Erosion and deposition are natural processes that alter existing landforms while also creating new ones such as beaches, spits, or deltas.
Waves, currents, ice, wind and flooding all contribute to erosion. Planting trees in areas where there is limited or no vegetation can help slow erosion while simultaneously replenishing nutrients in these regions.
Weathering
Weathering rocks depends on both their mineral makeup and exposure time. For instance, rocks with high concentrations of iron may break down when exposed to water through oxidation or chemical weathering processes that lead to corrosion – an action often observed along coasts where waves carrying sediment grind against cliff faces and headlands.
Physical weathering includes exfoliation, freeze-thaw cycles, root expansion and abrasion – each process contributing to its own unique form of physical weathering over long periods. To describe the specific kind of physical weathering experienced by any particular rock requires lengthy study of how it all interacts over time.
As weathering wears away at rock surfaces, erosion carries away its material to another location through deposition – when sediment falls from the air or from waterways such as rivers. Deposition may occur locally through abrasion and the breakdown of sand dunes; or it could occur as far away as when glaciers carry debris off mountainsides.
Entrainment
As streams flow, forces of gravity and adhesion bind loose particles to their beds or banks, but as stream velocity increases a critical point is reached where applied force exceeds these forces to dislodge these materials from suspension – this depends on particle size – so silt, sand and coarse gravel are more easily dispersed into suspension while coarse particles like pebbles and cobbles require greater force to entrain into suspension.
Researchers have established that the entrainment rate E of a debris flow depends on local topographic and hydraulic conditions, specifically critical Shields numbers and angles of repose at zero slope. Deposition rate Dp has been demonstrated as being determined by particle activity rather than bottom shear stress (Lajeunesse et al. 2010; Ancey et al. 2008).
Understanding the interaction between erosion and deposition is difficult due to their interdependent nature. Studies have revealed, for instance, that as channels widen their debris flows increase their rates of entrainment and deposition as their deposition rates rise exponentially.
Transport
Transport refers to the movement of particles by wind, water, glaciers or ice and can be caused by anything from wind and waves to glaciers and ice. Transport plays an integral role in shaping Earth’s landscape as it shifts materials upwards from lower sites into higher ones causing hills and valleys, shifting sediment across lakes or coastlines and shaping river channels – this erosion forms hills and valleys as it moves material uphill before depositing it at higher spots causing hills and valleys, sediment movement across lakes or coastlines and river channels all caused by transport.
Entrainment and transport are determined primarily by forces of gravity and frictional resistance, the latter of which arises from particle to medium interactions and cohesive bonds which hold particles together; weathering weakens these ties, as do forces from erosion agents (abrasion, plucking, raindrop impact or cavitation).
Transport capacity in physically-based models depends on flow velocity, volumetric flow, kinetic energy inputs, friction slope, and various process representations. GEOtopSed and MUSLE_G_TC models (Table 3) share identical hydrologic states while differing representations for erosion and transport processes – thus comparison of estimates generated from both model configurations will likely highlight their influence on suspended sediment yield estimation in streams.
Deposition
Erosion is the process of moving rocks and soil particles from one location to another through erosion, followed by deposition. Once moved, these particles must be placed somewhere for deposition to take place.
Deposition can happen over short or long time periods, from seconds or minutes up to years, eons and millennia. Deposition may occur simultaneously with erosion or after its completion and even during weathering processes.
Streams and rivers cause erosion by picking up and transporting away rock and soil particles. The rate at which erosion occurs depends on factors like its speed, strength, particle cohesion, surface charges and density affecting particles forming cohesion bonds or surface charges within particles, density of these forces as well as particle surface charges that determine cohesion and cohesion charges within particles that form cohesion layers in particle suspension systems affecting particle cohesion, surface charges density as well as its cohesion or density values.
Harder rocks tend to erode more quickly than soft silts and sands, explaining why we see coastlines and cliffs retreat more quickly than valleys or plains.