A beach is a narrow, gently sloping strip of land that lies along the edge of an ocean, river or lake. It is covered with loose materials, such as sand, pebbles, rock and seashell fragments, which are the result of erosion over many years. Beaches are also a habitat for a variety of plants and animals.
Sand is the main ingredient of beaches and it comes from a number of sources. The wind can blow sand from nearby dunes, or from other parts of the coast, and it can drift on currents. In addition, waves erode the coastline and carry sand away from or deposit it on beaches.
Often, sand is carried inland by longshore currents, and this sediment will be left behind on the shoreline. The type of sediment that is deposited on a beach tends to indicate the energy level of the waves and winds in that area. For example, beaches with a lot of energy from breaking waves may have coarse sand, while low-energy beaches are more likely to have fine sand.
Waves that are breaking close to the shore have a high level of energy. This means that they can transport sand and other materials from far out to sea, and they can also erode the coastline and create channels between the water and the land. Beaches with more energy tend to have coarser sand and are more likely to have gullies, while low-energy beaches tend to have finer sand and less erosion.
The back of a beach, the area between the beach face and the front dune or cliff base, is known as the backshore. This part of the beach is generally dry except during storms or very high tides. It is characterized by sand dunes and the wrack line, a thin layer of dislodged seaweed and other marine debris that is typically found on Atlantic and Pacific beaches, where kelp (also known as sargassum) grows.
The wrack line usually appears as a thin, muddy zone in the middle of the beach, and it can give an indication of the height of the last high tide. A runnel is a temporary pool of shallow water that forms parallel to the beach, and it can contain sand, shells and other marine materials. This water is drained when the tide goes out, and it can carry the material a distance of a few meters or hundreds of kilometers. Tidal flows and ocean currents also affect beaches, bringing in new materials and taking them away from other areas. Beaches are always changing, and it is difficult to predict what they will look like in a few years. It is important to protect the natural beauty of a beach and not spoil it with rubbish or other human activities. Beaches are the home of a variety of plants and animals, and they should be protected. For example, littering on the beach can have negative impacts on wildlife and it is best not to bring food or drinks to a sandbar because it could wash away into the ocean.