the top but quickly narrowing to little more than a foot toward the floor. It is too low to walk through without stooping. Although it is not tight by explorers' standards, this is as close a view of the limestone as most visitors wish.

Just as Fat Man's Misery looks as though it is going to pinch down to an impasse, it opens into a spacious tubular passage called Great Relief Hall (location #6 on map). This originally received its name from the relief that visitors presumably felt when emerging from the narrow canyon. Its name took on a new meaning when restrooms were installed in the Hall.

Great Relief Hall is also at level D (Figure 17). The ceiling is formed by the base of the thick-bedded, coarse-grained unit F3. Here the rock contains many joints enlarged upward by solution, as well as irregular chert nodules that protrude downward from the ceiling because they are so resistant to solution. The lower walls of this passage have a moth-eaten appearance caused by solution pockets in a dolomite bed in unit F2. This distinctive rock unit is seen at two other places on this tour. Can you spot them?

Figure 17: Great Relief Hall, at an elevation of 500 feet, is a typical tube at level D. In the ceiling, note the solutionally enlarged fissures and the "dikes" of resistant chert (flint) protruding from the limestone. Near the floor is a bed of dolomite that has a distinctive pock-marked texture.

The tubular passage descends about 20-30 feet into River Hall (location #7). This descent was originally part of a loop that the passage took below the water table. It is still level D, and drained to a former spring at the 500-foot elevation; but here its elevation is about 470 feet (143 m). The contact between the Ste. Genevieve Limestone and the underlying St. Louis Limestone is not very distinct in the Mammoth Cave area. It appears as a prominent contact between beds at the level of several old bowl-shaped electric lights. The upper St. Louis does not contain the bedded chert that is so typical lower down in the formation.

The opening at the lower end of River Hall leads to River Styx and Echo River, which are parts of one of the largest stream passages in the cave. These river passages are located at the same level as the present-day Green River (about 425 ft = 130 m above sea level).

Large scallops in the ceiling of River Hall indicate that the original water flow came from River Styx, joined the water from Great Relief Hall, and continued straight ahead in a passage now blocked with breakdown.

The passages at river level therefore developed at the same time as River Hall, which is the same age as Great Relief Hall. Together, these passages span a vertical range of 75 feet (23 m), and yet they all formed when the Green River was at 500 feet. River Hall, River Styx, and Echo River formed below the water table simply because those particular routes were most efficient at transmitting water.

Our tour descends into River Styx. This is the largest passage we have seen since leaving the Main Cave. No wonder it is large --it is still actively enlarging today, and has continued to do so since level D began to form more than a million years ago.

Those who think this explanation is too idealistic should follow the River Styx passage upstream to Echo River and beyond (Figure 18). The passage begins to climb in the upstream direction, still as a tube, but then as it passes above an elevation of 500 feet it changes to a canyon passage. Part of the canyon is shown in Figure 8. This was the former water table when the river passages first started to form.

Figure 18: The upstream end of Echo River is at exactly the same elevation as the present Green River and is nearly filled with water and sediment.

We return to River Hall and exit through an upper-level passage. On the way out, note the brass markers that indicate levels of recent floods. This entire part of the cave fills with water every couple of decades.

Soon the walls and ceiling draw near and the tour enters Sparks Avenue, a wide, low tube along the Ste. Genevieve/St. Louis contact (location #9 on map). The walls are obscured nearly everywhere by banks of sand and gravel deposited by the stream that once flowed through this passage. The gravel consists of white quartz pebbles weathered out of the Caseyville Formation that once capped Mammoth Cave Ridge (see Figure 6). These pebbles have been instrumental in helping to date the ages of the various cave levels (see page 6).

Large, fissure-like solution pockets occur here and there in the ceiling along joints in the thick-bedded F1 unit. At Leopard's Arch the passage rises abruptly into the F1 unit along a joint, a rare occurrence in Mammoth Cave. Sand on the floor contains cross beds that indicate water movement in the direction we are traveling. So the water that deposited the sand must have flowed upward at the point where the passage jogs into the F1 unit (Figure 19). Wall scallops also show this direction of flow, although their directions are complicated by the many back-eddies that occurred at the sharp bends in the passage.

Sparks Avenue opens into the impressive Mammoth Dome (location #10). This is one of the largest vertical shafts in the cave. It is about 190 feet (58 m) high and extends from the Beaver bend Member of the Girkin Formation through the entire Ste. Genevieve Limestone, and 29 feet (8.8 m) into the St. Louis. Water descends from the top of the shaft as a spray and filters into rocks that choke the bottom of the shaft. This water probably comes from a sinkhole located almost directly above. Several canyons open from the south wall of Mammoth Dome, and it is possible to see, by peering straight up through a haze of descending water drops, a narrow, wiggly canyon at the very top of the dome. The contact between the Ste. Genevieve and the St. Louis can be clearly seen 7 feet (2.1 m) below the floor of the lowest balcony in Mammoth Dome.

