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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 The absence clouds in tropical deserts Dayof Time & the overhead sun produces high day The sun’s heat time temperatures causes the outer layers of the rock to expand Most common in finegrained rocks (e.g. volcanic rocks) & boulders With no clouds Repeated daily heating & Night Time rocks cool quickly.cooling causes outer layers A process known asof rock to be weathered Cooling causes radiation cooling the outer layers Different minerals expand and contract at different rates causing stresses along mineral boundaries. Quarts increases in size by three times more than feldspar of the rock to contract Layers or shells of rock peel away Layers of rock collect on the desert floor 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?