What is Karst?
Karst is defined as a landscape with sinkholes, springs,
and streams that sink into subsurface caverns. The word "karst" was
developed in Europe, where early geologists first studied the nature
of groundwater flowing through limestone hills and valleys.
A land area that includes sinkholes, springs,
sinking streams, and caves.
- Approximately 10% of the earth's surface (and 20% of the
U.S.) is composed of karst; however, approximately 25% of the world's
population lives on these areas! The hollow nature of karst terrain
results in a very high pollution potential. Streams and surface runoff
sinkholes and caves, and bypass natural filtration through soil
and sediment. Groundwater can travel quite rapidly through these
underground networks - up to thousands of feet, or even miles, per
day - transmitting contaminants to wells and springs in the vicinity.
- In karst areas, the fractured limestone rock formations have been
dissolved by flowing groundwater to form cavities, pipes, and conduits.
Sinkholes, caves, sinking streams, and springs signal the presence
of underground drainage systems in karstlands.
- Unless watersheds are protected, these direct connections between
the surface and the subsurface can threaten the quality of our drinking
water. The safest watersheds are those in which all residents understand
the karst landscape and work together to reduce soil erosion, high-density
development, agricultural and urban storm water runoff, overgrazing,
improper waste disposal, and pollution.
How Karst was Formed
- Between 570 million and 320 million years ago, the geographic area
now occupied by the eastern United States was predominantly covered
by a calm, shallow, tropical sea. The sea was populated by microscopic
(and larger) organisms that lived, died, and sank to the bottom of
lagoons, or were washed into deeper parts of the basin by storms.
Over the eons, the deposits of calcium-rich shells and skeletons
solidified into the bedrock that we call limestone (CaCO3), dolomite
and gypsum (CaSO4.2H2O). These rocks are soluble in dilute acids.
becomes slightly acidic when it takes up carbon dioxide while passing
through decaying organic debris in the surface soils. The interaction
of acidic water with soluble rocks such as limestone produces the
characteristic landscape known as karst.
- During the Appalachian Orogeny,
a series of mountain-building events in the central and eastern
U.S., rocks were alternately
buried, uplifted, faulted, folded, and fractured. The geologic
mountain-building and subsequent erosion created cracks and fissures
in the rock through which rainwater and groundwater entered and
actively dissolved the organic limestone. Within the past 10
million years, caves, conduits, and underground drainage systems
have been dissolved into this rock by moving water. Surface water
and streams are captured by underground channels. These channels
convey the water to springs which sustain the water flow, cool temperatures,
and aquatic habitats of our rivers.