U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2007–3060

July 2007

Sinkholes

Printed on recycled paper

Catastrophic Sinkhole Collapse in Missouri

Sinkholes are a common feature in Missouri where limestone and dolomite outcrop. Though often considered a benign 

nuisance, sudden, catastrophic collapses can destroy property, 

delay construction projects, and contaminate ground water 

resources. 

What is a “Sinkhole”?

A sinkhole is an area of ground that has no natural external 

surface drainage—when it rains, all of the water stays inside the 

sinkhole and typically drains into the subsurface. Sinkholes can 

vary from a few feet to hundreds of acres and from less than 1 

to more than 100 feet deep. Some are shaped like shallow bowls 

or saucers whereas others have vertical walls; some hold water 

and form natural ponds. Two historic sinkhole ponds in southern 

Missouri are Tupelo Gum Pond and Cupola Pond. Typically, 

sinkholes form so slowly that little change is seen in one’s lifetime, but they can form suddenly when a collapse occurs. Such 

a collapse can have a dramatic effect if it occurs in an urban 

setting. 

Where do sinkholes form?

Sinkholes form in what geologists call “karst terrain.” Karst 

terrain is a region where the bedrock can be dissolved by ground 

water. Bedrock in a karst area typically is limestone, dolomite 

(a rock similar to limestone but with magnesium along with the 

calcium normally present in the minerals that form the rocks) 

or gypsum. Karst areas are characterized by special features not 

present elsewhere: springs, caves, dry streams that lose water 

underground, and sinkholes. 

These features all form because water that is slightly acidic 

from absorbing carbon dioxide from the air and soil dissolves 

the bedrock and forms pathways and channels in the rock. 

These pathways, called conduits, are like underground plumbing 

that carries water from the surface to springs located in valleys. 

Eventually, these conduits become exposed by erosion and, if 

large enough, become caves. 

Sometimes conduits are called underground rivers. Like a 

river system, they have an area where the water collects and 

supplies the flow. For a surface river, this is called the basin; for 

a conduit, it is called the “recharge area.” Conduits collect and 

transport surface water (runoff) from the recharge area—which 

can range from a few hundred square feet to hundreds of square 

miles—to springs where it rises to the surface to join the more 

typical stream and river system. Sinkholes form in the recharge 

area where the surface water is flowing into the subsurface and 

entering a conduit.

How do sinkholes form?

When water from rainfall moves down through the soil 

and encounters bedrock in karst terrain, the bedrock begins to 

dissolve along horizontal and vertical cracks and crevices in 

the rock. Eventually, these cracks and crevices, which are the 

beginning of a conduit system, become large enough to start 

transporting small soil particles. As these small particles of 

soil are carried off, the surface of the soil above the conduit 

starts slumping down gradually, and a small depression forms 

on the surface of the ground. This small depression acts like a 

funnel and gathers even more water, which makes the conduit 

larger and washes more soil into the conduit. Not all of the soil 

particles get carried into the conduit; if the soil contains a large 

amount of clay, the conduit can become plugged and the sinkhole may start to hold water and form a natural pond. 

What makes a sinkhole collapse suddenly?

Catastrophic collapse sinkholes are more rare than the bowlshaped type, but they are not uncommon. Between 1970 and 

2007, the Missouri Department of Natural Resources examined 

more than 160 collapses reported by the public. Most of these 

collapses were small—less than 10 feet in diameter and 10 feet 

deep; some, however, are quite large and spectacular. Sinkhole 

collapses drained a lake in the St. Louis, Missouri, area, drained 

Sinkhole distribution in Missouri. the West Plains, Missouri, sewage lagoon, and another in Nixa, 

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94° 92°

40°

38°

Collapses

Sinkholes (data from

 Missouri Department of

 Natural Resources, 2007)

EXPLANATION
Missouri, swallowed a car along with the garage that it was 

parked in!

Collapses form in essentially the same way as the more 

common bowl-shaped sinkholes. When the soil particles start 

washing into the conduit, the soil closer to the ground surface 

does not slump down, but starts forming a bridge. A void forms 

where the soil keeps washing into the conduit and, eventually, 

this hole grows large enough that the soil above it can no longer 

bridge it. The soil bridge then suddenly collapses into the void 

below and a sinkhole forms.

The process of forming a conduit and a soil bridge typically 

takes many years to decades to form and can be aggravated 

by human activities. Since the process of forming a sinkhole 

depends on water to carry away soil particles, anything that 

increases the amount of water flowing into the subsurface can 

speed up this process. Parking lots, streets, altered drainage 

from construction, and roof guttering are some things that can 

increase runoff; even weather can make a difference. 

Collapses are more frequent after intense rainstorms, and 

there is some evidence that droughts play a role as well. Areas 

where the water table fluctuates or has lowered suddenly are 

more prone to collapse formation. Collapses are not limited to 

karst areas as they can form above old mines and even from 

leaky pipes—though they are much more frequent in areas that 

have significant karst development. 

Formation of collapse—Soil bridges gap where sediment has been 

washing into a solution enlarged fracture, A. Over time, the void 

migrates upward through the soil, B. After the bridge thins, a sudden 

collapse, C, often plugs the drain and erosion will, after many years, 

transform the collapse into a more bowl-shaped sinkhole, D.

Bowl-shaped sinkhole.

By James E. Kaufmann

A B

C D

Fax: (573) 308-3652

Phone: (573) 308-3679

email: ecwitt@usgs.gov

Emitt Witt, Director

U.S. Geological Survey

Mid-Continent Geographic Science Center

1400 Independence Road

Rolla, Missouri 65401

Additional Information

For more information about this and 

other integrated science studies at the 

Mid-Continent Geographic Science 

Center please write or call: