This product contains all the work for Social Sciences (Geography & History) Grade 9, term 3 – based on the “Via Africa” textbook in English.
Geography – Surface forces that shape the earth
Unit 1: Weathering
Unit 2: Erosion and deposition
Unit 3: The impact of people on soil ...
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, Impact of human activities on weathering Concept of weathering
• Burning fossil fuels. • Weathering = the processes that break down rocks, soils
• Dynamite blasting. and minerals into smaller pieces through contact with
• Mining operations. the atmosphere, biota and water.
• Quarrying. • Responsible for soil creation and unique features on
Earth.
Biological weathering U1:
•
Physical weathering
Biological weathering = the physical and Weathering
chemical actions of living things. • Physical weathering = the breakdown of rocks
• Physical actions include rock breaking through into smaller components without altering their
plant root growth or animal burrows. chemical composition.
• Chemical actions involve the excretion of acids, • Granular disintegration - rocks break up into
which can weather rocks and minerals. small grains to form sand or small pieces of
• Decomposition of organic matter releases gravel.
corrosive substances into the environment. • Exfoliation - rocks peel off in sheets.
Chemical weathering • Block separation - rocks break up into large
fragments related to rock joints.
• Chemical weathering = the breaking of rocks into particles
with different mineral compositions from the original rock.
• Solution weathering - minerals or soluble chemicals in the
rock dissolve directly in water.
• Hydrolysis - minerals in the rock react with hydrogen in
rainwater.
• Oxidation - results in red or yellow oxides or hydroxides
produced when rock minerals react with dissolved oxygen.
• Hydration - minerals in rocks absorb water, expand and
break up.
• Carbonation – a weak solution of carbonic acid is formed
when carbon dioxide dissolves in water.
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