A beach is a narrow, gently sloping strip of land that lies along the edge of an ocean, lake, or river. It usually contains sand, pebbles, rocks, and seashell fragments. Most of these materials are the products of weathering and erosion.
The shape of a beach depends on how waves move the sand away from the shore. The sand on beaches varies in size and grain thickness. Coarse grains absorb more water than fine ones. The resulting backwash flows down the beach and flattens it.
There are several ways in which beaches change in shape over time, including the effect of tides and large cyclonic storms (hurricanes and tropical storms). In areas of moderate to low latitudes, hurricanes can erode the coastline by moving sand out from the beach, redistributing sediment, and reconfiguring the shoreface.
Delta: As rivers encounter stagnant bodies of water, they can spread out across the delta into multiple channels as they meander through this deposited sediment. Depending on the nature and rate of sediment delivery, this process will affect both the shape of the delta and its contours.
Long shore drift: As longshore currents pass between the banks of a river or lake, they often carry sediment to a beach and deposit it along the tidal margin, forming a beach terrace. This is a common feature in coastal regions where the longshore current meets an outflow from a river or lake and can be influenced by tidal movement, wind direction, wave action, and current direction.
Berms: During quiet weather, offshore sand bars may migrate onto the beach. These deposits are referred to as berms and usually form in zones where waves have depleted the sediment supply, leaving gaps in the beach ridges.
The profile of a beach changes seasonally as the wave energy changes in summer (calm seas) and winter (higher waves). In temperate areas, where the waves are calmer and have longer periods between breaking wave crests, the beach profile is higher in summer because the gentle wave action transports sediment up the beach and inland to the berm where it can be carried out to sea, forming dunes.
In contrast, the profile of beaches in areas with higher waves is lower in winter because the faster-breaking waves tend to mobilise sediment in the shallows, retaining it in suspension, and bringing it out to sea to form offshore bars.
Barrier-island beaches are particularly susceptible to damage from these waves and surges. Such beaches are typically on narrow sand islands, which are detached from the mainland by a lagoon or bay and are at risk of being submerged in storm surges.
A beach can also be a natural feature, such as an island that has been formed by sand accumulated by waves and currents on the shore. These are often called fossil beaches.
A beach is a unique part of the ecosystem, and is an important habitat for birds, plants, and animals that live on or near it. It is important to keep beaches clean so that visitors and wildlife can enjoy them.