Erosion and deposition are major processes that influence the landscape, shaping waterfalls, rockfalls, floodplains and river valleys, while also shaping lake edges, shorelines and beaches.
Erosion requires material to be transported by means such as wind, water or ice and then be deposited where it can settle and continue its course.
Weathering
Weathering refers to the gradual breakdown of rock into smaller particles (soil), while erosion involves transporting these soil particles by wind, water or gravity.
Most rocks form at high temperatures and pressure deep within Earth’s crust, before emerging onto its surface to find themselves subjected to temperature variations, lower pressure levels, oxygen and other gases which alters their mineral makeup and ultimately transform it.
Physical weathering smooths rough, angular rock surfaces while chemical weathering breaks apart minerals into more manageable substances that can be broken apart easily. Both processes contribute significantly to creating soils; tiny bits of weathered material combine with plants, animal remains, fungi and bacteria to form fertile fertile soil that eventually becomes the bed for crops or even creates unique landscapes such as Shilin in China with its towers of weathered limestone.
Rivers
Precipitation falling onto land can soak into the ground, evaporate or flow across as rivers and streams across its surface, either by soaking into it directly, flowing as rivers or being carried downhill as rivers – rivers being an especially powerful erosional force on Earth’s surface.
Water flowing over rock can erode it through attrition and solution; when rocks rub against each other in the current; or by dissolving minerals. Furthermore, cracks form within it allowing it to further erode, creating caves as large as football fields long and tall.
As streams lose energy through factors like evaporation, friction near banks and shallow areas and slows down, they deposit material such as sand, silt and clay as they travel downstream – usually toward the end of their journey when they form deltas or alluvial fans.
Ice Sheets
Ice sheets of our planet continue to change with astonishing regularity, forming stunning landscapes along their course. Their impact is immense; creating valleys, gorges, mountains and associated uplift through denudation of sediment evacuation processes during repeated Quaternary glacial cycles and uplift.
Glacial erosion is a multifactorial process with multiple contributing factors at play. At a regional scale, climate plays an essential role in shaping erosion rates and patterns as evidenced by strong correlations between erosion rates and glacial-age proxy records such as NGRIP d18O or latitudinal proxies1.
At local geological domain scales, geography also plays an important role. Hardness and fracture density help limit erosion rates in specific geological provinces due to less abrasion and plucking; for example, erosion rates in the Baltic Shield tend to be significantly slower than in other platform areas due to hard and dense rocks found there.
Landslides
Landslides are defined as any downward movement of rock, soil or debris caused by gravity and other forces. Landslides can take many forms: falls, topples, spreads or flows (mud/debris flows).
Gravity is the driving force of landslides, but other forces come into play such as friction between materials or their own weight to block its path.
Water, earthquakes and other external influences can reduce slope strength and increase the probability of landslides, including permeating through rock and soil to weaken its internal strength, erosion that makes slopes steeper, changes to rock layers arrangement and human activity such as mining or traffic vibrations that causes changes to rock layers to shift more suddenly or quickly, changes that change rock layers arrangement as well as traffic vibrations which may trigger landslides that move slowly or rapidly across any direction. These may all increase chances of landslides.
Beaches
Beaches form when erosion-eroded continental material such as sand, gravel and cobble fragments is washed to sea by storm surges. They constantly reform to form ever-evolving coastal environments.
Attrition and sedimentation are the two primary processes behind beach formation. Attrition refers to the process of grinding rocks down over time until their angular edges have become smooth and rounded, creating characteristic ridges and dunes on beaches.
Sediments are carried along by waves and winds depending on their particle size, state of compaction and presence of established vegetation. Compacted and dense sediments resist erosion as they are more resistant to flow and scouring; loss of flora on beaches allows more wave energy to disperse sediments more easily causing further erosion. Beach nourishment activities aim at placing new sediments at strategic positions for compacting.