Transcript Glacial Erosion and Wind Erosion

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 Processes
happen 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 welljointed.
Well-jointed rock
Abrasion
As 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 formed
Armchair shaped hollow – usually northerly aspect in UK and N.
Hemisphere.
Steep back wall
e.g. Llyn Cau on Cader Idris
Llyn Cau -Corrie lake - Or tarn
Back wall of corrie – plucking
Overdeepening of hollow – abrasion
Rotational slip at base of glacier
Corrie lip at front edge
Looking down into a tarn
From high up on the backwall
Backwall subject to freeze thaw
weathering in post-glacial –
periglacial times
An arete
A knife edge ridge formed
where two cories developed
back to back
This example is Striding
Edge on Helvellyn in the
Lake District.
A pyramidal peak or
horn
e.g. Matterhorn
Where 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 erosion
Ice more effective at eroding by
Plucking 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
level
The 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:
l desert (arid)
l steppe (semi-arid, surrounds deserts)
Question: how much rain do we get in Tempe every year?
1) Deserts: where & why
What causes deserts?
Important factors:
Global distribution of
l air pressure
l wind
Relationship between
l rainfall
l evaporation
www.weatherchannel.com
1) Deserts: where & why
1) Deserts: where & why
Low-latitude deserts
(recall: “latitude” = east-west line on the globe)
u Tropic of Cancer
u Tropic of Capricorn
In contrast….
u Equator:
hot air
u rises to 15-20 km
u low pressure belt
u
1) Deserts: where & why
1) Deserts: where & why
Deserts & winds
3) Wind erosion/ deposits
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?
Deserts & winds
3) Wind erosion/ deposits
Sand dune formation
3) Wind erosion/ deposits
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