Question

What are the reasons for physical weathering? Explain any three.

Answer 1

Instructions:
Give the reasons for physical weathering
Explain three reasons for physical weathering

Solution:
Mechanical or physical weathering mainly occurs due to physical changes​ in the rocks and minerals and reasons behind such changes are following -

1. Temperature
2. Frost
3. Crystal growth
4. Release of pressure
5. Water

Temperature: Temperature is one of the main reasons behind physical weathering and it acts in the following way-
Whenever there is a rise in temperature ,the minerals in the rocks expand and contract when temperature decreases.
Such continuous contracting and expanding of minerals causes tension in the rock particles.
Each mineral reacts differently to the temperature and there is more expansion in some minerals while others do not expand as much.Consequently, the tension formed in the rocks due to temperature also increases and decreases.
This process results in cracks development in the rocks which leads to Breaking of them,

Frost : The actions and effects of frost on rocks can be understood in the following way- we all know that the volume of the water increases when it freezes. So in the areas where the temperatures drop below 0oC for quite some time-
Water gets accumulated in the cracks and crevices. Then this water freezes in the rocks due to the drop in the temperature. Hence the volume of the water increases and this leads to tension in the rocks and they shatter.

Release of pressure: It is also an important reason for physical weathering.
Along with the temperature, freezing of water or crystallization, the outer layers of the rocks also exert pressure on the inner or lower layers.When this pressure ceases to exist, the lower or inner layers get freed from the pressure. (by the removal or degradation of upper layers}And removal of pressure leads to expansion of these layers This also leads to weathering and it appears like the layers of an onion.This type of weathering is Also called as exfoliation.