A beach is a sand-covered shoreline that stretches landward from a low water mark. It can be narrow or wide, and can range in shape and size. Beaches are generally some shade of brown or tan. They are usually flat and smooth, but they may have rocks and trees. Some beaches are also barren, and are sometimes found in deserts. In some areas of the world, beaches are covered with shells. These shells are the food of many marine animals. Sea turtles lay eggs on ocean beaches. Other animals, like birds and crabs, feed on the material left behind by waves.
The sand on a beach is a combination of sand, gravel, and pebbles. The materials may be transported from nearby coastal regions by wind or sea tides. Or they may be locally derived. For example, the sand on some beaches is made of quartz or feldspar. Others are made of other minerals. If a beach is exposed to the ocean, it will be coated with calcium carbonate. Calcium carbonate is a mineral that is precipitated on shells and other bits of sea sand.
During storms, waves carry sand from the continental shelf and sand bars. During the spring, a high tide can cause the sand on the beach to move back onto the shelf. However, sand can also be carried away from the continental shelf by a strong current. There are sandbars, cliffs, and islands that are formed when the sand on a beach is pushed off by a high tide. This can create an interesting landscape.
Many tropical beaches are covered with sand that is made of tiny round or oval particles called oolites. These oolites form when cold ocean waters flow onto warm shallow banks. Oolites are a common mineral on tropical beaches.
When the water is relatively still, beaches are relatively stable systems. Coastal erosion is the primary threat to beaches. Ocean waves and winds wear away the sand over time. Storms can erode the sand, as well as the berms and cliffs that line the beach. But, beaches are changing all the time, as ocean currents are constantly redistributing sediment.
The materials on a beach can vary widely, and can include sand, rocks, and shells. Depending on the area, the sand might be fine or coarse. The sand may be derived from a local source or from the sediment of the ocean. Sand, shells, and rock fragments are usually transported by wind, and the wind may move the material hundreds of kilometers from its original point.
While there are many types of materials on a beach, the most common are sand and shells. Shells can be collected for beach nourishment projects, and they may be used by birds or crabs for food. Small pieces of plastic are often a problem on beaches, as they can choke or trap sea plants and algae. Although visitors should not put trash in the ocean, they should never leave it on the beach.