soil layers

Entrainment is the process of particle lifting by the agent of erosion. In many circumstances, it is hard to distinguish between entrainment and detachment. There are several forces that provide particles with a resistance to this process. The most important force is frictional resistance. Frictional resistance develops from the interaction between the particle to its surroundings. A number of factors increase frictional resistance, including: gravity, particle slope angle relative to the flow direction of eroding medium, particle mass, and surface roughness. Physical, chemical, and biological weathering act to weaken the particle bonds found in rock materials. As a result, weathered materials are normally more susceptible than unaltered rock to the forces of detachment. The agents of erosion can also exert their own forces of detachment upon the surface rocks and soil through the following mechanisms: The energy for erosion comes from several sources. Mountain building creates a disequilibrium within the Earth's landscape because of the creation of relief. Gravity acts to vertically move materials of higher relief to lower elevations to produce an equilibrium. Gravity also acts on the mediums of erosion to cause them to flow to base level. The critical entrainment velocity curve suggests that particles below a certain size are just as resistant to entrainment as particles with larger sizes and masses (Figure 2). Fine silt and clay particles tend to have higher resistance to entrainment because of the strong cohesive bonds between particles. These forces are far stronger than the forces of friction and gravity. Once a particle is entrained, it tends to move as long as the velocity of the medium is high enough to transport the particle horizontally. Within the medium, transport can occur in four different ways: Figure 2: This graph describes the relationship between stream flow velocity and particle erosion, transport, and deposition. (Source: PhysicalGeography.net) * Suspension is where the particles are carried by the medium without touching the surface of their origin. This can occur in air, water, and ice.