erosion

Erosion is the wearing away of the land and movement of the broken parts from one place to another by forces such as water, wind, and ice. It is a natural process that has resulted in forming many interesting features of the Earth’s surface such as mountains, valleys, and coastlines. Erosion is a very slow process that happens over a period of several years.

Actually, there are two natural processes that work together – weathering which is the breakdown of land into smaller pieces, and erosion which is the movement of the pieces removed by weathering.

Weathering is breaking down or dissolving of rocks. It is caused by wind, water, heat, and cold. 

Erosion is the movement of broken materials from one place to another. It happens via wind, water, and gravity. 

Both weathering and erosion happen over many years. Big rocks become sand and mountains are reduced to smaller hills. The pieces move downhill, creating new landforms. It is a never-ending process.

The last step of erosion is ‘deposition’ – it is actually the opposite of erosion. During deposition, the little pieces of sediments that the wind or water carries is dropped off at a certain location. Over time, deposition can change the landscape of the Earth by building on piles of rock and sand.

If the wind is dusty, water or glacial ice is muddy, erosion is taking place. The brown color of mud indicates that bits of rock and sand are suspended in it and being transported from one place to another. This transported material is called sediment.

Plant growth can also contribute to physical erosion in a process called bioerosion.  Plants break up earthen materials as their root takes up space in the earth, and can create cracks and crevices in rocks they encounter.

Human activity has increased the rate of erosion in many areas. This happens through farming, ranching, cutting down forests, and the building of roads and cities. Human activity has caused large amounts of topsoil to erode each year.

 

Factors impacting erosion

1. Soil characteristics - Soil characteristics influencing erosion by rainfall and runoff are those properties which affect the infiltration capacity of soil and those which affect the resistance of the soil to detachment and transport by falling or flowing water.

2. Vegetation cover - Vegetation cover plays an important role in controlling erosion. It shields the soil surface, holds soil particles in place and reduces the speed of runoff. 

3. Topography - The size, shape and slope characteristics of a watershed influence the amount and rate of runoff. As both slope length and gradient increase, the rate of runoff also increases and the potential for erosion is magnified.

4. Climate - The frequency, intensity, and duration of rainfall are fundamental factors in determining the amount of runoff produced in a given area. Where storms are frequent, intense or of long duration, erosion risks are high. 

5. Deforestation and burning - The loss of forest cover removes the natural protection of soils against the sun’s rays and the direct impact of raindrops. There is a reduction in the infiltration of water into the soil and a simultaneous increase in surface runoff results and the level of organic material is also reduced. These factors necessitate planting on steep slopes. The natural susceptibility of certain soils to erosion and the coincidence of land preparation with erosive rainfall accelerate the erosion process and consequently intensify land degradation.

Effects of erosion

There are many harmful effects of soil erosion - it affects the quality of the soil and reduces the productivity of soil to a great extent. The soil loses its fertility which is difficult to be regained. 

Causes of erosion

There are many different forces in nature that cause erosion. Depending on the type of force, erosion can happen quickly or take thousands of years. The three main forces that cause erosion are water, wind, and ice.

1. Erosion by water

Liquid water is the main cause of erosion on Earth. Some of the ways that water causes erosion are discussed below:

• Rainfall – Rainfall can cause erosion.
  • Splash erosion - During rainfall, when the raindrops hit the Earth’s surface, it can scatter tiny soil particles as far as 0.6 meters or 2 feet – this is called splash erosion.
  • Sheet erosion - When raindrops accumulate and flow like small streams it causes erosion too, this is known as sheet erosion which is described as erosion caused by runoff. 
• Rivers – When rivers flow through mountains, they break up particles from these landforms along the way and carry them downstream. The effect of such erosion is not instant. It becomes noticeable over thousands of years.  An example of river erosion is the Grand Canyon which was caused by the Colorado River for thousands of years.
• Ocean waves – Waves on the coast can cause the coastline to erode. The immense energy and force of the waves hitting the cliff or rock cause pieces of rock and coastline to break off, thus changing the coastline over time. 
• Floods – Large floods can cause erosion to happen very quickly acting like powerful rivers.
• Glaciers are made of dense ice and are very heavy. When they pass through mountains, they erode them to create valleys.

There are four types of water erosion – interrill, rill, gully, and streambank erosion.

• Interrill erosion – When water particles continuously splash down and create a small imprint in the soil, it is called interrill erosion. Small dents in the road are examples of interrill erosion.
• Rill erosion – When water runs off the surface and creates a small channel in the soil, this is known as rill erosion. It is described as erosion that takes place as runoff develops into discrete streams (rills). Where streams of water have flown, it appears as clear lines in the ground.
• Gully erosion – When a rainstorm or downpour occurs, they create large cuts in the land that are usually more than one foot deep. This leads to huge holes and trenches in the land known as gullies. These gullies carry water for brief periods of time during rainfall or snowmelt but appear as small valleys or crevasses during dry seasons.
• Streambank erosion – This is caused by large flowing bodies of water. These streams move the soil and particles around and change the landscape of the environment.

2. Erosion by wind

Wind erosion is also known as eolian erosion. It is more pronounced in dry areas and in areas where there is insufficient rainfall to support vegetation and root systems. Wind erosion is responsible for the formation of the beautiful sandstone pillars of Bryce Canyon, Utah, USA. Another famous example of wind erosion occurred in the Dust Bowl, when wind erosion severely damaged farming communities.

Wind can erode by picking up and carrying loose particles and dust away - called deflation. 

It can also erode when these flying particles strike the land and break off more particles - called abrasion. 

Wind erosion is one of the weakest kinds of erosion. During wind erosion, there occur three types of soil movement

• Suspension – Suspension occurs when small sediment particles are thrown into the air. The process can cause particles to move very far and very fast over long distances.
• Saltation – Saltation is like suspension, except soil particles move horizontally across the ground. This can cause far worse damage to the soil and land than suspension. In contrast, particles moved by saltation travel approximately four times longer distance-wise.
• Surface creep – Surface creep occurs to particles that are too heavy to be lifted into the air. They simply roll across the surface, which also leads to severe soil deterioration.

 3. Erosion by glaciers: Ice erosion can happen in two ways: 

a. As the ice of the glacier moves downhill, water melts below the glacier and seeps into the soil. This causes the displacement of dirt particles as well as the weakening of soil layers. 

b. Cold weather causes the water inside tiny cracks in rocks to freeze. As it freezes, the ice gets bigger and pushes hard against the rock. This can break the rock.

Today, in places such as Greenland and Antarctica, glaciers continue to erode the earth.

4. Erosion by gravity: Gravity erosion is the simplest kind of erosion. Gravity simply pulls loose earth materials downhill. One example of gravity erosion is landslides. There are some other forces of erosion like thermal erosion and mass wasting.

• Thermal erosion is the erosion of permafrost along a river or coastline. Warm temperatures can cause ice-rich permafrost to break off coastlines in huge chunks, often carrying valuable topsoil and vegetation with them. 
• Mass wasting describes the downward movement of rocks, soil, and vegetation. Mass wasting incidents include landslides, rock slides, and avalanches.