Erosion and deposition are natural processes that shape Earth’s landscape over time, while human activities like road construction, farming and landscaping can accelerate these processes by disturbing ground surfaces or washing away loose soil particles.
Physical erosion wears away at rocks by breaking them apart or altering their shapes, creating new landforms such as spits and salt marshes in its wake.
Weathering
Weathering, or the natural process of disintegrating rocks and minerals over time, creates ever-evolving landscapes. This process may happen as quickly as mudslides or as slowly as the formation of stream beds.
Weathering, which involves the gradual disintegration and erosion of rocks and minerals near Earth’s surface, is caused by various forces including water, ice, wind, plants and temperature variations.
Chemical weathering occurs when porous materials such as clay come into contact with rocks. The clay absorbs lots of water from rainfall, expanding and eventually eroding them. Mechanical weathering takes place when curved plates of rock are stripped away from their surfaces through exfoliation; freezing-thawing cycles also contribute to mechanical weathering by widening cracks that eventually separate rocks apart.
Wind
Wind erosion refers to the loosening, removal and transportation of material by means of air or water flow. Wind can erode and deposit weathered rock, soil, sediment, or sand depending on its speed and direction of movement.
Wind can move soil particles by either suspending them into the air – known as saltation – or rolling them along surfaces, such as beaches. Sand, silt and clay particles are transported great distances as a result, creating dust storms.
Wind can also transport seeds, spores, and pollen to disperse new plant species more rapidly across an arid region. Wind erosion not only has local effects on abiotic resources and habitats; its global impacts are magnified through fine nutrient-rich soil particles eroding into water bodies or the air.
Water
Streams and rivers continually erode material along their banks, eventually producing waterfalls, flood plains, meanders and oxbow lakes. Much of this debris dissolves in water before making its way into the ocean.
Erosion can be worsened by human activities that strip away ground-covering plants, like plowing fields prior to or after growing crops and allowing livestock grazing freely. Climate change exacerbates erosion by creating more frequent rainfall events and longer wildfire seasons, further worsening erosion rates.
Geologists use rock sorting to understand the types and amounts of erosion. Well sorted rocks indicate wind erosion while poorly sorted ones suggest water erosion; additionally, the freeze-thaw cycle of ice/snow can also erode rocks, creating caves or sea stacks as caves form in this process.
Ice
Ice has an outsized effect on river erosion and deposition, particularly its effects on bank-attached ice and high sediment loads (see figure below).
Ice jam releases can lead to an immediate surge in suspended sediment concentrations that has the ability to adversely impact both water quality and habitat. During such times, particles reach concentrations high enough to have significant negative consequences on environmental sustainability and species habitat.
Previous studies have relied on cosmogenic nuclide concentrations or U-Pb ages on sediments to distinguish glacier-origin debris from supraglacial material, but these approaches have limitations when used to try to ascertain source contributions at specific sampling sites due to variable age-elevation profiles in detrital materials and difficulty discriminating between hillslope and glacial sources. Our approach uses bedrock age distributions instead; detrital SPDFs show two distinct age peaks at 5 Ma and 10 Ma which correspond with hillslope sources and glacial sources respectively.
Plants
Plants reduce erosion by trapping soil particles and keeping them in their places, while their roots bind the ground together and their leaves block wind currents that would otherwise erode it away.
Erosion of bare ground increases with rainfall, carrying sediment to storm drains or surface waters and decreasing water quality by increasing turbidity and decreasing oxygen levels in lakes and rivers (eutrophication). Furthermore, sedimentation promotes excessive algal blooms which consume vast quantities of water while depriving aquatic animals access to oxygen – leading them to die from oxygen deficiency.
Soil erosion depletes organic matter, diminishing soil productivity and thus leading to lower crop yields. According to one estimate, agricultural erosion costs the United States nearly $2 billion each year in lost productivity; and is an ongoing issue worldwide.