Chemical weathering is when rocks are dissolved because of a chemical reaction. Carbonation is an example of chemical weathering.
Carbonation • The atmosphere contains a gas called carbon dioxide (CO2
). • Rainwater (H2 form a weak carbonic acid (H2
O) mixes with the carbon dioxide (CO2 CO3
).
• This weak carbonic acid has a huge effect on limestone rock. This is because limestone contains 80 per cent calcium carbonate.
• The weak carbonic acid reacts with the calcium carbonate in the limestone and dissolves it.
• Limestone is a permeable rock, so rainwater can pass right down through the rock.
In the next section we will look at how carbonation has created a unique landscape in the Burren, a limestone region in Co. Clare.
: Figure 6.4 The effects of weathering on a gravestone
ACT VITY
How is weathering affecting the rock in Figures 6.4 and 6.5? Discuss in pairs, then compare your ideas with the rest of the class.
) to
( Figure 6.5 The Burren
(i) Name two common causes of erosion. (ii) Name two types of weathering. (iii) Where does freeze-thaw action commonly occur? (iv) How does the temperature influence freeze-thaw action? (v) Where in Ireland is there evidence of freeze-thaw action? (vi) Explain how carbonation occurs? (vii) Why does freeze-thaw action not usually occur in hot climates?
/ I can explain the difference between weathering and erosion. / I can explain processes of mechanical weathering and chemical weathering.
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Weathering and Mass Movement: The changing face of the Earth
