Woodville Karst Plain Overview

Woodville Karst Plain Overview


THE WOODVILLE KARST PLAIN

J. Michael Wisenbaker, Archaeologist, Florida Division of Historical Resources

First labeled a separate geomorphic unit in 1966, the Woodville Karst Plain (part of the Gulf Coastal Lowland physiographic region) stretches from the southern edge of Tallahassee, Florida, to the Gulf of Mexico. Its distinctive northern border known as the Cody Scarp formed about 100,000 years ago during a Pleistocene interglacial when the Gulf lapped ashore near the present Leon County Fairgrounds. The Apalachicola Lowlands (which begin just west of U. S. Highway 319) serve as the western boundary of the karst plain, while the Wacissa River in Jefferson County marks its approximate eastern extent.

The Woodville Karst Plain, capped by less than 20 feet of quartz sands, gently slopes toward the Gulf. Relict dunes and terraces associated with ancient sea stands now mantle St. Marks (early Miocene) and Suwannee (Oligocene) Limestones. The porous sands have allowed acidic water to move rapidly through the underlying soluble carbonates. Dolines, springs, and karst windows are the most obvious evidence of this process. Several lost rivers in the area flow a short way before being captured by subterranean conduits. Corrosion continues to wear down the entire foundation of this plain.

As for the hundreds of sinkholes found here, many remain dry depressions, others hold tannin-surface water, and those breaching the aquifer are filled with clear groundwater–unless fouled by murky runoff or topped with algae-laden thermoclines. One simple way to tell whether the water in a sink is groundwater or surface water is to measure its temperature. Groundwater in these sinks stays a constant 69 degrees throughout the year, whereas the temperature in surface water features varies with the seasons. Many “sinks” in the area would more accurately be called karst windows since they merely expose collapsed segments of underground streams.

Of Florida’s 27 first magnitude “springs,” 26% fall within the 288,000 acre Woodville Karst Plain. These include: Spring Creek Spring, St. Marks Spring, Wakulla Spring, Wacissa Springs, Group, Kini Spring, River Sink Spring, and Natural Bridge Spring. Four of these seven karst features, however, are not true artisan springs. St. Marks Spring represents a river rise, while Kini Spring (aka Upper River Sink), River Sinks Spring (aka Lower River Sink), and Natural Bridge are karst windows. Despite what we choose to call them, they comprise an impressive list of hydrologic marvels — as more than 64.6 million gallons of water a day course through each of them.

Presently, the Woodville Karst Plain contains more than 22 miles of known conduits, all of which have been physically tracked by cave diving explorers. The longest surveyed underwater cave in the United States, known as the Leon Sinks Cave system with its 58,444 feet (more than 11 miles) of mapped phreatic passages, makes up about half this total. This cave stream, exposed to the surface by 26 karst windows, probably contributes much of the 252 million gallons a day flow at Wakulla Springs.

E. H. Sellards, the first person to head the Florida Geological Survey, had predicted more than 80 years ago that this underground river fed Wakulla. For the past 25 years, exploration of this labyrinth by cave divers seems to have validated his theory. Divers made a quantum leap in the late 1970s when they began to extend their ranges with scooters. Staging air and other gas mixtures (needed for deeper areas because breathing air below certain depths is dangerous) within the caves allowed them to reach even greater distances.

In 1987, the U. S. Deep Caving Team surveyed over two miles of conduits in Wakulla Springs. They found that the primary passageway heads southwest from the spring entrance. About 900 feet into the cave, a chamber called the Grand Junction Depot splits into four separate passages known as Tunnels A, B, C, and D. The apparent water quality of one feeder cave differs from the others. While Tunnels B, C, and D carry air-clear water, Tunnel A bears a charge laced with tannic acid. The fluid in Tunnel A appears to match that in the Leon Sinks Cave System, and affects the day-to-day visibility at Wakulla Springs.

To explore the subaquatic caves and related karst openings more systemically, parker Turner founded and headed the Woodville Karst Plain Project (WKPP). In 1991, Turner tragically died in a freak diving accident that buried his safety line to the surface at Indian Springs. Fortunately, his efforts were not in vain. Florida State University established the Parker A. Turner Memorial Scholarship Fund in his honor. It will provide support for a graduate student to conduct research in underwater speleology. A committee representing the National Association for Cave Diving, the Cave Diving Section of the National Speleological Society, academia, and other friends of Parker will award the scholarship.

