Lecture 26 glaciers

Accumulations of glacial ice flow down slope under the influence of Flowing ice…... Norton How a glacier moves: Plastic flow... Norton How a glacier moves: Internal flow... Norton How

Chapter 12: Glaciers & glaciation

Chapter 12: Glaciers & glaciation

Today:

• Piedmont (small ice caps)

• Continental ice caps

 Part of Earth’s hydrological cycle

Fig 22.01 b

Stephen Marshak

Fig 22.04 a

W W Norton

Types of glaciers…

Fig 22.05 b

The Antarctic ice cap…

Fig 22.04 c

Stephen Marshak

Fig 22.06

At any given time, snow and ice accumulation

on the Earth varies with elevation and latitude.

Accumulations

of glacial ice flow down slope

under the influence of

Flowing ice…

Ice flows downhill under the influence of gravity.

The rate depends on thickness and slope.

Fig 22.11 c

W W Norton

Fig 22.11 b

W W Norton

How a glacier moves: Plastic flow.

Fig 22.10 b

W W Norton Modified from

Raymond, 1971

Velocity of ice flow is highest in the center

of the flowing mass and decreases to a minimum

where in contact with bedrock.

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Fig 22.08 b

W W Norton

How a glacier moves: Internal flow.

Cold glaciers

Fig 22.08 a

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How a glacier moves…basal slip.

Warm glaciers…

Fig 22.10 a

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Integrated model of glacier movement…

Glacier formation/movement

 Glacier “budget”

 Snowline

 Zone of wastage

Balance between accumulation

above snowline & loss (“ablation”)

Fig 22.13 a

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Whether a glacier is advancing or retreating depends

on the balance between accumulation at the head

of the glacier and ablation (loss) at the terminus.

Fig 22.13 b

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Short term glacial advances…

or “surges”

Two decades later…

Fig 22.13 c

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….23 years later

Short-term glacial retreat…

Fig 22.12

W W Norton

Fig 22.15 b

W W Norton Modified from

Skinner and Porter, 1995

The Antarctic ice cap advances and retreats on a seasonal basis…

Fig 22.15 d

Stephen Marshak

Fig 22.15 a

W W Norton

Glacial retreat by calving at terminus…

Glacial erosion

“Plucking” - glacier loosens/lifts/incorporates

fractured rock by the melting and freezing of ice in bedrock fractures.

Glacial erosion

2 ways: Plucking - Plucking glacier loosens/lifts/incorporates fractured rock

Abrasion - Glacier+rock fragments scrape over bedrock (like sandpaper), make rock flour

glacial striations

Fig 22.17 d

Stephen Marshak

Fig 22.17 c

Stephen Marshak

Fig 22.18 a

W W Norton

Begin with a young river valley system…

Fig 22.18 b

W W Norton

Global climate change leads to glaciation

Fig 22.18 c

W W Norton

Erosional landforms left behind by glaciers…

Glacially-eroded landforms

U-shaped valleys…

Fig 22.20

Stephen Marshak

valleys that were formed in

Glacially-eroded landforms

Tarns…

Lakes in shaped basins, (cirques) along

bowl-a glbowl-acibowl-al vbowl-alley…

Fig 22.17 b

W W Norton

Roche Moutonnees…

Forming truncated spurs and handing valleys…

Glacially-eroded landforms

Bridalveil Falls Yosemite, CA

Hanging Valleys…

Glacially-eroded landforms

Aretes:

Sharp-edged ridges separating glacial valleys…

What is this feature called?