A beach is a narrow gently sloping strip of land that lies along the edge of an ocean, lake, or river. It is covered with materials such as sand, pebbles, rocks and seashell fragments that have been deposited by waves and tides.
Sand is the most common beach material. It is made up of tiny particles of weathered quartz or other minerals. It can be sourced from many different sources, including offshore rocks and coral reefs or from headland erosion and slumping producing deposits of scree. The most important source of sand in North America is the Gulf of Mexico. Other major sources include beaches in the Appalachian Mountains, where sand particles are eroded from nearby rocks and mineral outcrops.
Beaches change in appearance and shape seasonally due to wind, water currents and eddies, tides, and erosion. During the winter, storm winds may toss large amounts of sand into the air and erode the beach. During the summer, the waves pick up these sand particles and build the beach back up again.
Seasonal changes also cause beaches to be wider and have a gentle slope during the summer and be narrower and more steeply sloping in the winter. This is caused by the sand piled up from sandbars that are uncovered during these seasons.
Coastal erosion, which is caused by the action of waves and wind, is one of the most significant threats to beaches. It can lead to the loss of sand, reed beds and the formation of groynes, as well as changes in the character of flora and fauna living along beaches.
The most effective defense against erosion is the presence of flora that requires freshwater runoff and has a network root system to hold in place the foredunes. The presence of this flora is essential to the stabilization of the foredunes, and it prevents the beach head from being eroded by high winds or subsiding floodwaters.
Another defense against erosion is the creation of seawalls, which are built to keep sand from drifting away. Seawalls can be made of plastic, concrete or rock.
Changing sea levels, which are caused by the Moon and Sun, and the movement of the Earth’s rotation, also play a role in affecting beaches. The sand on a beach can completely cover the ground during high tide and only reeds and other vegetation can be seen at low tide.
People combat coastal erosion by building seawalls or other structures that help protect the shoreline from powerful storms and high waves. They can also install devices to keep sand from being blown away by wind or rain, such as gutter drains that direct water off the beach.
Sandbars are areas of sand and sediment that are exposed just off a beach. They are formed when waves carry sand to the surface, then the water slows down and loses enough force to support it. This process is called longshore drift, and it happens repeatedly on beaches all over the world.