Download Science 7: Unit E: Planet Earth

Science 7: Unit E: Planet Earth
Topic 7: Mountains
How Are Mountains Formed?
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Mountains building takes
millions of years.
Most mountain ranges are
formed from the movement
of tectonic plates, usually in
a subduction zone from the
compression of the Earth’s
crust.
A large mountain range is
called a cordillera. The
Canadian Rockies are part of
the Western Cordillera which
also includes the American
Rockies and the Alaskan
Rockies.
Faulting and Folding
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Sedimentary rock can be faulted or folded
into mountains:
Faulting – The breaking of sedimentary
rock as parts are pushed up over other
rock.
Folding – The bending, but not breaking
of sedimentary rock as the crust is
compressed and forced upwards.
Syncline and Anticline
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Synclines and
anticlines are formed
through the folding
process.
Syncline – the
downward or bottom
part of the fold.
Anticline – The
upward or top part of
the fold.
Thrust Faulting and Fault Block
Mountains
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Thrust Faulting – Sedimentary rock is broken
into separate sheets or ‘slabs’ These sheets can
then be pushed over or under other sheets.
Fault Block Mountains – Compression forces
form the slabs and the continued pushing can
cause the older rock to slide on top of the newer
rock.
Basement Rock – The bottom layer of the
mountain which the other layers slide on top of.
Complex Mountains
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When an oceanic plate meets a continental
plate, it subducts under the continental plate.
This compression gives off heat and pressure
which help to form mountains.
Complex Mountains – mountains formed from
melting and compression when an oceanic plate
meets a continental plate.
The Rocky Mountains formed 500 million years
ago when the Pacific plate subducted under the
North America Plate and the N. America Plate
edge began to thrust fault.
Young and Old Mountain Ranges
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Young Mountain Ranges – are jagged and
rough. They have not been polished smooth by
weathering. The Himalayas and Rockies are
‘young’ mountain ranges. Young Mountain
ranges are growing higher every year due to
compression.
Old Mountain Ranges – smooth and rounded
peaks. They are polished smooth and are
growing smaller every year due to the processes
of weathering and erosion.
New Mountain Range
Old Mountain Ranges