Exfoliation occurs in hot desert regions which have a large diurnal temperature range. Clear skies and long hours of sunshine during the day bring very high temperatures. This causes the outer layer of rock to get extremely hot and to expand. At night, a lack of cloud cover allows heat to escape and temperatures to fall, causing the rocks outer layer to cool and contract. Repeated expansion and contraction exerts stress on the rock, eventually causing it to crack. Over time, the cracks join up and a thin outer sheet peels away, similar to peeling the layers off an onion (Fig. 6.2).
While temperature changes are the main cause of exfoliation, moisture has also been found to enhance thermal expansion in rock.
Rock surface heats up and expands
Rock surface cools and contracts
A-Z
Exfoliation: Removing the outer layer of an object. It is sometimes referred to as ‘onion peeling’.
Diurnal temperature range: The difference between the highest and lowest temperatures in a 24-hour period.
Daytime temperature = 40° Celsius
Cracks form and join together on the outer layer of the rock
Broken rocks
Night time temperature = −10° Celsius Original rock surface
