Glacial Systems- Lecture Compatibility Mode

8/8/2019 Glacial Systems- Lecture Compatibility Mode

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GLACIAL DEPOSITIONAL

ENVIRONMENTby

AP Dr Chow Weng Sum

Glacial Formation & Growth

• Glacier – a moving body of ice that formson land from the accumulation andcompaction of snow - moves downslopeunder influence of gravity

• Glaciers typically form at or above thesnowline –i.e. the lowest topographic limit

of year-round snow cover • Snow that falls below the snowline

typically melts in summer



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Glacial Budget• Budget consists of difference between the

glacier’s annual gain of snow & ice and itsannual loss (or ablation) of snow & ice by

melting & sublimation

• If budget is positive, glacier increases in

thickness and area; its outer margin (terminus)

advances downslope in confined glaciers and

outwards in unconfined glaciers

• If budget is negative,glacier decreases in size &

terminus retreats (by melting)• If budget is balanced, terminus remain stationary

Glacier budget• All glaciers have: zone of accumulation

: zone of ablation

: equilibrium line

Position of equilibrium line changes every year,depending on budget

Zone of accumulation can be identified by ablanket of snow that survives summer melting, isnourished by snowfall and sometimes from

nearby avalanchesZone of ablation is caused by summertime melting

of snow in middle and low altitudes; in highaltitudes, sublimation causes ablation



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GLACIAL MOVEMENT

Glacier Flow

• Accumulation zone: as snow is compacted

it flows at an angle downward toward the

glacier’s bed

• Ablation zone: ice flows at an angle

upward toward the surface and outward

toward the glacier’s edges



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From Steven Dutch, University of Wisconsin Green Bay,

http://www.uwgb.edu/dutchs/EarthSC202Notes/GLACIAL.HTM

Snowfall vs Melting & Evaporation (Ablation)

Glacial Flow• Glaciers flow by: a) Internal deformation

b) Basal sliding

Internal deformation: pressure from overlying snow

& ice deforms a glacier’s ice crystals, fracturing

them along planes of weakness, changing their

shapes, and causing them to slip past one

another

Basal sliding: In warmer glaciers, thawing occurs

at the bases, producing a film of water thatenables the glacier to slide across its bed

Ice flows when a glacier’s thickness exceeds about

60m



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Velocity of glacial Flow• Cold-based non sliding ice sheets

advances at only a few metres per year

• Warm-based alpine glaciers on steepslopes can flow 300m or more annually

• Some glaciers periodically ‘surge’ or accelerate in brief episodes lasting severalmonths to a few years at speeds of up to100 times the normal velocity

• Periods of surge are separated by longer

periods (10 to 100 years) of normal flow

Types of glaciers

CONFINED GLACIERS

• Alpine glaciers are confined by surroundingbedrock highlands

• a) Cirque glaciers- which create & occupy semi-circular basins or mountainsides, usually at headof valleys

• b) Valley glaciers- flow through and modify pre-existing stream valleys

• c) Ice caps – formed at tops of mountains

UNCONFINED GLACIERS

• The only unconfined form of glacier is acontinental ice sheet- covering the continent



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CIRQUE GLACIER

CIRQUE(Amphitheatre-like valley formed at head of valley)



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GLACIAL VALLEY

Glacial Erosion• Abrasion- occurs when rock fragments

embedded in the base of a glacier scrape the

surface of the underlying bedrock- giving rise to

striations or grooves on the polished bedrock.

• The abrading stones themselves become

abraded and eventually become pulverised into

a silky rock powder called glacial flour



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GLACIAL STRIATIONS

Glacial grooves- Kelly's island, Ohio:



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Polished rock surface due to glacial

abrasion in Aland

Polished floor of former glacier in Eckeroe



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Polished bedrock, Eckeroe

Glacial deposits• Glacial deposits are typically poorly sorted, often

ranging in size from fine clays to house-sized

boulders

• a) Glacial erratic : an exceptionally large,

glacially transported boulder that has been

eroded from one type of bedrock and then

transported atop another



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ERRATIC (A boulder that differs from the surrounding rock and is

believed to have been brought from a distance by glacial action )

Glacial deposits

• b) Glacial till- glacial drift deposited directly from

glacial ice ; till is exclusively deposited in the

ablation zone; it is generally unstratified, and

commonly consists of large rock fragments

surrounded by a finer-grained matrix of sand, silt

and clay



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GLACIAL TILL

GLACIAL TILL



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Glacial landform

• Glacial moraine: glacial till often forms a

moraine, a landform that typically accumulates

at the margin of a glacier.

• Moraines occur as bands of hills marking the

various advances and retreats of a glacier

Figure 8.29 From Boggs (2006), Principles of Sedimentology and Stratigraphy, 4th ed., p. 279

Glacial moraine:



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GLACIAL MORAINE

ICEBERGS IN ANTARTICA



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Figure 8.30 From Boggs (2006), Principles of Sedimentology and Stratigraphy, 4th ed., p. 280

Glaciomarine sedimentation:

THANK YOU

Glacial Systems- Lecture Compatibility Mode

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