Glaciation Flashcards

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1
Q

What is a glacier

A

Slowly moving mass or river of ice formed by the accumulation of snow on mountains or near the poles

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2
Q

Ice cap

A

Mass that covers less than 50,000 km of land area

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3
Q

Ice sheet

A

Mass of glacier that covers surrounding terrain and is greater than 50,000 km2

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4
Q

Quaternary period

A

Last c.2 million years

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5
Q

Pleistocene epoch

A

From 11,700-1.8 million years bp

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6
Q

Holocene epoch

A

Last 11,700 years

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7
Q

Describe the Pleistocene

A
  • at the time the continents had moved to their current positions
  • sheets of ice covered all of Antarctica, large parts of Europe, North America , South America and small areas inn Asia
    -consisted of about 20 cycles of glaciers retreating and thawing
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8
Q

Evidence for climate change

A

-ice cores:ice cores contain information about past temperatures and many other aspects of the environment. They enclose small bubbles of air that contains sample of the atmosphere(co2 levels indicate global temperatures at the time
-oxygen isotopes: they indicate past climatic conditions. The technique involves the ratio between heavy and light oxygen in marine sediments

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9
Q

Eccentricity

A

Earths orbit moving from circular to more elliptical, changing the amount of radiation the Earth receives. Occurs every 100,000 years

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10
Q

Obliquity

A

Tilt of the earths axis which affects the earths seasonal extent . Occurs every 41,000 years

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11
Q

Precession

A

The direction of the earths axis rotation it affects the timings of the seasons . It occurs every 21,000 years

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12
Q

Other causes of climate change

A
  • volcanic activity as it lowers global temperatures
    -variations in sunspot activity as sunspot activity significantly affects our climate
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13
Q

Periglacial environment

A

Cold climate typically near glacial regions,often marginal to a glacial environment and is subject to intense cycles of freezing and thawing

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14
Q

List the types of permafrost

A

Continuous
Discontinuous
Sporadic

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15
Q

Permafrost

A

Where the ground is frozen for more than 2 years in a row

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16
Q

Continuous permafrost

A

Sheet of frozen material

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17
Q

Discontinues permafrost

A

Where the permafrost melts partially, usually the lower layer remains frozen

18
Q

Sporadic permafrost

A

Occurs at margins of periglacial environments and is usually very fragmented and only a few meters thick

19
Q

Characteristics of periglacial environments

A

-found close to glacial environments
-characterised by permafrost and cycles of intense freezing and thawing
- talik( upper part ) may thaw

20
Q

Periglacial environments

A
  • frost heave: the concentration and cracking of rapidly freezing soils in which ice wedges and patterned ground are formed
    -suction: the migration of sub surface water to the freezing front which causes the formation of ice lens and pingos
    -solifluction: the mass movement of the saturated active layer downslope, largely by gravity,which leads to lobes and terraces
  • frost shattering(freeze thaw ): it is the 9% water expansion of water upon freezing which forms block fields and screes
    -wind erosion: high winds disturb sediment which can build up in certain areas to create loess deposits
21
Q

Formation of glaciers

A
  • Snow accumulates and compacts into an upland nivation hollow.
  • Over 3-4yrs, water is squeezed out of the ice, percolates down and refreezes onto the bottom of
    the glacier (firn/nevé).
  • Gravity and the weight of the ice above will gradually further compact the ice until it becomes
    glacier ice.
  • The glacier will then begin to flow over the lip as a result of gravity and the gradient of the
    underlying slope.
22
Q

Glacier mass balance

A

The net difference between accumulation and ablation over the course of one year

23
Q

Basal slippage

A

Lower ice melts allowing glacier to move as one body (temperate glaciers)

24
Q

Deformation

A

Individual ice crystals moving within the glacier. Ice at the surface and in the middle of glacier move faster due to less friction (temperate and polar glaciers).

25
Q

Compressional flow

A

Reduction in gradient leads to glacier de-acceleration so ice thickens.

