Lesson 25 Weathering and Erosion of rock

1
Lesson 25 Weathering and Erosion of rock

• What is the difference between weathering and
  erosion of rock ?
• Could you give a few examples of physical
  weathering ?
• Why are rocks containing calcite and iron
  particular vulnerable to chemical weathering ?

2
What is the difference between weathering and
erosion of rock ?

• Weathering is a slow process of breaking up of
  rock over a period of time.
• Erosion is a process of weathering and
  transporting of the weathered rock to somewhere
  else.

3
Could you give a few examples of physical
weathering ?

• Temperature weathering - Uneven contraction and
  expansion of different minerals under extreme
  temperatures.
• Frost Action Water seeps into the cracks in
  rocks and expand when it freezes. The expansion
  of ice break the rock apart.
• Abrasion - e.g. Wind blowing or water flowing
  over the rock and weather the edges of the rock.
• Organic activity By the action of plant or
  animal

4
Why are rocks containing calcite and iron
particular vulnerable to chemical weathering ?

• Calcite is a crystalline form of calcium
  carbonate (CaCO3(s)).
• It is soluble in acid (e.g. carbonic acid
  H2CO3(aq) from CO2(g) or nitric acid HNO3(aq)
  from acid rain).
• e.g. calcium carbonate(s) carbonic acid(aq) ?
  calcium hydrogencarbonate(aq)

5
Why are rocks containing calcite and iron
particular vulnerable to chemical weathering ?

• Iron expands when it reacts with oxygen and water
  to form rust.
• The expansion will force the rock apart and the
  rust formed is also more soluble in water than
  iron itself.

6
Classwork(Do them on your textbook)

• pg103 Q7,8,9,15,17