Spits and bars are landforms that develop along coastlines as a result of longshore drift and sediment deposition.

Longshore drift is a fundamental process in the creation of spits and bars. It involves the transport of sediment along the shore, driven by wave action. Waves typically approach the coastline at an angle, carrying sediment with them. As the waves retreat back to the sea, they do so directly due to gravity in a process known as backwash. This results in a zigzag movement of sediment along the beach, which is referred to as longshore drift.

Spits are created when longshore drift moves sediment along the coast until it encounters a change in the shoreline, such as a river mouth or a bay. At this point, the direction of the longshore drift shifts, leading to sediment deposition. Over time, this accumulation of sediment extends into the ocean, forming a narrow, elongated landform called a spit. Often, spits exhibit a curved or hooked end, which is influenced by variations in wind and wave direction.

Bars, on the other hand, are similar to spits but develop when a spit grows across a bay, effectively connecting two headlands and enclosing the bay. The mechanisms of longshore drift and sediment deposition remain the same; however, the spit continues to extend until it reaches the opposite landmass, forming a bar. This formation can sometimes lead to the creation of a lagoon or a salt marsh behind the bar.

In summary, the development of spits and bars is a complex interplay of sediment movement and deposition along coastlines. This process is shaped by various factors, including wave direction, the configuration of the coastline, and fluctuations in wind and wave patterns.