Rocks undergo physical weathering from temperature changes that cause their outer layers to crack and fall off. Onion skin weathering occurs when minerals in rocks expand and contract at different rates with temperature changes, causing the outside layers to crack and exfoliate. In hot deserts, rapid temperature fluctuations between day and night mean the outer rock layers cool and heat faster than the inner layers, resulting in different rates of expansion and contraction that cause the outer skin to split.

1. Weathering fact sheet
Onion skin weathering
Expand and contract
When solids warm up they expand and when they cool down they contract. Rocks are a mixture
of different minerals. Minerals expand and contract by different amounts. This causes the
outside layers of rocks to crack and fall off. The process is called exfoliation. This is an
example of physical weathering, as small pieces of rock are weathered as a result of changes in
temperature.
Hot desert
There are rapid changes in temperature between the day and night. The expose
outer layer of rock cools (or heats up) faster than the inside, this means
contracting (expanding) faster than the inside of the rock. The outer skin of the
rock splits due to this differentiation in expansion or contraction.