Chemical And Physical Weathering

Question 1

Define Weathering and name its influencing factors

Answer 1

The process by which rocks on or near the earths surface are broken down or decayed in situ (in original position)

Influenced by:
Rock Type
Climate
Topography (upland or lowland)

Question 2

Name the types of weathering

Answer 2

Physical/Mechanical

Chemical

Question 3

Define Physical Weathering and name the main types

Answer 3

Physical weathering is the breakdown of rock by physical forces into smaller particles - there is no change in chemical make-up

2 main types:
Freeze-thaw action
Exfoliation

Question 4

Describe Freeze-thaw action

Answer 4

Water fills up cracks in rocks during the day
The water freezes at night when temp drops below 0
As water turns to ice it expands by about 9% forcing gaps in the rock to open
This slowly weakens the rock and widens the cracks
Eventually particles of rock break off this is called scree
Scree may collect at the base of a steep slope under gravity
Scree can be seen on the sides of Craogh Patrick (Co. Mayo) and the Great Sugarloaf (Co. Wicklow)

Question 5

Describe Exfoliation

Answer 5

Exfoliation or onion weathering is caused by temperature change and is most effective in places with a great daily diurnal temperature change, it strips off outer layers of rock

In deserts this occurs often, due to such a large temp change, the layers of rock close to the surface cool and contract

Outer layers heat and cool much quicker than layers further in, dark rocks absorb heat faster than light coloured rocks, and minerals in rocks expand at different rates, this puts more stress on the rock

Fractures and flaking begin to occur, the outer layers of the rock peel off and collect in a pile of scree at the base of the slope

The Half Dome at Yosemite National park is a spectacular example

Question 6

Define chemical weathering and name the main types

Answer 6

Chemical weathering refers to the decomposition or decay of rocks, the make-up of the rock is changed

Carbonation
Hydrolysis

Question 7

Describe Carbonation

Answer 7

Rainwater absorbs carbon dioxide as it falls, and as water goes through the soil it absorbs more carbon dioxide from organic matter

They combine to form a weak carbonic acid, which reacts with minerals in the rock and dissolves them or turns them into other minerals

Rocks like limestone and chalk contain calcium carbonate, this reacts with the weak carbonic acid to form calcium bicarbonate which is soluble, this is then removed in solution

Carbonation is extremely effective at weathering limestone landscapes as it contains bedding planes and joints e.g of a landscape caused by carbonation is the Burren Co Clare

Question 8

Describe Hydrolysis

Answer 8

Form of chemical weathering where water reacts with chemicals in the rock and breaks them down to form a new substance

Fine grained rocks weather faster than coarse grained rocks
Hydrolysis occurs much faster in hot, wet conditions like the tropics as water percolates down to a considerable depth so hydrolysis occurs far below the surface

Hydrolysis is very effective in weathering rocks like granite, Feldspar, in granite, easily absorbs water, and decays to a clay-like material called kaolin

Feldspar is good at bonding material but kaolin is bad at bonding, it crumbles easily weakening the rock and causing it to break down, the granite, such as quartz and mica, are no longer held together and remain loose

Hydrolysis has helped shape the granite of the Leinster Batholith, the process took place when Ireland had a warmer climate