How Waves Form
The energy in waves comes from wind that blows across the waters surface. As the wind makes contact with the water, some of it's energy starts to transfer to the water. Large ocean waves will lead to the result of powerful storms far out at sea. But ordinary breezes can produce waves in lakes or small ponds.
The energy that the water picks up from the wind causes water particles to move up and down as the wave moves by. However, the water particles themselves, do not move forward.
A wave changes as it gets closer to land. In deep water, a wave only effects the water that is near the surface. But as the wave gets to shallow water, the wave begins to drag on the bottom. Because of the friction between the wave and the bottom, the wave slows down. Now the water actually does move forward with the wave. This forward-moving process is what provides the force that shapes the land along the shoreline.
Erosion by Waves
Waves are the major force of erosion along coasts. Waves shape the coast through erosion by transporting sand and other sediment, and breaking down rock.
How Waves Erode
One way waves erode the land is by impact. Large waves can be strong, and hit rocks along the shore with great force. This energy in waves can break apart rocks. Over time, waves can make small cracks larger. Eventually, the waves cause pieces of rock to break off.
Waves also erode by the process called abrasion. As a wave begins to get closer to shallow water, it picks up sediment, including materials such as sand, and gravel. This sediment is now carried forward by the wave. When the wave hits land, the sediment in the wave wears away at rock like sandpaper wearing away at wood.
Waves coming to shore gradually change direction. This change in direction takes place as different parts of a wave begin to drag on the bottom. The energy of these waves is concentrated on headlands. A headland is a part of the shore that sticks out into the ocean. Headlands stand out from the coast because they of harder rock, and resist erosion by the waves. Over time, waves erode the headlands, and make the shoreline even out.
Landforms Created by Wave Erosion
Whenever waves hit a steep, and rock coast, they strike repeatedly. An example of this process is an axe that keeps hitting a tree. The cut would become larger and deeper with every strike. At last, the tree would have to deep of a cut, and fall. The way that ocean waves erode the base of the land along a steep coast is similar to this process. In since some rock is stronger, the weaker and softer rock will erode faster. After a while, the waves may erode a hollow area in the rock known as a sea cave.
Eventually, waves may erode the base of a cliff so much that the rock above collapses. The result is known as a wave-cut cliff.
Another feature created by wave erosion is called a sea arch. A sea arch can form when waves erode a layer of softer rock that has a layer of harder rock above it. If a sea arch collapses, the result could be a sea stack. A sea stack is a pillar of rock standing above the surface of the water.
Deposits by Waves
Waves can form a coast when they deposit the sediment that they carry, forming coastal features that may include beaches, spits, and barrier beaches. Deposition occurs when waves slow down, causing the water to drop the sediment it was carrying.
As waves reach the shore, they drop all of the sediment that they carry, this results in a beach. A beach is an area of wave-washed sediment along a coast. The sediment deposited on beaches is usually sand. Most of the sand comes from rivers that carry eroded particles of rock into the ocean. But, not all beaches are made from sand. Some beaches are made from small fragments of sea shells or even coral. This happens when the materials such as coral or sea shells, are piled up by wave action. You can find many beaches like this in Florida.
The sediment on a beach usually moves down the beach after it has been deposited. Waves usually hit a beach at an angle, not straight on. These waves may create a current parallel to the coastline. As waves repeatedly hit the beach, some of the beach sediment moves down the beach with the current. This process is called longshore drift
One result of longshore drift is something called a spit. A spit is a beach that projects like a finger out in the water. Spits can form as a result of deposition by longshore drift. Spits occur where a headland or other obstacle interrupts longshore drift, or where the coast turns abruptly.
Sandbars and Barrier Beaches
Incoming waves carrying sand can build up sandbars. A sandbar is a long ridge of sand, parallel to the shore. A barrier beach is similar to a sandbar. A barrier beach can form as storm waves pile up large amounts of sand above sea level forming a long, narrow island parallel to the coast. Barrier beaches can be found in many places along the Atlantic coast of the United States, such as the Outer Banks of North Carolina. Some people have built their homes on barrier beaches. But the storm waves that build up these beaches can also wash them away. Barrier beach communities must be prepared for the damage that hurricanes and other storms may bring.