Which coastal feature is formed primarily by longshore drift transporting sand parallel to the coast?

• A. Barrier Island
• B. Atoll
• C. Thermocline
• D. Water Mass

Answer: (A)

Longshore drift describes how sediment moves along the coastline when waves hit the shore at an angle. The swash pushes material up the beach at an oblique angle, and the backwash carries it straight back down the beach, producing a net transport of sand parallel to the coast. Over time this continual deposition can build offshore sand bodies that grow into barrier islands—long, sandy features that align roughly parallel to the shoreline and often shelter bays or lagoons behind them. That makes barrier islands the coastal form most directly created by longshore drift.

The other options refer to different marine features: an atoll is a ring-shaped coral reef around a central lagoon formed through reef growth after volcanic islands subside; the thermocline is a temperature gradient within the water column; a water mass is a body of water distinguished by its temperature and salinity properties, not a landform.