A beach is a geologic formation that is located along a large body of water, including lakes, rivers, and oceans. Beaches are characterized by the presence of tiny pieces of organic sediment. The sediments may be composed of sand, rock, shell, algae, or pebbles. Natural beaches may take thousands of years to evolve, a process that is the result of constantly moving water that erodes the land located around its edge. Essentially, rocks or coral reefs located off the shore are worn down by moving waves. Additionally, rivers and rainwaters may erode rocks located further inland. These sediments are deposited along the coastline, forming a beach.
Characteristics of Beaches
Beaches are typically divided into 4 zones (known as the beach profile): swash, beach face, wrack line, and berm. The particles found within each of these zones are different. For example, finer sediment is found closer to the water. This is partially because the moving water constantly breaks down the particles located here. As the beach moves further inland, the particles along its surface grow in size. Along the outermost edge of the beach are typically large rocks that have been washed up during storms. Generally speaking, beaches and shorelines cover a narrow area of land and tend to slope downward toward the waterline.
How Are Beaches Formed?
Rocks or coral reefs located off the shore are worn down by moving waves. As these materials are worn down, they become small particles of sediment that are carried by the waves in a state of suspension. In the case of sediment from further inland, the particles are washed to the larger body of water, where they are swept up by the waves and into the same state of suspension. These suspended particles cause the moving water to have increased erosive ability, resulting in greater amounts of eroded particles in the water.
In some cases, fish and other marine animals contribute to the speed of erosion. This is particularly true in beaches that are located near coral reefs. Many of these animals rely on algae growing on the coral as a major dietary supplement. As they eat away the algae, they inadvertently cause the coral to break off into small pieces. Some pieces may even work their way through the digestive tracts of these animals, resulting in even smaller particles that are washed up into the waves.
Erosion is typically thought to decrease the size of certain landforms, however, this is not always the case. In fact, erosion actually works to increase the size and width of some beaches. This growth occurs as the waves deposit the aforementioned sediment onto the land. Additionally, beaches may experience growth in size near river deltas, where rivers carry eroded sediment to the ocean. This sediment is deposited along the beach before being carried off into the ocean.
The type of wave that reaches the coastline also plays a part in the formation of beaches. Constructive waves, which are those that allow the water to recede and the beach particles to stop moving between waves, result in compacted sediment. This firm beach surface prevents future erosion. Destructive waves, which are fast forming and do not allow the water to recede between waves, result in a near-constant state of sediment suspension in the water. Because the particles remain in the waves, rather than being deposited on the shoreline, the beach in these areas is more likely to suffer from future erosion. With destructive waves, the sediment is not given a chance to settle and become compacted.
Types of Beaches
Although beaches share the same basic characteristics, they also exhibit a variety of differences. These differences mean that beaches may be classified into several types, including sandy, rocky, tropical, and frozen.
Sand and rocky beaches get their names from the type of particle that can be found covering their surface. Sandy beaches are often characterized by their slowly sloping profile, whereas rocky beaches tend to exhibit more extreme slope angles. This difference in slope is because of the difference in particle size. The larger particles on rocky beaches, for example, cause the waves to lose their power more quickly. Because of this, the wave doesn’t reach as far inland as on a sandy beach and the slope becomes steeper as a result.
A tropical beach is typically home to a large variety of plant life, which is supported by fertile soil. A frozen beach rarely has vegetation and is most commonly covered in ice and rock.
In addition to these specific types of beaches, coastlines may also develop spits over time. A spit is an area of land that extends from the beach into the nearby body of water. These formations occur as a result of wind blowing at an angle against the beach. As the spit becomes larger, it works to protect the beach area from large waves and strong wind. This protected area often collects a very fine type of sediment known as silt, which results in the formation of marsh-like habitats.
What Causes Beach Recession?
Just as beaches can grow over time, they can also recede. Beach recession may occur at a rapid rate or take place over a longer period of time. Storms like tsunamis and hurricanes are known to cause extensive destruction to beaches in a very short time. The strong waves and winds from these extreme weather conditions carry away sand and other sediments that may have taken years to collect. Additionally, these storms take out most of the vegetation along shorelines that normally helps keep sand in place. Rising sea levels, that occur as a result of global climate change, also result in beach recession.
Human activity may also contribute to beach recession. In order for beaches to grow, for example, eroded particles are necessary. This means that waves require access to material that can be eroded and turned into sediment that can later be deposited along coastlines. Urban development, dam projects, and rerouting rivers may reduce the amount of erodible land found near bodies of water. As these human activities progress, the sediment found suspended in the waves is reduced. With less sediment in the water, fewer particles are deposited along the beach, resulting in recession. Beach recession can be seen on beaches all over the world, including in places like the Pacific coast of the US state of California, the Atlantic coast of France, and the Dutch coast in the Netherlands.