Sapelo Island Reserve, Georgia

Geology

Like other barrier islands along the Atlantic coast, Sapelo Island was formed as sediment gradually built up into a ridge along Georgia's shore through the actions of wind and waves. The formation of the estuarine marsh occurred during the Holocene period (15,000 years ago) when continental glaciers melted and increased the ocean's volume of water substantially. The ridge that had formed along the shore was then isolated from the land by this flooding, leaving the mainland and the ridge island as two separate land entities. Subsequent submergence and emergence further shaped the island. Today, the island continues to be molded by the powerful actions of wind and waves.

Soil Types

Georgia's barrier islands are composed of sands brought to the coastal area by rivers, such as the Savannah and the Altamaha, whose headwaters arise in the Georgia piedmont and mountains. The saltmarshes are dominated by slightly alkaline clays topped by a thin sandy layer at higher elevations. Upland soils are predominantly Ona and Rutledge sands that are very poorly drained and often highly acidic.