Madison Blue Springs Earthcache
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Madison Blue Springs State Park
8300 FL-6, Lee, FL 32059
Hours: 8am until sundown, 365 days a year
Fees: $4-5 per vehicle. $2 Pedestrians, bicyclists, or extra passengers
Park Contact Information: 850-971-5003
QUESTIONS TO ANSWER:
1. According to the sign near the parking area, how many feet of the Aqueduct tunnel have
been explored (as of 9/25/97)? (Checked on this on 4/23/23, and spoke to a park ranger. The sign has been temporarily removed while it is being updated. When it is replaced, the information will be available.)
2. At the time of your visit, is the water clear or not clear? If it is not clear, can you determine
why it is not clear? Is it due to silt, or overflow of the river? Does it meet the definition of a
“brownout”?
3. How high is the water level in the spring? Is it above or below the wooden steps to the
spring? Is it above or below the footpath around the spring?
4. If you can access the footpath, answer the following: Do you see any fossils imprinted in the
limestone rocks in the wall beside the footpath around the spring? Do you think the fossils
are from plants or animals?
Madison Blue Springs State Park is one of Florida’s newest State Parks. It is located
approximately ten miles east of Madison, Florida, on the west bank of the Withlacoochee River.
It is at the Madison-Hamilton County line on Florida 6, about 8 miles east of the US 90/Florida 6
intersection in Madison.
The park was established after a private owner sold approximately 38 acres at the spring site in
2000. Initially a county park, it was acquired by the state and was one of Florida’s best-kept
secrets until it was voted “Best Swimming Hole in America” by US News and World Report in
July, 2017. Since then, the park has become a popular destination for travelers from around
the world. In addition to swimming in the spring, it is an internationally known cave diving
destination.
Florida has more springs than any other region in the world. There are over 600 springs in
Florida, ranging from merely a trickle to some of the largest springs in the world. There are
more than 100 springs within 1km of the Withlacoochee and Suwannee Rivers. The presence of
springs in Florida is due to the aquifer system in the state.
An aquifer is an underground layer of water-bearing rock. Water bearing rocks are permeable,
meaning that they have openings that liquids and gases can pass through.
The Floridan aquifer system underlies all of Florida, and the primary rocks at or near the surface
of the ground are limestone and dolostone. These rocks are dissolved by acidic groundwater.
When rainfall absorbs atmospheric sulfates, nitrates, and carbon dioxide, it becomes slightly
acidic. As the rainwater seeps through the soil, it picks up more carbon dioxide from decaying
vegetation, making it more acidic. This relatively weak acidic solution reacts with carbonate
rocks, such as limestone and dolostone, and partially dissolves them, creating pore spaces and
fractures, and creating cavities, caves, and caverns. The limestone forms a swiss cheese-like
appearance, and is like an enormous rock sponge saturated with fresh water.
Water within an aquifer is constantly replenished by rainfall. The pressure of the water in the
aquifer forces water through the cracks in the limestone, where it emerges from the ground in
the form of a spring.
Spring water is actively dissolving away limestone as it moves through the earth. Springs are
actually excavating new caves through this process, called speleogenesis. Speleogenesis is the
origin and development of caves.
The dissolved limestone, along with the influence of the spring’s depth and the blue of the sky,
impart the blue color. Unique local conditions may give each spring its own tint. There are
several “Blue Springs” in Florida, differentiated by location (i.e. Madison Blue Springs, Jackson
Blue Springs, Gilchrist Blue Springs). Rainy conditions wash silt into the water and may make
springs appear milky, cloudy, or even brown. This spring feeds directly into the Withlacoochee
River and is the major source of water for the lower Withlacoochee River during times of low
rainfall. The spring is approximately 25 feet deep, and within a distance of approximately 300
feet, the depth changes from 25 feet to 6 inches at the riverbank.
Madison Blue Springs is one of the state’s 33 first magnitude springs. A “first-magnitude” spring
discharges water at a rate of at least 2800 liters or 100 cubic feet of water per second. This
spring discharges in excess of 100 million gallons daily. Springs are designated as magnitude 0-
8 depending on the flow rate. A first magnitude spring is the largest flow rate.
