Correct Option
The correct option is 1, 2, 3 and 4.
Explanation
Physical or mechanical weathering refers to the disintegration of rocks into smaller fragments without any change in their chemical composition. These processes rely on specific applied forces to break down rock materials.
Statement-wise Analysis:
- Statement 1 is Correct: Overburden pressure is a gravitational force. When overlying rock layers are removed (unloading), the release of this pressure causes the rock to expand upward, leading to disintegration processes such as exfoliation.
- Statement 2 is Correct: Shearing stress is another gravitational force acting on rocks. It contributes to the mechanical breakdown of rock masses, particularly when combined with other stress factors like load and pressure release.
- Statement 3 is Correct: Expansion forces due to temperature changes (thermal expansion) occur when rocks are subjected to diurnal or seasonal heating and cooling. This differential expansion and contraction create internal stresses that fracture the rock.
- Statement 4 is Correct: Water pressures controlled by wetting and drying cycles exert significant force. When porous rocks absorb water, the internal pressure increases; upon drying, it decreases. Repeated cycles (slaking) fatigue the rock structure, leading to disintegration.
Key Takeaway:
Physical weathering is driven by three main categories of applied forces: gravitational forces (overburden pressure, shearing stress), expansion forces (temperature changes, crystal growth), and water pressures (wetting-drying cycles).