Sunshine State Standards
In “Florida’s Sinkholes” you’ll learn how
mechanical and chemical activities shape
and reshape Earth’s surface to form aquifers,
caverns, and sinkholes. (SC.D.1.3.1)
Human activities, such as pumping too much
ground water from wells, may cause sinkholes
to form. (SC.G.2.3.4)
190 Unit 2: Earth’s Surface
This huge sinkhole in
Winter Park formed in
one day in 1981.
dolomite. Carbonate rocks are often porous, or full
of holes. As rain falls through the atmosphere, it
dissolves carbon dioxide and other gases and
becomes slightly acidic. When the rain falls on the
ground and moves through decaying plants, it
becomes more acidic. This acidic rainwater sinks
into porous limestone, dissolving some of the stone
and carrying it away. Over time, small holes can
become big holes. Big holes can become caverns.
The Sinkhole That
Swallowed a City Block
In 1981 a resident of Winter Park, near Orlando,
was astonished to see a tree suddenly disappear.
It had been swallowed up by a sinkhole that continued to grow rapidly. A day later, the hole had
consumed 118,520 cubic meters (160,000 cu yd) of
land, including a house, an auto repair shop, a
laundromat, five cars, and a swimming pool. The
resulting hole was more than 100 meters (330 ft)
wide and 38 meters (125 ft) deep.
The hole filled with water. The city of Winter
Park eventually sealed the bottom of the hole,
landscaped the area around it, and built a playground and recreation center nearby. Now the
sinkhole is a popular tourist attraction.
What caused this amazing hole to appear?
To understand sinkholes, it’s important to know
something about the geology of Florida.
That Sinking Feeling
What’s underneath your feet? If you’re outdoors,
you may be standing on a thin layer of clay and
sand, but what’s underneath that? The answer in
Florida is carbonate rocks, mostly limestone and
This type of erosion has created underground
caverns throughout Florida, like those in Florida
Caverns State Park in Marianna. When the roof
of a shallow underground cavern becomes so
thin that it collapses, a sinkhole is formed.
Regions in which erosion has produced sinkholes,
springs, underground streams, and caverns are
said to have karst topography. The landscape of
northern Florida contains almost eight sinkholes
per square kilometer.
Underground Cavern
soil
sand
clay
limestone
When erosion dissolves underlying limestone,
cavities form. Over time, the cavities can grow into
large caverns.
Collapse Sinkhole
soil
sand
clay
limestone
When the roof of a cavern becomes thin and weak,
it can cave in, forming a type of sinkhole called a
collapse sinkhole.
Florida Connection 191
Types of Sinkholes
Sinkholes are a fact of life in Florida, thanks to
the porous rock under its surface. There are three
general types of sinkholes.
Collapse Collapse sinkholes are the most common
type of sinkhole in Florida. They usually occur where
the surface of the ground is made up of thick soil
and heavy clay. When the roof of an underground
cavern grows thinner and becomes weak, it may
fall in suddenly. This often leaves a deep hole with
steep sides.
Solution Solution sinkholes form slowly over a
long period of time. They occur where limestone is
exposed at the surface or is covered by only a thin
layer of soil and sand. Surface materials are broken
down by erosion from wind and surface water,
forming a bowl-shaped hole. Water may collect in
this hole, forming a lake.
SPOTLIGHT ON Sinkhole Sightseeing
Just outside Gainesville you can visit Devil’s
Millhopper Geological State Park, which contains a
sinkhole that is 20 million years old. It became a
popular destination for curious tourists and scientists in the early 1880s. The hole formed when an
underground cavern roof collapsed. The bowlshaped hole is 37 meters (120 ft) deep and 153
meters (500 ft) across. Visitors can walk down a
232-step stairway to the bottom.
The sinkhole got its name because its funnellike shape reminded farmers of hoppers used to
hold grain at mills. Marine shells and fossils can be
found in the sinkhole. Much of Florida’s natural
history has been revealed by studying fossils of
shark teeth and remains of extinct land animals
found there.
Nearby is Paynes Prairie State Preserve, which
is also an enormous round sinkhole. Several times
this 21,000-acre prairie has become a lake when its
natural drain became blocked. The last time this
happened was in 1871. For 20 years, steamboats
carried people and goods across the lake. Then in
1891 the drain suddenly became unblocked, and
the lake drained in less than two weeks!
192 Unit 2: Earth’s Surface
Subsidence A subsidence sinkhole forms where the
ground cover is a thin layer made up mostly of
sand. Individual grains of sand slowly subside, or
settle down, into an underground cavern.
Subsidence sinkholes are usually only a few feet in
diameter and depth.
Dangers from Sinkholes
Sinkholes in Florida can appear suddenly and cause
threats to life and property. Roads and building
foundations can be damaged, and trees may be
uprooted. A sinkhole in a streambed can divert all
of the stream’s flow, causing what is called a disappearing stream.
Sinkholes also pose a major threat to drinking
water. Pollutants at the surface, such as farm and
lawn fertilizers and wastes from leaking septic
tanks, can get into ground water by traveling
Even though sinkholes are common in Florida,
most sinkholes are not catastrophic or even harmful. Don’t worry that the ground might give way
beneath your feet at any moment. The best
course of action is learning about the geology
of your area and knowing what signs to look for.
If you suspect that a sinkhole may be forming,
notify the landowner and the local water management district.
Sinkhole diving is a popular recreational activity for
experienced divers.
though sinkholes. Underground aquifers provide
more than 80 percent of the drinking water in the
state. When ground water is polluted, it is difficult to remove the pollutants and make the water
suitable for drinking.
As many as 150 new sinkholes are reported
each year in Florida. Forecasting where they will
occur is difficult and expensive. Geologists and
geotechnical engineering consultants attempt to
locate underground cavities by using drilling
machinery and radar surveys. Weather conditions
can give clues to potential sinkholes. Dry weather
followed by large amounts of rainfall can lead to
more sinkholes.
• What questions do you have about sinkholes
and their effect on Florida’s landscape?
• What questions do you have about other karst
landforms?
RESOURCE CENTER
CLASSZONE.COM
Visit
ClassZone.com for more information
on sinkholes.
Small streams and waterfalls run down
the sides of the Devil’s Millhopper sinkhole, described on page 192. Where does
this water come from? Since the hole
doesn’t fill with water and become a
lake, where does the water go? Write
two paragraphs explaining this process.
Signs of potential sinkholes include
• trees and fence posts that are slumping
or falling
Writing Tips
• cracked or bare soil
Plan, draft, and revise your writing using
the tips below.
• Think about what you know about the
water cycle.
• exposed parts of building foundations
or tree roots
• Skim the article to review how sinkholes form.
• doors and windows of buildings not
closing properly
• Make connections to explain the
process.
• circular areas of wilting vegetation
• Be sure that each paragraph has a
topic sentence.
• cracked building foundations
• Revise your paragraphs to make them
as clear as possible.
Florida Connection 193