Seashore

I

Introduction

Seashore, boundary between the land and the sea. This boundary is also called the shore or the shoreline.

A variety of landforms exists at the seashore, including sandy beaches, rocky cliffs, tide pools (also called tidal pools), and coral reefs. Each of these landforms is shaped by the wind, waves, tides, and currents. The wide variety of landforms yields a variety of habitats, or environments for plants and animals. For example, in shallow shore areas with low waves and weak currents, sea grasses flourish. They provide protected habitats where many species of animals lay their eggs and the young can grow in size and strength before facing the harsher environment of the open ocean. By contrast, in areas with stronger currents or waves, burrowing animals, such as clams, dig themselves into the mud or sand to avoid the vigorous water movement. However, these animals also depend on the moving water to supply food in the form of smaller animals and plant and animal debris suspended in the water.

II

Beaches

A beach is a section of the seashore where unconsolidated sediment, or grains of worn-down rock, has collected. Unconsolidated sediment is a sediment in which the individual grains are clearly separated and can move freely, like grains of rice. In contrast, consolidated sediment is a sediment in which the individual grains cling together, like particles of moist flour or mud. Most beaches are composed primarily of sand (grains of quartz and other hard minerals between 0.063 mm/0.025 in. and 2 mm/0.08 in. in size), although some are composed primarily of pebbles or fragments of seashells. The unconsolidated and small sediments that make up a beach are easily moved by the action of waves and wind. Consequently, the shape of a beach is constantly changing as sand is removed from or deposited along the shoreline.

A

Sources of Sediment

The sands that form a beach are produced through erosion, or the wearing away of rocks by wind and water. In some cases, the erosion takes place far inland, where winds and water erode mountains and plains, producing sediment grains of many sizes. Rivers carry the sediment to the coast. Waves and water currents move the sediment along the coast, depositing some of it on beaches. For many beaches sediment from inland is the most important source of sand. However, beach sand may also result from erosion that occurs at the shore, especially at bluffs, as a result of the action of wind and waves.

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Sand comes in a variety of colors, which indicate where the sand originated. The most common sand material carried in rivers is quartz, which ranges in color from pale yellow to brown. In tropical regions, the erosion of coral reefs may produce brilliant white beach sand. In contrast, beaches around volcanic islands, such as Hawaii, may have black sand, derived from the erosion of a black volcanic rock called basalt.

B

Transport of Sediment

The shape of a beach constantly changes as sediments are eroded from or deposited along the shoreline. The main mechanisms for moving sediment along a beach are longshore drift and wind transport.

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