A beach is usually a flat, gently sloping piece of land that borders an ocean, river, or lake. Beach materials like pebbles, rocks, sand, and shells cover most beaches. Most beaches are man-made creations of erosion and weathering. They provide good opportunities for beachcombers to photograph sunsets and sunrises, sunburns, and other events.
Although most beaches are man-made, a small percentage of beaches are made naturally, through sedimentary rock and vegetation. Erosion and beach nourishment increase the rate and depth of beach erosion and make it more difficult to prevent beach erosion. The effects of beach nourishment include the formation of dunes and ridges, the deposit of coarse sand into the sea bed, and the movement of tectonic plates across fault lines.
Dunes are narrow strips of beach, which can range from several yards to a few feet across. They form where the tide has washed ashore and deposited sand. Sand gradually makes its way to the sea bed, where it becomes part of the marine ecosystem. Dunes are common in most bays, but some are confined to a small area around the shore. Erosion causes the movement of the sand and can make dunes grow larger, forming large bluffs or eroding into narrow channels.
Seawater takes about seven years to move into the ocean from the shoreline. However, certain coastal erosion and water level rise can speed up this process. As the sediments move down the beach, they pile up against each other, shaping the shape of the beach. This can cause mats to form on the bottom of the beach, called dunes, while larger mats may cover the entire beach.
In addition to the large accumulations of sediment on the beach, there are other processes that drive beach development. Over the years, various types of shells have been washed along the beach. These come from oysters, clams, walnuts, crab shells, and other shells from the ocean. Other shells break loose from the surf and drift into the sea, carrying with them sediment and nutrients that nourish the seaweed that creates new beds of algae. All of these factors add to the creation of nutrient-rich water that makes it easier for beaches to develop.
Coastal erosion, sea level rise, and nutrient accumulation are all playing roles in the global environmental impacts of beaches. Scientists have been studying how to fix the issues that these factors have caused. One proposed solution is to build sea walls to separate low-lying areas from the high seas. However, building such a wall would require the bulldozing of natural habitats, which some environmentalists are opposed to.