Georgia
Off the southern coast of Georgia, pre–ice age and more recently formed barrier islands are sandwiched together to create the Golden Isles.
Georgia boasts about a hundred miles of coastline between Savannah and the St. Marys River, interwoven with eight major offshore islands and island groups known collectively as the Golden Isles. These formations are easily seen from on high, in a pattern of islands and inlets along the southern Georgia coast.
The geological histories of these barrier islands reveal two parallel sets of formations, created during two distinct time periods—one dating back to before the last ice age and one formed more recently.
Barrier islands form along coasts in places where sand is plentiful. Waves pile and carve sand into long, narrow spits, often forming chains of islands that parallel the coast, protecting the mainland from wave action. In the Golden Isles, six of the eight large islands closest to the mainland date back to the Pleistocene Epoch, around 40,000 years ago, during an interglacial period before the last great continental ice sheet began spreading south from Canada across North America. During this period, sea levels were about six feet higher than today and the elevation of the older islands represents the higher sea levels of that period.
Around 25,000 years ago, as the last ice age was in full force, sea levels were 300 to 500 feet lower than today, and the coast of Georgia was eighty miles out from the current shoreline, stranding the islands far inland. Around 18,000 years ago, as the ice sheets began melting, sea levels began to rise again, inundating forests that had flourished along the ice age coast. As sea levels rose, around 5000 years ago, the Holocene barrier islands began to form offshore, gradually migrating westward with the rising waters until they met the older Pleistocene-era islands. Today, the older Pleistocene and younger Holocene landforms can be found sandwiched together along the length of the Georgia coast.
A network of rivers and creeks delivers new sediment to the Golden Isles, helping sustain them against the ravages of wave action.
Unlike the long, narrow barrier islands of North Carolina’s Outer Banks, Georgia’s Golden Isles are short and wide. This difference in shape is a result of the positioning of the continental shelf, which is closer to shore in North Carolina, creating intense wave action that erodes the barrier islands and keeps them from growing wider. In Georgia, the continental shelf is farther offshore and the shallower, calmer water action allows for more sand to build up, producing wider barrier islands.
Complex interactions between wind, waves, currents, tides, sand supply, and slowly rising sea levels are constantly reshaping the Golden Isles. Sediment-laden rivers deliver new supplies of sand through the inlets between the islands, seasonally changing the shape of the isles. But as sea levels continue to rise (around twelve to fourteen inches per century), the barrier islands will eventually disappear.
You might fly over Georgia’s Golden Isles en route to Jacksonville, Florida; Savannah, Georgia; or Charleston, South Carolina.
