Along the coast of Georgia, eight clusters of barrier islands are
separated from the mainland by an extensive system of salt marshes and
sounds. Barrier islands get their name due to the protective role
the islands and their marshes play in shielding the mainland from
oceanic storms. Their formation is a completely natural and
dynamic process that has taken hundreds of thousands of years.
Over the past million or so years, from the Pleistocene Epoch to
present, climatic changes have caused Georgia’s shoreline to fluctuate
from the today’s continental slope 80 miles offshore, to 60 miles
inland from our present day shoreline. Seven sets of barrier
island profiles have been identified over the 60 mile inland stretch,
including the relic islands of Trail Ridge that were believed to
restrict flow and contribute to the forming of the Okefenokee Swamp.
Georgia’s present-day barrier islands are made up of two sets of
islands formed during distinctively different geologic time
periods. The older sets of islands were formed 35-40 thousand
years ago during the Pleistocene Epoch , before the last great “Ice
Age”.
Later, about 18 thousand years ago during the Holocene Epoch,
continental ice sheets began to melt. This was a time of sea
level rise and offshore islands rolled backward with the advancing sea
level, migrating up the continental shelf. Then about 4-5
thousand years ago, the rate of sea level rise greatly diminished,
allowing the establishment and growth of the new islands in their
approximate positions today.
Jekyll and Cumberland Islands are the only islands that still contain
both Pleistocene and Holocene island fragments. Much of the
Holocene formations which fronted Jekyll and Cumberland has been lost
to erosion, and the Pleistocene shorelines of these islands have once
again assumed those beaches.
The shape and sizes of sandy barrier islands change constantly under the influence of winds, waves, and tidal currents.
This is the typical progression of a barrier island starting with the
ocean beach, dune systems, inland area (maritime forests and/or barrier
flats), high and low salt marshes, and finally the lagoons or sounds
located between the islands and the mainland.
On some barrier islands, the ocean beach resides over what was once a
salt marsh. As barrier islands migrate or roll inland,
ocean beaches over wash dune ridges and bury existing salt
marshes. The salt marshes can adapt and reform on the new
interior side of the island.
Over time, portions of some barrier island’s ocean beaches may erode,
exposing underlying remnants of old salt marsh peat beds. This
can be seen on portions of Jekyll Island’s ocean beaches.
Jekyll Island’s beach has experienced the natural changes expected of a
sandy barrier island. While some sections have grown, others have
shrunk. Various factors have contributed to the erosion of our beaches
on Jekyll Island including storms, tides and human impact.
Large portions of the beach have been removed by storms, including
Hurricane Dora in 1964. President Lyndon Johnson ordered the placement
of a seawall composed of huge granite boulders known as the Johnson
Rocks on Jekyll and St. Simons Islands. The boulders were placed
along the northern shoreline in an effort to prevent further beach
erosion. During periods of high tides, the ocean reaches the rocks but
during low tide there is up to 30 feet of beach in places.
This is the Dexter Lane beach access point on Jekyll Island. You
can see some layers of peat have been exposed and are visible at low
tide. Although this is remnant peat beds from old salt marsh, its
texture and form have been changed over time by different geologic
processes. These peat beds are not squishy like present day marsh
mud. They have been covered by layers of soil, clay and sand for
thousands of years and have taken on an almost fossil-like
appearance. They are rock-like formations made of organic peat
material and will crumble if enough force is applied.
As you can see these exposed peat beds are providing great habitat for several types of plants and animals.
