Slopes & Weathering

Question 1

Explain thermal expansion (Arid climates, expansion,contraction)

Answer 1

• Absence of clouds in deserts & heat causes outer layers of rock to expand
• Radiation cooling at night causes outer layers to contract
• Process repeats, layers/shells of rock peel away

Question 2

Explain vegetation root action

Answer 2

• Tree roots grow in cracks and joints in rock
• Force cracks and joins to widen through physical pressure
• Eventually detaches rock

Question 3

Explain oxidation (iron,water,haematite)

Answer 3

• Rocks contain iron, water is present & oxygen is dissolved in soil/ is in atmosphere
• Iron oxidises to produce haemitate
• Rusting

Question 4

Explain carbonation (carbonic acid, CaCO3)

Answer 4

• Occurs in chalk and limestone
• CO2 is dissolved in water from atmosphere, forms Carbonic Acid
• Carbonic Acid reacts with calcium carbonate to form Calcium bicarbonate

Question 5

Explain freeze-thaw

Answer 5

• Occurs when water in joints freezes at 0C
• Expands by about 9% and exerts pressure up to 2100kg/cm3 at -22C

Question 6

Explain pressure release/dilation (layers, pressure)

Answer 6

• Layers of rock / ice that lie on top of rock layer is removed
• Lower rock expands as the pressure falls and fractures occur
• Form bedding planes

Question 7

Explain hydrolysis (feldspars, acidic water)

Answer 7

• Feldspars make up 40% of the earth’s continental crust by weight
• Reacts with acidic water, forms kaolinite
• Quartz not affected

Question 8

Explain salt crystallisation (water, salt, temperature, pressure)

Answer 8

• Water evaporates, leaves salt crystals behind
• Temperature increases, salt expands and exerts pressure on rocks
• Temp 26-28C, Sodium Sulfate and Sodium Carbonate expand by about 300%
• Creates pressure on joints, forcing them to crack

Question 9

Explain wetting and drying

Answer 9

• Common along coastlines
• Clay rich rocks prone to expand, contract when dry
• Makes cracks, which are vulnerable to freeze-thaw and salt crystallisation

Question 10

Explain hydration

Answer 10

• Addition of water to rocks, clays or soils
• Some minerals increase in volume, exerting physical strain within the rock
• Anydrite expands by 0.5% to become gypsum