Almost one third of the global coastline is comprised of sandy beaches. These beaches play an important cultural and economic role, providing recreational opportunities for millions of people. They also provide a protective buffer against high winds and storms. However, these beaches are threatened by increasing sea levels and erosion. In 2010, the small uninhabited island of New Moore Island in the Bay of Bengal was completely submerged by rising sea levels.
Depending on the type of material and the energy of the waves, the shape of a beach may change. There are four main types of beaches: dissipative, intermediate, intermediate sand, and intermediate beach. The beach may also have a surf zone, which is the most dynamic part of the beach. Beaches can also be classified based on the sediment type. The sediment type indicates the energy of the waves and how the wind interacts with the sea. The type of sediment may be delivered by the wind, by the tides, by glaciers, or by marine organisms in the sea.
The materials that make up a beach may include rocks, pebbles, sand, and seashell fragments. Some sand may be eroded from rocks offshore or bits of rocky reef. Others may be derived from land. Sand may also be sloughed off from nearby cliffs or transported by the wind. Sediments can be carried from distant ocean currents or by rip currents.
The most common method of erosion is by waves. These waves can break on an outer bar or on a steep slope and move shoreward as a spilling breaker or as a plunging wave. They are destructive when the wave crest period is short, such as on moderate gradient slopes. On the other hand, if the wave crest period is long, such as on a low gradient slope, the waves can produce small ripples and interact with the seabed. These waves may also form beach cusps.
Sediment is carried by the wind, by a tide, by ocean currents, by rivers, and by other moving water. Sediment may be carried hundreds of kilometers from its source. Sediment may contain shells, seaweed, and other organisms. If the sediment is in suspension, it will increase the erosive power of the fluid. Particles in suspension will also increase the density and viscosity of the moving fluid. If the sediment is compacted, it will be more resistant to erosion. If the sediment is not compacted, it will be more susceptible to erosion by longshore currents. The sediment may also be eroded before it is compacted, such as by scouring behind it.
Beaches can be influenced by a variety of factors, including the type of waves and the climate. These factors can change the shape and size of a beach. For example, in the summer, beaches tend to be wider and steeper. In the winter, beaches are less wide and shallow. The amount of sand that is deposited on the beach may also change during the year. This is caused by seasonal changes in the amount of seawater that flows into the sea. Seasonal changes can also alter the wind pattern at the surface. For example, in the summer, the wind may blow in an easterly direction, while in the winter, it may blow from the west.