A metal staircase leads almost to the top of the dome, giving a spectacular view of almost the entire Ste. Genevieve Limestone. Here the F3 is essentially a single massive bed of crystalline gray limestone. Looming to the left are the Ruins of Karnak, which are monolithic pillars of the Fredonia Member sculpted by descending water.

The flat ceiling above is the base of the thick-bedded Karnak Member. (Early explorers were fond of drawing from antiquity and mythology for their names of cave features. The Ruins of Karnak are named for the ancient ruins near the village of Karnak on the banks of the Nile River. However, except in name, the Ruins of Karnak have no direct connection with the Karnak Member, which was named for the little town of Karnak in southern  Illinois.)

The tour climbs to a final overlook of Mammoth Dome, then doubles back into Little Bat Avenue. This is a tube at level B, which at one time drained water from Audubon Avenue. Little Bat Avenue is located along the contact between the Aux Vases and Joppa Members. The tube suddenly opens into the enormous void of Audubon Avenue, which leads a short distance to the Rotunda. Having completed a long, intricate loop, the tour exits through the Historic Entrance.

Figure 19: Leopard's Arch is a fissure in Sparks Avenue that rises in the downstream direction. Like a hose, water filled it and rose under pressure. The direction of flow is indicated by scallops and by cross-beds in nearby floor sediment (like those in sand dunes).

BIOSPELEOLOGY OF MAMMOTH CAVE: A BRIEFING PAPER

By Rick Olson, Park Ecologist, Mammoth Cave National Park 2003, all photos by author reprinted by permission.

INTRODUCTION

In order to understand the biospeleology of Mammoth Cave, it must be viewed in context of the South-Central Kentucky Karst where there are two historical and four functioning ecosystems. In pre-settlement times, prairie and savanna maintained by fire were prevalent. These ecosystems were converted to agriculture over the past two centuries, but forest, river, and cave ecosystems are relatively intact. Mammoth Cave biota are among the most diverse in the world (Culver et al. 1999), with approximately 130 regularly occurring species roughly divided between troglobites, trolophiles, and trogloxenes (Barr, 1967 Poulson 1992, 1993). Troglobites are fully cave adapted, and cannot survive in surface habitats. Aquatic troglobites are also referred to as stygobites. Troglophiles are species that can complete their life cycle in both cave and surface habitats, and trogloxenes use caves for refuge or may come in to prey upon other species.

INTERCONNECTIONS AND HABITATS

Functionally, since sinking streams and cave streams are tributaries of base-level rivers by way of springs, they are all part of the river continuum, with the important distinction that the middle section is underground. These distinct but connected aquatic ecosystems are energetically supported by in-washed organic debris from the forest and former prairie/savanna ecosystems. Food transport is usually down gradient, but natural back flooding from the river into cave streams is also important.

Cave aquatic habitats can be roughly divided on the basis of water quantity. Ephemeral pools occur in rimstone dams, near terminal breakdowns, in passages rarely flooded, and shafts. These may feed nearby shallow streams tributary to master shaft drains grading into base level streams, which feed springs on the Green River. As the river lowers its channel, cave streams follow and leave dry upper levels.

These upper levels are habitat for the terrestrial cave ecosystem, also dependent upon forest and agricultural land for food. The import of food is mostly accomplished by cave crickets and to a lesser degree woodrats and bats, which feed in the forest, and use caves for refuge where guano accumulates. Crickets also lay eggs in caves, which support a separate community. Raccoons, entering caves to feed on bats and cave crickets, may leave significant quantities of scat. Habitats here are determined by proximity to entrances with variable temperature and humidity, which in turn determines the species leaving guano. Leaf litter falling into entrances, and flood debris deposited on passage surfaces are also locally important to the terrestrial cave ecosystem.

THE BIOTA AND THEIR INTERACTIONS

One prevalent aspect of aquatic life in the Mammoth Cave System is habitat partitioning by similar species within a taxonomic group. Two troglobitic species each of planaria (Sphalloplana percocea and S. buchanani), amphipods (Stygobromus vitreus and S. excilis), isopods (Caecidotea stygia and C. bicrenata), and fish (Typhlichthys subterraneus and Amblyopsis spelaea) occupy upstream and downstream habitats respectively. Troglobites found only in base level streams include a snail (Antroselates spiralis), and the endangered Kentucky Cave Shrimp (Palaemonias ganteri).

