Why do the Atlantic and Gulf coasts of the United States have many depositional landforms?

The Atlantic and Gulf coasts of the United States are characterized by numerous depositional landforms primarily because they are situated along the trailing edges of tectonic plates. These passive margins are associated with broad, low-relief coastal plains that have been repeatedly invaded by the sea and covered with layers of young, poorly consolidated sediment.123

The prevalence of these landforms is driven by several key factors:

• Sediment Supply: Rivers transport vast quantities of sand, silt, and clay from the continent to the coast. When these sediments reach the sea, wave and current energy redistribute them to form beaches, barrier islands, and deltas.241
• Tectonic Stability: Unlike leading-edge margins, which are often narrow and steep, these trailing-edge margins feature gentle continental slopes that facilitate the accumulation of extensive sedimentary packages.2
• Coastal Processes: The interaction between waves, tides, and longshore currents continuously shapes these materials. For instance, waves and longshore currents are responsible for building elongate barrier islands that parallel the shore, while estuaries and lagoons form in the low-lying areas between these barriers and the mainland.15

While these coasts may experience localized erosion due to storms or rising sea levels, the long-range geologic tendency remains one of sediment deposition.1