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Changing the earth’s relief
Evolution of the landscape
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
Laurentians Rocky Mountains
Why are they different?
?
Montreal streets :After the winter: worn down
Laurentians Rocky Mountains
Laurentians a lot older have been worn down
!
Why are they different?
?
Weathering
• Gradual destruction of rock on the earth surface.
• http://www.youtube.com/watch?v=z2nwiba0N0Y
Mechanical weathering
The power of water:
Rock is fragmented, but not changed in its composition
Mechanical weathering
• Fragmentation of rock through: - Variations in
temperature andpressure
- water example: freeze thaw
cycle of water- wind
• Composition of rock does not change
Minerals in rock are dissolved and changed.
Chemical weathering
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. Mechanical 2. Chemical
3. Mechanical + Chemical
1 2
3
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
The three stages of ErosionErosion
1.) Weathering
2.) Transport: water, wind, ice
3.) Deposition: in lake, stream,
ocean
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.
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