Wakulla Spring lies within the Woodville Karst Plain
(Hendry and Sproul, 1966), a low-lying area underlain by
Oligocene and Miocene aged limestone overlain by a thin
blanket of unconsolidated sands.
The Eocene Ocala Group is a widespread formation that is
an important part of the Floridan aquifer system. However,
near Wakulla Spring it lies well below all known cave
passages; the top of the Ocala was encountered between
120-180 meters below the land surface in oil test wells near
Wakulla (Rupert, 1988). The Lower Oligocene Suwannee
Limestone unconformably overlies the Ocala Group. The
Suwannee Limestone is a calcarenite containing miliolid
foraminifera, mollusks, bryozoans, echinoids, and corals.
Chert is common and was used by Paleo-Indians for tools and
weapons. The passages in Wakulla Cave are developed in the
Suwannee Limestone. The Lower Miocene St. Marks Formation
unconformably overlies the Suwannee and is the uppermost
bedrock unit at Wakulla Spring. The ledge above the Wakulla
Spring vent is St. Marks Formation. The unit is primarly a
calcilutite containing quartz sand, clay stringers and
mollusks. The lower contact of the St. Marks Formation lies
at approximately 27 meters water depth.
Samples collected during exploration in 1987, as well as
visual descriptions, and video footage from within Wakulla
Cave indicate a distinct lithologic and color change within
the Suwannee Limestone at a depth of about 65 meters. Above
lies a soft biocalcarenite, whereas below the contact is a
harder, recrystallized dolomitic calcarenite. Rupert (1988)
suggests the harder rock may have retarded additional
downward dissolution in the conduits. The 3D map produced
during the 1998-1999 diving project shows the floor level
for much of the cave is uniform at a depth of about 90
meters (Figure 2).
During the Pleistocene, the shoreline transgressed
across this area, reworking sands from older formations and
depositing the sediment over the limestone. (Hendry and
Sproul, 1966). Five marine terraces are recognized in
Wakulla County, and Wakulla Spring lies within the Pamlico
Terrace, ranging from 3 to 8 meters above sea level (Healy,
1975). The Cody Scarp (Figure 1) is an escarpment marking
the boundary between the northern Tallahassee Hills and the
Coastal Lowlands to the south (Rupert and Spencer, 1988).
The boundary represents the ancient shoreline location.
The first correct identification of the enormous bones
seen through the clear water on the bottom of the Wakulla
Spring basin was made by Sarah A. Smith for the Tallahassee
Floridian and Journal in 1850. This publication prompted a
local professor to collect a significant portion of a
mastodon skeleton, but the bones were lost in a shipwreck on
their way to a museum on the Atlantic coast (Revel,
Additional bones were collected over the next decades.
In 1930, more mastodon bones were discovered in shallow
water during construction of a swimming area at Wakulla
Spring (Revel, 2002). The Geological Survey was enlisted in
its collection and the skeleton remains on display today in
the Museum of Natural History in Tallahassee.
Dives by Wally Jenkins, Garry Salsman and their buddies
in 1955-56 (see exploration section below) resulted in the
discovery of mastodons, mammoths, deer, camels, giant ground
sloths, bears, as well as many spear points from
Paleo-Indians (Burgess, 1999). The divers used pillowcases
lined with plastic bags inflated by air from their tanks to
lift the heavy bones to the surface from depths up to 60
During later exploration Pleistocene mammal bones have
been discovered as far back as 366 meters from the
Wakulla Spring is one of 33 first order magnitude
springs in Florida (Scott, et. al., 2002). Average discharge
from 1907-1974 was 11 m3/s. Wakulla Springs display the
greatest range of discharge of any Florida spring. A minimum
flow of 0.7 m3/s was recorded on June 18, 1931, whereas a
maximum flow 54 m3/s [equivalent to 14,288 gal/sec]
was reported on April 11, 1973 (Scott et. al., 2002).
Rupert (1988) noted the collection of fossil mammal
bones located deep within the cave. This observation
prompted two theories that took into account the lower
Pleistocene sea level (and by extension, base level on
land). Rupert suggested that mammals wandered into the dry
cave entrance looking for water. Additionally, it was
hypothesized that the Wakulla Spring may have been a sink
where water entered the aquifer at the time. Indeed
Wisenbaker (1998) reports than another Florida spring,
contains an extinct land tortoise with a wooden stake stuck
in its shell at 26 meters below the current water level. A
less likely explanation for the presence of mastodon bones
in the spring was that "In winter, mastodons crossing frozen
pools broke through the ice and drowned" (Adler, 1977).
Directly north of the Wakulla area, an unconfined
surficial aquifer system is found in the unconsolidated
sands and gravels of the Tallahassee Hills. Recharge occurs
by direct precipitation. An intermediate aquifer system lies
below the surficial sediments ranging from about 15 to 46
meters thick. The bedrock contains interlayered clayey
sediments, limestone, and dolomite resulting in
discontinuous water-bearing zones. Water recharges into the
intermediate aquifer by leakage from the surficial aquifer
and from sinkhole-drained lakes (Clemens, et. al., 1998). A
dramatic example of flow into the aquifer from a lake in the
Tallahasee Hills occurred on September 16, 1999. Much of the
4000 acre Lake Jackson in the Tallahassee Hills suddenly
drained down Porter Hole, a 5-meter deep sinkhole in the
lake bed. The pit leading down from the sink, swallowed the
lake's southern half in a single day. Similar drainage
events have occurred in the past, as well.
