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Environmental Science > Glaciers > Flashcards

Glaciers Flashcards

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1
Q

Why study glaciers?

A
  • Glacial ice represents ~84% of earths fresh water

- Glacial deposits account for large areas of fertile soil in the Northern US and southern Canada

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2
Q

What is a glacier?

A

A glacier is an accumulation of snow and ice thick enough to flow under its own weight

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3
Q

What are the 3 types of glaciers?

A
  • Valley glacier
  • Ice sheet
  • Ice caps
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4
Q

Valley glaciers:

A

Are long, narrow glaciers confined to bedrock valleys that flow from high elevations to low elevations like a stream

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5
Q

Ice sheets:

A

Are unconfined glaciers larger than 50,000km squared. There are two ice sheets on earth in Greenland and the Antarctica

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6
Q

Ice caps:

A

Are unconfined glaciers that are smaller than ice sheets. Both ice sheets and ice caps exhibit radial flow

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7
Q

Where do glaciers form?

A

They form where snow persists year-round

  • High altitudes where temperatures are cooler than the surrounding country side
  • Snowline where the elevation above which snow persists throughout the year
  • High altitudes where seasons are colder
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8
Q

How thick are valley glaciers?

A

They are commonly 50-300 meters thick

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9
Q

How thick is an ice sheet?

A

The Antarctic ice sheet is as thick as 4km and contains 29 million km cubes of glacial ice

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10
Q

Snow metamorphism

A

Snow is a mineral that metamorphoses at temperatures and pressures close to Earth’s surface

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11
Q

Stages of snow metamorphism

A
  • Snowflakes turn to rounded ice grains and become more compact
  • Rounded grains recrystallize as contacting grains transfer molecules from one to another, diminishing air space
  • The result is interlocking crystals with a density of ~0.9gm/cm cubed
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12
Q

How long does it take for glacial ice to form?

A

In Alaska, hard ice has been found at 15m which are 3-5 years old

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13
Q

Areas such as Alaska have a ____ cycle

A

Freeze/thaw cycle

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14
Q

How do glaciers move?

A

They move faster in the middle and slower at the edges

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15
Q

Glaciers flow from the zone of ____ to the zone of ______ due to….

A

They flow from the zone of accumulation to the zone of wastage due to mass increase in the zone of accumulation

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16
Q

Which way do glaciers move?

A

They move downslope whether they are in advance or retreat at their toe

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17
Q

Glacial advance/retreat depends on…

A

The ratio of accumulation to wastage

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18
Q

The bottom temperature of a glacier is related to…

A

Sliding and sliding is related to erosion

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19
Q

Water lubricates which reduces…

A

Cohesion and friction

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20
Q

Water is pressurized by…

A

The weight of the overlying ice

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21
Q

Water pressure at the base of some glaciers is…

A

Nearly equal to the weight of the ice which substantially reduces friction by lifting the glacier off of the underlying rock

22
Q

How do glaciers erode and transport sediment?

A

Think of glaciers as “rivers of ice” they share similarities to rivers
- They flow downhill, erode sediment and transport it

23
Q

Where does erosion by glaciers happen?

A

Along the base, especially upslope where the ice is actively flowing downward, and along the valley walls

24
Q

Glaciers transport sediment along…

A

the base, within the ice, and atop the glacier due to mass wasting along the valley walls and by sediment exposure by thawing

25
Q

Where two glaciers meet…

A

their lateral moraines meet to form a medial moraine in the middle of the merged glacier

26
Q

Till

A

Is sediment directly deposited by the glacier. Cobbles often have edges and striations

27
Q

Outwash

A

Is sediment carried out by the meltwaters from a glacier. Cobbles are often stream-rounded

28
Q

How do glaciers deposit sediment?

A
  • Bottom sediment increases friction to the point where sediment sticks and bits are left behind
  • Fragments lodged in the ice or on the surface get left behind
  • Melting at the bottom of the glacier releases rock fragments frozen into the base of the flowing ice
29
Q

Meltwater streams

A

Deposit sediment alongside of and underneath the glacial ice forming sinuous ridges in the ice tunnels and channels that are left behind as benches and ridges

30
Q

Hoe do glaciers modify the landscape?

A
  • Glaciers do more erosive work than streams

- In some places, glaciers are the dominant force of creating landscapes, especially in high, cold, mountainous regions

31
Q

What are the 5 main glacial landscape features?

A
  • Moraines
  • U - shaped valleys
  • Knife edge ridges and pointed peaks
  • Overdeepened valleys forming glacial lakes
  • Hanging valleys
32
Q

Moraine

A
  • Any unconsolidated material dropped off by the glacier

- Composed of glacial till that is unsorted

33
Q

End moraine

A
  • Till at the end of the glacier

- the lowest elevation

34
Q

Medial Moraine

A
  • Middle of glacier

- Joining of lateral moraines where glaciers combine

35
Q

Lateral Moraine

A
  • Along the sides of a glacier

- A ridge of unconsolidated rock debris along the valley side.

36
Q

Crevasse

A
  • A crack in the upper 30 meters (100 feet) of a glacier

- often perpendicular to flow (not always)

37
Q

Arête

A
  • Narrow sharp ridges separating two valleys
38
Q

How do arêtes form?

A

From the erosion of two parallel valley glaciers OR erosion of two cirque glaciers headwards

39
Q

Horn

A
  • Meeting point of multiple cirques

- Forms a pyramidal peak

40
Q

Glacial Trough

A

A glacially eroded valley

41
Q

Hanging valleys:

A

Occur due to the more rapid erosion in the main glacier channel versus tributary channels causing a large vertical difference between the channels once the glacier melts

42
Q

What are the 4 main landscape features associated with ice sheets?

A
  • Large areas of scoured, plucked, and abraded rock surfaces
  • Large regions thickly covered by till
  • Streamlined ridges that parallel the direction of glacier movement
  • Landscape of countless lakes, ranging from small ponds to the largest lakes on Earth formed by erosional and depositional processes
43
Q

Drumlim:

A
  • Low oval hill made of deposited till
  • Upstream side is steep, downstream side is tapered
  • 100-5000m long
44
Q

Esker:

A
  • Narrow ridge of coarse sand and gravel, formed by subglacial meltwater channel
  • Sinuous but aligned parallel to glacial flow
  • Not always continuous
45
Q

Kettle:

A
  • Steep sided hole

- Formed by gradual melting of large ice block left behind by glacier over period while sediment accumulated around it

46
Q

Kame:

A
  • Any stratified ice deposit

- Deposited in openings within or between ice blocks

47
Q

What happens when glaciers reach the ocean?

A

Tide water glaciers

48
Q

Tide water glacier:

A

occurs when a glacier descends into the sea and does not float. But when it does, it becomes an ice shelf

49
Q

Icebergs

A

Are fragments that break off due to wave erosion oversteepening the face of the tidewater glacier

50
Q

Ice Shelf

A

Is a segment of a tidewater glacier that is sufficiently submerged to buoy up and float

51
Q

What must glacial ice be like in order to float on the ocean?

A

Glacial ice is nearly as dense as seawater, therefore it must be 9/10ths submerged before it can float

Environmental Science (12 decks)

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