Solution-Class 9-Geography-Chapter-3-Exogenetic Processes Part-1-Maharashtra Board

Breaking or weakening of rocks without any change in their chemical composition is called mechanical weathering.

Types : Exfoliation, granular weathering and block disintegration are the types of mechanical weathering.

Reasons : Mechanical weathering mainly occurs because of the following reasons :

• Temperature
• Frost
• Crystal growth
• Release of pressure
• Water

Chemical weathering :

The process of decomposition of rocks by changes in the chemical composition of it is called chemical weathering.

Water is a universal solvent. The solubility increases because the matter has dissolved in water. And those materials which do not dissolve easily in water get dissolved in such solutions. As its effect, chemical weathering occurs.

Carbonation, solution and oxidation are the main types of chemical weathering.

• Carbonation : Carbon dioxide in the air gets mixed in the rainwater leading to formation of dilute carbonic acid. Materials like limestone get easily dissolved in such acids. e.g. Water + carbon Dioxide = Carbonic Acid (H₂O + CO₂ = H₂CO₃ )
• Solution : Some minerals in the rock get dissolved in water. Limestone is formed due to chemical precipitation between water and alkalis. Similarly, because of solution, alkalis in the rock dissolve and make them brittle.
• Oxidation : The process of oxidation occurs in rocks which have iron present in them. Due to oxidation, rust is formed on the rocks.

Biological weathering : Biological weathering occurs due to human beings, animals and plants.

• Trees grow in cracks and crevices of rocks of old forts or buildings. Roots of trees grow bigger, they create tension in the rocks and start breaking them.
• Rats, mice, rabbits, etc. make burrows in the ground. Ants make large anthills. Because of the activities of these burrowing animals, biological weathering of rocks occurs.
• Algae, moss, lichen and other flora grow in the rocks. They also help in biological weathering.

• Breaking or weakening of rocks is called weathering. The process of moving down of weathered particles due to gravity alone is called mass wasting.
• Mechanical weathering, chemical weathering and biological weathering are the three types of weathering. Rapid mass wasting and slower mass wasting are the types of mass wasting.

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***This type of questions are excluded in the revised pattern

Biological weathering

Chemical weathering

Mechanical weathering

Mechanical weathering

Mechanical weathering