When waves lose their energy, they deposit the sediment they are carrying. Over time, the mass of sediment that settles creates depositional landforms. These landforms include beaches, spits, bars and sand dunes, each having its unique formations and features.
Beaches are made up of eroded materials transported and deposited by the sea. Their formation is influenced by wave energy and the surrounding coastal geography.
Sandy beaches tend to have a gentle slope, while shingle or pebble beaches can be steeper. The smallest material is typically found nearest the water, where the waves break and erode the rocks through attrition.
Spits are elongated stretches of sand or shingle that project into the sea from the land. They form due to changes in the coastal shape or the presence of river mouths.
1. Sediment is carried along the coastline by a process called longshore drift.
2. When there is a change in the shape of the coastline, deposition occurs, resulting in the formation of a long, narrow ridge known as a spit.
3. If there is a change in wind direction, a hooked end can develop on the spit.
Spits act as natural barriers, preventing waves from passing through and creating sheltered areas behind them. In these sheltered spots, silt is deposited, forming salt marshes or mud flats.
Sometimes, a spit can grow across a bay and connect two headlands, forming a landform called a bar. Bars can create lagoons (essentially a shallow lake) behind them, which gradually fill with sediment over time.
Sand dunes are found along many coastal areas and vary in their form, structure and appearance.
They are formed by the following process:
1. There is first an abundant supply of sand. This sand can originate from various sources, including eroded rocks, rivers or offshore sediments carried onto the shore by waves.
2. Prevailing onshore winds carry sand particles landward.
3. As the wind encounters obstacles, such as vegetation or man-made structures, it slows down, losing its carrying capacity. The sand particles are then deposited, resulting in the accumulation of sand in certain areas.
4. The initial dune formation stage involves sand accumulation in small mounds known as embryo dunes. These dunes are usually low in height and lack a well-defined shape.
5. Over time, sand accumulates, and the dunes grow in height and size. The shape of the dunes is influenced by wind direction, with prevailing winds moulding them into distinct forms.
6. As sand accumulates, hardy pioneer plant species like beach grass begin to colonise the dune. These plants help stabilise the sand by trapping it with their roots, forming a network that prevents erosion and aids in dune growth.
Sand dunes have different shapes and you’ll be expected to explain how they form. Remember, that it’s down to the wind and the way in which the sand is affected by it.
Here are three main types of sand dunes and how they are formed:
Sand dunes are not static features but are constantly in motion. They migrate and evolve as a result of wind patterns and changing environmental conditions.