Download Understand the effect of rock type and climate upon the rate, degree

Weathering – Summarized information for note card
CARD 1:
Understand the effect of rock type and climate upon the rate, degree and outcomes of chemical,
mechanical and biological weathering; and the importance of weathering as a component of mass
movement.
Weathering: a set of physical, chemical and biological processes that change the physical and chemical
properties of rocks and soil at or near the earth's surface.
Factors affecting rate of weathering:
 Mineral composition
 Joints: Joints are lines of weakness in rocks—roots of plants, rain water, etc. enter the joints and
cause weathering.
 Grain size: The bigger the grains, the faster the weathering.
 Relief: When the relief of a place is steep, landslides and slumping may occur, exposing rocks to
weathering.
 Climate
 Vegetation cover: Vegetation retains rain water and thus subject rock to chemical weathering.
 Men’s activities: Man-made pollution (E.g. Sulfur dioxide) form acid rain that breaks down rocks
rapidly
CARD 2:
Physical / Mechanical Weathering: a rock is broken down into smaller pieces without changing its
mineral composition.
 Frost action: freezing and thawing in cracks and pores in rocks, enlarging the cracks and pores—
eventually, pieces of rock (called scree) break off altogether.
 Exfoliation (“onion skin weathering”):
1. During the day the sun heats up the surface of the rock causing the rock to expand.
2. During the night the rock cools down and contracts.
3. As the rock expands and contracts over and over again, small pieces of surface rock
begin to flake and fall off.
 Pressure release: The release of pressure created by removal of overlying rock by erosion
causes expansion of the rock underneath, forming cracks on the rock surface. Over time, the out
layers of the rock break away in sheets.
 Crystallization: occurs primarily in hot, arid regions; when water containing salts evaporate, the
build-up of salts forming crystals create stress in the rock and break it down to grains.
CARD 3:
Chemical weathering: a rock is broken down by chemical reactions that change its mineral composition
and physical and chemical properties; occurs quickly in warm, moist environments because water is
needed for the chemical reactions.
 Carbonation: Carbon dioxide in rainwater or moisture in the air forms carbonic acid and react with
the minerals in the rock, weakening the rock and breaking it down in process.
 Hydrolysis: Chemical reaction between the minerals in the rock and hydrogen in rain water,
weakening the rock and causing it to break down.
 Oxidation: Oxygen combines with water and minerals in the rock; when iron reacts with oxygen,
iron oxide is formed; the iron-oxide crust crumbles easily, weakening the rock.
 Solution/Dissolution: process by which minerals in the rocks dissolve directly in water
 Hydration: Minerals in the rock absorb water and expand, creating stress and eventually
disintegrating the rock.
Biological weathering:
Weathering – Summarized information for note card
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Roots grow into the cracks and joints in rocks. Decaying plant roots also produce acids that can
chemically erode the rock.
Earthworms and termites make tunnels in the ground