Transcript Glacial Erosion - ASGeography

Cold environments
Some glacial
processes and
landforms
Glacial Erosion Processes
All of the rocks below have been broken down into smaller,
angular pieces by erosion by the glacier and frost shattering.
Note the
different
sizes
Note
the
angular
shapes
The rocks in the previous picture
have been broken down by:
Erosion
Processes
Involve
movement
Weathering Processes
happen in situ (one place)
Frost Shattering
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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
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 groundup bedrock incorporated into
the base of a glacier.
Striations
Bedrock surfaces, such as this, commonly bear polished and
scratched (‘striated’) surfaces, as well as various gouge-marks.
Ossian Sarsfjellet in NW Spitsbergen
Erosional landforms
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Corries, cirques or
cwms
Arêtes
Pyramidal Peaks or
horns
Glacial Troughs
and other associated
landforms
Corrie [also known as cwm or corrie]
An armchair-shaped hollow with steep sides and back wall,
formed as a result of glacial erosion high on a mountainside, and
often containing a rock basin with a tarn.
Cwm Cau on the peak of Cadair Idris, Snowdonia National Park, Wales.
Corrie formation
Snow collects in a natural hollow on the side of a mountain. Over time,
further snow collects. This extra weight compresses the snow underneath,
turning it into ice.
The hollow is deepened and widened by the corrie glacier through the
processes of abrasion and plucking. This overdeepening leads to the
characteristic ‘armchair’ shape of a corrie and causes a ‘rock lip’ to be
formed.
Bergschrund
An irregular
crevasse,
usually running
across an ice
slope in the
accumulation
area, where
active glacier
ice pulls away
from ice
adhering to the
steep
mountainside.
Corrie
Coire Mhic Fearchair, Torridon, Northwest Highlands.
Tarn
A small lake occupying a hollow eroded out by ice or dammed by
a moraine; especially common in corries
Two tarns on the Glyderau range, Snowdonia, North Wales, both occupying
cirques. The tarn on the left is Llyn Bochllwyd and that in the centre is Llyn Llyn
Idwal ("llyn" is Welsh for "lake").
Arête
(from the French) A sharp, narrow, often pinnacled ridge, formed
as a result of glacial erosion from both sides.
Nevado Jirishanca, Cordillera Huayhuash, Peru.
Formation
of corrie,
arête and
pyramidal
peak
Pyramidal peak
A steep-sided, pyramid-shaped peak, formed as a result of the
backward erosion of corrie glaciers on three or more sides.
Matterhorn, on Swiss/Italian border.
U shaped valley formation
Water formed valley
Ice-formed valley
Glacial trough
A glaciated valley or fjord, often characterised by steep sides and
a flat bottom, resulting primarily from erosion by strongly
channelled ice.
Valley of Lauterbrunnen, Switzerland. The extremely steep valley sides result in
impressive waterfalls, such as Staubbachfall.
Truncated Spur
Former spur eroded
away in its lower part
by the power of a
valley glacier
Hanging valley
A tributary valley whose mouth ends abruptly part way up the side
of the main valley, as a result of the greater amount of glacial
down-cutting of the latter
Hanging valley below
Mitre Peak, Milford
Sound, New Zealand.
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 90º.
Roche moutonnée
A rocky hillock with a gently inclined, smooth up-valley facing
slope resulting from glacial abrasion, and a steep, rough downvalley facing slope resulting from glacial plucking.
Ice flow was from right to left
Roche moutonnée in front of Steilimmigletscher, Bernese Alps, Switzerland.
Fjord
A fjord is a long, narrow arm of the sea, formed as a result of
erosion by a valley glacier.
Kejser Franz Josef Fjord in East Greenland, looking east towards the peak of
Teufelschloss and the edge of the Greenland Ice Sheet, from which the
icebergs were derived
A glaciated valley: a fjord
Field sketch of Geiranger Fjord
Fjord
Visible light satellite image of Scoresby Sund, the largest fjord
system on Greenland’s east coast. On the left is the (white)
Greenland ice sheet. The grey area on the right is low cloud.
Note the many icebergs.