Physical weathering
Also called: Mechanical weathering · Topic: Geomorphic Processes: Weathering, Mass Movement, Erosion and Soil Formation · NCERT: Class 11, Ch 5 "Geomorphic Processes"
Meaning
Physical weathering, also called mechanical weathering, breaks rock into smaller pieces without changing its chemistry. The forces behind it are:
- gravity, through the weight of overlying rock, load and shear stress (a force acting along a surface);
- expansion from temperature change, from crystal growth (ice or salt), or from animals;
- water pressure during wetting and drying.
Most of it comes from thermal expansion and from pressure release (unloading). Each change is tiny. Repeated many times, however, it tires the rock until it breaks. Physical weathering dominates in hot deserts and cold regions, where chemical weathering is slow.
Example
In the Thar Desert of Rajasthan, strong daytime heat and cool nights make rock surfaces flake and crumble into sand and angular pieces.
Don't confuse with
- Chemical weathering: it changes the minerals themselves. The two often work together, because broken rock gives chemicals more surface to attack.