Caves and Karst

Cave_Interior_Morgan_County.jpg

Photo of interior of Jacob's Cave showing a variety of speleothems.
Missouri has many commercial and some public caves that offer tours.

Caves, springs, sinkholes, and natural bridges are all features of karst regions. Much of Missouri is a karst landscape of porous limestone and dolomite. Our caves, sinkholes, and springs support unique communities of animals.

In This Section

Photo of the opening to a small terrestrial cave on the side of a bluff.

Terrestrial Caves (Dry Caves)

Created long ago by water, but now high and dry, terrestrial caves offer shelter to a variety of animals. These caves are specially important to bats, many species of which are declining.

Cave Spring

Aquatic Caves

Missouri is known as “the cave state.” Caves with creeks, groundwater, or springs are fascinating, diverse, yet poorly understood. Many rare and vulnerable animals call these dark, wet tunnels home.

Sinkhole

Sinkholes and Sinkhole Ponds

Sinkholes, just like the caves beneath them, are common in regions with karst geology. When sinkholes are blocked and form ponds, they support unique wetland communities.

Photo of Alley Spring's pool of blue water.

Springs

Springs are openings in the ground or rock where underground streams or seeps release water into caves or on the ground. Missouri has many great examples of springs.

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.

Photo of the natural bridge at Clifty Creek CA
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.

Dry Caves

Photo of the opening to a small terrestrial cave on the side of a bluff.
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.

Aquatic Caves

Cave Spring
Cave Spring Park, Carter County.
Susan Flader

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 Ponds

Photo of sinkhole pond at Grassy Pond Natural Area
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.

Springs

Photo of springwater flowing among rocks and mosses
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.

Distribution in Missouri
Missouri has more than 7,000 caves identified (so far); if their tunnels were all combined and straightened out, they would run for more than 500 miles. Most of our caves are in the Ozark Highlands ecoregion, where they occur in soluble dolomite or limestone. Caves also occur in sandstone or igneous rocks and may be found in the Osage Plains and Central Dissected Till Plains ecoregions. There are almost no caves in northwestern Missouri and in the Bootheel lowlands.
Related Content

A Guide to Missouri's Cave Life

Get to know the seventy cave species brought to light in this 40-page booklet.

Ozark Cavefish Best Management Practices

Manage your Missouri cave streams to help this endangered species.

Spring Cavefish Best Management Practices

Manage your Missouri caves and karst to conserve this endangered species.