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.