Four Types of Agents of Erosion

Waves, glaciers, wind and running water are all agents of erosion.

When rocks break down due to chemicals, vegetation, temperature change, water or ice, they are weathering. The process of erosion is the transport of these broken pieces away from their original location, and the term deposition refers to the final destination of these broken pieces or sediment. The agents of erosion include wind, ice, water and waves.

Wind

Erosion by wind is sometimes called Aeolian erosion, named after Aeolus, the Greek wind god. For examples of this, look to the desert, with its sand dunes and the wind- and sand-blasted face of the Sphinx. The wind picks up light objects like sand and hurls it at landforms, breaking off pieces, which are also carried off by the wind and hurled at yet other landforms. Wind-carried sand often collects around obstacles, creating mounds or dunes.

Ice or Glacier

Although it moves slowly, a glacier covers vast expanses, freeing and transporting bits of rock with it through processes called abrasion and plucking. Water seeps into the rock and freezes, cracking the rock into bits that are carried away by the glacier. This is called plucking. Abrasion refers to the way the glacier and the rocks it carries grind against underlying rock. This action breaks off bits of that underlying rock, which are then carried away by the slow-moving glacier.

Water

The most common of the erosion types, running water, typically occurs in the form of a stream whose currents carry off sediments collected from the stream's bed and banks. However, water erosion also refers to rainwater and the watershed created during a rainfall. As they fall to the ground, raindrops either sink into the ground or collect and move as runoff, temporary streams of water that pick up and carry off bits of rock and soil. The amount of erosion that occurs depends on how fast the water is moving; a faster current can transport heavier objects. The amount of sediment carried in a stream is called its "load" and a stream's load can be heavier when current picks up speed, as during or after a heavy rain.

Wave

Produced by oceans and other large bodies of water, waves move toward and away from the shoreline, carrying sediment toward beaches and picking up beach sediment and carrying it back out to sea or further up the coastline. Waves free and collect the sediment they carry in several ways: the force of the waves breaks off bits of existing rock, water enters and widens existing cracks in rock, bits of rock carried by the waves scrape against other rocks, and salt in the seawater weakens and breaks off bits of rock. Waves vary in power--especially during storms or high winds--and rate and volume of erosion varies along with that power. Aside from the back-and-forth lapping rhythm of the waves, a seasonally cyclical pattern is also evident along beaches. Waves may carry off most of the sandy beach during one season, only to build the sand back up in that same location for another season.

References

• Poway Unified School District: Earth Science: Weathering and Erosion
• Poway Unified School District: Erosion Caused by Waves
• Poway Unified School District: Erosion Caused by Running Water
• Water Encyclopedia: Erosion and Sedimentation; William Arthur Atkins
• Earth Science is Cool: Laboratory Investigation 4-3 Erosion