Class 9 MAHARASHTRA STATE TEXTBOOK BUREAU Solutions Social Studies Chapter 3 - Exogenetic Processes Part-1
Exogenetic Processes Part-1 Exercise 29
Solution 1(a)
- Mechanical weathering is the weathering or the breaking down of rocks without any change in their chemical composition.
- It takes place in regions of extremely hot and dry climatic conditions as the temperature in such regions varies during the days and nights.
- The minerals in the rocks expand because of heat and contract when the temperature decreases. Due to such continuous contracting and expansion, tension develops in the rock particles creating cracks and breaking down of rocks.
Solution 1(b)
The process of decomposition of rocks due to changes in their chemical composition is called chemical weathering.
Following are the main types of chemical weathering:
Carbonation: Many rocks contain constituents which have carbon dioxide present in them. When it comes in contact with water, carbonic acid is produced. Many rocks like marble and limestone get dissolved in such acids. This kind of weathering is known as carbonation.
Solution: Some minerals in the rocks get dissolved in water. Limestone is formed because of chemical precipitation between water and alkalis.
Oxidation: This process occurs in rocks which have iron present in them. When water comes in contact with iron present in the rock, a chemical reaction takes place between iron and oxygen. When rainwater comes into contact with the iron compounds in the rocks, iron begins to rust. This may also change the colour of the rocks to red, brown or yellow.
Solution 1(c)
- Biological weathering is also known as organic weathering. Animals, insects, plants and humans are the main agents of this kind of weathering.
- Biological weathering is also known as organic weathering. When the rock decomposes and decays due to the action of plants, animals and humans, it is known as biological weathering.
- Biological weathering involves both physical disintegration and decomposition. Many animals like rats and rabbits loosen the soil by making tunnels leading to the weathering of rocks. Human activities like mining, quarrying also results in physical disintegration of rocks.
Solution 1(d)
- Weathering is the disintegration or the breaking down of rocks due to external factors. It is of three types- mechanical, chemical and biological.
- The large-scale movement of waste materials, derived from weathering of bed rocks, down a slope is known as mass wasting or mass movement. Water, wind and glaciers are main agents of mass wasting. Mass movements can be classified into slow and rapid movements
Solution 2(a)
False. Internal movements causes earthquakes.
Solution 2(b)
True.
Solution 2(c)
True.
Solution 2(d)
True
Solution 2(e)
False. Lateritic rocks are formed through oxidation.
Solution 3
Solution 4(a)
Biological weathering
Solution 4(b)
Chemical weathering
Solution 4(c)
Mechanical weathering
Solution 4(d)
Mechanical weathering
Solution 4(e)
Mechanical weathering
