Texas Speleological Survey

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This page last updated September 13, 2013

Overview of Texas Caves & Karst

by William R. Elliott, Ph.D.

© Texas Speleological Survey, All Rights Reserved

The TSS defines a cave as a naturally occurring, humanly enterable cavity in the earth, at least 5 m (15' 6") in traverse length, and where no dimension of the entrance exceeds the length or depth of the cavity.

Note: This definition is used by the Texas Speleological Survey to classify karst features, but five meters is not universally accepted.   Other states and the Texas Commission on Environmental Quality have different standards.

Orion Knox in the entrance room of Electro-Mag Cave, Sun City, Williamson County, Texas - photo George Veni - click for a larger image in a new window

Orion Knox in the entrance room of Electro-Mag Cave, Sun City, Williamson County, Texas.

- photo George Veni

At least 9,500 caves, sinkholes and springs are known in Texas, distributed in karst regions covering about twenty percent of the state.  Karst is a terrain formed by the dissolution of bedrock, and generally is characterized by sinkholes and caves that channel water underground.  Texas caves and karst aquifers are important economic, scientific, and recreational resources.

Karst requires soluble rocks, and Texas has many karst regions (see map).  The majority of Texas caves occur in the Cretaceous limestones of the Edwards Group, Glen Rose, and Austin Chalk, distributed in the Balcones Fault Zone, the Edwards Plateau, the Stockton Plateau, and the Cibolo Creek and the Guadalupe River basins.  In the Llano Region, the Ellenburger Group carbonates (Ordovician age) are intensely cavernous.  Permian reef limestones in West Texas contain important caves.  Two gypsum karst areas (Permian age) occur north of Van Horn, Culberson County, and in fourteen counties in Northwest Texas.  Some unusual caves occur in "pseudokarst" (false karst), where caves did not form primarily by dissolution in groundwater.  Examples of pseudokarst are granite (Enchanted Rock Cave, Llano County), volcanic tuff and conglomerate (Big Bend), sandstone, travertine, shale, caliche, and other materials.  Many caves are being degraded, filled, or quarried by humans before their contents can be adequately studied.

Long caves: At least 129 Texas caves are 300 m (984 ft.) long or longer.  Honey Creek Cave is the state's longest at 32 km (20 mi.), and is still being actively explored.  The cave is a tributary to the Guadalupe River, and it extends under Comal and Kendall counties.  Powell's Cave System, a complex of three caves in Menard County, is at least 21 km (13 mi.) long and "growing" as cavers continue to map it.

Deep caves: At least 118 caves are 30 m (99 ft.) deep or deeper. Sorcerer's Cave (Terrell County) is the deepest at 170 m (558 ft.).  The largest cave in terms of volume may be Fern Cave (Val Verde County), estimated at about 300,000 cubic meters (10 million cubic ft.).

The scientific resources of Texas caves are many.  Hundreds of ancient species, specially adapted to an energy-efficient life in permanent darkness, are scattered through the karst of Central Texas.  Cave-adapted salamanders, catfishes, shrimps, isopods, amphipods, snails, spiders, harvestmen, pseudoscorpions, beetles, millipedes, centipedes, and other types have been described.  Most of these eyeless "troglobites" occur in the Balcones Fault Zone, where geologic isolation in faulted, river-dissected karst blocks has resulted in an evolutionary history like that of an archipelago.  Some of these species are endangered by land development, overuse of groundwater, pollution, and pests such as the red imported fire ant.

About two dozen Texas caverns harbor a total of about 100 million Mexican free-tailed bats from April to November every year.  These migratory bats consume 6,000 to 18,000 metric tons of insects annually in Texas.  The largest known mammal colony in the world is the colony of 20 million or more Mexican freetails in Bracken Bat Cave, Comal County.  Bats are recognized as important but are feared by many nevertheless.  A 1917 state law protecting bats was rescinded during a rabies scare in 1957.  Several other insectivorous bat species inhabit hundreds of Texas caves, but have been killed or driven out of some caves by vandals.  Bat Conservation International moved its headquarters to Austin in 1986 and has been educating the public on the ecological importance of bats.

