Shorelines waves that erode coastal structures. Learn

Shorelines constantly change due to the pounding of waves that erode coastal structures. Learn about shoreline features that are formed through coastal erosion, such as wave-cut cliffs, wave-cut platforms, sea arches and sea stacks.

The Shoreline

If you visited the beach as a kid and then went back with your children 30 years later, chances are the beach and shoreline would look different. This is because coastal areas are constantly changing in form and shape due to the impact of waves.The pounding of waves is constantly eroding the shoreline, and this creates some interesting shoreline features. In this lesson, you will learn about the effects of coastal erosion, and how the relentless pounding of waves carves out unique features, such as cliffs, platforms, sea arches and sea stacks.

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Coastal Erosion and Headlands

Coastal erosion, which is the wearing away of coastal land or beaches, is mainly caused by the impact of waves along the shoreline. This is accentuated during storms when waves are large and crash on shore with a lot of energy.If a coastal structure, such as a headland, which is a narrow strip of land that projects out into a body of water, contains cracks or crevices, the waves can force water into the openings, dislodging land and rock fragments. Rocky structures along the coast are also subjected to erosion caused by sand and rocks stirred up by and carried within the waves. As the sand and rocks crash into the coast, they grind away land and rock.

Wave Refraction

Waves do not typically strike the shore head on. Wave refraction is the bending of waves as they travel toward the shallow waters of the shore.

When waves move from the deep ocean waters to the shallow waters of the shore, the part of the wave closest to the shore hits bottom and slows first.However, the part of the wave that is still in deep water proceeds at full speed. This contrast in speed causes a bending of the wave crest. As the wave approaches the coast, it is almost parallel to the shore.

Because of wave refraction, the energy carried by waves pummels the sides and ends of shoreline protrusions, such as headlands leading to greater erosion.

Wave-Cut Cliffs and Wave-Cut Platforms

Shorelines are carved over time, leaving unique and oftentimes spectacular shoreline features. A wave-cut cliff is a steep rock face created by the eroding action of waves. As waves continue to hit the supporting rocks of the cliffs, a notch is carved into the cliff face. Rocks overhanging the erosion weaken and crumble, causing the cliff to retreat farther inland.This leaves behind a somewhat flat area found at the base of a wave-cut cliff, called a wave-cut platform.

These may be seen during times of low tide when the overlying water recedes. These platforms are sometimes referred to as coastal benches because when they are exposed during periods of low tide, they resemble large benches made of flat rock.

Sea Arches and Sea Stacks

As mentioned earlier, headlands that project into the ocean are savagely attacked by refracted waves.

The waves erode the rocky headlands and chip away at any fractured rocks. This can lead to the creation of a sea arch, which is a natural hole carved through a headland, due to erosion by waves. Sea arches can be found along many coasts and each is uniquely beautiful.

However, these structures are not stable due to continual erosion by the waves. Sea arches eventually collapse, leaving behind an equally beautiful and intriguing structure referred to as a sea stack, which is a pillar-shaped rock formation detached from the coast, due to erosion by waves. Sea stacks resemble smokestacks, as you might see on a factory. These impressive structures can be seen just off the shore of many coastlines where they contribute to the natural beauty of the shoreline.

Lesson Summary

Let’s review. Coastal erosion is the wearing away of coastal land or beaches and is mainly caused by the impact of waves. Waves do not typically strike the shore head on. Wave refraction is the bending of waves as they travel toward the shallow waters of the shore.

Because of wave refraction, the energy carried by waves pummels the sides and ends of shoreline protrusions, such as a headland, which is a narrow strip of land that projects out into a body of water.One of the shoreline features that is created by erosion is a wave-cut cliff, which is a steep rock face created by the eroding action of waves. As waves continue to hit the cliff, it retreats farther inland, leaving behind a wave-cut platform, which is a somewhat flat area found at the base of a wave-cut cliff.Another feature created by erosion is a sea arch, which is a natural hole carved through a headland, due to erosion by waves.

Sea arches eventually collapse, leaving behind a sea stack, which is a pillar-shaped rock formation detached from the coast, due to erosion by waves.

Learning Outcomes

When the lesson is over, you might be able to:

  • Analyze the changes to coastlines due to coastal erosion and wave refraction
  • Display familiarity with shoreline features like wave-cut cliffs and platforms
  • Impart knowledge of erosion features such as sea arches or sea stacks
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