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GLACIER FLOW

A. Introduction

Learning outcomes - You should be able to:

Readings:


Image source: NASA/JPL http://scijinks.jpl.nasa.gov/en/educators/gallery/glaciers/greenland_L.jpg

photo: ice flow, GreenlandB. Ice Temperature Characteristics

PMP: pressure melting point of water

Heat sources

Ice temperature profile dependent on: Link: glacier temperature profile

Thermal classification of glaciers


C. Internal Deformation

Occurs in warm- and cold-based glaciers, and polythermal glaciers

Stress and strain

greek eta= strain rate

A = constant related to ice temperature

greek tau= shear stress

n = exponent with an average value of 3

Photo credit: Knight, P.G. Folded basal ice, Greenland.
Photo credit: ©Bruce Molnia, Terra Photographics. Source: Earth Science World Image Bank

Creep

Folding & fracturing LInk: photo of folded ice Link: photo of folded ice Link: photo of crevasses Link: photo of crevasses


photo: ice sliding on bedrockPhoto credit: Knight, P.G. Ice sliding on bedrock, Greenland.

D. Basal Sliding LInk: photo of striations LInk: photo of striations LInk: photo of striations

Occurs with warm-based glaciers and portions of polythermal glaciers

Enhanced basal creep

Regelation (pressure melting) Link: regelation video

diagram: regelation

Factors controlling sliding


E. Subglacial Bed Deformation

Occurs with warm-based glaciers and portions of polythermal glaciers underlain by a soft bed

Strain response of sediment beneath glacier to stress of overlying ice

Sediment strength function of porewater pressure

Bed composition


F. Flow Patterns

Continuous Movement

  • vertical dimension Diagram: vertical velocity profile

  • transverse dimension diagram: transverse velocity  pattern

  • longitudinal dimension

    • extending flowDiagram: extending flow





      • ice falls and ogives

 

produces transverse crevasses Link: Glaciers Online transverse crevasses photo

diagram: transverse crevasses


Photo: ice fall
Photo credit: USGS
diagram: ice fall & ogives
Image: ogives
Photo credit: B. Molnia. USGS

Image: ogives
Photo credit: L. Freeman. Used with permission.

 

    • compressive flowDiagram: extending flow

produces longitudinal crevasses Link: chevron & longitudinal crevasses

diagram: longitudinal crevasses

diagram: extending & compressive flow in alpine glaciers

Periodic Movement: surging glaciers

  • flow velocities 10-100X normal

  • extensive crevassing

  • contorted moraines

  • Bering Glacier, Alaska

    • 1993 surge terminus advance ~ 36 feet/day;

    • 1995 surge terminus advance ~ 70 feet/day

    photo: surge related crevasses
    Image credit: ©Bruce Molnia, Terra Photographics. Image source: Earth Science World Image Bank, Photo ID hgmzl3. http://www.earthscienceworld.org/images

Susitna Glacier
photo: contorted moraines
Image credit: Austin S. Post (1970) Susitna Glacier: From the Online glacier photograph database. Boulder, Colorado USA: National Snow and Ice Data Center/World Data Center for Glaciology. Digital media.


G. Summary

Thermal classification of glaciers

Processes of glacial flow

Glacier flow patterns


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©Karen A. Lemke: klemke@uwsp.edu
Last revised February 12, 2018