Beaches are areas of loose sediment (sand, gravel, cobbles) controlled by ocean processes. Waves and currents move the accumulated sediment constantly creating, eroding and changing the coastlines.
Most beaches have several characteristic features. First are offshore bars, which help protect beaches from erosion. Next is the foreshore, which rises from the water toward the crest of the next feature: a berm. On low-lying shores, dunes form behind beaches. Dunes look like rolling hills of sand and are blown into place by the wind. New, smaller dunes are often changing shape as the wind continues to affect them. More established (older) dunes hold sand in place with vegetation, such as sea oats.
But did you know some beaches have black sand? Some islands in the Pacific Ocean do. This comes from the weathering of volcanic rock.When people picture beaches, they often think of the ones near where they grew up. Most of the shores along the US’s East Coast and Florida’s Gulf Coast are white. The white sand comes from granite, which has been broken down, or weathered, into quartz and feldspar.
Other beaches are made of cobbles, or small stones. Waves and currents cause these stones to churn and pound over each other. Little life can exist in such a severe environment.
A primary influence on the formation and evolution of a beach is something called a longshore current. This current flows parallel to the beach, causing waves to strike the beach at an angle. The longshore current can carry large amounts of sand along the coast and can form spits (narrow peninsulas of sand), barrier islands and tombolos (narrow sand deposits connecting a near-shore island with the beach).
There are many different types of coasts; beaches are just one type.
Coasts are divided into two categories: primary coasts, which were created by non-marine processes, and secondary coasts, which were formed by marine action. Primary coasts happen because of changes in the land, such as river deltas or lava flows. Secondary coasts are caused by changes in the ocean, such as the creation of barrier islands or coral reefs.
Primary coasts are created by erosion (the wearing away of soil or rock), deposition (the buildup of sediment or sand) or tectonic activity (changes in the structure of the rock and soil because of earthquakes). Many of these coastlines were formed as the sea level rose during the last 18,000 years, submerging river and glacial valleys to form bays and fjords (a type of estuary).
River deltas are an example of a primary coast. They form where a river deposits soil and other material as it enters the sea. River deltas are divided into three groups: the river-dominated delta, the tide-dominated delta and the wave-dominated delta.
River-dominated deltas, such as the Mississippi or Nile river deltas, are formed when there are large amounts of material in the water, and tidal action is relatively low. Tide-dominated deltas, which are found where the daily tidal range is more than a meter, have many branching channels and long narrow islands formed as the tide and river flow in different directions. Wave-dominated deltas are little more than a bulge on the shoreline since there is so much wave activity that all the sediment is spread evenly along the coast and does not accumulate at the river’s end.
Primary coasts are divided into two categories: submergent coasts and emergent coasts. Submergent coastlines result from a general sea-level rise and crustal subsidence (a lot of heavy sediment on top of the bedrock is forcing the bedrock deeper into the earth). Most of the eastern United States has submergent coastlines. One example is the Chesapeake Bay. Emergent coastlines result from the land being lifted, either by tectonic activity or rebound from the weight of heavy glaciers, which exposes the former sea bottom bit by bit forming continuously new shoreline. A characteristic feature of emergent coasts are marine terraces, formed as tectonic uplift moves the land upward in short bursts, which are then worn by wave action into relatively flat surfaces, somewhat like a large staircase. Beach ridges can be formed by rebound, and are composed of cobblestones piled at the surfline by storm activity, which is slowly lifted higher over time.
Secondary coasts are caused by the action of the sea or by creatures that live in it. Sea cliffs, barrier islands, mud flats, coral reefs, mangrove coasts and salt marshes are all examples of secondary coastlines. While most of the eastern United States is considered submergent, a great deal of the coastline formed between submergent features is secondary, such as marshes, mangroves, sand beaches and islands. Large portions of the US Pacific coast are secondary as well, with eroded headlands and wave terraces.
Beaches are full of life – the very grains of sand are host to diatoms, bacteria and other microscopic creatures. Some turtles and fish return to certain beaches each year to lay eggs in the sand. Many kinds of birds, such as terns, gulls, sandpipers, pelicans and loons, make the beach their home. Aquatic mammals, such sea lions, seals and sea otters, are found along rockier coasts. Crabs, clams, periwinkles, shrimp, corals, starfish and sea urchins are common on nearly all beaches.
Surfers, swimmers and sunbathers use beaches for recreation (play). People fish off beaches for food. Since many people take their vacations at the beach, lots of beaches in tropical locations are important to their country’s economy. Entire cities, regions and countries depend on the money tourists spend while visiting the beach.
Erosion (the wearing away of rock and soil) is one of the primary creative forces of many beaches. Erosion provides sand for new beaches and the maintenance of old ones; erosion forms the stacks and arches found on irregular rocky coastlines; and erosion provides the material which forms deltas and barrier islands.
Beaches are naturally very dynamic (always-changing) places, but people try to control them and build permanent structures, such as houses, restaurants, shops and hotels, on or near the shore. The natural erosion and deposition of beaches becomes a problem. Beaches can disappear over time, or even over night during severe storms.
Of all the kinds of pollution that beaches endure, oil spills can be the most deadly. A layer of thick oil smothers most small creatures fairly quickly, and larger animals that get away are fouled and poisoned soon after. Beaches do recover in time, but years may pass before new communities of plants and animals move back to an affected area.
Other kinds of pollution take their toll as well. Garbage that washes up can strangle or entrap wildlife – to a sea turtle, for example, see jellyfish and plastic bags in nearly the same way, and many have died as a result of eating the bags. Industrial waste is often toxic to many kinds of sealife, particularly to filter feeders. Raw sewage has caused dangerous algal blooms, and may play a part in the formation of deadly red tides along with excessive fertilizer runoff.