Why Do Cliffs Erode?

Wind

• One of the primary agents of erosion is wind. Wind can pick up dirt or rock and blow it away, and the stronger a gust of wind is, the larger the size of the rocks it is capable of eroding. Cliffs are particularly vulnerable to erosion by wind for two reasons. First, because cliff faces are usually surrounded by open space, there are no nearby objects to act as windbreaks and protect the cliff from wind erosion. Second, cliff faces are often areas of bare rock or dirt with little vegetation to hold soil in place.

Water

• Another force of nature that erodes cliffs is moving water. A hard rainfall is capable of washing away rocks and soil. Areas of heavy vegetation are partially protected from erosion by water because the root systems of trees, shrubs, and grasses hold soil in place. Cliffs are often relatively bare of vegetation, making them especially susceptible to erosion by moving water.

Gravity

• The third common agent of erosion that affects cliffs is gravity. This occurs when loose rocks fall from a cliff because of their weight. Erosion by gravity is especially pronounced in cliffs because their slopes are so severe. The forces of gravity also exacerbate erosion by wind and water; often, rocks only need to be loosened by wind or water, and gravity takes care of the rest. Additionally, the force of gravity makes water flow faster down the slope of a cliff, and therefore capable of eroding larger particles of soil. Landslides are another way that gravity can erode soil from cliffs.

Coastal Cliffs

• Cliffs on the ocean are especially prone to erosion, because they are also subjected to the actions of the sea. The constant pounding of large waves eats away at the base of seaside cliffs. As more and more of the base is eaten away, cliffs become top-heavy until they crack because of their own weight and fall to the sea. The California Department of Boating and Waterways says that some seaside cliffs in California are eroding at rates of more than 4 feet a year.

Other Factors

• Other factors contribute to the erosion of cliffs. One is earthquakes and tremors, which, according to the U.S. Geological Survey, can loosen the soil of cliffs and make them more susceptible to common agents of erosion. Another factor is weathering by abrasion, or the rubbing together of soil particles. Erosion by wind and water often abrades rocks that remain on the cliff, making the soil particles smaller and thus more susceptible to erosion.