Erosion is the detachment, removal, and movement of rock, soil, or other surface material by flowing water, wind, moving ice, and related processes. It shapes landscapes by excavating channels, wearing down exposed surfaces, and redistributing sediment. Erosion differs from weathering, which breaks down or chemically alters material in place, and from deposition, which occurs when transported material accumulates. These processes commonly operate together: weathering supplies loose particles, erosion removes them, and deposition builds new sedimentary features elsewhere. (nps.gov)
Processes and controls
Erosion involves both the availability of removable material and the ability of an agent to detach and carry it. Flowing water and wind exert forces on particles; movement begins when these overcome resistance associated with particle weight, cohesion, or surface protection. Grain size, moisture, sediment supply, flow conditions, and surface characteristics therefore influence erosion and sediment transport. Fine particles may remain suspended, whereas larger grains commonly travel close to the ground or channel bed. (home.nps.gov)
Erosion is not uniform across a landscape. Resistant rocks may remain as prominent features while adjacent, less resistant materials are removed more rapidly. Channels also adjust to changes in slope, water flow, and sediment supply by changing their width, depth, or course. Consequently, erosion and deposition can occur simultaneously in different parts of the same landscape or river reach. (home.nps.gov)
Water erosion
Rainfall initiates erosion by striking exposed soil and dislodging particles. Surface runoff then transports this material downslope. Sheet erosion removes thin layers across relatively broad surfaces; rill erosion produces small channels; and gully erosion develops where concentrated flow cuts larger drainageways. Permanent gullies cannot ordinarily be removed by routine cultivation, whereas smaller, ephemeral gullies may be filled and subsequently re-form along similar flow paths. These categories describe increasing concentration of runoff rather than a sequence that every slope necessarily follows. (nrcs.usda.gov)
A river erodes its bed and banks while transporting material supplied from upstream and surrounding slopes. Particles moving near the bed form the bed load; particles supported by turbulent flow form the suspended load. Transport depends on flow velocity, depth, turbulence, grain properties, and available sediment. Coarse particles often move intermittently, while sufficiently fine sediment can remain in suspension even at relatively low flows. (usgs.gov)
Within a drainage basin, erosion links hillslopes to channels and downstream sediment stores. River erosion helps shape valleys, while deposition contributes to floodplains and deltas. Changes in water flow or sediment supply can shift the locations of channel erosion and accumulation, so the same discharge does not necessarily produce the same sediment response under different conditions. (usgs.gov)
Coastal erosion
Coastal erosion is the loss of shoreline sediment or other coastal material. Waves, currents, tides, wind, geological characteristics, sediment supply, and changes in sea level all influence its occurrence. A shoreline may retreat where material is removed faster than it is replenished, although the balance varies between locations and over time. (oceanservice.noaa.gov)
Waves approaching a coast at an angle generate currents parallel to the shoreline. These currents, together with wave-driven movement on and off the beach, transport sediment through longshore drift. Thus, erosion at one location can be connected to sediment movement elsewhere along the coast. Sea-level rise and extreme weather can worsen erosion of barrier islands, whose beaches, dunes, and vegetation also absorb wave energy. (oceanservice.noaa.gov)
Wind and glacial erosion
Aeolian processes comprise wind-driven erosion, transport, and deposition. Wind removes loose surface material and moves grains by surface creep, hopping movement called saltation, or suspension. Saltating sand can strike the surface, ejecting finer particles and pushing larger grains along. Moisture, salts, and soil crusts increase resistance to entrainment; removal of loose material can create deflation hollows. Wind-blown sediment also supplies depositional features such as dunes. (home.nps.gov)
A glacier erodes principally through abrasion and plucking. In abrasion, rock fragments embedded in basal ice scrape and grind underlying bedrock, sometimes leaving scratches called striations. In plucking, blocks separate from fractured bedrock and are carried away by the ice. Glaciers can also deform and entrain unconsolidated sediment beneath them. Their erosion widens and deepens valleys, producing characteristic U-shaped profiles; melting ice subsequently deposits debris or releases it to meltwater streams. (nps.gov)
Environmental effects and management
Soil erosion can remove nutrient-rich topsoil and reduce agricultural productivity, particularly where soil lacks protective vegetation or crop residues. Downstream effects include reduced water clarity, altered channel form, and changes to aquatic habitat. Sediment accumulating in reservoirs reduces water-storage capacity, while nutrients and chemicals attached to particles can impair water quality. Sediment is also a natural component of rivers: both excessive supply and substantial reductions can disrupt aquatic ecosystems. (nrcs.usda.gov)
Soil conservation practices address detachment and transport through surface protection and runoff management. Cover crops protect soil during otherwise fallow periods; reduced tillage preserves surface residues; contour farming redirects runoff around slopes; and vegetative strips intercept material moving downslope. Wind barriers and shelterbelts reduce wind exposure and erosion. Their functions differ, reflecting the distinct mechanisms of water and wind erosion. (nrcs.usda.gov)
Measurement and modelling
Erosion assessment distinguishes material removed from a source area from sediment transported through a channel or deposited downstream. River studies measure sediment concentration, particle characteristics, and transport alongside water flow, with attention to sampling errors and temporal variability. Sediment discharge alone does not identify where all the transported material originated. (usgs.gov)
The Revised Universal Soil Loss Equation family estimates rainfall-driven soil loss. RUSLE2 combines empirical and process-based science to predict rill and interrill erosion caused by rainfall and runoff. Its scope is therefore narrower than erosion as a whole: channel-bank erosion, coastal retreat, wind erosion, and glacial excavation involve different processes and assessment methods. (nrcs.usda.gov)