Erosion and deposition

Erosion is the acquisition and transportation of rock debris by running water, groundwater, glaciers, wind and waves. Debris carried by these agents scrapes the surface (abrasion), which greatly helps erosion. Erosion wears the landscape down and is largely responsible for the continuous changes on the earth's surface.

• Weathering aids erosion, but it is not a pre-condition for it.
• Weathering, mass wasting and erosion are degradational processes. Erosion and transport are driven by kinetic energy.

Agents and what controls them:

• Wind (gas), running water (liquid) and glaciers (solid) are controlled by climate.
• Waves are not: their work depends on location, the coast where land meets sea.
• Groundwater is not either: its work depends on rock type. Only where rocks are permeable and soluble and water is available does karst topography develop.

Deposition is a consequence of erosion. When agents lose velocity, and so energy, on gentler slopes, the material they carry settles. So deposition is not really the 'work' of an agent. Coarser material settles first, finer material later, and depressions fill up. The same agents (running water, glaciers, wind, waves, groundwater) are therefore also depositional (aggradational) agents.

Example (new): where a fast hill stream reaches the plain and suddenly slows, pebbles and gravel drop out right at the foot of the hills, while fine silt is carried much farther before it settles.