WHAT ARE SINKHOLES?
A sinkhole is a pit formed in the
ground due to a collapse in the surface
layer. Sinkholes are a common feature
of Florida's landscape. In fact, Florida
experiences more sinkholes than any
other state! Sinkholes are most common
in Central Florida, including the Tampa,
Orlando, and Ocala metro areas. Pasco,
Hernando and Hillsborough Counties,
on the west coast, are home to around
two-thirds of reported sinkholes.
Nevertheless, sinkholes can form
anywhere in the state.
Florida is vulnerable to sinkholes
because of its karst terrain. Karst terrain
refers to underground structures that
contain many connected openings and
caves, sort of like a piece of swiss
cheese. These openings form due to
chemical weathering and erosion. Most
of Florida is made of two types of weak
rock: limestone and dolomite. Both of
these rocks are made of calcium
carbonate, which dissolves quite easily.
The breaking down of carbonate
rocks begins when they are exposed to
acidic water. Most rainwater is slightly
acidic and usually becomes more acidic
as it moves through decaying plant
debris. Limestone in Florida is porous,
meaning it has a lot of tiny holes within
it. This allows acidic water to penetrate
through the rock layers, dissolving some
limestone and carrying it away in
solution. Over long periods of time, this
erosional process has created extensive
underground voids and drainage
systems in much of the carbonate rocks
throughout the state. Collapse of
overlying sediments into the
underground areas produces sinkholes.
Sinkhole formation often increases
following a heavy rainstorm. Hurricanes
can also accelerate the formation of
sinkholes. The increased water makes
the ground unstable, and increases the
rate of weathering.
Additionally, sinkholes can also
form when there is not enough water.
During a drought, underground caves
that are normally filled with water can
become empty. Without the mass of the
water to support it, the top layer of rock
collapses. Humans pumping too much
water out of the aquifer can worsen this
effect.
Florida’s karst landscape also is
responsible for the many spectacular
caves and springs in our state. When
groundwater discharges from an
underground drainage system, it is a
spring, such as Wakulla Springs, Silver
Springs, or Rainbow Springs. Sinkholes
can occur in the beds of streams,
sometimes taking all of the stream's
flow, creating a disappearing stream.
Dry caves are parts of karst drainage
systems that are above the water table,
such as Marianna Caverns located on
the Florida Panhandle.