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Glaciers and Glaciation > Week 13: Glacial landsystems > Flashcards

Week 13: Glacial landsystems Flashcards

1
Q

Landsystem =

A

area of common terrain attributes, different from those of adjacent areas, in which recurring patterns of topography/soil/vegetation reflect underlying geology, past erosion and depositional processes and climate

(climate = glacial)

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2
Q

Process-form model =

A

conceptual, emphasises genetic interrelationships of specific landform-sediment associations at both local/regional scales in terms of known processes and form linkages

Another way of thinking about landsystems

Relates depositional/erosional forms to processes beneath ice sheet margins

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3
Q

Holistic approach to glacial landsystems

A

Geomorphology and sediments that characterise landscape are genetically related to the processes that generate them

Individual landforms/elements –> land facets –> landsystems

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4
Q

Different suites of landforms

A

Fringe

Marginal

Transitional

Inner

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5
Q

Concept development of landsystems

A

1970s-80s = styles of glaciation landsystems

  • subglacial
  • supraglacial
  • glaciated valley
  • Eyles 1983

1990s-present = continuum of styles and glaciation dynamics i.e.
- surging glacier
- ice stream
- plateau ice field
- Evans 2003
= relative importance of thermal regime and topography

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6
Q

Active temperate glaciers =

A

strong seasonal climatic control and predominantly warm bed

active i.e. flow maintained (moving forwards) during both advance and recession

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7
Q

Where are active temperate glaciers found?

A

Maritime locations e.g. Iceland/Alaska

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8
Q

Component domains of active temperate glaciers

A
  1. Marginal morainic
  2. Glacifluvial (+glacilacustrine)
  3. Subglacial
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9
Q

Characteristic formations in active temperate glaciers

A

Flutings/minor drumlines running into push moraines, representing retreat

LANDSYSTEM SIGNATURE INDICATIVE OF DEFORMING BED

Inset push moraines related to recession

Ponds between

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10
Q

Who came up with a landsystems model for actively receding temperate glaciers?

A

Evans and Twigg 2002

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11
Q

What does each ridge of an inset push moraine (active temperate glacier) represent?

A

One year’s worth of sediment being produced at margin

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12
Q

Surging glaciers =

A

short rapid surge/advance phase followed by longer quiescent phase

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13
Q

How are surging glaciers linked to the reorganisation of the subglacial drainage system?

A

Build up of subglacial meltwater until ice crosses threshold then decoupled from bed = surges

GIVES A CONSISTENT AND PREDICTABLE LANDSYSTEM

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14
Q

Examples of surging glaciers

A

Modern = Iceland
Tungnaarjokull

Pleistocene ice sheet = S margin of Laurentide Ice Sheet

  • Evans et al 1998/2008
  • surging global with thrust block moraines (glacitectonic compression) at outermost edge of lobe
  • megaflutings
  • crevasse-squeeze ridges
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15
Q

Surging glacier characteristics

A

Extensive crevassing
Catastrophic meltwater dischrage
Rapid snout advance
Fracturing in association around margin/within surge zone

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16
Q

The surging glacier landsystem (distal to proximal)

A
  1. Proglacial outwash fan
  2. Thrust block moraine
  3. Hummocky moraine
  4. Stagnating surge snout
  5. Flutings
  6. Crevasse-squeeze ridges
  7. Overridden thrust block moraine
  8. Concertina/zig-zag esker
  9. Crevasse-squeeze ridges emerging

Evans and Rea 1999, Evans et al 1999

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17
Q

How can you recognise crevasse-squeeze ridges in aerial photographs?

A

Sparse vegetation

  • starved of moisture on ridge summits
18
Q

Plateau Icefield examples

A

Iceland

Ellesmere Island, Canada

19
Q

What are plateau ice fields characterised by?

A

Cold-based plateau ice

Topographically constrained outlets and niche glaciers
- warm based?

Critical summit breadth concept

20
Q

Critical summit breadth concept

A

Manley 1955, 1959
Applied more recently to glaciation styles in the Lake District

y = height of summit over regional firn line (m)

x = breadth of summit (m)

21
Q

Concept of a plateau icefield

A

High altitude over large area
= colder climate
= thin, cold-based ice
= relatively inert

Moves to warmer based where spills over plateau
= topographically constrained outlets e.g. niche glacier

22
Q

Components of a plateau icefield

A
  1. Summit block fields
  2. Abraded bedrock
  3. Later (ice marginal) meltwater channels
23
Q

Plateau ice field; summit block field =

A

large area of intense frost shattering and thaw-freeze processes due to little action of inert ice in subsurface

24
Q

Plateau ice field; abraded bedrock =

A

where ice begins to pick up speed and flow around edge

25
Q

Plateau ice field; lateral meltwater channels =

A

when glacier retreats back into centre of plateau = meltwater generated cuts

26
Q

Why are plateau ice fields commonly mipmapped?

A

no evidence of glaciation on summit plateau other than potential meltwater channels

BUT if you had ice in valley at a lower altitude it must have been present at higher altitude on plateau too

27
Q

Trimline moraine =

A

line of moulders which shows where the ice margin was

28
Q

Spatial/temporal continuum of plateau ice fields and valley glaciers

A

Depends on debris flux vs ice flux (Benn et al 2003)

29
Q

English Lake District; glacial history/mapping

A

Sissons 1980

  • no ice on summits
  • alpine style of glaciation
  • based on depositional evidence i.e. ablation zone

Rea et al 1998, McDougal 2001/2014, Brown et al 2013
- plateau ice field concept

Bickerdike et al 2016/2018

  • “different styles of glaciation landsystems that occurred during Younger Dryas in upland areas of Britain”
  • Lake District = between plateau and alpine
30
Q

Younger Dryas glaciation systems

  • decreasing glacier size/thickness
  • increasing topographic constraint

AND EXAMPLES

A

Bickerdike et al 2016/2018

ICE CAP
- Glen Lyon and surrounding valleys

PLATEAU ICE FIELD
- Monadhliath mountains, Scotland

LOWLAND PIEDMONT LOBE
- Lomond valley, Scotland

ALPINE ICEFIELD
- Isle of Mull, Scotland

CIRQUE/NICHE GLACIERS
- Snowdonia, Wales

31
Q

When was the Younger Dryas?

A

12.8-11.5ka BP

32
Q

Ice streams =

A

relatively fast moving streams of ice with sheets

33
Q

Should ancient ice sheets have ice streams?

A

Yes, based on modern-day ice streams

Potential location of major ice streams in N hemisphere ice sheets predicted by Denton and Hughes 1981

34
Q

How were the two types of ice stream developed?

A

Dyke and Morris 1988

Used collected till samples for geochemical signatures = spatial distribution of bedrock

  1. BOOTHIA TYPE
  2. DUBAWNT TYPE
35
Q

Boothia type ice stream

A

Two rock types (A/B) give rise to plume of erratic dispersal beneath faster flowing stream ice

36
Q

Dubawnt type ice stream

A

Produces apparent plume because of restricted source area

37
Q

Why are marine components of ice streams more common in modern settings?

A

Our ice sheets terminate in the ocean

Clear break between streamline and non-streamline terrain at margin (clearer than terrestrial ice lobes/stream)

38
Q

Example of marine based ice stream

A

Ice Stream B, WAIS

39
Q

Example of terrestrial ice lobe/stream

A

Des Moines/Lake Michigan lobes

40
Q

What happens to ice streams during ice sheet retreat?

A

Younger imprints on older

Glaciers and Glaciation (29 decks)

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