Weathering

Question 1

What is weathering?

Answer 1

• The exposure of geomaterials to weather

- A series of physical, biological and chemical alterations that change the characteristics of rocks

Question 2

What is the difference between weathering and erosion?

Answer 2

• Weathering needs to occur before erosion

Question 3

Why is weathering important for soil?

Answer 3

• needed as a substrate for plant growth
• Controls soil chemistry
• Provides nutrients for ecosystems and plants
• Regulates global chemical cycles - carbon and nitrogen

Question 4

Why is weathering essential to landscape evolution?

Answer 4

• Nature and variety of geomaterials and weathering processes provide geo diversity
• ## Controls landscape

Question 5

Why is water important for weathering?

Answer 5

• Delivery of solutes to surface water - controls water chemistry
• Without weathering water would be hydrogens and oxygen
• Source of essential dietary minerals (electrolyte)

Question 6

Where does weathering occur?

Answer 6

Occurs at or near the earths crust - in the critical zone

Question 7

What are the 3 key changes that happen when material is weathered?

Answer 7

1) Decrease in chemical and mineralogical complexity and structural integrity
2) Takes complex minerals and turns them into much simpler - fewer complex minerals
3) Reduction in complexity

Question 8

What are the original materials which are weathered?

Answer 8

Primary materials:
- often formed through igneous and crystallise as magma cools
Mechanically strong materials:
- Granite, diamonds, abrasive materials with complicated structures

Question 9

What are the weathering products produced through weathering?

Answer 9

• Soluble cations (Na, Mg, K, and Ca)
• Mechanically weaker/softer materials - clay, ion oxides
• Easier to erode

Question 10

What is the role of water in weathering?

Answer 10

• Interaction of geomaterials with water
• physically removing and transports material
• Water expands as it freezes and aids freeze-thaw processes

Question 11

Outline the process of chemical weathering

Answer 11

• 5 main processes
• Solution - minerals dissolve in water - salt
• Hydration - combinations and incorporation of water into mineral structure
• Oxidation/reduction
• Hydrolysis - chemical reaction between water and mineral
• Carbonation - reaction between calcium carbonate and weak carbonic acid
• Primary chemicals are chemically altered

Question 12

Outline the process of mechanical weathering

Answer 12

• Physical breakdown due to the application of stress
• Fracturing process
• Dilation caused by pressure release caused by unloading
• Thermal expansion
• Salt weathering - dried salt water creates crystals which expand and open up fissures

Question 13

Outline the process of biological weathering

Answer 13

• Biological processes influence both chemical and physical weathering
• Does not exist on its own
• Breakdown of organic matter by microbes produce organic acids which break down minerals
• Physical fracturing from tree roots

Question 14

Why does most weathering combine all 3 weathering processes

Answer 14

• Mechanical weathering caused by wave action
• Biological weathering caused my grazing molecues
• Chemical weathering depends on geology