Weathering Flashcards
Define weathering
Breakdown of rocks by physical (mechanical), chemical or biological means. The weathered rock (scree) stays in situ
Define scree
Weathered rock
Define in situ
Not removed from the area
Define erosion
Breakdown of rocks by wind, water or glacial action. The broken down rock may be transported to another location
What are two types of physical weathering?
Freeze thaw action and exfoliation (onion weathering)
What is the main factor that causes freeze thaw action and exfoliation?
Temperature
What are the ideal conditions for freeze thaw action?
Upland, mountainous areas that drop below 0°C
What are the ideal conditions for exfoliation?
Desert climates that are 45°C+ during the day and below 0°C at night
What is chemical weathering?
Reaction of minerals in rocks to chemical agent. Rocks dissolve
What are the different types of chemical weathering and what rock type do they affect?
*Oxidation - Sandstone
* Carbonation - Limestone
* Hydrolysis - Granite
* Hydration - Granite
In what climate does chemical weathering speed up?
Hot humid climates
What is biological weathering?
Plant/animal life that leads to the breakdown of rock
What are some different causes of biological weathering?
- Trees: Growing up through rocks. Tree roots break rock.
- Animals: Burrowing
- Fungi/Lichen/Moss: Attach to rock and break it down
What are the processes of fluvial and marine erosion?
Hydraulic action, attrition, solution and abrasion
What are the processes of glacial erosion?
Plucking, abrasion
Where does freeze thaw action occur?
Mountainous regions eg. Croagh Patrick
During what periods does freeze thaw action occur?
Glacial periods - Now and 12,000 years ago
What factors affect freeze that action?
- Temperature: above and below 0°C
- Altitude: Higher up is more effective
- Rock type: Permeable rocks and rocks with natural fractures/pore spaces affected more
Explain the steps of freeze thaw action
- Water fills the cracks of the rocks during the day
- At night temperatures fall below 0°C and water turns to ice, expanding by 9-11%, putting pressure on the rock
- Over time this cycle causes rock to fracture and break off, creating scree
Where does exfoliation occur?
Desert and arid climates
Give an example of somewhere exfoliation occurs
Sahara Desert, Africa
What happens during exfoliation?
The outer layer of rock heats and expands, then cools and contracts repeatedly. This causes is to fracture and peel away
What factors affect exfoliation?
- Temperature: Large diurnal range eg. 40°C day, 0°C night
- Lack of vegetation: Nothing to cover rocks/provide shade
- Lack of cloud cover: Blue skies during day (hot) and loss of heat during night
- Stone colour: Dark rock attracts heat causing it to expand more rapidly
Give an example of somewhere carbonation occurs
The Burren, Co. Clare
What is the area of the Burren?
250 km squared
What kind of landscape is the Burren?
Karst landscape - exposed limestone, no soil or vegetation
Explain the process of carbonation
- Rainwater (H20) mixes with Carbon Dioxide (CO2) to form a weak carbonic acid (H2CO3)
- Limestone is a permeable rock. The limestone in the Burren is made up of 55% Calcium Carbonate
- Calcium Carbonate is insoluble however when H2CO3 comes into contact with it it turns it into the soluble Calcium Bicarbonate
- It dissolves and is washed away in solution
Draw a diagram of carbonation
N/A
Explain hydration
- Soil-forming minerals in rock absorb water causing them to expand
*This causes stress to build in the rock, eventually leading to it fracturing and shattering
*Mechanical weathering furthers the disintegration
Explain hydrolysis
*Carbonic acid causes rock-forming minerals eg. feldspar to turn into softer weaker kaolin
* Kaolin doesn’t bond well and breaks down easily, weakening rocks structure, eventually causing it to break down and decompose
Explain oxidation
Oxygen dissolved in water reacts with metal in rocks to produce oxides of iron (rust) in rock particles
Explain two types of physical weathering with reference to examples from Ireland (30m)
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