| Georgia Barrier Islands |
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| Written by Kelly O'Rourke & Elizabeth Cheney |
 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. |