Erosion and deposition form many landscape features such as beaches, river deltas and mountain canyons. While erosion and deposition is a natural process, human activity can accelerate or retard it accordingly.
Erosion occurs when small particles of Earth break apart and are carried away by wind, water or ice currents to be carried to another location through deposition. Once there, they become part of their new surroundings by way of deposition.
Weathering
Weathering, or geomorphic weathering, is the physical disintegration of rocks, minerals and soils on Earth’s surface through chemical and physical interactions with water, air, living organisms and the atmosphere. Weathering typically takes place on site whereas erosion requires movement of materials across geographies.
Examples of weathering include rock fracturing, the expansion and contraction of rocks in response to temperature changes (known as thermal stress), freezing-thaw cycles on rocks, as well as plant or lichen growth on them. Weathering influences how much sediment is eroded over thousands to millions of years and shapes local soil quality, nutrient levels, biodiversity, as well as regional biodiversity levels.
Erosion resistance of rocks varies based on their mineral makeup and structure, giving rise to unique geological features like Utah hoodoos or Bryce Canyon National Park hoodoos. Conversely, rocks with less resistant minerals tend to erode more quickly over time and disintegrate over time.
Entrainment
Studies have demonstrated that for water to effectively move across a bed of sediment it must overcome gravity and adhesion forces to erode and transport material. When velocity of passing water over the bed is sufficient to overcome these forces and sediment will eventually be entrained; energy required varies with particle size – for instance 0.01 mm silt grains require much higher water velocity for ingestion compared to 0.5 mm sand grains.
Biologically speaking, entrainment refers to the synchronization of an organism’s internal rhythm with external stimuli such as light or sound, such as fireflies flashing synchronously or birds singing harmony. Entrainment should not be confused with synchronization – its adaptive significance lies in scheduling incompatible physiological processes at different times rather than all at the same time, which would happen if they were all tied into one phase angle.
Detachment
Erosion occurs when gravity, water or wind detach rock and soil sediments from their location on the earth’s surface and break them apart into smaller fragments that are then carried off by an eroding agent and can then deposit these newcomers elsewhere.
Raindrops or flowing water exert great impact on erosion by their impact energy, breaking apart surface aggregates of soil and carrying off particles that become part of sheet, rill or gully erosion or runoff that enters downstream bodies as sediment or dissolution products.
Studies of land use effects on soil erodibility and detachment rates conducted under various flow rate and slope gradient treatment conditions revealed that detachment rates increased with increasing flow discharge and slope gradient rates across 25 combinations of treatment conditions studied, well fitting power functions of wet bulk density and average aggregate median diameter for average aggregate median diameter rates. Erosion also varied according to land use with crops being significantly more susceptible than grasslands, shrublands, wasteland and woodland soils when it comes to critical shear stress ratings – especially cropland soil erodibility being higher.
Transport
Erosion can occur through wind, water, ice and plant growth – each process requires disconnection, entrainment and transport for it to work effectively.
Transport forces vary between mediums. A glacier may move particles more effectively due to their firm attachment by ice, without breaking their bonds as frequently as rainwater or air does.
Water erosion transports sediments downhill and forms lake and ocean shorelines, as well as cave formation. Rushing rivers that sculpt valleys can also be caused by this natural process of erosion.
Physical Erosion
This form of erosion breaks rocks into smaller pieces and smoothens them out, creating stunning landforms such as those found in China’s Badain Jaran Desert or Arches National Park in Utah – not to mention contributing to mass wasting events like North America’s “Dust Bowl”. Furthermore, physical erosion plays an integral part in creating clastic sediments composed of pieces from older rocks.