Karst Geology
Kentucky can be divided into five major physiographic regions:
the Mississippi Embayment or Jackson Purchase in the west, the
Mississippian Plateaus or Pennyrile, the Western Coal Field, the
Bluegrass, and the Eastern Coal Field.
Kentucky is one of the most famous karst areas in the world.
Much of the state's beautiful scenery, particularly the horse farms
of the Inner Bluegrass, is the result of development of karst
landscape. The karst topography of Kentucky is mostly on limestone,
but also some dolostone. The areas where those rocks are near the
surface closely approximate where karst topography will form. The
map above shows the outcrop of limestone and dolostone and closely
represents the karst areas. In humid climates such as Kentucky's
you should assume that all limestone has karst development,
although that development may not be visible at the surface.
The outcrop area of the limestone bedrock in Kentucky has been
used to estimate the percentage of karst terrain or topography in
the state. About 55 percent of Kentucky is underlain by rocks that
could develop karst terrain, given enough time. About 38 percent of
the state has at least some karst development recognizable on
topographic maps, and 25 percent of the state is known to have
well-developed karst features. As can be seen on the map, Princeton
is near the northwestern most tip of the heavy karst-concentrated
region.
Karst Chemistry and Spring Formation
Karst landforms are generally the result of mildly acidic water
acting on soluble bedrock such as limestone or dolostone. The
carbonic acid that causes these features is formed as rain passes
through the atmosphere picking up CO2, which dissolves in the
water. Once the rain reaches the ground, it may pass through soil
that may provide further CO2 to form a weak carbonic acid solution:
H2O + CO2 ? H2CO3 (the acid). Recent studies of sulfates, in karst
waters, suggest sulfuric acid and hydrosulfuric acid may also play
an important role in karst formation.
This mildly acidic water begins to dissolve the surface along
with any fractures or bedding planes in the limestone bedrock. Over
time, these fractures enlarge as the bedrock continues to dissolve.
Openings in the rock increase in size, and an underground drainage
system begins to develop, allowing more water to pass through the
area, and accelerating the formation of underground karst
features.
Karst springs occur where the groundwater flow discharges from a
conduit or cave. Karst springs or "cave springs" can have large
openings and discharge very large volumes of water. The sinkholes
and sinking streams that drain to a large karst spring can be many
miles away from the spring. Frequently, groundwater flow rises to
the surface from a completely water-filled conduit. The depth of
the clear water in the spring pool gives the water a deep blue
color so they are termed "blue holes." The Princeton "Big Spring",
part of the Pennyrile Physiographic Region, is an excellent example
of this process.
The amount of water that flows from springs depends on many
factors, including the size of the caverns within the rocks, the
water pressure in the aquifer, the size of the spring basin, and
the amount of rainfall. Human activities also can influence the
volume of water that discharges from a spring—ground-water
withdrawals in an area can reduce the pressure in an aquifer,
causing water levels in the aquifer system to drop and ultimately
decreasing the flow from the spring.
Springs are often classified by the volume of the water they
discharge. The largest springs are called "first-magnitude,"
defined as springs that discharge water at a rate of at least 2800
liters per second (L/s). The scale for spring flow is as
follows:
Magnitude = Flow in liters per second
1st Magnitude = 2800 L/s
2nd Magnitude = 280 to 2800 L/s
3rd Magnitude = 28 to 280 L/s
4th Magnitude = 6.3 to 28 L/s
5th Magnitude = 0.63 to 6.3 L/s
6th Magnitude = 63 to 630 milliliters/second
7th Magnitude = 8 to 63 mL/s
8th Magnitude = up to 8 mL/s
0 Magnitude = no flow (sites of past/historic flow)
Historic Context
In the center of Princeton, KY at the above listed coordinates
is the "Big Spring". This spring is the source of the founding of
the city and has a great deal of historic significance to the
surrounding area and Native Americans.
The importance of the Big Spring as a prehistoric and early
settlement communications center is most evident when one considers
that all trails leading northward from the Cumberland between what
was later Nashville and Palmyra converged at the Big Spring. From
the Big Spring these trails branched off and led to five principal
crossings of the Ohio River that were located between the mouth of
the Cumberland and the mouth of the Tradewater River. These trails
were first forged by the buffalo, later used by the Indians, and
then the pioneers. These "traces", or trails, eventually developed
into today's modern roads.
When the town of Princeton was formed in 1817 all of the
territory west of the Tennessee River was Tribal lands of the
Chickasaw. In 1818 when the Federal Government made the Jackson
Purchase the newly formed town of Princeton was a site of land
sales, a staging area for settlement and a supply point for its
settlers until merchants were established beyond the Tennessee
River. The Champion-Shepherdson House now Guild House, built on lot
number one in the town of Princeton was a merchants store and home.
Standing above the Big Spring it is the oldest building in
Princeton.
The Big Spring takes on further significance with the "Trail of
Tears" — the forced migration of the Cherokee Indians in
1838. The Cherokee came through Princeton and camped by the Big
Spring on their march to Oklahoma. The trek began in the Great
Smokey Mountains and led westward into Indian Territory costing the
Cherokees nearly one-third of their population. The tribe came to
Princeton in 12 groups comprised of approximately 16000 people.
Logging Requirements
To get credit for this Earthcache e-mail me
with answers to the following questions:
1. Approximately what percent of Kentucky is
underlain by rocks that could develop karst terrain?
2. Approximate the flow rate of the spring.
What is that rate in liters per second (L/s)? One method is to take
a leaf or other floatable and measuring how many feet it travels on
the water in 10 seconds. Take an estimate of width and depth at
that spot in feet. Multiply the three numbers together and multiply
this result by 2.83168.
3. Based on the above rate of flow what
magnitude is this spring?
4. What is the estimated width and height of
the spring opening in the rock?
5. Please take a photograph of yourself with
your GPSr in front of the spring. Post this photograph with your
online log.
Please no spoilers in your logs!