Once the rock has been weakened and broken up by weathering it is ready for erosion. Erosion happens when rocks and sediments are picked up and moved to another place by ice, water, wind or gravity. Over time pieces of rock can split off a rock face and big boulders are broken into smaller rocks and gravel.

5.1 Mechanical Weathering

• The decrease in pressure that results from removal of overlying rock.
• Freezing and thawing of water in cracks in the rock.
• Formation of salt crystals within the rock.
• Cracking from plant roots and exposure by burrowing animals.

Mechanical weathering breaks rocks into smaller pieces without changing their composition. Ice wedging and abrasion are two important processes of mechanical weathering. Chemical weathering breaks down rocks by forming new minerals that are stable at the Earth’s surface.

igneous rocks

Another type of mechanical weathering is called salt wedging. When it rains and water flows everywhere, it usually has ions and salts dissolved inside.

Mechanical weathering involves mechanical processes that break up a rock: for example, ice freezing and expanding in cracks in the rock; tree roots growing in similar cracks; expansion and contraction of rock in areas with high daytime and low nighttime temperatures; cracking of rocks in forest fires, and so forth.

Quartz

Weathering breaks things down into smaller pieces. The movement of pieces of rock or soil to new locations is called erosion. Weathering and erosion can cause changes to the shape, size, and texture of different landforms (such as mountains, riverbeds, beaches, etc).

Positive Impacts • The weathering of rocks helps to form the basic component of soil. Soil is very essential for Human Activities . Negative Impacts • Erosion by flowing water during floods causes extensive damage to human properties and they also destroy lives. Floods can cause crops and livestock destruction.

Some examples of physical weathering mechanisms:

• Frost wedging. Frost wedging happens when water filling a crack freezes and expands (as it freezes, water expands 8 to 11% in volume over liquid water).
• Heat/Cold Cycles.
• Unloading.

These are landslides, mud flow, earth flow and sheets wash.

Landslides and soil erosion are two major effects of weathering.

Weathering is often divided into the processes of mechanical weathering and chemical weathering. Biological weathering, in which living or once-living organisms contribute to weathering, can be a part of both processes. Mechanical weathering, also called physical weathering and disaggregation, causes rocks to crumble.

These examples illustrate physical weathering:

• Swiftly moving water. Rapidly moving water can lift, for short periods of time, rocks from the stream bottom.
• Ice wedging. Ice wedging causes many rocks to break.
• Plant roots. Plant roots can grow in cracks.

Biological weathering is weathering caused by plants, animals, and microorganisms. Plants, animals, and microorganisms release acid forming chemicals that cause weathering and also contribute to the breaking down of rocks and land forms. It is the disintegration of rocks as a result of the action by living organisms.

Common agents of mechanical weathering are ice, plants and animals, gravity, running water, and wind.

Agents of mechanical weathering include ice, wind, water, gravity, plants, and even, yes, animals [us]!