The more adaptable cave crayfish Orconectes pellucidus occupies habitats ranging from base level to tiny streams, and can travel out of water if necessary. The troglophilic amphipod Crangonyx packardi, crayfish Cambarus tenebrosus, the sculpin Cottus carolinae, and the springfish Chologaster agassizi often occur in organically rich situations. With the exception of sculpin, fish and crayfish are predators and the remaining species are primarily grazers.

  

Figure 1. The Southern Cavefish at left and the Kentucky Cave Shrimp at right are good examples of fully troglobitic aquatic cave life, otherwise known as stygobites.

  

Figure 2. Note how slender the white eyeless cave adapted (troglobitic) crayfish at left is compared with the robust surface (troglophilic) crayfish at right. This cave crayfish has eggs, which are shown in the middle photo.

Common organisms living within the sediments of Mammoth Cave streams (Whitman 1989) are nematodes (undescribed), copepods (Maraenobiotus, Moraria, Nitocra, and Parastenocaris), tardigrades (Macrobiotus), and oligochaete worms (Aeolosoma). Worm castings and tracks are also visible on mud banks of cave streams, and these organisms are preyed upon by the troglobitic beetles Pseudanophthalmus striatus, P. menetriesi, and Neaphaenops tellkampfi (Kane and Ryan, 1983). This zone is an ecotone between aquatic and terrestrial cave ecosystems. As part of the community dependent upon flood-deposited organic films, the springtails Folsomia candida and Pseudosinella are preyed upon by the troglobitic harvestman Phalangodes armata. Another major ecotone exists at cave entrances where litter from surface vegetation accumulates via gravity and woodrats. Here are found the collembolans Tomocerus, Hypogastrura, Sinella, and Arrhopalites. Predators include the beetle Pseudanophthalmus, and a rhagidid mite (Poulson, 1992).

The cave cricket Hadenoecus subterraneus buries its eggs in sandy passages with moderate moisture in the constant temperature zone (Hubbell and Norton, 1978), and the blind beetle Neaphaenops is especially skilled at finding those eggs. After cave crickets, this beetle has the highest density of any species in Mammoth Cave, and a small community subsists on beetle feces (Poulson 1992, 1993). The springtail Arrhopalites and the dipluran Litocampa are consumers, which are preyed upon by the mite Arctoseius, the spider Anthrobia, and the pseudoscorpion Kleptochthonius. These latter two are in turn preyed upon by Neaphaenops cave beetles.

In addition to eggs, Hadenoecus guano is also important. Crickets feed in surface habitats at night, and return to the cave to roost. Here their guano supports the millipedes Scoterpes and Antriadesmus, the springtails Hypogastrura, Arhopalites, Pseudosinella, Tomocerus, and Lepidocyrtus, plus the bristletail Litocampa, the beetles Ptomophagus hirtus and Batrisodes henroti, the snail Carychium stygius, and the mites Ceratozetes and Belba.

 

Figure 3. Tiny springtails such as these shown at left are prey for several predators including the troglobitic harvestman or daddy longlegs shown at right.

 

Figure 4. The blind cave beetle at left is especially adept at finding the buried eggs of the cave cricket seen in the right photo.

  

Figure 5. The troglobitic millipede, snails, and troglophilic springtail, (left to right) are all consumers of cricket guano.

  

Figure 6. Gray bats (left) were once abundant and are now listed as endangered, Rafinesque's Big Eared bat (center) populations were never large, but are today a matter of concern. The Eastern Pipistrelle bat shown at right is an example of a very adaptable and tolerant species.

Figure 7. Populations of Indiana bats once numbered in the millions within park caves, but today are counted in the low thousands and are considered critically endangered. These individuals were photographed in Long Cave in 2003.

These in turn are preyed upon by the pseudoscorpion Kleptochthonius, the beetle Pseudanophthalmus menetriesi, the larval dipteran Macrocera nobilis, and the spider Phanetta. As well, the spider Meta americana, and the cave salamander Eurycea lucifuga are present to prey upon crickets.

Woodrats and raccoons were formerly abundant in Mammoth Cave, and though today reduced, their feces support specialized communities. Latrines of the Eastern Woodrat Neotoma floridana sustain larva of the fly Psychoda and fungus gnat Bradysia, and the beetle Ptomaphagus hirtus, which are preyed upon by the rove beetle Quedius (Richards, 1989, 1990). Raccoon feces support a similar community with the exception that cave crickets may preempt fly larvae, most notably Spelobia, and Amoebelaria.

