Erosion by Waves
Is this erosion or deposition?
The power of the ocean modifies landforms by erosion and deposition. Landforms
modified by both erosion and deposition are seen in this photo. The cliff is being
eroded by incoming waves. The beach is being created as sand is being deposited.
Wave Erosion
Wave energy does the work of erosion at the shore. Waves erode sediments from
cliffs and shorelines. The sediment in ocean water acts like sandpaper. Over time,
they erode the shore. The bigger the waves are and the more sediment they carry,
the more erosion they cause (Figure below).
Waves erode sediment from sea cliffs. The
sediment is then deposited on beaches. These
sandy cliffs are in Greece.
Wave refraction either concentrates wave energy or disperses it. In quiet water
areas, such as bays, wave energy is dispersed. This allows sand to be deposited.
Land that sticks out into the water is eroded by the strong wave energy. The wave
energy concentrates its power on the wave-cut cliff.
Landforms From Wave Erosion
Erosion by waves can create unique landforms (Figure below).
• Wave-cut cliffs form when waves erode a rocky shoreline. They create a vertical
wall of exposed rock layers.
• Wave-cut platforms are level areas formed by wave erosion. Since these
platforms are above sea level, it means that either sea level was higher
relative or the rock was lower.
A wave-cut platform is exposed in
Pembrokeshire, South Wales.
• Sea arches form when waves erode both sides of a cliff. They create a hole in
the cliff, like the one pictured below (Figure below).
A sea arch creates a natural bridge in
California.
• Sea stacks form when waves erode the top of a sea arch. This leaves behind
pillars of rock.
Sea stack near Yesnaby, UK
Sediment Transport
Rivers carry sediments from the land to the sea. Sometimes the sediments are
deposited in a delta. But if the waves are powerful, the water will transport the
sediments along the coastline. Sediments eroded from cliffs near the shoreline may
also be transported.
Wave Refraction
Most waves approach the shore at an angle. The part of the wave that is nearer the
shore reaches shallow water sooner than the part that is farther out. The shallow
part of the wave "feels" the bottom first. This slows down the inshore part of the
wave and makes the wave "bend." This bending is called refraction.
Most waves strike the shore at an angle. This creates longshore currents, which are
described in the concept "Surface Ocean Currents."
Summary
• Ocean waves have a tremendous amount of energy and so they may do a great
deal of erosion.
• Some landforms created by erosion are platforms, arches, and sea stacks.
Longshore currents are created because water approaches the shore at an angle.