1. Onion skin weathering
Weathering is the physical, chemical and biological breakdown of rocks in situ (same place).
Onion skin weathering is also known as:
Exfoliation
Thermal Expansion
Insolation weathering

2. Most common in fine-grained rocks
Day Time
The absence of clouds in tropical deserts & the overhead sun produces high day time temperatures
The sun’s heat causes the outer layers of the rock to expand
Most common in fine-grained rocks
(e.g. volcanic rocks)
& boulders

3. Night Time RADIATION COOLING
With no clouds rocks cool quickly. A process known as radiation cooling
Night Time
Repeated daily heating & cooling causes outer layers of rock to be weathered
RADIATION COOLING
Cooling causes the outer layers of the rock to contract
Different minerals expand and contract at different rates causing stresses along mineral boundaries.
Quarts increases in size by three times more than feldspar
Layers or shells of rock peel away
Layers of rock collect on the desert floor

4. Onion skin weathering
Exfoliation is caused by alternate expansion & contraction caused by temperature changes.
What happens in the day time?
(Dark rock can reach over 50oC)
What happens at night time?
The outer layers of rock are exposed to extreme temperatures (no vegetation or soil). Outer layers of rock break away from the cooler inner layers.
Where can we find extreme temperature changes?