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Mountains > Chapter 6 > Flashcards

Chapter 6 Flashcards

1
Q

What is the basic definition of glaciers

A
  • it is a mass of relatively slow moving ice
  • > created by the long term accumulation of snow
  • in mountain regions, glaciers form whenever snow accumulation during the winter exceeds that which is removed by melting during the summer
  • > the weight of accumulating residual snow eventually begins to convert the lower layers to ice as it is compressed and made denser
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2
Q

Describe the specifics of how glaciers form

A
  • compaction of the surviving snow under a mass of new snow
  • > this compaction causes the expulsion of air bubbles within the buried layers
  • after about two winters, residual snow turns into firn
  • > firn is an intermediate state between snow and glacier ice
  • > this usually occurs once its density is around 400 kilograms per cubic meter
  • when the firn density reaches 600 to 700 kg per cubic meter
  • > any air that hasn’t been squeezed out is now trapped as bubbles as the snow pack is sealed off
  • > firn becomes glacial ice when its density hits around 850 kg per cubic meter
  • > any remaining air bubbles are isolated from one another and locked into the ice
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3
Q

What is the color of firn

A

-if it has a whitish color

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4
Q

What is the color of glacial ice

A

-if it has a bluish color

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5
Q

What are the shapes of the snow crystals

A
  • very complex shapes with intricate arms or branches when they fall from the sky
  • > once on the ground, they come into contact with one another
  • > once they connect, there are pore spaces left between them
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6
Q

Where does melting first occur in crystals

A
  • it occurs at the contact point between each snow crystal

- >melt water flows into the spaces between the crystals where the pressure is lower and the freezing point is higher

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7
Q

What is the process of sintering

A
  • when melt water flows into the spaces between the crystals where the pressure is lower and the freezing point is higher
  • > here water refreezes
  • > binds snow crystals together and enlarges individual grains
  • > with time and increased pressure, snow crystals tend to slowly interlock with each other and grow in size
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8
Q

How does snow to glacier ice form in dry snow zones

A
  • in dry snow zones, there is rarely any melting
  • > it is too cold for melting
  • instead there is the mechanical breakdown of snow crystals as they’re blown by the wind
  • > they are broken into smaller rounder, grains
  • > smaller, rounder grains pack together more efficiently
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9
Q

What are the largest glaciers on the planet known as

A
  • they are known as ice sheets
  • > they are found only in Antarctica and Greenland
  • note an ice sheet is a massive glacial land ice extending more than 50,000 square kilometres
  • > their flow is completely independent of the topography beneath
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10
Q

What mountains are the east and west Antarctic ice sheets separated by

A
  • they are separated by the Transantarctic mountains

- >but these mountains are almost completely buried by ice

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11
Q

What are iceacaps

A
  • they are miniature ice sheets covering less than 50,000 square kilometers
  • > they form primarily in the polar and sub-polar regions that are high in elevations
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12
Q

Are icecaps constrained by topographical features

A
  • no
  • > they lie over the top of mountains
  • > dome of an icecap is usually centered on the highest point of the massif
  • > ice flows away from this high point which is called the ice divide towards the icecap’s periphery
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13
Q

Are mountain glaciers confined to the topography of the landscape

A
  • yes
  • > unlike ice sheets or icecaps
  • > the largest type of mountain glacier is an icefield
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14
Q

What is the difference between an ice cap and an icefield

A

Icefield

  • > the flow of an icefield is constrained by the underlying topographic features
  • > eg; Columbia Icefield in the southern part of Jasper National Park
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15
Q

Valley glaciers

A
  • glaciers expanding from an icefield
  • they are sometimes referred to as outlet glaciers
  • can be very long
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16
Q

What is piedmont glacier

A
  • occur when steep valley glaciers spill into a relatively flat plain
  • > they fan out into bulblike lobes
  • > eg; Malaspina Glacier in southeastern Alaska
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17
Q

What are tidewater glaciers

A
  • they are valley glaciers
  • > that flow far enough to reach into the sea
  • > eg; Columbia Glacier in the Chugach Mountains
  • as the ice reaches the sea
  • > pieces break off, forming small icebergs
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18
Q

What are hanging glaciers

A
  • when a major valley glacier system retreats and thins
  • > tributary glaciers are left in smaller valleys high above the shrunken central glacier’s surface

-note these glaciers often terminate at or near the tops of cliff bands

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19
Q

What are circue glaciers

A
  • much smaller than valley glaciers
  • named for the isolated bowl-like hollows or basins they occupy(cirques)
  • they are typically found high on mountainsides and tend to be wider rather than longer
  • its survival requires snow deposited by avalanches from the surrounding rock walls
  • > walls also provide the glacier with some shade
  • > greatly reducing the direct solar radiation and limiting melting
  • > shading also limits the size of these glaciers, constraining the glacier to the shaded area
20
Q

