While waves can erode coastlines, they also build them up through deposition. Depositional landforms occur when waves and currents lose energy and drop the sediment they've been carrying. These features create some of the world's most beautiful beaches and unique coastal landscapes.
Key Definitions:
Before we look at depositional landforms, we need to understand the process that creates many of them: longshore drift.
1. Waves approach the beach at an angle (usually due to prevailing winds).
2. Swash carries material up the beach at the same angle as the waves.
3. Backwash pulls material straight back down the beach under gravity.
4. This creates a zigzag movement of material along the coast.
5. Over time, sediment is transported along the coastline in the direction of the prevailing wind.
Longshore drift is like a conveyor belt that moves sand and pebbles along the coast. This process is responsible for creating many depositional landforms including beaches, spits and bars.
Understanding longshore drift helps us:
Beaches are perhaps the most common and well-known coastal depositional landforms. They're more than just holiday destinations - they're dynamic systems that protect our coastlines.
Beaches form when waves deposit material like sand and pebbles along the coast. The shape and composition of a beach depends on:
A typical beach profile includes:
Spits are finger-like ridges of sand or shingle that extend from the land into the sea, often with a curved end.
1. Longshore drift carries sediment along a coastline
2. The coastline changes direction (e.g., at a river mouth or bay)
3. Material continues to be deposited in the original direction
4. A finger-like ridge extends into the water
5. The end often curves due to secondary winds/currents
Hooked end: The curved tip caused by wave refraction
Salt marsh: Forms in the sheltered water behind the spit
Dunes: Wind-blown sand accumulations on the spit
Lagoon: The sheltered water area behind the spit
Spurn Head: A 5.5km spit at the mouth of the Humber Estuary, UK
Hurst Castle Spit: A 2.5km shingle spit in Hampshire, UK
Dungeness: One of the largest spits in Europe, on the Kent coast
Spurn Head is a classic example of a spit located at the mouth of the Humber Estuary in Yorkshire. It extends about 5.5km into the Humber Estuary and is only 50m wide in places.
Formation: Longshore drift carries material southwards along the Holderness Coast. When the coastline changes direction at the Humber Estuary, the material continues to be deposited in the same direction, forming the spit.
Challenges: Spurn Head is constantly changing. In 2013, a storm surge breached the spit, making the tip temporarily an island at high tide. The area is now managed as a nature reserve by the Yorkshire Wildlife Trust.
Ecological importance: The sheltered areas behind the spit provide valuable habitats for birds and marine life. The area is designated as a National Nature Reserve.
Bars are ridges of sand or shingle that connect an island to the mainland or link two headlands across a bay.
Bars form when:
Examples include Slapton Ley in Devon and Chesil Beach in Dorset, which connects the Isle of Portland to the mainland.
The main difference between bars and spits:
Bars can sometimes begin as spits that eventually grow long enough to connect to another piece of land.
A tombolo is a bar of sand or shingle that connects an island to the mainland or another island.
Tombolos form through a specific process:
Chesil Beach, UK: Connects the Isle of Portland to the mainland
St Ninian's Isle, Shetland: One of the finest examples of a tombolo in Europe
Monte Argentario, Italy: Connected to the mainland by three tombolos
Tombolos are relatively rare compared to other depositional features, making them particularly interesting to geographers.
Chesil Beach is an 18-mile long shingle barrier beach in Dorset, England. It connects the Isle of Portland to the mainland, making it both a bar and a tombolo.
Unique features:
Formation: Chesil Beach formed after the last ice age when rising sea levels pushed shingle deposits onshore. Longshore drift then shaped the beach into its current form over thousands of years.
Protection: The beach provides natural coastal protection for the communities behind it and is now part of the Jurassic Coast World Heritage Site.
Human activities can significantly affect coastal depositional processes and landforms.
Groynes: Wooden or stone barriers built perpendicular to the shore to trap sediment and prevent longshore drift. They cause build-up on one side but erosion on the other.
Harbours and marinas: Can interrupt longshore drift, causing sediment build-up that requires dredging.
River dams: Reduce sediment supply to coasts, leading to beach erosion.
Beach nourishment: Adding sand or shingle to beaches to replace lost material.
Managed retreat: Allowing natural processes to occur in less developed areas.
Offshore breakwaters: Structures that reduce wave energy but allow some sediment movement.
Effective coastal management requires understanding depositional processes to work with nature rather than against it.
Coastal depositional landforms are created when waves and currents lose energy and drop sediment. The main types include:
These landforms are primarily created through longshore drift, the zigzag movement of sediment along the coast. Understanding these processes and landforms is essential for coastal management and protection.
Remember that coastal depositional landforms are dynamic and constantly changing. They represent a balance between erosion and deposition that can be easily disrupted by both natural events (like storms) and human activities (like building sea defences).
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