1.8 - How Deposition forms Coastal Landforms
The formation and characteristics of beaches
Beaches are key coastal features created through the process of deposition, where materials are laid down by the sea. They are located between the highest and lowest points that the sea level reaches on the land, known as the high water mark and low water mark respectively.
How beaches are formed and their distinct features
- Constructive waves - These waves have a stronger swash than backwash, bringing material like sand and pebbles onto the shore and depositing it to form beaches.
- Sand beaches - These are typically broad and have a gentle slope. The small size of sand particles allows the weak backwash of waves to drag them down slightly, resulting in a flatter profile.
- Shingle beaches - These are narrower and steeper due to the larger size of shingle particles. The weak backwash struggles to move these heavier materials back down, leading to a build-up that creates a pronounced slope.
The development of spits as depositional landforms
Spits are elongated stretches of deposited material that extend from the coastline into the sea, connected to the land at one end. They are formed through a combination of wave action and sediment transport along the coast.
Processes and features of spit formation
- Location of formation - Spits often develop at significant bends in the coastline, such as near inlets or estuaries, where the direction of sediment movement changes.
- Longshore drift - This process moves sand and shingle along the coast. When it encounters a bend, the material is deposited into the sea, gradually building up to form a spit.
- Recurved ends - Strong winds and waves can bend the tip of the spit, creating a hooked or curved shape at the far end.
- Sheltered zones - Behind the spit, a calm, low-energy area forms, shielded from powerful waves. This allows fine sediments to settle, fostering the growth of vegetation.
- Evolution over time - The protected area behind the spit can develop into mud flats or salt marshes as sediment accumulates and plants establish themselves.
The creation of bars and associated features
Bars are another type of depositional landform, formed when deposited material connects two points of land, often altering the coastal landscape significantly.
Formation and impact of bars
- Connection of headlands - A bar is created when a spit extends across a bay and joins two headlands, effectively linking them with a ridge of sediment.
- Isolation of water bodies - As the bar forms, it blocks off the bay from the open sea, creating an enclosed area of water behind it.
- Lagoon development - The isolated water body behind the bar becomes a lagoon, a shallow area of water separated from the sea, often with unique ecological characteristics.
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