Currently sponsored by the National Speleological Society, the WKPP supplies data on groundwater and hydrogeology and provides support for private and government entities. A few months ago, WKPP divers made a major push into Tunnel A at Wakulla Springs. They reached 6,129 feet from the cave mouth at depths averaging just under 300 feet. This added several hundred feet of surveyed passage to the system. last year, the aquanauts also discovered and explored a conduit in the long stretch between Sullivan and Cheryl sinks. This uncharted artery led toward Big Dismal Sink (with its 12,000 feet of mapped passages). Now, only about 400 feet of unexplored cave separates the two systems. If linked to Big Dismal, the Leon Sinks Cave System would encompass almost fourteen miles of underwater cave. Thus, with each season, we move ever so close to solving the riddle of the sinks in the Woodville Karst Plain.

In contrast to the shallow clear conduits of Mexico’s Yucatan peninsula, which presently hold the world’s longest surveyed water-filled cave, the deep dark tunnels in the Leon Sinks Cave System can only be dived a few months each year. Explorers must wait for droughts to allow for the tea-colored surface runoff to be flushed out of the system. Still, the Leon Sinks Cave System covers more than twice the distance of the state’s longest dry cave — Warren Cave in Alachua County.

Underwater cavities in the karst plain range in size from a room named the Black Abyss — large enough to hold a sixteen-story building — to minuscule fissures. While the caves here lack calcite speleothems found in the cenotes of Mexico or the blue holes in the Bahamas, many possess colorful bands and formations of chert and geothite. The absence of speleothems suggests the grottos must have been filled with water for most of their existence.

Several species of globally imperiled blind crayfish and other rare troglobites inhabit the caves. These include Hobb’s cave isopod (Caecidotea hobbsi), Hobb’s cave amphipod (Crangonyx hobbsi), Horst’s cave crayfish (Procambarus hortsi), and Woodville cave crayfish (Procambarus orcinus). Although not especially common around small karst windows, some specialized flora fill ecological niches along the rims and walls of dolines. For example, rare plant such as Venus-hair fern (Adiantum capillus-veneris) sprout in the rock cracks and crevices of sinks in the Woodville Karst Plain.

Researchers from various institutions have begun making small strides in understanding this important karst region. For example, investigators have employed dye and isotope tracing studies. One graduate student in geology wrote her master’s thesis on uranium isotope disequilibrium studies at Wakulla Springs. Another geology student is using this method in an attempt to show how stormwater runoff may be affecting groundwater quality at springs and wells in the karst plain. An oceanographer is examining how tides influence spring flow in the region. Biologists are sampling the DNA of cave crayfish to get a better handle on their population genetics, while others are delving into photo and chemical reception of the troglobites.

Opportunities still abound for serious scientific research in the Woodville Karst Plain. hardly any archaeological work has been done on karst features in the area. The one thesis produced so far lacks guidance from anyone truly knowledgeable about prehistory and karst. For example, the student never mentions the possibility that some shallower drowned sinks in the karst plain may have served as rock shelters for Paleo-Indian and Early Archaic peoples when water tables were much lower than now. The silty cavern floors may harbor a lode of information about early human settlement and subsistence.

In terms of vertebrate paleontology, Wakulla Springs preserved many Pleistocene megafauna, including almost an entire mastodon (Mammut americanum) skeleton. A Mastodon tooth also turned up in the down stream siphon at Venture Sink, one of the 26 openings into the Leon Sinks Cave System. A WKPP diver recently reported and gathered samples of an extensive scatter of fossil dugong (a Miocene relative of the manatee) bones about 1,200 feet into the cave at Indian Springs. Although the Florida Geological Survey has produced excellent background reports on regional geology, karst geologists still have ample opportunities to do site-specific studies.

Some work of the cave explorers, scientists, and government officials has already paid dividends. Specifically, Wakulla County recently passed a “Green Line” ordnance prohibiting any businesses that deal in potentially dangerous substances, such as gas stations and dry cleaners, from operating within a specified distance of the Leon Sinks Cave System. The water quality at Wakulla Springs, however, still seems to suffer from development and lodging activities upstream. Circumstantial evidence of this rests in the time the water stays clear seasonally. The springs’ clarity seems to be diminishing as more and more growth spreads into this fragile landscape.

With these thoughts in mind, perhaps other karst scientists and students throughout the country may wish to become involved in the fascinating research potential of the Woodville Karst Plain.

KWI Conduit, Winter 1995, Volume 3, No. 2