Missouri Caves, Karst, and Springs
This is a basic intro to Karst topography, should you ever have to give a five minute lecture
on the subject. There are many sorts of Karst. The name itself comes from the Karst region of
Slovenia, along the Adriatic coast, where the landform was first noted. Karst is any terrain based
on a layer of soluble bedrock, usually, though not always, of carbonate rocks. In the American
Midwest, karst forms on limestones (calcium carbonate) and dolomites (magnesium calcium
The precise erosional forms which the karst takes depends on many variables. The mechanical
structure and chemical composition of the rock, the local climate and temperature range, and the
amount of vegetation and rainfall a region has all determine how fast a carbonate landscape
erodes. Karst along a seaside is quite different than that inland, and tropical karst does not
resemble karst in temperate or sub-Arctic zones. Landforms in zones with earthquake activity are
quite different than that in quiet zones, or places where mountain-building have turned the layers
of carbonate rock on edge. Some karst is formed as a result of sulfuric acid welling up from below
instead of carbonic acid percolating down from above. Some places in the American West are a
mix of the two processes.
But the karst of the Missouri Ozarks is almost textbook, and is characterized by well eroded
rolling hills, deep hollows, springs, caves, sinkholes, losing streams, natural bridges, and tunnels.
A few definitions:
- A spring is a natural resurgence of groundwater, usually along a hillside or
from a valley floor.
- A cave is an airfilled underground void, large enough to be examined in some way
- A sinkhole or sink is a collapsed portion of bedrock above a void. Sinks may be a
sheer vertical opening into a cave, or a shallow depression of many acres.
- A losing stream is one with a bed with allows water to flow directly into the
groundwater system. There are many chert bottomed losing streams in the Ozarks.
- A natural bridge or tunnel is a void beneath still standing bedrock, usually of short
extent, and allowing human passage from one end to the other, at least part of the time. A natural
bridge is somewhat shorter than a tunnel, and is more inclined to be air filled than partly water
Missouri, especially south of the Missouri River, has all the natural resources to make, (in the
words of Jerry Vineyard, one of our best known geologists and cavers) a wonderful cave
In order for temperate karst to form, there must be sufficient layers of carbonate rock (in
Missouri, anywhere from none to thousands of feet thick); adequate rainfall (about 45 inches
annually); a reasonable vegetative cover to provide humus and carbon plant debris (oak-hickory
forest and grassland over much of the state); suitable entrances to the bedrock (faulting and
dipping from the Ozark uplifts and seismic activity); and a variable climate (bored with our
weather? Just wait a few minutes.)
Karst is formed when rainwater picks up carbon dioxide from the air, and dead plant debris in
the soil, then percolates through cracks dissolving the rock. The bedrock becomes saturated with
water at some level, and dissolving continues as the water moves sideways along bedding planes
(horizontal cracks between rock layers) and joints (or fractures) in the rock itself. These conduits
enlarge over time, and move the water, via a combination of gravity and hydraulic pressure,
further enlarging the conduits through a combination of solution and abrasion of water on the
Eventually, much of this water under pressure reaches the surface of the land as a spring. A
spring may emerge high on a cliff, at the base of one, or even forced upward from below the level
of the surrounding surface streams, depending on nature of the surrounding rock, and the altitude
of the groundwater level, with respect to the base level of the controlling stream in a drainage
area. Often in Missouri, springs have little relationship to surface drainage, because so much of
our water movement is actually groundwater movement. In some areas of the Ozarks, more than
70% of all water goes underground via karst processes.
As groundwater levels in an area drop, more and more of the underground passage becomes
air filled. When it is sufficiently air filled, springs become cave entrances, passable by humans.
Other voids never develop a natural opening, and are intersected by drilling, notably of wells
looking for water. At this point, due to changes in chemical equilibrium underground, the
resulting caves begin to fill with dissolved mineral, called cave deposits or speleothems. Caves
may refill with water or continue to dry out, or even cycle several times as water levels change.
Erosion continues underground, and eventually a cave hollows enough for the roof to thin,
and the cave collapses. Such cave collapse may actually unroof the cave if it is near enough to the
surface, or simply form a slump in the level of the land. In either example, a sink forms. Natural
bridges and tunnels can be formed as resistant remnants of a cave collapse, or independently, if a
block of bedrock becomes cut off from the main land mass, and it is hollowed out by wind, ice
wedging, and rain.
Many karst areas have poor soil, and do not retain water easily, allowing it to go directly
underground. Sinks also act as "swallow holes" for rainwater; some sinks take water under certain
conditions, and resurge it at others. These reversible sinks, called estavelles, are among
the curiosities of karst. Some springs in the Ozarks are periodic, or "ebb and flow" springs, whose
discharge can be measured to rise and fall independent of local rainfall. Many theories, but no one
knows why, for sure. Another oddity of Missouri karst is the karst window, where one
may look into a cave or water filled sink below, but getting down there is another matter entirely.
Karst makes for beautiful scenery, but it is very vulnerable to groundwater pollution, due to
ease of water flow. Natural filtration is nearly non-existent in karst. To make matters worse, the
use of cave conduits as natural sewer lines, and sinkholes as garbage dumps in small towns and
rural areas puts the local drinking water supplies at risk. It is only recently that these problems are
being addressed. Urban expansion in karst areas often means the building of houses on land which
cannot support them and problems with septic tanks, underground pipeline breaks and landfills.
Some of the most beautiful sites in Missouri are a result of karst processes, as are some of our
most pressing land use problems. Public education about our karst jewels and our karst
nightmares is the best way to preserve what we have, and to fix what needs fixing.
2003 Jo Schaper.
Return to Webster's Home Cave.