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EASC 225 (Geomorphology) > Topic 4: Glacial systems > Flashcards

Topic 4: Glacial systems Flashcards

1
Q

What is a glacier? Some important characteristics

A
  • body of ice, minimum of 30 meters thick
  • flows under its own weight, doesn’t need gravity to move
  • acts as a freshwater bank, and is a part of the water system
  • A large part of Earths albedo system - cools down the earth
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2
Q

What are 3 sections of a glacier?

A
  • zone of ablation
  • equilibrium line
  • zone of accumulation
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3
Q

What is the zone of ablation? zone of accumulation?

A

Ablation: Where the glacier is loosing ice, melting (edges/front)

Accumulation: where snow falls, accumulates, and crystalizes into ice (center)

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4
Q

What are the three ways to classify glaciers based on temperature?

A

Cold based: Ice is frozen to the bed, basal temperature below pressure melting point

warm based: basal temperatures at pressure melting point

polythermal: variable bed conditions result in both warm and cold based components

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5
Q

What are the three ways to classify glaciers based on topography?

A

Plateau ice caps: cover plateaus and feed valley glaciers

ice sheets: Not constrained by topography, motion driven by mass balance

valley glaciers: Strongly controlled by topography

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6
Q

What does MIS stand for?

A
  • Marine Isotope Stages
  • Stages derived from paleoclimate records from marine cores
  • sediment that gets accumulated at the bottom of the sea and doesn’t get disturbed
  • these sediments are filled with marine organisms, which we can radio carbon date
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7
Q

What is a climate proxie?

A
  • some kind of sediment or material that was can test to determine approximate climates in the past
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8
Q

What does high levels of 18O oxygen isotopes in shells suggest? High levels of 16O?

A

18O: cold climate, glacial period

16O: warm climate, interglacial period

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9
Q

What was MIS2?

A
  • our last glacial period
  • dubbed the ‘wisconsinan’
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10
Q

What was the Laurentide ice sheet?

A
  • large ice sheet that developed at the beginning of MIS2
  • covered a majority of canada, parts of the US
  • at times, was connected with the Cordilleran ice sheet, when they started melting they developed a ‘corridor’ between them
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11
Q

In general, the closer we got to the Holocene, what were the climate patterns?

A
  • 2.5 million yrs ago was warmer, even glacial periods were much warmer than our most recent ice ages
  • as we got closer to the holocene, we got cooler/more intense climate, and periods of glacials and interglaicals were more spaced out
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12
Q

What is the LGM?

A
  • Last glacial maximum
  • our last glacial period (MIS2)
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13
Q

How much of the earth today is covered by glaciers?

A

10%

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14
Q
  • glaciers form where…..
A

climate and topography permit accumulation to exceed ablation

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15
Q

glaciers today are controlled by

A
  • elevation, aspect, and continentality….
  • which pretty much means temperature and precipitation
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16
Q

Why do we study glaciers?

A
  • can discover records of past environments from ice cores
  • help us project future climate scenarios
  • helps us study hydrology, the source of rivers and sea levels
17
Q

What are direct glacial geomorphology processes? Proglacial?

A

glacial: Ice, erosion, deposition

proglacial: water, deposition ad erosion by melt water, wind

18
Q

What does “proglacial” mean

A

processes occurring next to/in front of the glacier

19
Q

How is glacial ice formed?

A
  • snow is compressed by weight of more snow falling on top of it
  • snow is compressed into firm crystals
  • further compressed into glacial ice
20
Q

Why would the line of equilibrium on a glacial move?

A

if climate/weather changes

21
Q

If accumulation is greater than ablation, a glacier will

A

advance

22
Q

What are the 2 types of glacier motion?

A

Internal deformation: occurs with both warm and cold-based glaciers, but this is the only way a cold-based glacier will move (all glaciers do this!!)

Basal sliding: only occurs for warm-based ice, tied to presence of water at base

23
Q

What is ice flow or creep?

A
  • type of internal deformation in glaciers
  • result of stress and strain
  • the strain of the ice under the load stress
24
Q

in glaciers, strain _______ with depth, and motions due to internal deformation ___________ with depth

A

in glaciers, strain increases with depth, and motions due to internal deformation decreases with depth

25
Q

What is glens law?

A
  • law detailing the relationship between creep and stress for ice
  • e = AT^n
  • strain is determined by temperature (hardness), shear stress, and an exponent related to ice properties (n=3)
  • Warm ice flows faster than cold ice (the colder or harder the ice, the harder it is to move)
26
Q

Why does motion due to internal deformation increase as you get closer to the top of a glacier?

A
  • glaciers will move faster at the top due to internal deformation because of a piggy-back effect
  • ice overlying inherits motion of underlying ice, and intended deformation to that depth
  • these effects stack on top of each other
27
Q

what is a consequence of internal deformation?

A
  • crevasses
  • these are essentially ‘cracks’ in the rigid layer at the top of a glacier that occur due to internal deformation
28
Q

what is the only way a cold-bed glacier can move?

A

internal deformation

29
Q

Warm bed glaciers can move by 2 ways:

A
  • internal deformation
  • basal sliding
30
Q

What type of movement by glaciers disrupts the bed?

A
  • basal sliding, as it is actually moving across a landscape, and the ice scraps the ground and leaves impressions
31
Q

What is basal sliding? How does it work?

A
  • type of movement by warm-bed glaciers
  • motion at the BED of the glacier due to sliding
  • largely proportional to the amount of water at the bed
  • contributes much more glacial motion than internal deformation!!!
32
Q

What is sub-glacial deformation?

A
  • extension of basal sliding
  • motion due to strain in bed below the glacier-bed interface
  • dependent on the shear-strength of the bed
  • water layer of warm-bed glaciers seeps into bedrock, cohesiveness of ground material will decrease, bed moves
33
Q

What is abrasion?

A
  • an erosional process of glaciers
  • friction interaction between bed and debris-rich zone at the base of ice!
  • material gets ‘picked up’ by ice and sandpapers the ground
34
Q

What is plucking/quarrying?

A
  • erosional process of glaciers
  • larger blocks of bedrock picked up due to pressure differential
  • ice flows over obstacle, pressure changes, sucks up material to equalize pressure
  • only occurs in warm-bed glaciers
35
Q

What is regelation/entrainment?

A
  • an erosional process of glaciers
  • where a glacier has material at bed, and as it re-freezes at base of ice, it ‘sucks up’ the material
36
Q

described the three areas where free water may accumulate at the base of a glacier

A
  • Nye channels - Inside the bed of ground
  • R-channels - within the glacier, ontop of the bed
  • Clarke channels - both areas, in-between
37
Q

What are striations? how are they caused?

A
  • erosional landforms caused by glaciers
  • abrasion occurs, caused by basal sliding of clasts in contact with the bed
  • orientation indicates the direction of glacier movement

EASC 225 (Geomorphology) (4 decks)

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