JUMPING INLETS, SPITS AND ISLANDS ON THE GEORGIA COAST, U.S.A

Tidal inlet position on the Georgia coast is controlled by the location of river mouths and relict Pleistocene barrier islands, as well as by spit development. Longshore transport is southward, leading to erosion on the north ends of islands and deposition on the south. This combination of spit building on the north side of tidal inlets and erosion on the south leads to southward migration of the inlets and islands, partly constrained by the location of indurated sands of the Pleistocene Silver Bluff shoreline. Tidal channel migration progressively displaces the tidal inlet south from its river, behind the Holocene dune ridge. Extension of the spit combined with erosion along the channel makes this geometry increasingly unstable and eventually a new inlet is breached closer to the river mouth. Because of relative resistance, breaching usually occurs either north or south of the Pleistocene core of the modern islands. If the breach is to the north, flow is captured at the next inlet up the longshore transport system; if to the south the spit is dissected. The detached spit continues to migrate southwards until it accretes to the next island. Various stages in this process are evident on the coast. For example, the Altamaha River may have originally emptied through St. Simons Sound and the Ogeechee via St. Catherines Sound. Altamaha and Ossabaw sounds are probably new distributaries. St. Simons Sound has recently captured drainage from the Brunswick River. Blackbeard Island, Sea Island and the northern tip of Jekyll Island are detached spits originally connected to northerly adjacent islands.