Below the surficial and intermediate aquifers lies the
Floridan aquifer system that is a major carrier of water and
extends through much of the northern part of the state. In
the Woodville Karst Plain the Floridan aquifer is comprised
of the St. Marks Formation, Suwannee Limestone and Ocala
Group. Transmissivities are high and range from
5,000-125,000 feet squared per day (Pratt et. al., 1996).
Recharge comes from downward leakage from the intermediate
aquifer in the Tallahassee Hills and through sinkholes
(Hendry and Sproul, 1966). The Woodville Karst Plain also
forms a recharge area via direct rainfall and through
sinkholes (Scott, et. al., 1991). Four streams sink
underground, also contributing to recharge, though one
re-emerges again (Clemens, et. al., 1998).
Regional groundwater flow of the Upper Floridan aquifer
is to the southeast across Wakulla County (Figure 3). In the
Woodville Karst Plain the Floridan aquifer is unconfined and
no low-permeability units lie between the surface and
carbonate aquifer units (Lane, 2001).
Using uranium isotopes, Cowart, et. al. (1998)
determined that the primary source of Wakulla Springs is
southward flowing Floridan aquifer water. Further, they used
strontium isotopic ratios to conclude that the spring water
has not come solely from local recharge, but rather comes
from water having been in contact with Floridan aquifer
bedrock for considerable time. However, Katz (1998) reports
that the shallow and deep ground water was recharged during
the past 30 years based on tritium age dating.
The conduit flow of groundwater in the Wakulla Spring
cave and the Woodville Karst Plain is remarkably complex
considering the relatively uniform pieziometric surface of
the area (Figure 3). Kincaid (1999) reports that a
groundwater divide occurs 1 to 2 km inside the main tunnel
of Wakulla Spring. The divide marks a divergence between
water flowing north to the Wakulla Spring vent and water
flowing approximately along the regional groundwater
gradient south, presumably to the Spring Creek Springs Group
of thirteen submarine springs. This flow divergence is
perplexing because one would not expect diffuse aquifer
percolation to supply water to a tunnel approximately 30
meters in diameter.
The Spring Creek Springs Group has pulsating changes in
flow where the surface of the water alternates between flat
quiescence and boiling surface turbulence (Lane, 2001). The
alternating surges generally last for several minutes and
thought to be do to flushing through complex, tortuous
passages. Since the Spring Creek Springs Group is likely to
be connected, at least indirectly, with the nearby Wakulla
Spring, much remains to be learned about the flow within the
Woodville Karst Plain.
The importance of understanding the sources of water for
Wakulla Spring is apparent when considering the clarity of
water discharging from the spring. The vertigo-inducing
clarity of the water in the 19th and early 20th centuries
has diminished during the last few decades. One of the first
reports of low visibility came in 1894 where "The water has
been stirred up by the heavy rains, and we could only see
down 80 feet" [24 meters] less than the maximum of
125 feet [38 meters] (Savery, 1998). Reports in 1945
and 1946 by the commercial operation run of Ed Ball noted
that visibility was affecting the ability to run
glass-bottom boat tours and turn a profit. The visibility is
diminished primarily from tannic and humic acids in
surficial swamp or river waters that enter the karst.
Particulate matter may also contribute to lower visibility,
but the dark color of the tannic water is a bigger problem.
Savery (1998) quotes long time boat guides stating that dark
water has become a more frequent, longer duration problem at
Wakulla. Records of dark water indicated water visibility
was poor for 58% of the time over the last 12 years and that
the poor visibility is correlated to rainfall events. The
best chance for crystal clear water is during the dry months
of May and June.
Another significant problem with water quality at
Wakulla Springs is the increase in nitrates, presumably the
result of runoff from fertilizers used on lawns and
agriculture. Simultaneous has been the introduction of
exotic algae, particularly hydrilla. A virtual explosion of
algae growth has choked much of the Wakulla Spring basin and
river in recent years, probably enhanced by the high nitrate
levels. The state park has attempted to manage the hydrilla
using mowers and divers to remove as much as they can, but
it has been a losing battle. Recently, the park applied a
herbicide to the spring basin to improve visiblity of the
spring by glass bottom boat tours and to regain a healthy
ecologic balance in the river system (Ritchie, 2002). It is
hoped that native plants re-establish themselves and that
the hydrilla will not be re-introduced.
Little work has been conducted on the speleogenesis of
Wakulla Spring cave system considering its magnitude. The
reason is probably because the cave system is entirely
flooded and averages approximately 88 meters water depth.
Rupert (1988) took advantage of recent exploration to do
rudimentary description and analysis.
Chen, et. al. (1998) studied the development of the
Woodville Karst Plain, including its offshore extension.
They examined the regional structural geology, sea-level
fluctuations, climatic change, and groundwater flow and
proposed that karstification began approximately 9,000 years
Kincaid (1999) developed a model for the origin of
Wakulla Spring. He defined Wakulla as a branching,
flow-dominated, saturated cave, and described a four-stage
sequence of development. Speleogenesis development began
through self-initiation. Small, random variations in
permeability created positive feedback loops. The
up-gradient process was based on geochmical feedback.
Down-gradient, hydrodynamic processes governed the feedback
loop and was enhanced by corrosion from mixing of waters.
The largest conduits were developed in the cave when sea
level was lower during the Pleistocene. Discharge occurred
in springs that are presently submarine, while recharge
entered through a sinkhole that now is the current Wakulla