Weathering

Weathering

Denudation, weathering, mass wasting and erosion

Weathering is the breakdown of rocks exposed on the earth's surface by the elements of weather.. Mass wasting is movement of weathered material down a slope. Erosion is removal of material, for example by rivers or the sea. Eroded material is transported by rivers or the sea, and deposited in a new location. Erosion, transportation and deposition make up the process of denudation.

Land forms are altered by weathering, mass movement, erosion, transportation and deposition. This makes up the process of denudation. Erosion may be by running water, the sea, wind, or moving ice (glaciers). Constructional land forms such as volcanoes are not the result of denudation.

Multiple Select

The process of denudation consists of --

• erosion

• transportation

• weathering

• deposition

Multiple Select

Erosion is not ---

• removal of material

• removal of materials by water

• removal of material by ice

• breaking down of rocks

Weathering and the regolith

Weathering breaks down rocks at or near the surface. The layer of weathered and broken rock fragments at the surface is the regolith. At the base of the regolith is the weathering front. Beneath the weathering front is unweathered rock.

Types of weathering

Physical weathering

​Frost action occurs in temperate latitudes and mountainous areas

where there is a large amount of moisture and temperature fluctuate above and below freezing point.At night, water in the cracks of the rocks freezes.This increases the volume of the water by 9%, which exerts pressure on the cracks, thereby enlarging them.

​In the day when temperature rises above 0 degree celcius the ice in the water thaws and more water enters the widened cracks.

Pressure release creates joints and cracks when the weight of overlying rocks is removed.

​Types of weathering

​Thermal expansion and contraction

​Occurs in areas where the diurnal temperature range is

large, such as in deserts.In the day, intense heating causes the rocks to expand. At night, the low temperature cools the rocks, causing them to contract.

Repetition of this process leads to cracks in the rocks

Over time, the rocks split along the cracks into smaller fragments.

Multiple Select

Which of the following is not a type of weathering

• chemical

• electrical

• biological

• physical

Multiple Choice

Frost action takes place when

• weight of overlying rocks is removed.

• minerals such as feldspar react with water.

• when water freezes in cracks of rocks.

Types of weathering

Chemical weathering

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Hydrolysis: Occurs when minerals in rocks such as granite react

chemically with rainwater to form new compounds.Feldspar, a mineral found in granite, turns into a clay mineral called kaolin upon contact with water.

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Carbonation. When carbon dioxide in the atmosphere dissolves in rainwater, it form carbonic acid. This acid reacts with the calcium carbonate present in rocks such as limestone to form calcium bicarbonate, which is soluble in water

Solution weathering then takes place



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Oxidation: Oxygen in water or air oxidises the minerals present in

rocks to form oxides

The oxides are structurally weaker than the minerals. As a result, the rocks crumble more easily

This is common in rocks that contain iron.

​When oxidised, the iron in rocks becomes ferrous oxide

which gives the rocks a reddish-brown colour

Types of weathering

Biological weathering

Tree roots or burrowing animals break up rocks.

Dead plants and animals produce acids which aid chemical erosion.

Algae and molluscs break up coastal limestone at the water line.

Types of weathering

Carbonation

Carbonation is an important form of chemical weathering.

Rainwater and CO2 produce a weak carbonic acid.

This reacts with the calcium carbonate in limestone.

The reaction produces calcium bicarbonate, which is soluble and easily removed by water.

Multiple Choice

Limestone is weathered by rainwater. This statement is referring to which type of chemical weathering?

• Hydrolysis:

• Solution:

• Oxidation

• Carbonation

Multiple Choice

Dead plants and animals produce acids which aid chemical erosion.

Which type of weathering is the statement above referring to?

• biological weathering

• chemical weathering

• physical weathering

• carbonation

Multiple Select

Which statement does not apply to the process of carbonation.

• Carbonation is an important form of chemical weathering.

• Rainwater and CO2 produce a strong carbonic acid.

• This reacts with the calcium carbonate in limestone.

• The reaction produces calcium bicarbonate, which is soluble and easily removed by water.

Multiple Choice

Oxidation occurs in rocks that contain---

• calcium

• oxide

• iron

• ferrous oxide

Factors which influence weathering

Climate

Frost shattering operates in cold climates.

Most chemical weathering processes are faster in a region with a warm, moist climate such as the Caribbean.

Biological weathering is effective in warm, moist climates where plants grow rapidly.

Factors which influence weathering

Rock type

Chemical and physical weathering are faster in rocks with joints and fissures.

Limestone contains calcium carbonate, which is weathered by carbonation.

Rocks containing feldspar are weathered by hydrolysis.

Rocks with minerals such as quartz resist erosion.

Multiple Select

Which is not a factor that affects weathering/

• river

• climate

• rock type