A sandy beach is a zone along the ocean shore that is composed of eroded tiny particles of rock, such as sand, pebbles, and cobblestone, as well as the remainders of mollusks, shells, corals, and skeletons of plankton. A beach often separates a body of water from inland zones, such as in a river, lake, or ocean. Sandy beaches usually occur along the shoreline where the action of waves, tides, winds, and human activity often change its landscape. Storms and weather can cause a beach to grow or decrease in size, often depositing large amounts of sediment materials, which are slowly eroded away with the passing of time.
Beach structure
A beach may be divided into distinct sections. The berm is the point that is less influenced by the action of waves and is at the outer most edge of a sandy beach. The back beach is the area beyond the berm and it consists of sand dunes and some vegetation. The berm has a crest and a beach face, which is the down slope, leading to the water and is affected by high and low tides. Seawards is the surf zone, which is produced by the breaking waves. The swash is the zone, which is alternatively covered and exposed as the ocean water retreats.
Beach formation
Sandy beaches are formed when sediment, most commonly sand, is transported from the ocean to the beach. The process of formation can take thousands or even millions of years, beginning with the erosion of land rock and cliffs caused by the action of winds and waves on the shoreline. Over time, a beach along where the ocean waves hit the shore starts to form. As the action of waves brings sand and other types of sediment to the beach, some of these particles are deposited after the wave recedes. Coastal winds add to the formation of a beach as they push the sand beyond the action of the ocean by saltation.
Types of sand
Sediment particles deposited in sandy beaches can be classified by their size, ranging from very tiny sand particles of less than 0.004 inches (0.1 millimeters) to very coarse 0.04-0.08 inches (1-2 millimeters) in diameter. The size of sand particles determines the way in which they stick to one another, how they´re carried by the wind, and the way in which they retain water. Finer sand particles retain more water and adhere together more efficiently than coarser particles. Sandy beaches, along with sand dunes that form beyond the reach of the high tide are formed by onshore winds carrying fine-medium sand grains. Sand dunes are formed inland and they can migrate further inland depending on the wind conditions.
The structure of a beach is due to the erosion of rocks offshore. Beaches situated along continents in temperate regions are often formed of brown to yellow quartz sands, which usually stem from the action of weathering and erosion (details on weathering vs erosion). Some white sandy beaches due their color to tiny fragments of corals and shells, along with precipitated carbonate grains. Coral reefs contribute with a significant amount of sand particles for the formation of beaches. Pebble or shingle beaches are formed from the erosion of a nearby line of sea cliffs. Volcanic fragments may give a beach a black appearance around volcanic islands. The green sand beaches in Hawaii contain crystals of the mineral olivine from volcanic origin.
The shape of a beach depends on the type of waves acting on it. Constructive waves carry sand particles up the beach, while destructive waves remove it from the beach. Beaches made of pebbles or shingles tend to be steeper than those made of sand. A beach is limited by sand dunes inland, vegetation and sometimes man-made structures, such as roads and hotels. Beaches are deposition land masses, which are formed by the deposition of sediment and varied materials. Beaches can form anywhere land comes in contact with a body of water and the process of their formation can take thousands of years.
