U.S. Geological
Survey
Marine and Coastal Geology Program
Hurricane Impacts on the Coastal Environment
In terms of insured losses, Hurricane Andrew is the most severe
catastrophe in the Nation history. Prior to the arrival of
Andrew, the
U.S. Geological Survey (USGS), in cooperation with the Louisiana
Geological Survey (LGS), acquired an extensive body of
information and
data on the behavior and long-term erosion of Louisiana barrier
islands. As a result, we have a clear understanding of pre-storm
conditions in this area; Andrew provided an opportunity to learn
in
detail the impact of a very large storm on Louisiana coastal
environment.
- Dr. Abby Sallenger, U.S. Geological Survey
Of the most severe catastrophes in the Nations history,
hurricanes
account for two-thirds of the insured property losses.
During August and September 1992, Category 4 hurricanes, with
sustained
winds between 131 mph and 155 mph, made four landfalls in the
United
States and its territories. The resulting damage in south
Florida,
Louisiana, Guam, and Hawaii was in the tens of billions of
dollars.
Hurricanes and extreme extratropical storms cause elevated sea
level,
known as storm surge, and extensive shoreline erosion and other
geologic effects leading to the loss of property and life. We
cannot
yet predict with confidence the magnitude of this erosion and the
extent of geologic impacts. The variability of shoreline types,
including barrier islands of Louisiana, mangroves of south
Florida,
coral reefs and pocket beaches of Hawaii and Guam, make
predictions
especially difficult.
Rapid-response surveys of Hurricane Andrews impact zone
conducted by
the USGS reveal surprising results.
For Hurricane Andrew, the loss of human life and property is well
documented. However, the environmental effects are less
well-known.
In south Florida, Hurricane Andrew completely stripped vegetation
from
the northernmost Florida Keys. In the case of mangrove trees,
defoliation and wood damage killed large old stands along the
shoreline.
Area studies reveal the immense change brought about by these
storms.
In Louisiana, Dr. Shea Penland and his
colleagues at the LGS
reported
that Andrew stripped sand from 70 percent of the barrier islands
leaving exposed old coastal marsh. More than 80 percent of
oyster
reefs behind the barrier islands were smothered by a
0.3-0.9-meter
thick blanket of sediment. More than 70 kilometers of valuable
dune
habitat providing storm protection to estuaries, wetlands, and
the
coastal population were destroyed. In Hawaii, Dr. Charles
Fletcher and
his colleagues at the University of Hawaii cooperated with USGS
scientists in a study of the effects of Hurricane Iniki, the most
powerful hurricane to strike the Hawaiian Islands this century.
They
report that Iniki caused massive beach-face erosion and overwash
of the
coastline which penetrated up to 300 meters reaching elevations
of
nearly 9 meters.
USGS scientists have used historical data to show that
Louisiana is eroding rapidly.
The
Louisiana barrier island shoreline is eroding at a rate, in some
places, exceeding 20 meters per year as a result of both
hurricanes and
normal processes. The land is subsiding because of compaction of
the
Mississippi delta sediments. The net effect of subsidence is
that sea
level is rising at a rate of about 1 centimeter per year, ten
times the
world rate. USGS scientists take advantage of this natural
laboratory
to study erosion and deposition patterns resulting from sea-level
change. The Louisiana barrier islands protect productive
estuarine and
wetland environments that support a $10 billion per year fishing
industry. Erosion of the barrier islands is so severe that their
ability to function as effective buffers for the prevention of
wetlands
loss has been dramatically reduced. Louisiana's wetlands are
disappearing at rates of 40 square kilometers per year. In a few
decades the barrier islands may be gone and the wetlands will be
lost
even faster.
USGS scientists plan studies of the high-energy processes
responsible for storm damage.
In order to help mitigate the impacts caused by hurricanes such
as
Andrew and Iniki, environmental managers and engineers must
understand
the geological processes that cause erosion and environmental
change.
Results of the recently-completed Louisiana Barrier Island
Erosion
Study are presently used in formulating erosion-mitigation
strategies.
Documentation of impacts by Andrew to this area, for example,
when
compared and interpreted in relation to previously-gathered data,
provide an invaluable baseline for mitigation projects and
loss-reduction strategies for other areas affected by such
storms.
For more information please contact:
Dr. Abby Sallenger
USGS Center for Coastal Geology
600 4th St. Sourth
St. Petersburg
FL 33701
Phone: (813)893-3684
email: asallenger@usgs.gov
This USGS Fact Sheet can be found at
<URL:http://marine.usgs.gov/marine/fact-sheets/>
Maintained by jrobb@bramble.er.usgs.gov
