Barrier islands form naturally along coastlines as waves and wind build up sand deposits in shallow waters. An island may begin as a sandbar and eventually rise above the water. Once enough sand accumulates, the seeds of typical beach and dune vegetation blow in and begin to grow, stabilizing the soil. Strand communities and maritime forests develop on these islands over time. Florida has more than 700 miles of coastal barriers, which in 1980 covered more than 500,000 acres.
Barrier islands are very much affected by the action of waves and wind.
As oceans have risen during the last century, Florida's barrier islands have moved inland because the rising water has pulled sand from outlying dunes and redeposited it closer to the mainland . Large storms can drastically alter or even destroy some barrier islands. Dunes provide some protection from the ocean, and marshes absorb storm water and cushion the impacts of waves, but the islands can be completely inundated if the storm surge is high. Although barrier islands themselves are vulnerable to storms, they buffer the mainland from winds and large waves, and provide especially important protection in severe storms.