Due to low populations, bat guano in Mammoth Cave is today negligible as an energy source (Barr and Kuehne, 1967), but would have been highly significant during pre-settlement times since Mammoth Cave was formerly one of the largest bat hibernacula in the world. Indiana Bats (Myotis sodalis) and to a lesser extent Gray Bats (M. grisescens) were prominent species in Mammoth Cave only 150 years ago, but are today listed as endangered. Little Brown Bats (M. lucifugus) were also abundant with the Big Brown Bat (Eptesicus fuscus), and Eastern Pipistrelle (Pipistrellus subflavus) being less common (Toomey et al.,1998). All together, these and more rare bat species such as M.leibii and M.septentrionalis had estimated populations of 9-12 million just in the Historic Section (Tuttle, 1997). Ecological restoration of this portion of Mammoth Cave, and facilitating the return of bats is an ongoing effort (Olson, 1996).

MAJOR CONSERVATION ISSUES

In addition to correcting ecological distortions to the Historic Section of Mammoth Cave, lampflora such as algae and mosses are a problem as in all show caves, and elimination via wavelength selection has been achieved on a small scale (Olson 2001). On a karst landscape scale, contamination of groundwater recharge is a major issue, especially from Interstate Highway 65 (Olson and Schaefer 2002). However, nothing is known about likely contaminants entering park waters from the CSX Railroad. Finally, a problem exists downstream on Green River in the form of Lock and Dam #6, which ponds water up into Mammoth Cave and degrades habitat for the endangered Kentucky Cave Shrimp (Olson and Leibfreid 1999).

REFERENCES CITED

Barr, T., 1985, Cave Life of edited by P.H. Dougherty, Kentucky Geological Survey, Series XI, Special Publication 12, Lexington, Kentucky, p. 146-167.

Barr, T., 1967, Ecological Studies in the Mammoth Cave System of Kentucky, I. The Biota. International Journal of Speleology, 3:147-203.

Culver, D., Master, L., Christman, M., and H. Hobbs, 1999, Obligate Cave Fauna of the 48 Contiguous United States14:386-401.

Hubbell, T. and R. Norton, 1978, The Systematics and Biology of the cave crickets of the North American Tribe Hadenocini (Orthoptera Saltatoria: Ensifera: Raphidophoriinae: Dolichopodinae). Miscellaneous Publication of the Museum of Zoology, University of Michigan, 156:1-80. Kane, T. and T. Ryan. 1983. Population Ecology of Carabid Cave Beetles. Oecologia, 60:46-55.

Olson, R., 1996, This Old Cave: The Ecological Restoration of the Historic Entrance Ecotone of Mammoth Cave, and Mitigation of Visitor Impact. Proceedings of the Fifth Annual Mammoth Cave National Park Science Conference. Mammoth Cave National Park, KY: National Park Service, p. 87-95.

Olson, R., 2001, Control of Lamp Flora in Mammoth Cave National Park. International Conference on Cave Lighting Proceedings, edited by Tamas Hazslinszky, Hungarian Speleological Society, Budapest, Hungary, p. 131.

Olson, R., and T. Leibfreid, 1999, The Importance of Inventory and Monitoring Data sets in Resolving Ecosystem Management Problems at Mammoth Cave National Park. In: On the Frontiers of Conservation, Proceedings of the 10^th Conference on Research and Resources Management in Parks and on Public Lands, edited by Dave Harmon, p.149-155.

Olson , R. and J. Schafer, 2002, Planned Spill Retention and Runoff Filtration Structures on Interstate 65 in the South-Central Kentucky Karst. 15th National Cave and Karst Management Symposium Proceedings, USDA Forest Service, Tucson, AZ, p. 203.

Poulson, T., 1992, The Mammoth Cave Ecosystem. In The Natural History of Biospeleology, edited by A.I. Camancho, Monographs of the National Museum of Natural Sciences, Madrid, Spain, p. 564-611.

Poulson, T., 1993, Cave Animals of Mammoth Cave National Park. Unpublished guide on file at Mammoth Cave National Park. 35 p.

Richards, P., 1989, Predation in the Cave Rat Fecal Latrine. Cave Research Foundation Annual Report, p. 45-47.

Richards, P., 1990, The Effects of Predation on Invertebrate Community Structure in the Cave Rat Fecal latrine. Cave Research Foundation Annual Report, p. 58-61.

Toomey, R., Colburn, M., Schubert, B., and R. Olson, 1998, Vertebrate Paleontological Projects at Mammoth Cave National Park. Proceedings of Mammoth Cave National Park's Seventh Science Conference. Mammoth Cave National Park, KY: National Park Service, p. 9-14.

Tuttle, M, 1997, A Mammoth Discovery. Bats. Bat Conservation International, 15:4, p. 3.

Whitman, R., 1989, Sand Dwelling Animals of Mammoth Cave. Unpublished report on meiofauna in Mammoth Cave on file at Mammoth Cave National Park. 75 p.