Erosion is the natural process by which surface materials, such as rocks, sand and silt are worn away from surfaces through detachment, entrainment and transport forces.
Rain, waves, ice and floodwater all play a part in erosion. Wind can also damage surfaces quickly. Plants such as trees can act as natural wind breakages.
Erosion transports the weathered particles downriver where they will eventually be deposited at new locations – this process is known as deposition.
Wind
Wind erosion may seem weak compared to waves or cascading water, yet over time it still shapes landscapes via deflation (picking up particles and carrying them along) or abrasion (sandblasting).
Vegetation serves as a natural barrier against soil erosion, anchoring it down through its roots. When vegetation coverage decreases or disappears entirely, erosion rates increase rapidly.
Sediment particles eroded by wind can form sand dunes or loess deposits that travel great distances by wind to their final resting spots, often desert regions on other continents.
Erosion alters soil nutrients by dislodging fine particles and exposing mineral surfaces to sunlight, creating what is known as saltation, an ecosystem-wide phenomenon which disperses soil nutrient components accumulated over thousands of years in one location. Loss of these vital particles may reduce crop yields, leading to food insecurity; and also contribute to air quality issues and reduced visibility.
Water
Water can erode soil by flowing swiftly over rocks and other particles, as well as by dissolving chemicals such as carbon dioxide and sulfates that make the soil less stable, dissolving chemical bonds in its structure, leading to its collapse and leaving behind sediment which will be carried off later.
Water erosion can be affected by many factors, including temperature, slope of land and the presence of vegetation. A rough streambed may reduce its ability to erode as friction reduces it erosive power.
Human activities also can hasten erosion rates, including clearing away vegetation and overgrazing livestock that disturb roots that anchor sediment to soil, while paveing increases rates 10 to 100 times greater than natural processes.
The amount of sediment deposited by rivers depends on their velocity. For instance, a particle measuring one millimeter will typically be washed away with flow velocities between 10 centimeters per second and 15 cm/s; as particles grow larger however, their minimum flow velocity required for erosion decreases accordingly.
Soil
Soil, all of that dirt between living plants and animals on Earth’s surface and its bedrock at its core, is an astonishing natural system. Ever-changing and surprising to those who study it, its wonder remains fascinating for soil scientists who study it.
Erosion is most noticeable and dramatic when occurring during short, intense thunderstorms; however, erosion caused by long-duration rainfall can also have devastating results for soil.
Soil’s ability to resist erosion depends on its texture, which refers to the ratio between various sizes of sand, silt and clay particles. Soils with higher levels of organic matter, improved soil structure and greater permeability tend to be less erodible than those lacking such characteristics.
Erosion rates can also be affected by the size and type of plant cover on soil surfaces. Vegetation/crop residue combinations that cover an entire field with enough cover vegetation to intercept all falling raindrops can help mitigate erosion; this is particularly relevant where land management practices like plowing or overgrazing have resulted in ground-cover vegetation being removed, which then allows rainwater to seep into it more readily and cause increased erosion rates.
Landslides
Landslides are defined as the movement of weathered sediment that fails in depth and slides downhill along a distinct rupture or slip surface, caused by various natural and human-related factors like rainfall, snow melt, river erosion, burst water mains or floods.
Landslides differ from other flow types in that they gain energy during their erosion process and increase mobility, so an accurate description of landslide energy must include both this energy source as well as any momentum gained during entrainment.
A novel mechanical energy generation model offers the first ever mechanical quantification of erosional energy and precise description of mobility, with concepts like erosion velocity, entrainment velocity and energy velocity providing information to accurately describe excess energy regimes, while mobility scaling and erosion number provide explicit measures of mobility; whil dynamical equations incorporated within this model include net momentum production due to erosion.