Ice Streams und Isbr 1 Ice Streams: Causes for Rapid Ice Flow Fast - - PowerPoint PPT Presentation

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Ice Streams und Isbr 1 Ice Streams: Causes for Rapid Ice Flow Fast - - PowerPoint PPT Presentation

Mar 13, 2024 440 likes •589 views

Ice Streams und Isbr 1 Ice Streams: Causes for Rapid Ice Flow Fast ice flow is controlled by many different factors which change on different time scales. Panel Controlling Factor Time Scale 7 meltwater fluxes short < 1 - 100 a 4

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SLIDE 1

Ice Streams und Isbræ

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SLIDE 2

Ice Streams: Causes for Rapid Ice Flow

Fast ice flow is controlled by many different factors which change on different time scales.

Panel Controlling Factor Time Scale 7 meltwater fluxes short < 1 - 100 a 4 position of calving front short < 1 - 100 a 3 bed roughness middle 100-1000 a 6 geothermal heat flux middle 100-1000 a 5 softness of subglacial sediments middle 100-1000 a 2 topographic steps middle 100-1000 a 1 topographic focussing long 1000-100’000 a

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Winsborrow (2019)

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SLIDE 3

Ice Stream Archetypes

Isbræ: e.g. Jakobshavn

  • topographically fixed
  • deep fjord in bedrock
  • fast ice deformation
  • rapid basal motion

Ice streams: e.g. Siple Coast

  • flat sediment bed
  • sediment deformation

controls flow

  • position variable
  • Shutdown possible

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Raymond & Echelmeyer (2001)

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SLIDE 4

Marginal Zone of Ice Stream B / Whillans Ice Stream

  • localized, fast flow

→ wide crevasse zones

  • Influence on dynamics

and ice temperatures (cooling)

  • almost no inclination
  • surface very flat
  • bed mostly flat

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SLIDE 5

Jakobshavn Isbræ: Kalbungsfront 2004

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Photo: A. Bauder

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SLIDE 6

Greenland: Fjord Systems Under the Ice

Eisschild

  • marginal mountain ranges

→ "bath tub"

  • large ice streams are mostly

topographically fixed Jakobshavn Isbræ

  • deepest outlet glacier fjord
  • up to 1500 m below sea level

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SLIDE 7

Greenland: Ice Stream Flow Patterns

  • (a) Jakobshavn Isbræ
  • (b) Peterman Glacier
  • (c) Nioghalvfjerdsbræ (79N)
  • (d) Zachariæ Isbræ

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Lemos (2018)

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SLIDE 8

Greenland: Ice Stream Flow Patterns

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Lemos (2018)

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SLIDE 9

Greenland: Ice Stream Flow Patterns (2)

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Lemos (2018)

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SLIDE 10

Siple Coast: Ice Streams, Ice Rises

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USGS

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SLIDE 11

Antarctica: Cross Sections Through Ice Streams

  • Siple Coast: A-E: not topographically fixed

(B = Whillans; D = Raymond; E= Mac Ayeal)

  • Lambert, Byrd: topographically fixed

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Bennet (2003)

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SLIDE 12

Ice Streams / Isbræ: Temperatures

Whillans Ice Stream (IS B)

  • width 30 km / thickness 800 m
  • vertically ∼ homogeneous
  • abrupt horizontal transition

Jakobshavn Isbræ

  • width 5 km / thickness 2500 m
  • ∼ half circle
  • dynamic influence on margins

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Truffer & Echelmeyer (2003)

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SLIDE 13

Ice Streams / Isbræ: Velocities and Stresses

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Whillans Whillans Jakobshavn Jakobshavn

Truffer & Echelmeyer (2003)

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SLIDE 14

Theoretical Velocities

Whillans Ice Stream

  • only lateral stress transfer
  • almost friction-free at bed
  • shape factor f = 1.0
  • half width W = 15 km
  • slope α = 0.1◦
  • temperature −20◦ C

→ A = 3.79 MPa−3 a−1 v = 2A n + 1(ρg sin α)3W 4 ∼ 350 m a−1 Jakobshavn Isbræ

  • stress transfer to sides and bed
  • half width W = H = 2.5 km
  • shape factor f = 0.5
  • slope α = 1.2◦
  • temperate bed

→ A = 75 MPa−3 a−1 v = 2A n + 1(ρg sin α)3W 4 ∼ 1150 m a−1

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