Q 1. Answer in brief. 

(a) What is mechanical weathering ? 

Ans: 

(i) The disintegration of rocks without any change in their chemical composition is called mechanical weathering.

(ii) The minerals in the rocks expand because of heat and contract when the temperature decreases. Due to such continuous contracting and expanding, tension develops in the rock particles.

(iii) Each mineral reacts differently to temperature; some minerals expand more, while others do not expand as much. Consequently, the tension formed in the rocks also increases and decreases. As a result, cracks develop in the rocks, and they break.

(iv) In areas where the temperatures drop below 0°C for quite some time, the water accumulated in the cracks and crevices in the rocks freezes. Its volume increases, which leads to tension in the rocks, and they shatter.

(v) When the alkaline water of the sea fills in the cracks of the rocks, the soluble minerals in the rock get dissolved, leading to the formation of small holes in the rocks. Because of the heat, this water turns into water vapor, and only crystals of alkaline materials remain in the rocks. Crystals occupy more space, which causes tension in the rock.

(vi) Sometimes the outer layers of the rocks exert pressure on the inner or lower layers. When this pressure ceases to exist, the lower or inner layers get freed from the pressure. This also leads to weathering.

(vii) In areas of heavy rainfall, the soaking of rock water also causes weathering of some rocks like sandstone and conglomerate. When water penetrates such rocks, the particles get loose and separate from the main rock.

(b) What are the main types of chemical weathering? 

Ans: The process of decomposing rocks due to changes in their chemical composition is called chemical weathering. Its main types are:
(i) Carbonation:
(a) When the rainwater mixes with the carbon dioxide in the atmosphere, it leads to the formation of dilute carbonic acid.
(b) Many rocks, like limestone, get easily dissolved in such acids.
 
(ii) Solution:
(a) Some minerals in the rock get dissolved in water.
(b) Because of this solution, the alkalis in the rock dissolve and make them brittle.
 
(iii) Oxidation:
(a) This process occurs in rocks that have iron present in them. The iron in the rock comes into contact with water, and a chemical reaction takes place between iron and oxygen.
(b) Hence, a reddish coloured layer forms on the rocks. This is called rust.
(c) It occurs in rocks in areas with high rainfall.

(c) How does biological weathering occur? 

Ans: 

(i) It is the process by which rocks are broken into small fragments and fine particles due to the action of plants, animals, and human beings.

(ii) The roots of the plants enter the joints and cracks of the rocks in search of moisture.

(iii) As the roots grow bigger, they create tension in the rocks and start breaking them.

(iv) Animals such as mice, rabbits, and rats dig holes, anthills, etc. and weaken the rock, which makes it loose and break into pieces.

(v) Besides these, algae, moss, lichen, and other flora grow in the rocks. They also help with weathering.

(vi) Thus, the weathering caused by living organisms is called biological weathering.

(d) Distinguish between weathering and mass wasting.

Ans: