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GLGY 201 > Glaciers > Flashcards

Glaciers Flashcards

1
Q

Glaciers

A
  • Thick masses of recrystallized ice (from snow) that lasts all year long, flow via gravity, and can be in the form of mountains or spread continentally
  • Presently cover about 10% of the Earth, expands to 30% during ice ages (most recent ice age ended 11ka)
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2
Q

How a glacier forms

A
  • Snowfall accumulates and survives the following summer
  • Snow is transformed into ice
  • May occur rapidly (10s of years) or slowly (1000s of years)
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3
Q

Three conditions necessary to form a glacier

A
  1. Cold local climate
  2. Snow must be abundant; more snow must fall than melt
  3. Snow must not be removed by avalanches or wind
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4
Q

Two types of glaciers

A

Alpine (Mountains) and Continental (Ice Sheets)

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5
Q

Alpine glaciers

A

From high to low elevation in mountain settings
Many types:
- Cirque glaciers that fill mountain-top bowls
- Valley glaciers
- Ice caps covering peaks and ridges
- Piedmonts glaciers spreading out at the end of valleys

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6
Q

Continental Glaciers (Ice Sheets)

A
  • Vast ice sheets covering large land areas
  • Ice flows outward from the thickest part of the sheet
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7
Q

Where are the two major ice sheets that still remain on earth?

A

Greenland and Antarctica

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8
Q

How do glaciers move?

A
  • Basal sliding - significant quantities of meltwater form at the base of the glacier, water decreases friction, and ice slides along the substrate)
  • Plastic deformation - occurs below 60 m depth, grains of ice change shape slowly, crevasses form at the surface because the upper layer is too brittle to flow)
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9
Q

Why do glaciers move?

A

The pull of gravity is strong enough to make ice flow, which can cause the glacier to move down a slope or the ice at the base of the glacier can flow up a local incline
Ice sheets are also thicker in the middle, so they slowly spread toward the edges

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10
Q

Factors affecting the rate of movement of glacial ice

A
  • rates vary from 10 to 300 m. per year, sometimes (rarely) 20 to 110 m per day
  • Steeper slopes = faster movement
  • Basal water (wet bottom) = faster movement
  • Location within the glacier (Greater velocity in ice center, friction slows ice at margins
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11
Q

Zone of accumulation

A

Area of net snow addition (the area that is gaining mass)
- Colder temperatures prevent melting
- Snow remains across the summer months

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12
Q

Zone of ablation

A

Area of net ice loss (area that is losing mass)

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13
Q

Where do zone of ablation and zone of accumulation meet?

A

At the equilibrium line

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14
Q

Toe of the glacier and how it relates to the zone of ablation and zone of accumulation

A

The leading edge of a glacier
If accumulation = ablation, the toe stays in the same place
If accumulation > ablation, the toe advances (spreads down)
If accumulation < ablation, the toe will retreat upslope

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15
Q

Tidewater glaciers

A

Valley glaciers entering the sea

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16
Q

Ice shelves

A

Continental glaciers entering the sea

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17
Q

Sea ice

A

Nonglacial ice formed of frozen seawater

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18
Q

Iceberg

A
  • Usually fourth-fifths beneath the waterline
  • Icebergs are always greater than 6 m above the water
  • Ice shelves yield tabular bergs
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19
Q

How do glaciers change landscapes?

A

Erosion, transport, deposition

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20
Q

Glacial erosion and its products

A

Glaciers carve deep valleys, such as Yosemite Valley
- Polished granite domes and vertical cliffs are the results of glacial erosion
Glacial abrasion - a “sandpaper” effect on substrate
- Substrate is pulverized to fine “rock flour”
- Sand in moving ice abrades and polishes
- Large rocks dragged across bedrock gouge striations
- Run parallel to the direction of ice movement

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21
Q

Erosional features of glaciated valleys (7)

A

-Cirques
- tarns
- aretes
- horns
- u-shaped valleys
- hanging valleys
- fjords

22
Q

Cirques

A

Bowl-shaped basins high on a mountain
- Form at the uppermost portion of a glacial valley
- After ice melts, cirque often supports a tarn (lake)

23
Q

Arete

A

A “knife-edge” ridge
- formed by two cirques that have eroded toward one another

24
Q

Horn

A

A pointed mountain peak
- formed by three or more cirques that surround the peak

25
Q

U-shaped valleys

A

Glacial erosion creates a distinctive trough
- Relative to V-shaped fluvial valleys
- Constant erosion everywhere

26
Q

Hanging valleys

A
  • Intersection of the tributary glacier with trunk glacier
  • Trunk glacier incises deeper into bedrock
  • Throughs have different elevations
  • Often results in waterfalls
27
Q

Fjords

A
  • U-shaped glacial troughs flooded by the sea
  • Accentuated by isostatic rebound
28
Q

Roche Mountonee

A

Asymmetric ice hill
- Glaciers can erode by plucking
- Ice freezes around bedrock fragments and plucks chunks as the glacier advances

29
Q

End moraine

A

Debris at toe of a glacier

30
Q

Moraines

A

Unsorted debris deposited by a glacier

31
Q

Lateral moraines

A

Form along the flank of a valley glacier

32
Q

Medial moraines

A

Mid-ice moraine from merging of lateral moraines

33
Q

Types of glacial sedimentary deposits from glacial drifts (6)

A
  • Glacial till
  • erratic
  • glacial marine sediments
  • glacial outwash
  • loess
  • glacial lake-bed sediment
34
Q

Stratified vs Unstratified drift

A

Stratified drift is water sorted, unstratified is not sorted

35
Q

Glacial till

A

Sediment dropped by glacial ice
- Consists of all grain sizes - boulders to clay
- Unmodified by water: Unsorted and Unstratified
- Accumulates: beneath glacial ice, at the toe of a glacier, along glacial flanks

36
Q

Erratics

A

Boulders dropped by glacial ice and carried through long distances; rocks existing where they don’t “belong:

37
Q

Glacial marine deposits (Carving vs Melting Icebergs)

A

Sediments from an oceanic glacier
- Calving iceberg rafts sediments
- Melting iceberg deposits drop stones

38
Q

Glacial outwash

A

Sediments transported by meltwater
- Mud is removed
- Sizes graded and stratified
- Grains abraded and rounded
- Dominated by sand and gravel

39
Q

Glacial lake-bed sediment

A

Fine rock flour settles out of suspension in deep lakes
Muds display seasonal varve couplets (seasonal variations in depositional sequences)
- Finest silt and clay: winter
- Coarser silt and sand: summer

40
Q

Loess

A

Wind-transported silt

41
Q

Glacial depositional landforms (7)

A
  • End moraines
  • terminal moraines
  • recessional moraines
  • ground moraines
  • drumlins
  • kettle lakes
  • eskers
42
Q

Where / how do end, terminal, and recessional moraines form?

A

End - the stable toe of the glacier
Terminal - farthest edge of the flow
Recessional - form as retreating ice stalls

43
Q

How do kettle lakes form?

A

They form from stranded ice blocks

44
Q

Drumlin

A

Long, aligned hills of molded till
- Asymmetric form
- Commonly occur as swarm aligned parallel to flow direction

45
Q

Eskers

A

Long, sinuous ridges of sand and gravel that form as meltwater channels within or below ice; channel sediment is released when the ice melts

46
Q

Consequences of continental glaciation in relation to earth’s mechanical layers

A

Ice loading and glacial rebound
- Ice sheets depress the lithosphere
- Slow crustal subsidence follows the flow of asthenosphere
- After ice melts, depressed lithosphere rebounds
- Glacial rebound continues today

47
Q

What happens to sea level during ice age and deglaciation?

A

Ice age - sea level falls
Deglaciation - sea level rises
If ice sheets melted, coastal regions would be flooded

48
Q

Pluvial features

A

Large lakes formed during ice age

49
Q

Periglacial environments

A

(near ice)
Characterized by year-round frozen ground (permafrost)
Freeze-thaw cycles generate unusual patterned ground

50
Q

Pleistocene Ice Ages

A

All climate and vegetation belts were shifted southward
Giant beavers, sloths, and mammoths were the existing animals

GLGY 201 (24 decks)

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