Sediment Supply or Source
Barrier islands are normally composed of sand, mostly quartzitic for the Gulf Coast and Eastern U.S., and is sourced from weathered rock transported to the coast from via rivers. These sands are transported hundreds of kilometers before being deposited at the mouth of these rivers in the river delta. The beaches found near these river mouths are normally wider due to the higher influx of sediment. Littoral currents transport these sands away from the river mouth are deposited along the coasts. In environments where there is not enough sand, the beach can be comprised of volcanic ash or pumice, gravel or cobblestones, or even seashells.