Mechanical Weathering

Rocks are the natural source of materials, and there are many types of rocks in nature. There are many types of rock in nature being sourced by geologists. Rocks are solid crystals formed by various minerals which have been fused together to a significant mass of solid. Rock takes millions of years to form a rock, and it further takes many years to undergo changes.

Rocks undergo a process known as weathering. Weathering is the process of breaking down or dissolving rocks and minerals on the surface of the Earth. There are four types of weathering:

• Chemical weathering
• Physical weathering
• Biological weathering
• Mechanical weathering

In this article, let us know in detail about the mechanical weathering process.

What Is Mechanical Weathering?

Rocks break due to various reasons like wind, ice, weather, water, acids and chemical reactions. Even if an external force like the growing of plants takes place on rocks, the roots lead to weathering. Let’s see how mechanical weathering takes place.

Mechanical weathering is also known as physical weathering. In this type of weathering, a large rock is disintegrated into smaller pieces of rocks. When rocks disintegrate or break up without experiencing any change in their chemical composition, it is known as mechanical weathering. Thermal expansion and contraction that happens due to the increase or decrease in temperature. This process causes the rock to break into fragments.

Types of Mechanical Weathering

There are two main types of mechanical weathering:

• Freeze-thaw weathering or Frost Wedging
• Exfoliation weathering or Unloading
• Thermal Expansion
• Abrasion and Impact
• Salt weathering or Haloclasty

Let us see in detail about each type of weathering.

Freeze-Thaw Weathering or Frost Wedging

Frost Wedging occurs when water seeps into cracks of the rocks, freezes and expands, gradually breaking the rock apart into pieces. This expansion leads to the cracking of the rocks from inside and eventually breaks them apart. The freeze-thaw cycle happens repeatedly and finally breaks the rock, and hence it is called Freeze-thaw weathering.

Exfoliation Weathering or Unloading

This type of weathering takes place when the cracks develop parallel to the land surface. As a result, a consequence of the reduction in pressure takes place during uplift and erosion. In exfoliation, rock breaks apart in layers that are parallel to the Earth’s surface. Exfoliation is common in plutonic igneous rocks since they are exposed to great pressure.

Thermal Expansion

Heating and cooling of rocks repeatedly result in the expansion and contraction of the rock. When rock is exposed to high temperatures, it expands and as the temperatures cool, it contracts. This continual expansion and contraction cause the rocks to weaken and eventually break into pieces. Thermal expansion weathering is similar to Freeze-Thaw weathering.

Abrasion Weathering

When a rock collides with one another, grinding of rock fragments takes place, and the rock is broken into pieces. Abrasion cuts them into smaller particles. Gravity causes abrasion when the rocks tumble down a mountainside and hit another rock, and break into the fragment. Moving water causes abrasion as particles in the water collide and bump against one another. High-speed winds which carry pieces of sand have the capacity to break the rock when they sandblast on the surface of the rock. Abrasion makes rocks with sharp or jagged edges round-shaped and smooth.

Salt Weathering or Haloclasty

Salt Weathering or Haloclasty is the process by which saline solutions enter the cracks in a rock and evaporate, leaving behind salt crystals. When the temperatures rise, the accumulated salt crystals get heated and start to expand and release pressure on the rock, causing it to break.

Factors Affecting Mechanical Weathering

Some of the factors that are responsible for mechanical weathering are:

• Growth of plants on the rock.
• Temperature and pressure changes in nature.
• Freezing and thawing of water in cracks of the rock.
• Formation of salt crystals within the rock.
• Burrowing by animals.

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