At times of high water in the Withlacoochee River, the river water may overflow into the
Madison Blue Spring and discolor the spring water. During flood stage, the spring begins to act
as a siphon or inflow point into the Upper Floridan aquifer. This inflow, as surface waters and
groundwater mix, can cause substantial changes in groundwater quality, including the input of
significant loads of nutrients into the aquifer. The marked changes in water clarity that are
observable within the Madison Blue Spring system are dependent on factors such as flow
velocity, clarity of the Withlacoochee River (i.e., tannic or clear) and the height of the river
stage. Partial or complete “brownouts” of the Madison Blue system may occur. A complete
brownout is considered to have happened when tannic river water covers the entire spring run
and head spring and water clarity is reduced to less than four feet of visibility.
When surface water and groundwater mixing occurs, the result can be a rather rapid and
potentially large-scale change within the usually stable aquatic cave environment. Changes in
water temperature, oxygen levels, and organic carbon levels determine the magnitude of
changes that occur. Warm waters increase the rate of change. Most significant in the Madison
Blue Spring system is the introduction of organic carbon into the spring. Normally, limestone
caves are formed slowly because rainwater picks up some carbon dioxide in the air and
becomes slightly acidic, and this dissolves some of the calcium carbonate in the limestone. But
the Withlacoochee River water contains more organic carbon, so when the river floods and
backs up into the spring, the water dissolves as much limestone in one day as it would take
regular rainwater to dissolve in 55,000 years. Even when the flood waters recede, the river
water does not immediately leave the spring. Studies have shown that more than 10% river
water remained in the system for approximately 25 days. The Withlacoochee River overflows
into the Madison Blue Springs system on an almost annual basis. This may contribute
significantly to the existence of the large cave system associated with this spring.
The extensive cave system under Madison Blue Springs has underwater passages in excess of
25,508 feet (as of a survey in 09/12/97). Once the survey is complete, it is estimated that more
than 40,000 feet of passage will be mapped. The crystal- clear water in the caves draws cave
divers from around the globe.
There is a fenced walking path around the Madison Blue Spring. The path has a stone retaining
wall constructed from local limestone. If the limestone is examined closely, it is possible to find
vertebrate fossils and fossilized coral colonies in the stone. Walk along the pathway and
observe the porous limestone rocks. Take time to enjoy this geological treasure!
To get credit for visiting this Earthcache, send answers to the following questions to the cache
owner. Do not post the answers with your log.
QUESTIONS TO ANSWER:
1. According to the sign near the parking area, how many feet of the Aqueduct tunnel have
been explored (as of 9/25/97)?
2. At the time of your visit, is the water clear or not clear? If it is not clear, can you
determine why it is not clear? Is it due to silt, or overflow of the river? Does it meet the
definition of a “brownout”?
3. How high is the water level in the spring? Is it above or below the wooden steps to the
spring? Is it above or below the footpath around the spring?
4. If you can access the footpath, answer the following: Do you see any fossils imprinted in
the limestone rocks in the wall beside the footpath around the spring? Do you think the
fossils are from plants or animals?
Optional: Post a picture of yourself at Madison Blue Spring.
References:
Roadside Geology of Florida (Bryan, 2008)
Florida Department of Environmental Protection (http://www.dep.state.fl.us/springs/)
Florida’s Springs (http://www.floridasprings.org/)
U.S. National Park Service (https://www.nps.gov/ozar/learn/nature/springs/htm)
Florida State Parks (http://www.floridastateparks.org)
“Groundwater-surface water interaction in Florida’s karst springs: Tropical storms and spring floods” by Brown, Amy
et al
http://www.alachuacounty.us/Depts/epd/WaterResources/GroundwaterAndSprings/SFRSBWG%20Presentations/140
725-Groundwater-Surface%20Water%20Interactions_Brown.pdf
https://en.wikipedia.org/wiki/Speleogenesis
https://floridadep.gov/sites/default/files/MadisonBlueSpringsStatePark.pdf
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