? Flashcards
Continental glacier
As this glacier grows it collapses down and outward moving the sediment at its base.
- the rock fragment has been eroded (set in motion by the moving ice)
- as ice moves across the bed rock it has little affect. If there is friction the ice melts. This rock fragment, however will scrape against the bedrock
- as a result of this abrasion both the rock fragment and the bedrock are ground down and small pieces of rock are created.
- as a result of the two weathering processes – frost action and abrasion – sediment is created that has two distinct sizes - large and small.
- it also means that scratches or striations occur in bedrock and the large rock fragments have a number of flat surfaces.
- multiple flat surfaces occur as this rock is reowrked at the base of a glacier
Weathering processes that occur in a glacier
Frost Action and Abrasion
What happens when there are “bumps” in the bedrock beneath a glacier?
At A, on the up-ice side of this bedrock protrusion, the ice slows down as it encounters this obstacle.
With increased pressure and friction the ice melts.
The ice also bends and flows around the obstacles. n
What happens when there are “bumps” in the bedrock beneath a glacier?
- At A, on the up-ice side of this bedrock protrusion, the ice slows down as it encounters the obstacle.
With increased pressure and friction the ice melts. - The ice also bends and flows around the obstacles. If there is any sediment at the base of the ice it will start to grind away, smooth and polish the bed rock.
- ar B the solid ice and meltwater have moved around the obstacle where there is less pressure. On this down-ice side meltwater refreezes
- as a result the bedrock is physically weathered by frost action
- the end result is a change in the shape of the bedrock obstacle into an asymmetrical hill with smooth, more gentle sloping up-ice and a jagged down-ice side.
- ROCHE MOUTONNEE
ROCHE MOUTONEE
An erosion bedrock glacial feature.
Glacial Weathering
- Frost Action
2. Abrasion
Abrasion
The grinding of one rock against another.
Glacial weathering FROST ACTION end result
Large Pieces
Glacial weathering ABRASION end result
Small Pieces
Glacial Erosion
Sediment is set in motion by moving ice, and to a lesser degree melt water.
Glacial Transport
(3)
- Supra-glacial (on the ice)
- Englacial (in the ice)
- Subglacial (beneath the ice)
how does sediment get into the ice?
- buried by snow
- ice and sediment at the base was deflected upwards as the glacier moved
How/When does Glacial Deposition occur? Where?
This occurs most often when the ice melts. It may also occur when sediment beneath the moving ice becomes detached and is left behind by the ice.
This can happen in:
- Hollows in the bedrock
- Behind obstructions
- when the sediment becomes too thick/heavy to move
- When sediment is frozen to the underlying bedrock.
Glacial deposition
This happens when sediment is left behind by the glacier, often beneath it, or when the ice melts.
Till (4)
- A poorly sorted, coarse sediment
- often with a bi-modal grain size distribution
- and a massive structure
- that is deposited in contact with a glacier - underneath it or next to it.
Bi-modal grain size distribution (TILL)
Means that it has two sizes.
- large (result of frost action)
- small (result of abrasion)
Massive structure (TILL)
all the grain sizes are uniformly mixed.
What happens when till is deposited?
It forms a number of landforms
Ablation till
Till deposited at the edge of a glacier
- Not compressed
- May show signs of having been reworked by running water
Lodgment till
Till deposited beneath a glacier.
- It is compressed
- may be deformed by the ice passing over the top of it
- langara is built on lodgement till
Glacial Landforms
- horns
- cirques
- u-shaped valley
- moraine
- truncated spur
- spur
- hanging valley
- drumlin
- col
- arete
Moraines
Long linear ridges composed of till and deposited at the edge of a glacier.
Types of moraine (4)
- lateral
- terminal
- recessional
- medial
Terminal
Marks the furthest advance of the glacier.
Recessional moraine
Marks the position of the front of the glacier during its retreat.
Medial moraine
Form when two lateral moraines merge. Medial moraines are found “within” the glacier when two other glaciers merge.
Moraines can be found in what settings? Differences?
Continental glacial and alpine glacial settings. In continental settings, moraines can be quite big.
Moraines in continental settings
There are large till plains instead of well defined ridges that form moraines.
Till plains
Area of land covered in till. They often have irregular or hummocky topography.
Hummocky topography
Defined by many closely spaced highs and lows.
