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SCIPAD - BIG IDEAS - BOOK 2
EARTH SYSTEMS
The Water Cycle’s Effect on Landforms - Weathering
Weathering is the process of breaking down rocks into smaller pieces. The water cycle and the
effect of gravity are constantly working to smooth and flatten the Earth’s features. Whether it’s
mountain ranges or coastlines, the effects of weathering are all around us.
The water cycle can lead to two main types of weathering.
•
Chemical weathering: the breakdown of rocks by dissolving them in rainwater.
•
Physical weathering: the breakdown of rocks due to the effects of wind, rain and waves.
No new substances are made, the rocks are just broken into smaller pieces.
1. Decide if the examples given in the table are examples of physical weathering (P) or
chemical weathering (C).
The force of water running through a valley after rain causes rocks to roll
down a stream. This breaks up the rocks, rounding and smoothing their
surfaces.
Rainwater runs into a crack in a rock and at night the water freezes. When
water freezes it expands, widening the crack. Repeated freezing and
thawing of the water within the crack will lead to the rock breaking into
smaller pieces.
Rainwater is slightly acidic because it contains dissolved carbon dioxide
from the air, forming carbonic acid. This weak acid can dissolve some
types of rock, especially limestone.
Rocks are mixtures of minerals. When they are heated by the Sun, the
minerals expand by different amounts which can lead to cracking of the
rocks. This is common in deserts, where days are very hot and nights are
very cold.
The action of waves breaks up rocky coastlines into boulders, pebbles and
sand.
The burning of coal releases chemicals that react with water in the
atmosphere, forming sulfuric and nitric acids. These acids react with
minerals in rocks, breaking them down.
2. The two rocks in the photos have both been weathered in different ways. Rock ‘A’ was
photographed near the peak of Mount Ruapehu, while Rock ‘B’ was found on the banks
of the Tukituki River. Using clues from the table above, suggest how the
water cycle has caused the weathering of these two rocks.
Rock A: 





Rock B: 





A
B














































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