Erosion and deposition are natural processes that shape Earth’s landscape over long periods.
Heavy rain can lead to erosion as water runs off mountain slopes, carrying away loose material (sediment). The sediment may then travel downstream through lakes, rivers or streams before eventually ending up as lakes or other bodies of water.
Dams and reservoirs alter the erosion pattern of rivers, altering their flow rates while also increasing deposition rates.
Water erosion is one of the primary forces determining landforms. Rivers, streams, brooks, gullies and bayous all possess the ability to wear away soil through rapid drainage systems like rivers. Water erosion becomes especially critical where there is high rainfall or snowmelt but few vegetation to hold onto it in place.
Physical erosion of rocks refers to the gradual wear and tear on their surfaces caused by weathering processes like frost action or mechanical forces such as waves hitting shorelines or cars rolling down hills. Plants and animals also play a part in physical erosion by tearing at or nibbling away at rocks.
Water erosion forms features such as waterfalls, flood plains, deltas, meanders and ox bow lakes. Rivers also lose energy through erosion by depositing sediment such as rocks, pebbles, sand and silt into their beds and banks; this process forms alluvial fans on hillsides or slopes eroded by river flow.
Soil is an intricate combination of organic and inorganic material found on Earth’s surface, made up of minerals and the remains of living things, with small spaces known as pores to hold water and air.
Erosion occurs when soil is exposed to strong winds and heavy rainfall, or when people till (plow) the land and clear forests for crops or livestock grazing purposes.
The sediments produced can wash into streams and rivers, where they may clog natural and engineered conveyances to cause flooding conditions. They may also clog drainage channels with silt, sand and other particles contaminating waterways; their loss from erosion contributes to degradation of productive agricultural land as well as decreased water quality; it may even contribute to land degradation through loss of top soil cover, with restoration of vegetation covering once barren areas being an effective way of mitigating this loss of material from land.
Wind is an effective force that can erode land. From light breezes smearing soil particles across surfaces to strong gusts that lift sand and rock into the atmosphere and form dust storms, wind erosion is a significant threat that threatens agricultural lands.
Wind erosion is particularly evident in arid regions where plants cannot provide enough soil support. Sand and rock that are carried away by wind can scour surfaces and polish them into interesting shapes – this process is known as abrasion.
Dust ejected by wind can travel great distances, eventually reaching the sea floor. In 2004, winds carried 45 million tons of sand from an isolated depression in northern Chad all the way to Brazil – some may land where it lands but much of it remains suspended and travels much further.
As glaciers move forward, they encounter layers of sediment whose composition changes with time and distance. Sediment packages deposited along successive trajectories crossing an indicator source (trajectories 0-6 in Figure 15) contain gradually less indicator lithology until reaching maximum concentration at point where 6 and 7 have crossed it; this will produce the train depicted in Figure 16.
In the deformation zone, an increase in longitudinal or temporally increasing ice flux leads to higher shear stresses and reduced friction, thus decreasing frictional forces between deforming A horizon and stable B horizon (Fig. 3a) allowing hitherto undeformed material to be drawn into flow either grain by grain or in thin cohering layers as deformation till.
Low bulk density deformation tills reduce the amount of clast energy they carry, leading to decreased average clast size and an increasing erosion rate over time. This produces zones dominated by erosion while their surroundings become increasingly deposition-dominated.