Glacial Geomorphology

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Glacial Geomorphology

• Lab 10

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Concepts

• Glacier Formation
• Accumulation and Ablation, Sublimation
• Movement
• Glacial Mass Balance
• Categories of Glaciers
• Where were they located? (Last Ice Age)
• Where are they located now?
• Glacial Processes
• Continental Landforms
• Those formed by deposition
• Alpine Landforms
• Those formed by deposition
• Those formed by erosion

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Glacier Formation

• Large, long-lasting accumulation of snow ice
  that develop on land
• Time passes ice mass begins moving due to pull
  of gravity
• Periods of
• ADVANCING (cold temps moisture accumulation)
• RETREATING (warm temps melting)

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Glacier FormationZones of Accumulation Ablation

• Zone of Accumulation
• Area where glacier is gaining precipitation
• Upslope higher elevations
• Zone of Ablation
• Area where glacier is melting
• Downslope lower elevations
• Sublimation occurs when ice is directly changed
  into water vapor (skips the steps of the ice
  actually melting and changing to water, then
  evaporating)

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Glacier FormationMovement

• To be called glacier, mass of ice must be
  capable of MOVEMENT.
• Movement within glacier is not uniform.
• Middle and top of glacier moves faster than sides
  and bottom.

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Glacier FormationMovement Advancing Retreating
http//www.wwnorton.com/earth/egeo/animations/ch18
.htm Animation 18.1 (Glacial Advance Retreat)
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Glacier FormationGlacial Mass Balance

• Calculated by the difference in amount of snow
  accumulated (winter) and the snow melted
  (summer).
• Snow accumulated gt Melted snow,mass balance is
  positive and the glacier has increased in volume.
• Melted snow gt Snow accumulated,mass balance is
  negative and the glacier volume decreased.
• Reported in equiv. meters of water.

Measuring thickness in a crevasse
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Categories of Glaciers

• Continental
• Largest type only 2 exist
• ANTARCTICA and GREENLAND
• Surface coverage of at least 2M sq. miles
• Mountain/Alpine
• Occupies a U-shaped valley on a mountain

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Categories of GlaciersLast Ice Age Where were
they located?

• 2 MYA (Pleistocene), max extent 1/3 land covered
• Now 10 land covered
• 96 glacial ice is tied up in Antarctica
  Greenland

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Categories of GlaciersWhere are they located now?
0o
0o
0o
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Glacial Processes

• 1. Erosion
• Erosion is possibledue to presence of till
• Combination of all sizes ofsediments (pebbles
  toboulders) carried withinglacier and
  eventuallydeposited.
• 2. Transportation Deposition
• 3. Glaciofluvial

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Glacial ProcessesErosion

• Plucking
• Water gets in cracks, freezes, lifts up bits of
  rock and carries them in the glacier itself
• Leaves a blocky and irregular surface
• Scouring
• Abrasive action of rocks within glacier as
  glacier moves over surface
• Leaves striated surface
• Enough scouringcreates a polished surface

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Glacial ProcessesTransportation Deposition

• Debris within glacier transported
• Debris ahead or to sides of glacier deposited
• Moraines form when till gets pushed into linear
  piles by the movement of a glacier.

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Glacial ProcessesGlaciofluvial

• Meltwaters can deposit materials far away from
  the glacier
• Braided streams are formed think of all that
  till moving inside the glacier, and what happens
  to it as it is carried by meltwaters.
• If needed go back tothe Fluvial
  Geomorphologynotes (Lab 8) and reviewhow
  braided streams areformed.

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Continental GlaciersGreenland Antarctica
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Continental GlaciersFeatures

• All formed by deposition of materials
• Moraines
• Kames
• Kettles/Kettle Ponds
• Braided Outwash Streams

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Continental GlaciersDepositional Features
Moraines

• Concentrated line of till
• Numerous types of moraines, 2 associated with
  continental glaciers
• Terminal Morainemarks the maximumextent of the
  glacier
• Recessional Morainedevelops behind theterminal
  moraine asthe glacier retreats

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Continental GlaciersDepositional Features
Moraines
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Continental GlaciersDepositional Features Kames

• Steep-sided, conical hill of debris that
  originally collected in a hole in the glacier.

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Continental GlaciersDepositional Features
Kettles

• Large chunks of ice leave a depression in the
  landscape because
• Isolated ice issurrounded by till(which
  becomespart of thelandscape).Ice melts
  leavinga depression.
• If filled with water,called kettle lakes

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Continental GlaciersDepositional Features
Glacial Outwash Meltwater
Note how braided streams form when glacial
meltwater passes through the moraines and picks
up till. It will eventually drop this till into
channel bars and begin flowing around them,
forming braids.
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Alpine Glaciers
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Alpine GlaciersFeatures due to Deposition

• Erratics
• Moraines
• Terminal
• Recessional
• Medial
• Lateral

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Alpine GlaciersDepositional Features Erratics

• Boulders that are carried far from their place of
  origin by a glacier

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Alpine GlaciersDepositional Features Moraines

• Lateral Moraines

Medial Moraine Will often form when two glaciers
meet and continue down a valley
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Alpine GlaciersDepositional Features Moraines
(cont)
Note End moraines are more commonly called
Terminal and Recessional moraines.Which is
which in this example?
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Alpine GlaciersFeatures due to Erosion

• Cirque
• Tarn
• Horn
• Arete
• Glacial Valley
• Hanging Valley
• PaternosterLakes

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Alpine GlaciersErosional Features Cirques

• Bowl-shaped depression (think amphitheatre)
• Area where snow first accumulates and modifies
  into glacial ice

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Alpine GlaciersErosional Features Tarns

• After a glacier is no longer present, a lake may
  form in a cirque

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Alpine GlaciersErosional Features Horns

• Pyramidal peak that forms when cirques chisel a
  mountain from 3 sides

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Alpine GlaciersErosional Features Aretes

• Narrow ridge
• Formed when two glaciers move down valleys and
  erode the area between them into a ridge

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Alpine GlaciersErosional Features Glacial Valley

• Valleys become deeper wider over time
• Guide the path of glacial ice flow
• U-Shaped

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Alpine GlaciersErosional Features Hanging Valley

• When smaller valleys join with larger glacial
  valleys, the floors are not at the same elevation
• Waterfalls are often present here

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Alpine GlaciersErosional Features Paternoster
Lakes

• Chain of tarns that are formed when a valley
  steps down
• Lakes are all connected by streams and/or
  waterfalls