A beach is a broad, shallow stretch of sand and seaweed along a coastline. It is often formed by wave action but may also be created by the wind. A beach can be a source of food and shelter for birds, marine organisms such as crabs and sea anemones, and plants such as dunes and sea grass. Beaches are continuously being changed and reshaped, with new materials arriving and old ones disappearing.
A beach usually has a mix of different types of sediments, ranging from sand to silt to clay. These are mainly the weathering products of rocks offshore that have been eroded by waves, longshore currents and receding tides. Beach materials can be carried from far inland, as well as from other beaches further south by the prevailing winds and ocean currents.
Wave action is the main way that beaches are made and change. When a wave is constructive (the period between each wave crest is longer than the previous one), beach sediments are deposited. When the wave is destructive (the period between each wave crest is shorter than the previous one), beach sediments are removed. The type of sediments that arrive on a beach often indicates the energy of the waves in that area.
Beaches can gain or lose sand, depending on whether they are accreting or eroding. Generally, the horns of a beach are gaining sand and the embayments are losing it. However, this is not always the case and it depends on the wave conditions. For example, when the incoming waves are large and rough, erosion of the horns can be faster than accretion.
Some of the sand in a beach comes from the land: rock outcrops, sand drifting on the wind or from the breakdown of rocks and other organic material resulting from headland erosion or slumping (scrubby deposits known as scree). In tropical areas, coral reefs are major sources of beach sand. The sand particles that are released when the coral fragments break down in the water are washed up on the beach by pounding waves and then broken down into sand-sized pieces.
Besides sediments, a beach can contain many other materials including shells and seaweed. The smallest sand particles are what we call silt and clay, which make up mud when wet. Mud is rarely found on beaches but can be deposited in lagoons and marshes behind barrier islands.
The beach is a valuable natural resource, but it can also be a dangerous place. Beach pollution, such as litter and plastic bags, can choke and entangle marine organisms and birds. People should always remove their trash from the beach and throw it away. In addition, they should not take shells or other objects from the beach, as doing so interferes with the natural processes that form and protect beaches. If these steps are taken, we can enjoy a healthy and beautiful beach for generations to come.