1. Karst and
The Buffalo River
What is Karst?
Karst is a landscape that is characterized by
sinkholes, caves, springs, underground
drainage, and sinking streams (a stream
that loses its flow to underground
drainage). These features are created as
carbonate rocks are dissolved. The time it
takes to develop karst features depends on
the amount of water introduced to the
rock, the acidity of that water, and the rate
at which the water flows through cracks,
fissures or conduits. Twenty-five percent of
the world’s drinking water comes from
karst aquifers.
What are Carbonate Rocks?
Carbonate rocks are sedimentary rocks that
are formed by an accumulation of calcium
rich debris such as shells and corals which
were deposited on warm shallow sea floors
where biological activity thrived. The two
major types of carbonate rock are
limestone and dolostone. Limestone is
primarily made up of the mineral calcite
(CaCO3), while dolostone is made of the
mineral dolomite (CaMg(CO3)2). Limestone
and dolostone are common all over the
world, and are abundant around the Buffalo
River where they form massive bluffs, steep
hillsides, and wide valley bottoms.
How does Karst Form?
Water acidity plays a large role in the
dissolution of carbonate rock. Water can
become acidic though the decomposition of
vegetation, the weathering of sulfide
minerals, and the absorption of carbon
dioxide from air (carbonic acid). When
acidic water comes into contact with
limestone or dolostone, complex
interactions occur that dissolve the
carbonate rocks through a cycle of chemical
reactions. As the passages get large enough
to carry sediments, additional enlargement
of openings may occur as this abrasive
material is washed through the karst
system.
Groundwater Hydrology
In the Buffalo River area, much of the water
that enters the river has passed through
karst groundwater systems. Karst
groundwater recharge is the movement of
water from the surface to the water table,
and this happens in two ways. Diffuse
recharge is the slow seepage of water down
through the soil and rocks to the water
table. Discrete recharge is the rapid
movement of water to the water table
through sinkholes, losing streams, fractures,
faults and conduits. Discrete recharge areas
are very vulnerable to pollution, as there is
little time for bacterial die-off to occur.
Because of the highly fractured nature of
the bedrock in the Buffalo River watershed,
discrete recharge is very common.
Is Spring Water Safe to Drink?
Water that passes through karst aquifers is
unfiltered. Karst groundwater moves
rapidly, with little chance for reduction of
contaminants through soils and plant
uptake, or from UV radiation. Runoff from
roads, farms, sewers, etc., passes through
large underground conduits and is
transported to springs where it emerges
unfiltered.

2. Hazards to the Buffalo River
In the Buffalo River area, karst groundwater
supplies many homes with drinking water,
and also feeds the river. The National River
serves as a major source of tourism and is
an economic mainstay of the area.
Agricultural land use in the area is
considered a primary threat to water
quality, but contamination from septic
systems, service stations, dumping in
sinkholes and losing streams, and the
transport of hazardous materials along the
highways all contribute contaminants.
Animal waste acts as the primary source of
the harmful bacteria Eschericia coli (E. coli).
It is also the primary source of nutrients
such as Nitrogen (N) and Phosphorus (P)
reaching the river. These pollutants can be
harmful to human health, and reduce the
aesthetic appeal of the river and its
tributaries. During summer, high water
clarity, low flows, slow velocity, and warm
temperatures make the Buffalo River a
perfect place for algae blooms from the
elevated nutrient levels. The algae covers
the bottom, giving the river a green slimey
appearance, makes the rocks very slick, and
can cause a reduction in water clarity. The
increased plant activity causes the amount
of oxygen dissolved in the water to
fluctuate widely, reaching supersaturation
in the daytime and critical depletion at
night. These wild swings cause severe
problems for fish and other aquatic life.
Collapse of Karst Features
Sometimes catastrophic failure of a cave
passage causes sinkholes to appear
overnight. This is the result of collapse
occurring into a cave. As the width of a
cave passage widens, stress on the rocks in
the ceiling will cause some rocks to collapse
into the passage to create a stable arch. As
this collapse is occurring, the distance
between the roof and surface will be
reduced until the roof can no longer
support itself. Solution sinkholes form
when a point of favorable downward
drainage is initiated in the rock and
enlarged by dissolution. Where thick soil
deposits exist, rapid subsidence of soil into
the opening leaves a cylindrical hole
surrounded by a bowl shaped depression.
How do You Know Where Karst is?
Unlike surface water sources, karst
watershed boundaries do not always follow
topographic divides (valleys and ridges). In
order to understand how karst groundwater
travels, geologists use non-toxic dyes to
figure out where the water emerges after
sinking underground. Travel time, dye
concentration, and flow rate are all
recorded, giving scientists a good
understanding of how the water moves
beneath the surface. Studies have been
conducted within much of the Buffalo River
watershed, demonstrating complex
interconnectivity amongst springs and
streams that don’t otherwise appear to be
connected on the surface. The studies have
shown that some of the Crooked Creek
watershed supplies water to the Buffalo
River, particularly Mitch Hill Spring and
Dogpatch Spring. Mitch Hill Spring has been
determined to have a recharge area of
49.65 square miles.
Sources Cited
Mott, D., Aley, T., Hudson, H., Bitting, C., Luraas, J., Mays,
N., Henthorne, J., and, Henthorne, B. 2002. Delineation
and characterization of karst groundwater recharge in
the vicinity of Davis Creek and John Eddings Cave, Buffalo
National River, Arkansas. U. S. Department of Interior,
National Park Service, Buffalo National River.
Mott, D.N., Hudson, M.R., and Aley, T., 1999, Nutrient
loads traced to interbasin groundwater transport
at Buffalo National River, Arkansas, in Harmon, D., ed.,
Proceedings of the 10th Conference on Research and
Resource Management in Parks and on Public Lands,
George Wright Society, Hancock, Michigan, p. 114-121.
Whitley, L. D., 1986. Karst Topography and its Occurrence
in Kentucky. Hydrologic Problems in Karst Regions.
Western Kentucky University, Bowling Green, KY. p. 41.
Aley, T. 1982. Characterization of Groundwater
Movement and Contamination Hazards on the Buffalo
National River. Ozark Underground Laboratory. Protem,
Missouri.
Brochure Created by Blake Stone, 2015
NPS Geoscientist-in-the-Parks Program
GSA GeoCorps America Program