Study GuideGeology–Weathering and Erosion1. Processes of Mechanical WeatheringMechanical weathering is the process that breaks rocks into smaller pieceswithout changing theirchemical makeup. It happens slowly, but over long periods oftime, it can completely change thelandscape.1.1 Ice: Freezing and ThawingOne of the most powerful agents of mechanical weathering isice.Water can seep into tiny cracks and joints on the surface of rocks. When temperatures drop, thiswater freezes and expands. As it expands, it pushes against the sides of the crack. Over thousands ofyears, this repeated freezing and thawing slowly forces the crack to widen and deepen.This process is calledfrost wedging. Eventually, pieces or even large slabs of rock break off. Frostwedging works best in climates where temperatures regularly move above and below freezing.Another ice-related process isfrost heaving. This happens in soil. Water beneath rock fragmentsfreezes first and forms ice. As freezing and thawing happen again and again, the growing ice pushesrocks upward. Over time, the rocks are slowly lifted to the surface of the soil.1.2 ExfoliaƟon: Peeling Away Rock LayersExfoliationoccurs when large bodies of rock deep underground are exposed at the Earth’s surface.When molten rock cools below the surface, it is under great pressure from the rocks above it. Iftectonic uplift raises this rock and erosion removes the overlying layers, the pressure on top issuddenly released. However, pressure from below still remains. This imbalance causes the rock toexpand outward. This process is known asunloading.As the outer layers expand the most, cracks calledsheet jointsform. These cracks run parallel to thecurved surface of the rock. Over time, curved layers of rock break off, much like the peeling of anonion. This is exfoliation.Preview Mode
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