The Woodville Karst Plain
J. Michael Wisenbaker, Archaeologist, Florida Division of Historical
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
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
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.