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Deformation in the Vicinity of Ice Divides

  • Charles F. Raymond (a1)
Abstract

Numerical calculations by finite elements show that the variation of horizontal velocity with depth in the vicinity of a symmetric, isothermal, non-slipping ice ridge deforming on a flat bed is approximately consistent with prediction from laminar flow theory except in a zone within about four ice thicknesses of the divide. Within this near-divide zone horizontal shear strain-rate is less concentrated near the bottom and downward velocity is less rapid in comparison to the flanks. The profiles over depth of horizontal and vertical velocity approach being linear and parabolic respectively. Calculations for various surface elevation profiles show these velocity profile shapes are insensitive to the ice-sheet geometry.

Résumé

Des calculs numériques aux éléments finis montrent que la variation de la vitesse horizontale avec le profondeur au voisinage d’une diffluence de glace symétrique isotherme et sans glissement sur un lit plat est à peu près cohérente avec les prévisions de la théorie de l’écoulement laminaire sauf dans une zone éloignée de la diffluence de moins de quatre fois l’épaisseur de la glace. A l’intérieur de cette zone la déformation visqueuse horizontale est moins concentrée vers le fond et la vitesse vers le bas est moins rapide que vers les rives. Les profils selon la profondeur des vitesses horizontales et verticales sont approximativement l’une linéaire, l’autre parabolique. Les calculs pour différents profils d’altitude superficielle montrent que les formes des profils de vitesse sont indépendants de la forme géométrique de l’appareil glaciaire.

Zusammenfassung

Berechnungen mit finiten Elementen zeigen, dass die Änderung der horizontalen Geschwindigkeit mit der Tiefe in der Nachbarschaft einer symmetrischen, isothermen, nicht-gleitenden Eisscheide, die sich auf einem flachen Bett deformiert, mit den Vorhersagen der laminaren Fliesstheorie annähernd übereinstimmt, mit Ausnahme einer Zone innerhalb von etwa vier Eisdicken um die Eisscheide. Innerhalb dieser Nahzone ist die horizontale Scherspannungsrate weniger nahe dem Untergrund konzentriert und die Abwärtsbewegung ist im Vergleich zu den Flanken weniger schnell. Die Tiefenprofile der horizontalen bzw. vertikalen Geschwindigkeit nähern sich einem linearen bzw. parabolischen Verlauf. Rechnungen für verschiedene Oberflächenprofile zeigen, dass die Geschwindigkeitsprofilformen unabhängig von der Geometrie des Eisschildes sind.

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Copyright
References
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Journal of Glaciology
  • ISSN: 0022-1430
  • EISSN: 1727-5652
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