Physical (mechanical) Weathering

Question 1

What is physical (mechanical) weathering?

Answer 1

• weathering affecting rocks + rock formations

Question 2

What are the diff. types of mechanical weathering?

Answer 2

• freeze-thaw
• salt crystallisation
• heating + cooling (exfoliation)
• pressure release (dilatation)
• vegetation root action

Question 3

Where does mechanical weathering take place?

Answer 3

• at/near Earth’s surface, where there’s more T°C changes

Question 4

What is freeze-thaw (frost action)?

Answer 4

• when water in cracks, freezes at 0°C + repeatedly expands as it cools by 10%
• puts pressure up to 2100kg/cm2 on surrounding rocks: shatters + break off
• most effective in areas w cycles of T°C above + below 0°C (e.g. Mts. + glacial envi.)

Question 5

What is salt crystallisation?

Answer 5

• salts left behind in cracks by evaporation of salt solutions
• inc. Na2CO3 + NaSO4 which expands by 300% as temps inc. from 26-28°C
• eventually rocks break off or disintegrate
• usually occurs on coasts + desert regions

Question 6

What is heating + cooling (exfoliation)?

Answer 6

• when rocks repeatedly expand + contract unevenly due to T°C changes
• causes to separate into layers + break away
• usually occurs in desert areas where temps can be 40°C during day + freezing at night

Question 7

What is pressure release (dilatation)?

Answer 7

• when overlying rocks removed by erosion
• causes underlying rocks (granite), which has formed under extreme pressure, to expand + fracture parallel to surface
• forming pseudo bedding planes

Question 8

What is veg. root action?

Answer 8

• when veg. grows, roots need more space
• so exerts pressure onto surrounding rock causing it to break apart