Result of different rates of deposition.
Factors affecting the formation of hummocky topography
Different rates of ice released by the glacier will also affect topography as they melt.
As a glacier melts it may leave blocks of ice stranded on the ground in front of it. This ice block may be completely or partially buried by sediment (till) from the glacier.
When this ice block melts a basin or depression is left behind.
If his basin fills with water it is a kettle lake.
Drumlins
An asymmetrical teardrop shaped hill composed of till that is deposited beneath an advancing ice sheet.
- lodgment till
How are drumlins found?
Drumlins are found in swarms of many closely spread Drummond in continental glacier settings.
Erosional Alpine Glacier Landforms
Horns
Cirques
U shaped valleys
Hanging valleys
Arêtes
Cols
Truncated spurs
Horn
A tall, pointed mountain formed by glacial erosion.
Cirque
A bowl-shaped depression on the side of a mountain formed by a cirque glacier. Roughly As long as it is wide
Tarn
The lake that sometimes occupies the cirque once all the ice has melted.
U-shaped valley
A long alpine valley with steep sides and a flat bottom carved by the passage of a valley glacier. It is longer than it is wide.
Hanging valley
This occurs when a small u-shaped valley merges with a larger u-shaped valley. The smaller valley that is suspended above the other is the hanging valley.
Arête
A sharp, continuous, linear ridge. Typically horizontal.
Col
A low point or “mountain pass” often found between two horns or on an arête.
spur
A spur is a sharp ridge that begins at a mountain peak (a horn) and drops in elevation away from the peak.
Truncated spur
The truncated spur is one that has been cut off or eroded by the passage of an alpine glacier.
Products of continental glacial till deposition
Moraines and drumlins
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Pieces of glacial ice carried into the lake contains larger rock fragments when this ice melts the rock fragments are released and they drop to the bottom where they become part of the deposit.
Varve
layers of clay and silt of contrasting color and texture that represent the deposit of a single year (summer and winter). It is made up of pairs of summer and winter layers AND dropstones.
Periglacial environment
an environment that includes cold temperatures but a glacier is not present. the most common feature is permafrost.
Permafrost
Ground that has been frozen for at least 2 years.
In all permafrost regions you can find two layers in the ground
Active layer and permafrost layer underneath it
Active Layer (permafrost)
surface layer that thaws during the summer
Permafrost layer depth
may extend to a depth of several 100 metres.
Permafrost composition
can be:
- frozen rock
- mineral
- organic sediment (peat) that may or may not contain water
When water is frozen, it expands by _%
9%
Why is water important to permafrost landform formation?
When ice forms the ground around it is heaved or pushed upward.
Pingos
Ice cored hills formed by the growth of an ice lens inside.
Patterned ground (i.e. rock circles)
the result of the different way large and small rock fragments respond to repeated freezing and thawing cycles where the ground is expanding and contracting.
What happens when the permafrost ice melts?
liquid water is different from ice in that it has heat and it can move. when ice melts the ground contract/collapses and may start to move as a flow. may melt more of the permafrost as it moves.
Vegetation’s role in permafrost environments
insulates the ground beneath.
constructing a pipeline in a periglacial environment
for an oil pipeline it is necessary to build it above ground the warmer oil is separated from the permafrost beneath it.
As a result cold was entering the ground through the steel supports and ice lenses grew around the supports, and heaving the ground around them. So the supports themselves have to be heated to sustain itself.
The last ice age
The last ice age began aprox. 1.65 million years ago and ended aprox. 10,000 years ago
Causes of the last ice age
- Variations in the amount of solar radiation (heat) received by the Earth
- Plate tectonics ( isolation of the polar regions)
- Removal of atmospheric CO2 due to increased weathering in the Himalaya.
Variations in the amount of solar radiation that caused the last ice age were a results of:
- changes in the size of the Earth’s orbit around the sun
- change in the tilt of the Earth axis
- change in the wobble of the Earth’s axis.
Plate tectonics as a cause of ice age
caused isolation of polar regions from warmer ocean currents so that cold temperatures can persist.
also caused the formation of the isthmus of panama. This helped form the warm Gulf Stream current that made possible the snow fall in the north, forming glaciers.
Removal of atmospheric CO2 as a cause of ice age
Removal of atmospheric CO2 due to increased weathering in the Himalayas because of a change in the monsoon
