Glacial Erosion and Wind Erosion

GMIS Geography

Glacial Erosion Processes

The rocks in the previous picture have been broken down by:

Erosion Processes

Involve movement

Weathering Processeshappen in situ (one place)

Frost Shattering• Happens in mountainous or hilly

areas where the temperature regular rises above and falls below freezing.

• Water collects in cracks in rocks.• Overnight the water freezes and

expands.• This expansion puts stresses and

pressure on the sides of the crack.• During the day when the temperature

rises the ice thaws/melts and contracts releasing the pressure on the crack.

• This happens over and over again and eventually the rock cracks open.

• The rocks that break off are jagged and angular - scree.

• If they are on a slope they roll down hill and collect on what are known as scree slopes.

Jagged, angular rocks

of different sizes

Plucking• The water at the bottom

of the glacier freezes onto rock on the valley base.

• As the glacier moves the rock is pulled away from the valley base.

• Plucking mainly occurs when the rock is well-jointed.

Well-jointed rock

AbrasionAs a glacier slides over its bed, it picks up rock fragments that act like sandpaper, on a giant scale, rubbing against and wearing away the sides and floor of the valley. This leads to the valley getting steeper, deeper and wider.

Rocks carried by the glacier grind at the

base and sides of valley

Rock fragments and ground-up bedrock incorporated into the base of a glacier.

MORAINES Moraines - deposited particles once glacier

recedes • 1. Ground moraines - in glacier before

deposited•   2. Lateral moraines - deposited on sides

of glaciers•   3. Medial moraines -deposited on the

sides of two converging glaciers, resulting between the two

•   4. End moraines - deposited at the ice front

Examples of a Medial Moraine, End Moraine, and Terminal Moraines.

Picture of an End Moraine: End moraine of a piedmont glacier (large valley glaciers meet to form an almost stagnant sheet of ice) , Bylot Island, Canada. The sharp-crested ridge of till (end moraine) was pushed up at the

ice margin during the glacier's maximum advance, probably during the Little Ice Age.

Lateral and terminal moraines of a valley glacier, Bylot Island, Canada. The glacier formed a massive sharp-crested lateral moraine at the maximum of its expansion during the Little Ice Age. The more rounded terminal moraine at the front consists of medial moraines that were created by the junction of tributary glaciers upstream.

Corrie, cirque, cwm – hollow where a glacier formedArmchair shaped hollow – usually northerly aspect in UK and N. Hemisphere.Steep back walle.g. Llyn Cau on Cader Idris

Llyn Cau -Corrie lake - Or tarnBack wall of corrie – pluckingOverdeepening of hollow – abrasionRotational slip at base of glacierCorrie lip at front edge

Looking down into a tarnFrom high up on the backwallBackwall subject to freeze thaw weathering in post-glacial – periglacial times

An areteA knife edge ridge formed where two cories developed back to backThis example is Striding Edge on Helvellyn in the Lake District.

A pyramidal peak or horne.g. MatterhornWhere 3 or more corries form back to back

A glacial trough or U shaped valley.Steep sides are truncated spurs prexisting river valley profile altered by glacial erosionIce more effective at eroding byPlucking and abrasion

A hanging valley and waterfall called Bird Woman Falls near Mt. Oberlin, Canadian Rockies.

A smaller tributary glacier could not erode the base of its valley as deep as the main valley glacier. Thus after the ice melts the smaller valley is left hanging above the main valley floor and enters it at up to 90*.

A fjord is a drowned glaciated valley. The ice did not use present day sea level as its base levelThe ice could erode much deeper than today’s sea level.So after the Ice Age the sea enter and drowned glaciated valleys.Many examples in Norway

Wastwater

In some areas the glaciated valley can be overdeepened by glacial erosion. Perhaps the rocks locally were less resistant.Alluvial fans may be formed where a post glacial stream flows into the lake. The lake may be split into two.

Keswick lies between Derwentwater and Bassenthwaite. Interlaken is another example.Lakes are temporary features – they fill up with sediment or the post glacial reiver cuts down through the dam blocking the lake so that all the water drains away.

These striations are on rocks in the Indian Peaks Wilderness, Utah. They were formed as individual particles carried at the base of a glacier moved across the bedrock and scratched the rock. The striations provide important clues to the orientation of ice flow, particularly important if we were not around to observe the glacier when it existed.

Definition: rock hills shaped by the passage of ice to give  a smooth up-ice side and a rough, plucked and cliffed surface on the down-ice side. The upstream surface is often marked with striations.

Wind Erosion

1) Deserts: where & why

Earth’s dry regions: 30% of all land

2 climate types of dry regions:

desert (arid)

steppe (semi-arid, surrounds deserts)

Question: how much rain do we get in Tempe every year?

1) Deserts: where & why

What causes deserts?

air pressure wind

Important factors:

Global distribution of

rainfall evaporation

Relationship between

www.weatherchannel.com

1) Deserts: where & why

1) Deserts: where & why

Low-latitude deserts

Tropic of Cancer

Tropic of Capricorn

(recall: “latitude” = east-west line on the globe)

Equator: hot air rises to 15-20 km low pressure belt

In contrast….

1) Deserts: where & why

1) Deserts: where & why

3) Wind erosion/ depositsDeserts & winds

Wind erosion: Important in arid environments

Example: Types of sand dunes:

Sand dune shape depends on:

Flat or hilly? How much sand? Winds steady or intermittent? Wind direction constant? Vegetation present?

3) Wind erosion/ depositsDeserts & winds

Sand dune formation

3) Wind erosion/ deposits

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