Barrier islands are
coastal landforms and a type of dune system that are exceptionally flat or lumpy areas of sand that form by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything from a few
islands to more than a dozen. They are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish. A barrier chain may extend uninterrupted for over a hundred kilometers, excepting the tidal
inlets that separate the islands, the longest and widest being
Padre Island of Texas. The length and width of barriers and overall morphology of barrier coasts are related to parameters including
tidal range,
wave energy,
sediment supply,
sea-level trends, and
basement controls.