26
Q

Extensional flow

A

Gradient becomes steeper so glacier accelerates, and ice thins.

27
Q

Rotational flow

A

Ice in cirque pivots around a point which deepens corrie floor

28
Q

Regelation creep

A

Due to pressure melting point (melting point drops below 0 degrees), water melts, flows to an area of less pressure and re-freezes

29
Q

Glacial surge

A

Excessive build up of meltwater leads to ice moving forward rapidly.

30
Q

Factors affecting rate of movement

A

-thickness : a glacier moves because pressure generated by its own weight causes it to deform and/or slide, consequently, thick glaciers often flow faster than thinner glaciers.
- temperature: : in general, temperate glaciers flow at greater velocities than polar glaciers. This is because temperate glacial ice is warmer and is therefore able to deform more easily and, further, the presence of meltwater at their base promotes basal sliding
-bedrock: more rapid movement occurs over easily deformable rock, such as clay or shale, because bedrock deformation increases the rate of basal sliding. Greater velocities also occur over impermeable rock surfaces as compared to permeable since the percolation of meltwater into permeable rock masses will reduce lubrication at the ice/rock interface and retard flow.
- gradient: glaciers with steep surface gradient flow faster than those with gentler gradients, since the former are affected by greater gravitational forces.
-bedrock permeability: temperate glaciers move faster over impermeable surfaces as basal meltwater is retained – aiding slippage.

31
Q

Erosional processes

A

Abrasion=occurs when rocks and stoned become embedded in the base and sides of the glacier. These are then rubbed against the bedrock as the glacier moved. This causes the wearing away of the landscape as the glacier behaves like sandpaper

Plucking =occurs when rocks and stones become frozen to the base or sides of the glacier and are plucked from the groud or rock face as the glacier moves. It leaves behind a jagged landscape

32
Q

3 types of glacial transportation

A

-supra-glacial:it is mainly weathered material,carried on top of a glacier
-englacial:formally supraglacial material,but now carried by fresh snowfall and carried within the ice
-subglacial:is the material carried below the ice,which is dragged and pulverised by the overlying glacier.

33
Q

List the different glacial landform environments

A

-periglacial: exist at the edges of the glaciers and can be extensive in scale.Landforms which occur here are macro scale
-glacial:within the actual physical mass of the glacier ice,forming the glacier system,wichury includes the proces of flotę ,erosion and deposition
-marginal-at the side or end of the glacier.weathering and deposition operate here to create landforms such as moraines
-proglacial-in front of ,at,or immediately beyond the margin of a glacier.Fluvioglacial processes operate here,creating outwash plains , meltwater channels and proglacial lakes.

34
Q

Causes of glacial deposition

A
  • as a result of ice melt , mainly in the ablation zone
    -when the glacier lacks the energy to continue to transport the material being carried
35
Q

Glacial drift

A

Collective name for all the sediments and debris deposited under glacial conditions

36
Q

Till

A

Material directly deposited by the glacier , such as moraines and intra-glacial material dropped in situ by retreating ice

37
Q

Landforms formed by cirque glaciers

A

-cirques,arêtes and pyramidal peaks

38
Q

Landforms formed by valley glaciers

A

-u shaped valley
-truncated spurs
-hanging Valleys
-ribbon lakes

39
Q

Landforms formed by ice sheet scouring

A

-basins
-knock and lochans
-Roche moutoness

40
Q

Formation of a cirque glacier

A

Snow accumulates in a nivation hollow where nivation processes enlarge and deepen it.As more ice accumulates ,over time it forms into glacier ice and begins to flow forming a cirque glacier.Freeze thaw weathering loosens material which is entrained and gathers as sub glacial basal ice.The rotational flow of the glacier deepens it while plucking of the back wall erodes it backwards creating an armed chair shape.Deposition take place where flow is weakest and a lip can form on the edge of the cirque.when the glacier retreats and melts it often fills with water to create a tarn.
When 2 cirques erode back it creates a knife edge ridge called an arête,whereas where 3 or more erode back it creates a pyramidal peak