Weathering

Question 1

Weathering

Answer 1

Weathering is the breakdown of rocks over time

3 types of weathering include:

• Physical
• Chemical
• Biological

Question 2

Mechanical (Physical) Weathering

Answer 2

The breakdown of rocks due to the exertion of physical forces without any chemical changes taking place.

• Freeze-thaw - This occurs in areas where temperatures fluctuate above and below freezing. Water enters the cracks in rocks and then the water freezes overnight during the winter. As it freezes, water expands by around 10% in volume which increases the pressure acting on a rock, causing cracks to develop. Over time these cracks grow, weakening the cliff.
• Salt Crystallisation - As seawater evaporates, salt is left behind. Salt crystals will grow over time, exerting pressure on the rock, which forces the cracks to widen. Salt can also corrode ferrous (material that contains iron) rock due to chemical reactions.
• Wetting and Drying - Rocks such as clay expand when wet and then contract again when they are drying. The frequent cycles of wetting and drying at the coast can cause rocks and cliffs to break up.

Question 3

Chemical Weathering

Answer 3

The breakdown of rocks through chemical reactions

• Carbonation - Rainwater absorbs CO2 from the air to create a weak carbonic acid which then reacts with calcium carbonate in rocks to form calcium bicarbonate which can then be easily dissolved. Acid rain reacts with limestone to form calcium bicarbonate, which is then easily dissolved allowing erosion.
• Oxidation - When materials become exposed to air through cracks and fissures, the mineral will become oxidised which will increase its volume, causing the rocks to crumble. The most common oxidation within rocks is iron minerals becoming iron oxide, turning the rock rusty orange after being exposed to air.
• Solution - When rock minerals such as rock salt are dissolved.

Question 4

Biological Weathering

Answer 4

The breakdown of rocks by organic activity

• Plant roots - Roots of plants growing into the cracks of rocks, which exerts pressure, eventually splitting the rocks.
• Birds - Some birds such as Puffins dig burrows into cliffs weakening them and making erosion more likely
• Rock Boring - Many species of clams secrete chemicals that dissolve rocks and piddocks may burrow into the rock face.
• Seaweed Acids - Some seaweed contain pockets of sulphuric acid, which if hit against a rock or cliff face, the acid will dissolve some of the rock’s minerals.
• Decaying Vegetation - Water that flows through decaying vegetation and then over coastal areas, will be acidic, this causing chemical weathering.