* Deposition of sediment: Barrier islands are built up by the accumulation of sand, silt, and other sediments carried by ocean currents and waves. These sediments are deposited along the coastline, gradually forming a long, narrow island parallel to the shore.

* Role of erosion: While deposition is the primary force in barrier island formation, erosion also plays a role. Waves and currents can erode the landward side of the island, transporting sand to the ocean side, contributing to the island's growth and shaping.

* Dynamic process: Barrier island formation is a dynamic process. They are constantly evolving due to the ongoing interplay of deposition and erosion, influenced by factors like storms, sea level changes, and human activities.

In summary: While erosion plays a role in shaping barrier islands, their formation is driven by the deposition of sediments.