WEATHERING

WEATHERING

• DEFINITION:

– Breaking down of rock to form soil.

– Rock is continually broken down into smaller and smaller particles, resulting in the formation of soil.

– Discuss the importance of soil formation

WEATHERING

• PHYSICAL WEATHERING – Also known as mechanical

weathering – The physical breaking

down of rock through physical means such as temperature change.

– The rock particles simply become smaller but the chemical composition does not change.

– Physical weathering generally leads to coarse soils.

WEATHERING

• PHYSICAL WEATHERING – Also known as mechanical

weathering – The physical breaking

down of rock through physical means such as temperature change.

– The rock particles simply become smaller but the chemical composition does not change.

– Physical weathering generally leads to coarse soils.

• CHEMICAL WEATHERING – The rock is broken down

through chemical processes such as dissolving.

– The rock particles undergo a change to the chemical composition.

– Chemical weathering generally leads to fine and fertile soils.

PHYSICAL WEATHERING: EXFOLIATION

PHYSICAL WEATHERING: EXFOLIATION

– Rocks heat up during the day, and the outer layer expands

– Rocks cool down at night and the outer layer contracts

– The continual expansion and contraction eventually weakens the rock, leading to the outer layer “peeling”.

– The result is rounded rocks. – Exfoliation often occurs in

desert regions which experience extremes of temperature.

PHYSICAL WEATHERING: FREEZE THAW

PHYSICAL WEATHERING: FREEZE THAW

Water is present in cracks and crevices in the rock.

PHYSICAL WEATHERING: FREEZE THAW

Water is present in cracks and crevices in the rock.

At night, the temperature drops below 0°C and the water freezes. The ice expands outwards putting pressure on the rock. The crack widens due to the pressure.

PHYSICAL WEATHERING: FREEZE THAW

Water is present in cracks and crevices in the rock.

At night, the temperature drops below 0°C and the water freezes. The ice expands outwards putting pressure on the rock. The crack widens due to the pressure.

Over time this pressure eventually causes the rock to split apart, leading to sharp, jagged mountain peaks. This process would be found in Alpine Mountain regions.

CHEMICAL WEATHERING

CHEMICAL WEATHERING: OXIDATION

• OXIDATION

– Also known as “rust”

– Iron particles in rocks may rust when coming into contact with oxygen and water.

– The formation of iron oxide weakens the rock and leads to it crumbling.

– Oxidation can be identified as reddish-brown streaks on the rock.

CHEMICAL WEATHERING: CARBONATION

• CARBONATION

– Acid rain

– Gases such as carbon dioxide and sulphur dioxide may mix with rain water to form a weak acid.

– This acid “eats” away at the rock surface.

– The Limestone tombstone on the right has been affected by carbonation.

CHEMICAL WEATHERING: SOLUTION

• SOLUTION – Certain rock minerals

simply dissolve when they are exposed to water.

– Examples include the dissolving of calcium in Dolomite and Limestone.

– This process leads to large underground caves, and may even lead to sinkholes.

CHEMICAL WEATHERING: SOLUTION

LIMESTONE CAVE

CHEMICAL WEATHERING: SOLUTION

LIMESTONE CAVE SINKHOLE

BIOLOGICAL WEATHERING

There is a third type of weathering that involves plants and animals that may be physical OR chemical in nature.

BIOLOGICAL WEATHERING: PLANTS

• Plant roots grow into cracks and the pressure eventually forces the rock to break apart physically.

• Plants may also secrete sap or gum which may be acidic, and weather the rocks chemically.

BIOLOGICAL WEATHERING: ANIMALS

• Animals and insects may weather rocks in the following ways:

– Digging and burrowing

– Licking or chewing

– Physical contact

– Earthworms play an important role in soil formation.