About twenty-five Texas caves have yielded important fossils of vertebrate animals.  Extinct species, such as the scimitar cat, dire wolf, Columbian mammoth, ground sloth, glyptodon, spectacled bear, and flat-headed peccary, denned in, fell in, or were eaten in Texas caves.  Radiocarbon dates up to 23,000 years before present have been recorded.  Bats have utilized Texas caves for many millennia.  The remains of small mammals found in cave soil and flowstone strata have chronicled the climatic shifts in Texas since the ice ages ended about 11,000 years ago.  Central Texas was a cool, moist environment until about 3,000 years ago.  Burrowing mammals, such as moles and gophers, were common.  With the increasing aridity there was a massive loss of soil.  A second episode of soil loss was caused by the loss of fire ecology and the overgrazing by domestic animals that continues to this day.

Paleoindians utilized Texas cliffs and rockshelters for "animal kills."  As long as 12,400 years ago, Bonfire Shelter near the Rio Grande received animals driven off the cliff.  People processed the carcasses in the shelter.  Kills of mammoth, bison, and horse occurred several times.  In the Archaic Period (9,000-1,000 years ago) many shelters in the Lower Pecos River and Devils River area were inhabited by hunter-gatherers.  Fine pictographs may still be seen in Fate Bell Shelter at Seminole Canyon State Historical Park near Comstock.  Pit burials, where the dead were dropped into deep sinkholes, also have been documented.  Important archeological materials no doubt remain to be found in caves and are protected by law.

Early scientific work in Texas caves began in 1896 with the description of the Texas blind salamander Eurycea rathbuni from an artesian well at San Marcos.  Important bat guano caves were documented in 1901; the caves had been sources of nitrates for gunpowder but became fertilizer mines for citrus and vegetable farms.  Serious speleology in Texas began with the 1948 publication of The Caves of Texas by the National Speleological Society (NSS).  Caving groups (grottos) formed in the 1950s and systematic documentation of the state's caves began, first by the grottos and the Texas Cave Survey, then by the Texas Speleological Survey (TSS), founded in 1961. NSS conventions were held in Texas in 1964, 1978, and 1994; the 2009 NSS Convention will be held in Kerrville in conjunction with the 15th International Congress of Speleology.  Today's Texas Speleological Association includes eleven grottos in major cities.  Caves are conserved and managed by the Texas Cave Management Association, The Nature Conservancy, Texas Parks & Wildlife Department, Bat Conservation International, and many private landowners.  The State Caverns Protection Act protects caves from vandalism and destruction.  Another statute protects landowners from liability for injuries to cave visitors, unless they have paid for access to the cave.

The Edwards Aquifer, which extends from Brackettville to north of Austin along the margin of the Edwards Plateau, is a karst aquifer that supplies drinking water to 1.5 million people in the San Antonio area.  As pumping begins to exceed natural recharge and water levels decline, several rare species and the human economy are threatened.  The Comal and San Marcos rivers, which originate from large karst springs, are important in maintaining the Guadalupe River ecosystem all the way to the San Antonio Bay estuary on the Texas coast.

Texas caves abound with natural delights.  Seven show caves are open to the public: Cascade Caverns and Cave Without A Name (both at Boerne), Caverns of Sonora (Sonora), Inner Space Cavern (Georgetown), Longhorn Cavern (Burnet), Natural Bridge Caverns (New Braunfels), and Wonder Cave (San Marcos).  Caverns of Sonora is considered by many experts to be the most beautiful cave in the world.  The other caves offer an amazing variety of beautiful speleothems (mineral formations), fossils, and history.  Wild Caving tours are now offered at Colorado Bend State Park, Kickapoo Caverns State Natural Area, and West Cave (a botanical preserve and travertine cave near Austin).

BIBLIOGRAPHY:

Elliott, W. R. 1994. Texas' caves. Texas Almanac, Dallas Morning-News. p. 109.

Elliott, W.R., and G. Veni (eds.). 1994. The Caves and Karst of Texas. 1994 Convention Guidebook. National Speleological Society, Huntsville, Alabama. 342 pp. + viii + 13 maps.

Mohr, C. E. (ed.). 1948. The Caves of Texas. National Speleological Society, Bulletin 10. 137 pp.

Turpin, S.A. (ed.). 1985. Seminole Sink: Excavation of a vertical Shaft Tomb. Texas Archeological Survey, Research Report 93, Univ. of Texas at Austin. 216 pp.

Revised from The New Handbook of Texas, 1996, Texas State Historical Association.

Revised statistics from the TSS database - August 11, 2008