Download Year 8 Lesson 6 Weathering

Do now!
Can you stick the freeze-thaw
weathering paragraph into
your book?
Last lesson
• Weathering of rocks – Freeze-thaw
weathering
Freeze-thaw weathering
In high mountainous areas, rain water can seep
into the small cracks in a rock. At night-time the
air gets very cold and the water freezes. When
water freezes it expands making the crack wider.
During the day the water melts and falls deeper
into the now larger crack. This happens repeatedly,
the crack gets bigger and bigger, and eventually a
piece of rock is broken away from the mountain.
Educational freedom fighters!
This class is being held hostage by
educational freedom fighters (just outside).
We have to decide as a class which is the
most important word in the paragraph. If we
get it wrong, they are going to shoot us!!!!!
Today’s lesson
• Chemical and physical weathering
Can you gather around Mr Porter?
Chemical
weathering
Rain is
slightly acidic
as it contains
substances
dissolved from
the air. It can
react with
rock,
dissolving it.
Chemical weathering
Some rocks are dissolved more by acid rain
than others
Limestone
“pavement”
Physical weathering
Rocks can be weathered by physical
changes
Physical weathering
When rocks are hot they expand, and when
they cool they contract. Repeated changes
cause the rock to crack, often causing rock
to peel off.
Sometimes
called
“onion-skin
weathering”
You now know all about
freeze-thaw weathering
Physical weathering
Freeze-thaw weathering is another example
Let’s try some questions!
Pages 84 & 85