Changing the earth’s relief
Evolution of the landscape
Textbook p. 314, 333-335
Changing the earth’s relief:
mountain formation
• Relief = shape of the earth surface
• Formation of mountains = Orogenesis
 through convergent tectonic plate
movements
 mountain: - steep slopes
- at least 600m high
• Mountains in the making:
➔ Himalaya, Rocky mountains, Alps
?
Why are they different?
Laurentians
Rocky Mountains
Montreal streets :
After the winter: worn down
?
Why are they different?
Laurentians
!
Laurentians a lot older
 have been worn down
Rocky Mountains
Weathering
• Gradual destruction of rock on the earth
surface.
• http://www.youtube.com/watch?v=z2nwiba0
N0Y
Mechanical weathering
The power of water:
Rock is fragmented,
but not changed in
its composition
Mechanical weathering
• Fragmentation of rock through:
- Variations in temperature and
pressure
- water
example: freeze thaw cycle of
water
- wind
• Composition of rock does not change
Chemical weathering
Minerals in rock
are dissolved
and changed.
Chemical Weathering
• Dissolving and changing minerals in rocks
Composition of rock changes.
• Through: - washing out of certain minerals
 enhanced through acid rain
Biological Weathering
Living organisms
destroy rock.
Biological weathering
• Plant roots can break rocks
• Living organisms release acids
 changes and weakens the rock
Practice: what kind of weathering?
1
1. Mechanical
2
2. Chemical
3
3. Mechanical + Chemical
Water erosion
Glacial erosion
Wind erosion
Erosion of soil
• Soil Erosion rates on farmed land
between 17 and 40 tons per ha and year
• average natural soil production only 1
ton per ha and year !!!
Journey’s end: Deposition
Erosion
1.) Weathering
2.) Transport:
water, wind, ice
3.) Deposition:
in lake,
stream,
ocean
The three stages of Erosion
Changing the earth’s relief:
Erosion
• Erosion is the gradual wearing away
(destruction and /or removal) of land surface
material, for example rock or soil.
• Three step process:
– Weathering of rock (destruction of rock)
– Transportation of soil and rock debris (through
water, wind, glaciers).
– Deposition of material at another location
View from the mountain:
Montréal
Montréal
Effects of erosion
• Hole on
Sherbrooke May
2012
• Caused by hole
in water
collecting pipe
• What
happened?
homework
• Worksheet to be collected next class
Categories of Weathering / Erosion
• Mechanical Weathering
– Composition of rock does not change
– Through: - Variations in temperature and pressure
 example: freeze thaw cycle of water
- Wind and water
• Chemical Weathering
– Composition of rock changes
– Through: - washing out of certain minerals
 enhanced through acid rain
• Biological Weathering
– Living organisms release acids  change + weaken the
rock
– Plant roots can break rocks.