Erosion is the natural process by which landforms change over time, while deposition results from erosion by depositing rocks and soil far away from their original locations, often creating landforms like spits, salt marshes or beaches as a result of deposition.
As streams flow towards the ocean, they perform both weathering and erosion processes as they make their journey to meet it. Erosion consists of three components: abrasion, entrainment and sedimentation.
Weathering is the natural process of breaking down rocks and minerals by physical, chemical and biological means. This process may occur at either the surface of Earth or deeper within.
Physical weathering includes the grinding action of fast-moving water in stream valleys and coastal erosion; biological weathering refers to trees and plants breaking down and moving soil; chemical weathering involves changing silicate grains within rocks into clay particles – similar to how coffee granules disintegrate when stirred up in hot coffee cups.
Weathering processes include gravity, wind, ice and water; when broken minerals and rocks are carried away by these elements they end up deposited elsewhere on land or ocean floors. Erosion also plays an important part in shaping landscape features such as Scotts Bluff National Monument’s beautiful bluffs – while at times can also cause harm by carrying chemicals, fertilizers, pesticides or other potentially harmful material downhill to be washed away along with soil that washes away carrying harmful materials with it.
Erosion is the natural wear and tear process which leads to rocks and soil being worn away over time, often by water, wind, ice or gravity. However, it should be remembered that erosion only impacts on Earth’s surface layer – not its mantle or core!
Erosion can result in various erosional features such as gullies, river channels and stream beds, as well as shaping mountain sides, valleys and coastlines with spits and salt marshes along their borders.
Abrasion is one of the primary types of erosion. It occurs when glaciers scrape against rock surfaces, pebbles grind against each other in stream channels or when wind-blown sand particles collide with each other. Geologists can use characteristics associated with abrasion to identify what kind of process was at play – for instance if sediment has well-sorted grains it likely came from wind while poorly-sorted sediment is usually related to glacial deposits; using such information helps make predictions regarding future erosional processes.
Entrainment refers to the process by which particles are lifted and transported along a flowing medium such as a stream or debris flow, typically as a result of weathering (e.g. abrasion and plucking), rainfall impact (cavitation and avalanches) or fluid dynamics (e.g. flow velocity gradient and surface roughness).
Entrapment may result from impact erosion of bed materials as well as by reworking of deposits. Entrainment increases with debris flow size and may become significant near its conclusion.
Assumptions about the entrainment velocity uev often differ from landslide velocity; this assumption, which ignores energy production and changes in momentum due to erosion, are incorrect and should be disregarded when considering erosion dynamics. Only when mass entrainment moves faster than landslide mobility will entrainment consume energy and lower mobility levels significantly.
Sedimentation refers to the tendency for particles suspended in water to settle out due to gravity, usually leading to sediment or, for water treatment purposes, sludge formation. Sedimentation has profound effects on sediment transport and deposition processes such as erosion and entrainment processes.
Sediment transport in flowing water generally comprises erosion, deposition and sedimentation processes. The rate at which mineral particles settle out depends upon factors like their diameter, density and concentration within the flow as well as channel geometry, translational velocity of fluid flow turbulence and other considerations.
Cohesionless sediment transport can be defined by two parameters, the critical shear stress for erosion (tau_c), and deposition strength (tau_d). For cohesive flocs, their classification requires more considerations: deposition requires that their buoyant weight surpass the hydrodynamic lift force; erosion calls for floc shear strength to exceed both buoyant weight plus shear force that holds it to its bed surface (tau_b).