The word Karst is the German name for the Krš (or Kras) region on the border between Slovenia and Italy, which has a similar limestone topography. It’s used to describe this type of unique geology of caves, sinkholes, and springs, no matter where on earth it occurs.
The Karst Cycle
Slightly acidic groundwater flows through cracks in limestone or dolomite, slowly dissolving the rock. The cracks widen to form cavities and eventually a subterranean drainage system. The creeks that flow through caves come from surface water that has seeped downward.
When a cave is below the water table, it is filled entirely with water. (Well-drillers search for these water-filled pockets.) When the cave is above the water table, the cave has air in it and its water flows ever downward. Wherever cave water exits the rock and flows into the open air, it is called a spring.
Some of our largest caves formed ages ago as completely water-filled cavities. Over geologic time, the Ozark Plateau was uplifted, and rivers carved valleys ever deeper into the bedrock, creating bluffs and causing cave passages to be above the water table and to drain.
As the slightly acidic water continues its etching of the rocks, sinkholes can occur where the roof of a cave, and the soil above it, collapse downward into the cave system. When rainwater collects in these depressions, sinkhole ponds form.
When an otherwise normal surface creek disappears underground, emptying into the water table below, it’s called a losing stream.
The natural bridge at Clifty Creek CA is part of a collapsed cave system.
Natural bridges (in karst landscapes) represent the last vestiges of an otherwise completely collapsed cave.
Inside a cave, the formation of speleothems (stalactites, stalagmites, soda straws, dripstone, flowstone, and so on) represent the cave’s old age, as water crystallizes previously dissolved minerals, basically reversing the cave-making process, slowly filling the cave back up with rock.
All the land through which water moves into groundwater or into springs or caves is called a recharge area. For a single cave system, this area can be many miles wide. Pollutants, such as agricultural chemicals and animal waste, roadway runoff, leaking septic tanks, contaminants from trash thrown into sinkholes, and even excess silt from a variety of construction and agricultural earthworks, can seep into the groundwater, polluting caves, springs, and well water.
Karst System Features
Cave and karst ecological communities are interdependent and often overlap, but it’s helpful to think of the following divisions.
Created long ago by water, but now high and dry, terrestrial caves offer shelter to a variety of animals.
Long ago created by water, but now high and dry, terrestrial caves are home to a variety of animals, but because of the dark, very few plants. Although water may collect at times on the floor of these caves, there is no permanent flowing water in them. Many mammals, including foxes, skunks, and bobcats, seek temporary shelter in these caves. The basis of the food chain in such caves is not plants but organic detritus, including corpses of cave animals and dung. Many species of bats roost in terrestrial caves, and the nutrients in their guano are the foundation of a diverse animal community.
Terrestrial caves are often linked with bluffs and glade habitats, with their important plant and animal species, and with riparian (streamside) habitat below. Many dry caves contain — or used to contain — prehistoric human artifacts. It is illegal to remove, damage, or destroy such archeological treasures.
Cave Spring Park, Carter County.
Aquatic caves — ones with permanent or nearly permanent water — are fascinating, unique, and fragile. Humans have only a limited understanding of aquatic cave species and their interconnections.
Many animals living in aquatic caves lack body pigments, are sightless or nearly so, and are adapted to economize their energy expenditures, since their food supplies can be unsteady.
There are many remarkable animals that are so specialized for living in caves that they cannot survive outside the cave environment. These include cavefishes, cave crayfishes, the grotto sculpin and grotto salamander, and several species of flatworms, cave snails, arachnids, amphipods, copepods, isopods, millipedes, insects, and more.
Because they cannot live outside the cave, and because many species are limited to a single cave system, a single pollution event affecting the groundwater seeping into the cave can potentially wipe out an entire population, which might constitute all the members of a species.
Sinkhole Pond at Grassy Pond Natural Area, Carter County
When a cavern’s ceiling collapses, a sinkhole may be formed on the ground above. The sinkhole sometimes becomes blocked with soil and other surface materials and fills with water, creating a pond. Some sinkhole pond communities are dominated by trees, while others may have only shrubby or herbaceous plants.
In upland areas, sinkhole ponds are important water sources for wildlife, including deer, turkey, and wood ducks. Sinkhole ponds are important feeding and breeding areas for salamanders, frogs, and toads.
Many plants are specialized to live in sinkhole pond areas. For example, Virginia sneezeweed, a federally threatened member of the sunflower family known only from Missouri and Virginia, occurs in areas with sinkhole ponds, low, wet meadows, and swales underlain by karst geology.
Missouri's Ozarks have many, many springs, large and small.
Springs are places where water discharges from the ground due to gravity or to the very pressure of standing water. Missouri has many great examples of both freshwater springs and mineral or salt springs. Springs fall into two general categories: seeps, and underground streams (usually associated with aquatic caves). Some springs are the merest trickle, while others churn out hundreds of millions of gallons each day.
Missouri’s large, cool, aqua-blue springs are a source of wonder — and tourism revenue — in our state. Some of our most beautiful rivers and float streams are spring fed. Few people are aware of it today, but between 1800 and 1930, our mineral springs, and at least 80 resorts and spas that developed around them, drew hundreds of thousands of visitors to Missouri seeking “healing waters.” Our earliest settlers, notably Nathan Boone, boiled the water from natural salt springs to yield the salt necessary for frontier survival.
Because many springs are associated with caves, many aquatic cave-dwelling animals appear where the caves open into springs. Where springs flow into streams and rivers, their cool, clear, well-oxygenated water creates a special habitat inhabited by a unique community of plants and animals: certain ferns, watercress, gilled aquatic snails, isopods, crayfish, salamanders, sculpins, and more. Trout, which are coldwater fish, can be successfully stocked in some spring-fed Ozark streams because of the springs’ cooling influence on the water.