The beaches of South Carolina  are almost all situated on barrier islands, long islands parallel to the shoreline and separated from the mainland by a sheltered body of water. Because they’re formed by the deposit of sediment by offshore currents, they change shape over the years, with the general pattern of deposit going from north to south (i.e., the northern end will begin eroding first).
Most of the barrier islands are geologically quite young, only being formed within the last 25,000 years or so. Natural erosion, by current and by storm, combined with the accelerating effects of dredging for local port activity has quickened the decline of many barrier islands. Many beaches in the area are subject to a mitigation of erosion called beach renourishment, which generally involves redistributing dredged material closely offshore so that it will wash up on and around the beach.
As the name indicates, barrier islands are another of nature’s safeguards against hurricane damage. Historically, the barrier islands have borne the vast bulk of the damage done by hurricanes in the region. Sullivan’s Island  near Charleston  was submerged by Hurricane Hugo. Like the marshes , barrier islands also help protect the mainland by absorbing the brunt of the storm’s wind and surging water.