How is material from a glacier removed

A
  • through surface melting, evaporation and glacier calving

- material added is annual input and material removed annual output

21
Q

How is mass balance calculated? What does it mean to have positive mass balance vs negative mass balance

A
  • annual input-annual output
  • positive mass balance=glaciel advance
  • negative mass balance=glacier shrinkage
  • steady state=glacier remains approximately the same size
22
Q

What is the accumulation zone and the ablation zone

A

Accumulation

  • > snowfall is greatest at the highest point in the glacier where it is the coldest
  • > here the annual input exceeds the output

Ablation

  • > output in the form of evaporation and melting exceeds the inputs
  • > here the annual mass balance is negative
23
Q

What is the area between the accumulation zone and the ablation zone

A
  • area of equilibrium
  • > it is the equilibrium line altitude
  • > where conditions favor glacial advancement, the ELA is low
  • > where conditions favor glacial retreat, the ELA is high
24
Q

What would happen if the glacier could not move

A
  • because of accumulation, the area above would get thicker and area below would get thinner
  • > the terminus would end up retreating further
25
Q

Who was the first one to record the observations that glaciers flowed

A
  • sveinn Palssen in 1794
  • > observed bow-shaped bands that are known as ogives
  • > he predicted that ice has some fluidity without actually melting
26
Q

What is the main reason glaciers flow

A
  • they flow due to gravity

- >the downward flow causes the ice to deform and flow downwards

27
Q

Are glaciers continually changing in surface area, shape, and slope over time

A

-yes

28
Q

Does ice flow towards the terminus

A
  • yes

- >the terminus position is moving back but the ice still moves down to the terminus

29
Q

What is basal sliding

A
  • slippage of ice over mass of rock

- >leaves striations on bedrocks below

30
Q

How does basal sliding

A
  • temperature of ice at the base

- presence of water to serve as lubricant

31
Q

Does balar sliding occur in polar regions

A
  • no
  • > since ice is frozen to the bedrock layer
  • in other regions, where the temperature is higher and there is water on the basal surface
  • > basal sliding is more pronounced
32
Q

What is bed deformation

A
  • ice is carried over time like a deforming carpet
  • flow rates due to ice deformation is constant
  • > it is due to gravity, ice thickness and slope angle
  • > but introducing water to this equation varies the flow rate greatly
  • > it isn’t just about these three factors anymore
33
Q

What is the Little Ice Age

A
  • it lasted from 1500 to 1850
  • > it was a short period of time
  • > a window when most of the world’s glaciers were actually advancing
  • > there was a great cultural shift in our understanding of glaciers and ice
34
Q

What are crevasses and why do they form

A

Crevasses

  • > deep cracks or fractures found in the glacier
  • > as opposed to crevices which form in rocks
  • they form due to tension stress
  • > so their distribution, size and arrangement provide useful information on the flow behavior of ice
35
Q

Do crevasses occur most often when the middle and the sides of the glacier move at different rates?

A
  • yes
  • > especially when ice curves around a bend
  • > or where the slope steeps and the rate of movement increases
36
Q

Are crevasses transverse or horizontal to the direction of flow?

A
  • yes

- >but they can be oriented really in any direction

37
Q

Are crevasses largely restricted to the surface

A
  • yes

- >where the ice is much more brittle and fractures more easily than down lower

38
Q

How does the presence of crevasses benefit glaciers

A
  • it increases the efficiency of rock transport
  • rock debris that falls into crevasses becomes incorporated into the glacier
  • > often not seen again until the glacier releases the material at the terminus
  • they also hasten ablation by increasing the glacier’s surface area
  • > by the pooling of melt water and by the disaggregating the ice near the terminus
39
Q

How do you protect yourself against crevasses when travelling over glaciers

A
  • when traveling over glaciers
  • > experiences mountaineers protect themselves with ropes and with harnesses
  • > they also regularly practice crevasse rescue scenarios and hire professional mountain guides
40
Q

What is a moraine

A
  • it is the linear accumulation of rocky debris oriented in the direction of the flow
  • > they are created when the glacier pushes or carries rocky debris as it moves
41
Q

hat are lateral moraines

A
  • vertical partitions between two ice masses

- >incorporated into the glacier

42
Q

Does the presence of moraines alter the mass balance

A
  • since the rock material is dark in color and can absorb more solar radiation
  • > so yes it does affect it
43
Q

Are glacial valleys trough shaped

A
  • yes

- >they are the most visible glaciated landforms

44
Q

Is there a glaciated valley in Yosemite National park

A

-yes

45
Q

What are aretes and horns

A

Aretes

  • > jagged narrow ridges where the backwall of two glaciers meet
  • > erode the ridge on both sides

Horns
->when glaciers erode the mountain to the point where a steep point is left on the top

Mountains (6 decks)

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