Even though Fantastic Caverns is a small family business, we strongly support science education. It is only through better understanding and wise stewardship that the Ozarks will remain such a wonderful place to live.
Learning about Caves and Karst
The southern half of Missouri is cave country. Water has carved into the surface and through the subsurface to create our rugged Ozarks terrain … a land of ridges and hollows laced with thousands of sinkholes, springs and caves. Karst is another name for cave country. Specifically, we’ll look into:
1. Natural History: The Nature of Cave Country.
How do caves and karst show geological and biological process at work?
2. History: Man in Cave Country.
How are people living in karst areas affected by the unique geography?
3. Conservation: Protecting Cave Country.
How do we take care of the land, water, wildlife, and ourselves?
THE NATURE OF CAVE COUNTRY
Much of the significance of caves is due to their unique natural histories. We can actually enter the earth and watch geology at work: water first carries off soluble rock to hollow out a cave and then brings in minerals to build formations. And small, white, blind cave animals are living examples of adaptation to total darkness.
A cave is a natural underground cavity large enough for people to enter. Here in Missouri, we only add caves to the state list which are at least 20 feet long. A mine is not naturally formed, and so is not a cave. Folks generally use the word cavern as a synonym for cave. A cave system includes all passages that interconnect. Some of these may be very small or water-filled.
TYPES OF CAVES
1. Most caves are in rocks that can be dissolved by a weak natural acid (usually carbonic acid). This acid forms when rainwater mixes with carbon dioxide in the upper layers of the soil. Soluble rocks include limestone, dolomite, gypsum and marble. Caves formed in the rocks are solutional caves. Ozark caves are solutional.
2. Caves form inside lava flows during cooling. First a crust hardens on the lava. A break in this crust allows molten lava to flow out leaving tunnel-like passages hundreds or even thousands of feet long called lava caves or lava tubes. Ice Cave at Grants, New Mexico, is a lava tube open to the public. Others are found in Hawaii, California, Idaho, Oregon and Arizona.
3. Waves create sea caves. The waves force water into cracks in the rock, breaking of the rock and forming caves. Sea Lion Cave in Oregon is open to the public.
4. Huge rockfalls from cliffs can create large spacious chambers within the resulting boulder piles. Such talus (ta’ les) caves are found in the northeastern United States. One cave contains over 12,000 feet of walking and crawling passage. Polar Cave in New Hampshire is a talus cave open to the public. Others are found in Pinnacles National Monument in California.
5. Melting water moving through glaciers creates glacier caves in places such as Canada, Alaska, and high on Mt. Ranier in Washington.
6. The movement of rock along a fault can make an earthquake cave. Sipapu Caverns in Wupatki National Monument in northern Arizona is one such cave. Explorers have descended about 500 feet into this natural crack in the rock. The bottom is plugged with debris washed down from the surface. Seneca Caverns in Ohio is an earthquake cave open to the public.
7. In desert areas, flash floods can move through the soil and hollow out openings. This commonly occurs near the edge of terraces that have been cut by gullies. Caves of this type are found in the Mojave Desert in California and are called soil tubes.
The most common kind of cave by far is the solutional cave. All the caves in Missouri are of this type. With more than 5500 known caves, Missouri is known as the “cave state”.
The Ozarks, called by geologists the Ozark uplift or Ozark dome, is the result of repeated episodes of submergence, deposition, uplift, and erosion.
During times when the area was submerged under the ocean, creatures took lime from the seawater to make their shells. As they died these shells, together with limey mud, settle to the ocean floor and built up in layers. After millions of years of accumulation, the weight of seawater and overlying sediments pressed these layers into rock. So most of the rocks in the Ozarks are old ocean floor – limestone and dolomite. The limestone, in particular, contains a lot of fossils.
More recently (geologically speaking), during the last couple of hundred million years, the area has been mainly in an uplift and erosion mode. The geologic center of the uplift is the St. Francois Mountains in southeast Missouri. These are the oldest rocks in the Ozarks. Like a huge dartboard, the rocks get younger in irregular bands moving outward from the St. Francois Mountains.
As the area lifted in a broad plateau, agents of erosion (mainly water) worked to carry off the rock. Rivers cut their channels, creating the rugged Ozark topography. At the same time, subsurface water made caves.
SOLUTIONAL CAVE PATTERNS
Solutional caves can be divided into two patterns – maze and branchwork. Which pattern a particular cave becomes depends mainly on how water moves into and through the subsurface (type of recharge).
Maze caves form in several ways: by flood water pouring down through sinking streams, by water percolating through the rock (diffuse recharge), or by rising deep-seated water.
Any of these conditions causes the simultaneous enlargement of many openings, forming a pattern of many interconnecting passages and closed loops.
The maze pattern can vary greatly – from a regular criss-crossing network of passages (Mark Twain Cave near Hannibal, Missouri) to a giant 3-dimensional inkblot pattern with irregular rooms and passages wandering away from the areas of main development (Carlsbad Caverns, New Mexico).
But the largest number of solutional caves form when water moves underground via sinkholes. The water simply moves down through these point sources into a system of conduits. The overall pattern is a branching system of joining tributaries, much like a river system, and thus is called branchwork caves.
CAVES ARE DRAINED SPRING SYSTEMS
About 90% of solutional caves, both branchwork and maze, form by the movement of water from overlying recharge areas to springs in nearby valleys. The process of forming such a cave in soluble rock (usually dolomite or limestone) begins with rain.
As rain falls through the air and seeps into the soil, it absorbs a small amount of carbon dioxide. Water mixed with carbon dioxide forms a weak carbonic acid solution that dissolves the rock.
The openings forming below grow larger and join creating an underground river as part of a spring system. Water hollows out and enlarges the passages as it enters this system (often through sinkholes), moves below ground, and surfaces at a spring. Finally, in response to surface rivers eroding ever deeper, the subsurface water drains away … leaving behind a cave. Often the draining is incomplete, and a stream still flows through part of the cave. This stream can flood during heavy rains.
Three-fourths of the runoff in the Ozarks moves underground through caves. Rivers here not only flow on the surface, they flow below the surface. Springs are the drainage points for caves: caves are really drained spring systems.
A large Ozark spring, such as Big Spring near Van Buren, discharges millions of gallons per day and each 1000 gallons contains about one pound of dissolved rock. Indian Spring, which flows from Fantastic Caverns, discharges 9000 gallons per minute during peak flow.
Imagine the enormous volumes of water and long lengths of time to form caves. And with thousands of springs, you can think of Missouri as a “cave factory”.
Fantastic Caverns is a two level branchwork cave. Each was at one time full of water, but over a very long period of time this changed.
The jeep tours run on the dry upper level. The lower level is a wet weather stream, carrying water during the rainy season through the cave to the discharge point at Indian Spring.
Rarely, big rains will back up water from the lower level into the upper level, flooding it. Below the cave, all openings in the rock are water filled – that is, below the water table. This water supplies wells in the area.