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How are rocks weathered?
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Learning objectives
What is weathering?
What is freeze-thaw weathering?
What is onion-skin weathering?
What is biological weathering?
What is chemical weathering?
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What is weathering?
weathering
erosion and transportation
deposition
Weathering is the break-up of rocks due to the exposure
of the atmosphere.
There are two main types of weathering – physical (or
mechanical) and chemical.
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What happens to weathered rock?
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Learning objectives
What is weathering?
What is freeze-thaw weathering?
What is onion-skin weathering?
What is biological weathering?
What is chemical weathering?
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Weathering – freeze-thaw
You may have heard of the saying, “hard as rocks”.
Most rocks are hard, but despite this they can be broken
by just a small amount of water getting into cracks in the
rock.
This is because water freezes as it expands.
This creates powerful forces that can enlarge the cracks.
As this freeze–thaw process is repeated and cracks
spread through the rock. Eventually small pieces of rock
(called scree) break off altogether.
scree
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Freeze-thaw
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Learning objectives
What is weathering?
What is freeze-thaw weathering?
What is onion-skin weathering?
What is biological weathering?
What is chemical weathering?
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Exfoliation or onion-skin weathering
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Exfoliation or onion-skin weathering
During the day the
sun heats up the
surface of the
rock, causing the
rock to expand.
During the night the As the rock expands
rock cools down and and contracts over
contracts.
and over again,
small pieces of
surface rock begin
to flake and fall off.
Onion-skin weathering is a form of physical weathering.
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Learning objectives
What is weathering?
What is freeze-thaw weathering?
What is onion-skin weathering?
What is biological weathering?
What is chemical weathering?
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Biological weathering
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Biological weathering
Plant roots can get into tiny cracks and
can physically open them up further.
In addition, decaying plant roots also
produce acid which can chemically eat
away at the rock.
Similarly lichens produce acids which
weather the rocks upon which the lichens
are growing.
plant roots can
cause cracks in
rocks
What type of weathering is biological weathering?
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Biological weathering
What has caused the cracks to appear?
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Learning objectives
What is weathering?
What is freeze-thaw weathering?
What is onion-skin weathering?
What is biological weathering?
What is chemical weathering?
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Chemical weathering
How do you think these rocks have become weathered?
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Chemical weathering
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Weathering – chemicals
There are also acids in the rain
that can chemically eat away at
rocks – especially rocks consisting
of metal carbonates (such as
chalk, limestone and marble).
Firstly, there is carbon dioxide gas which dissolves in rain to
form weak carbonic acid. This very slowly eats away at
certain rocks.
Secondly, there are nitrogen and sulphur oxides which
produce much more acidic rain that can rapidly chemically
dissolve the rocks.
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Can you explain…
Colin forgot to chill the wine so he put
it in the freezer to quickly make it cold
– but then forgot it was there!
Next time he went to the freezer he
found it totally shattered.
Explain what has happened.
The water expanded as it
froze, creating huge forces.
These shattered the glass
bottle.
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