- Rocks expand when heated and contract when cooled much like all solid materials.
- In deserts and areas with scant vegetation, diurnal temperatures can exceed 50°C.
- During the excessive day heat the rocks expand.
- The outer layers of the rocks expand faster than the inner layers.
- At night the when temperatures drop, in deserts evening temperatures can and usually fall to below freezing point, the rock contracts and again the outer layers cool faster than the inner layers.
- This results in stresses being set up within the rock causing outer layers of the rock to peel off like the rings of an onion.
- Thus the process is sometimes called onion weathering.
- Also several different minerals withing the rock expand and contract at different rates depending on their physical characteristics.
- This will result in granular disintegration with the rock.
- This is the process that was thought to result in the creation of exfoliation domes like Domboshava.
- This form of weathering is also known as thermal expansion or insolation weathering.
NB At Ordinary Level you are supposed to accept this method of weathering as fact. The occurrence of this method of weathering in the real world is nowadays seriously doubted after a series of experiments by people like David Griggs and others.