Physical or mechanical weathering is the physical disintegration of minerals into fragment particles without any change in their chemical properties. The transformation of rocks into fragment particles occurs through mechanical methods such as freezing, thawing, salt weathering, and thermal cracking. During physical weathering, the forces responsible for breaking the rock may originate from within or outside the rock mineral. This Weathering activity is more dominant in deserts, high mountains, and arctic regions.
Physical Weathering Types
Physical Weathering processes can be of several types. For example,
- Frost wedging is a phenomenon that occurs when accumulated water in a fracture area freezes and creates pressure in the rock.
- Change in diurnal temperatures in hot deserts causes the rock to break apart.
- Tree-root wedging enlarges cracks in rocks, thus aiding the process of weathering.
- In dry climatic regions, salt crystallisation leads rocks to split.
Physical Weathering Freezing, Thawing & Frost Shattering
While most substances expand when heated and contract when cooled, water behaves differently. Water expands when it freezes. This expansion results in generating cryostatic pressure. In cold regions, rocks have small cracks that freeze and expand to break the rock when filled with water during the day. This occurs only when cryostatic pressure exceeds the tensile strength of the rock. This process is called frost shattering.
Read More: Chemical Weathering
Physical Weathering Expansion Resulting from Unloading
The release of pressure in the rock also causes physical weathering. The pressure is released due to the removal of overlying material by erosion. This process is known as unloading. It is a typical phenomenon resembling the elastic property of rubber. As the pressure is released above the rock, the underlying rock elastically compensates for the erosional loss by expanding perpendicular to the direction of pressure release. This unloading of pressure by the rock results in a horizontal fracture. These fractures are arranged horizontally and are called sheet fractures or exfoliation sheets.
Read More: Biological Weathering
Physical Weathering Thermal Expansion & Contraction or Insolation
Minerals have their limits of expansion and contraction. With rising temperatures, the mineral expands and pushes against the neighbouring rocks. On the other hand, the fall in temperature results in the contraction of the rocks. The diurnal temperature changes are accompanied by contraction and expansion regularly. The process is effective in dry climates and high-elevation areas. The exfoliated surface is more rounded because of the differential heating (leading to expansion) and cooling (leading to contraction). For example granites.
Read More: Types of Rocks
Physical Weathering Salt
The saline water present in the pore spaces evaporates with the rise in temperature in the daytime and leaves behind salt crystals. The expanding salt crystals exert pressure on the walls of rock pores, thus, causing disintegration or foliation of rock. Such types of weathering are mostly found in areas where a high range of temperatures are found.
Physical Weathering Processes
Rocks undergo physical weathering when their structure is disrupted by the impacts of temperature change. Water can sometimes help the process. When water seeps into cracks over time, freezes, and then expands, it undergoes a process called freeze-thaw, which eventually breaks the rock.
Physical Weathering Diagram
The effects of physical weathering processes can be seen in many landforms. The diagrammatic illustration is below:
Physical Weathering Significance
- It reduces the original rock to tiny bits, preparing the rock for the development of soil. As a result, the rock’s weathering determines how deep the soil is.
- Forests (vegetation), which are reliant on the thickness of the weathering layer, are ultimately what give rise to biomes and biodiversity.
- If the rock is not weathered, erosion is not significant. In other words, erosion causes undulations, changes to the terrain, and enormous amounts of garbage, all of which are reduced by weathering.
- Weathering of rocks and deposits aids in the concentration and enrichment of some valuable ores from iron, manganese, aluminium, copper, and other elements that are crucial to the country’s economy. An essential step in the creation of soil is weathering. When certain rock fragments and particles are broken down, sediment is eventually produced. Sedimentary rocks like sandstones and limestones are formed from these sediments. Sedimentary rock is typically formed when shattered rock fragments are compressed under intense pressure and deposited by rivers.
- Rocks become more easily exploitable through mining and quarrying as a result of weathering.
- Some worn rocks are incredibly fascinating, like granite tors. They act as tourist attractions as a result.
Read More: Mass Movement
Physical Weathering UPSC
Materials on hillslopes deteriorate and fall apart as a result of physical deterioration. The effects of physical weathering processes can be seen in many landforms. Rocks are eroded by weathering, resulting in the formation of soil. Additionally, it aids in mass transfer and erosion. The result is that the plant prospers. Terrain changes are a result of weathering, which encourages erosion and mass depletion. The national economy benefits from the enrichment and enrichment of ores such as iron, copper, and others.
The topic “Physical Weathering”, which is an important element of the UPSC Exam’s Geography Syllabus, should be thoroughly studied by candidates.