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The Difference Between Weathering and Erosion

Eoin is an Undergraduate student studying Geography in the National University of Ireland Galway.

The Main Difference Between Weathering and Erosion

Weathering is the breaking down of rocks by physical or chemical means while erosion is the carrying away of sediment by natural processes.

Key Differences

  1. Weathering does not transport broken down rock particles whereas; erosion does transport broken down rock particles.
  2. Weathering occurs due to atmospheric pressure provided by elements such as heat and air pressure; erosion occurs as a combined result of weathering and natural processes such as wind, water and ice.
  3. Weathering does not rely on erosion, but erosion does rely on weathering. Due to the fact erosion cannot occur unless rock particles have been broken down by the processes of weathering. Only when the rock particles have been broken down or weathered, can erosion take place.

Types of Erosion

The four main types of erosion are hydraulic action, abrasion, attrition and solution.

  1. Hydraulic Action: see physical weathering.
  2. Abrasion: occurs when a material is being dragged along a surface for a long time. An example of abrasion would be large rock boulders dragged along the bed of a river eventually breaking down over time.
  3. Attrition: happens when materials are continually making contact with either each other, a surface or both during transportation. This is common during river transportation of sediment.
  4. Solution: minerals are broken down in the water then transported away as solution.




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Types of Weathering

There are two main types of weathering, physical and chemical.

Physical Weathering

Physical weathering, otherwise known as mechanical weathering, is the breaking down of rocks by mechanical means. Physical weathering does not alter the chemical composition of rocks. There are many different types of physical weathering. Here is a list of the most common varieties:

Onion Weathering: this type of weathering occurs commonly in desert climates. The extreme heat from the sun causes the rock to expand during the day and at night, the temperatures lower, causing the rock to contract. Over time this results in pieces of rock peeling away from the surface of the rock similar to the removal of the outer cells of an onion.

Biological Weathering: animal, plant and microbe activity can over time lead to the break down of a rock’s surface. An example of this would be the pressure exerted on a rock by the growth of a large plant root.

Freeze-Thaw Action: typically, this form of weathering occurs at altitude. Rainwater falls and collects in the cracks or on the surface of rocks. Come nightfall the water freezes and expands by roughly 10%, which places pressure on the surface of the rock, weakening it. As day breaks the temperatures rise thawing the ice, and the process repeats itself until eventually, the rock shatters. Broken down pieces of rock located at the foot of a mountain are known as scree and form as a result of freeze-thaw action.

Hydraulic Action: the force of moving water contacts the surface of a rock, it causes it to breakdown. Typically, the rock has already been weakened, and the water is exploiting the cracks in the rock which have been left behind by this process previously. Pockets of air present in the rock can further weaken the rock. This is because as the water subsides, it sometimes generates a large amount of pressure on the surface of the rock, which weakens the rock when released.

Salt Crystal Growth: water moves into cracks or openings in the rock by capillary action where it then begins to evaporate and form large salt crystals which over time put pressure on the rock and cause it to breakdown. This form of weathering is typical in arid climates.

Thermal Weathering: when a rock is exposed to an excessive amount of heat, it causes the minerals inside the rock to expand placing pressure on the rock. When the temperature cools from the rock, it shatters.

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Chemical Weathering

Chemical weathering involves changing the chemical composition of a rock which causes it to break down over a prolonged period. The following are varieties of chemical weathering:

Oxidation: occurs when a substance reacts with oxygen. Rocks contain iron which reacts with oxygen to create iron oxide subsequently weakens the rock. An interesting fact to about oxidation is it is responsible for the formation of rust. Uluru, better known as Ayer’s Rock, is an example of the impact oxidation has on rock formation.

Hydrolysis: is the chemical breakdown of rocks which occurs when rocks come into contact with water.

Biological: do not let this variety of weathering confuse just because it is also a physical form of weathering. Plant, animals and microbes can release acidic substances which react with the chemical composition of a rock, causing it to breakdown; therefore, it is a form of chemical weathering. Plants, animals and microbes also breakdown rocks themselves without the aid of any acidic fluids, making them a type of physical weathering simultaneously.

Carbonation: this process of weathering is crucial to cave formation. Water takes in carbon dioxide from the atmosphere creating a weak carbonic acid. This carbonic acid reacts with minerals inside rocks, causing them to breakdown.

Conclusion

Weathering and erosion are two very different processes, but both play a role in the breaking down and transportation of rocks. The critical difference is weathering does not transport the rocks whereas erosion does transport the stones. Once weathering has occurred, the rock will not break down further. During erosion, the rock will be broken down into smaller particles.

Comments

Frankie Vanderhoff from Lower Saxony, Germany on May 21, 2019:

Incredible! So informative and well-written article. I had read it with pleasure.