C2 Weathering

Types of physical weathering

1. Pressure release

2. Thermal weathering

3. Freeze-thaw weathering

4. Salt weathering

Pressure release

Intrusive igneous rocks under Earth’s surface experiences tremendous pressure, if overlying materials are removed, intrusive rocks are exposed and pressure on them is released, causing rocks to expand and fracture parallel to surface. Exfoliation occurs where sheets of rock break away from exposed rocks

Conditions: long period of time, erosion and transportation of materials

Thermal weathering

Rocks have low thermal conductivity, hence outer layer expands much faster than inner layer when temp rises. Repeated uneven contraction and expansion creates stress on rock, exfolation occurs

Conditions: large diurnal temperature, but mostly theoretical

Freeze thaw weathering

Water from precipitation seeps into cracks in the rock. When temperatures fall at night, water freezes and turns to ice, expanding and putting pressure on rock, and in the day when ice melts water seeps deeper into cracks and freezes again. Over time, this can shatter rocks

Conditions: seasonal freeze-thaw cycles (cold, alpine environments)

Salt weathering

Saline solution seeps into cracks and joints in rocks and evaporate, leaving salt crystals that expand when heated and exert pressure on rocks, causing granular disintegration of rocks

Conditions: Arid climates with strong heating, coastal areas with high saline content

Models in weathering

1. Peltier’s Diagram (shows temperatures where physical or chemical weathering occurs)

2. Strakhov’s Model (shows regolith depth associated with climates)

3. van’t Hoff’s law (10ºC increase in temperature doubles most chemical reaction rates)