Waves create several distinctive depositional landforms along coastlines, primarily through the transportation and accumulation of sediment. The most common and recognizable features are beaches, spits, and bars.
Beaches
Beaches are perhaps the most well-known depositional feature created by wave action. They are accumulations of sand, gravel, or shells along the shoreline.
- Formation: Waves transport sediment towards the shore. The swash (the water rushing up the beach) carries the sediment, while the backwash (the water flowing back down) removes some. When the swash is stronger than the backwash, sediment accumulates, forming a beach.
- Characteristics: Beaches vary in width, slope, and composition depending on wave energy, sediment supply, and coastal morphology.
Spits
A spit is an elongated ridge of sand or shingle that projects from the mainland into a bay or estuary.
- Formation: Longshore drift, the movement of sediment along the coast by waves approaching at an angle, is the primary process in spit formation. When the coastline changes direction, the longshore current spreads out, loses energy, and deposits sediment.
- Characteristics: Spits are typically attached to the mainland at one end and often have a curved or hooked end due to wave refraction or secondary wind and wave patterns. Over time, vegetation may colonize the spit, stabilizing it further.
Bars
A bar is an elongated deposit of sand or shingle that is found offshore, parallel or sub-parallel to the coast.
- Formation: Bars can form in several ways. They can be created by waves breaking offshore and depositing sediment in a line. They can also form by the longshore movement of sediment that eventually extends across a bay or estuary mouth.
- Characteristics: Bars can be submerged or exposed at low tide. When a bar completely encloses a bay, it is called a baymouth bar, creating a lagoon behind it.
Here's a table summarizing the depositional features:
| Feature | Description | Formation Process |
|---|---|---|
| Beach | Accumulation of sediment along the shoreline | Wave action depositing sediment; swash stronger than backwash |
| Spit | Elongated ridge of sand or shingle projecting from the mainland | Longshore drift depositing sediment where the coastline changes direction |
| Bar | Elongated deposit of sand or shingle offshore, parallel to the coast | Waves breaking offshore and depositing sediment; longshore drift extending across a bay |
These depositional features are dynamic and constantly changing due to wave action, sediment supply, and other coastal processes. Understanding their formation and behavior is crucial for coastal management and protection.
