The Role of Shear Heating in the Dynamics of Large Ice Masses

• Published in: Journal of Glaciology
• Main Authors: Yuen, David A., Schubert, Gerald
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1979
• Subjects: Journal of Glaciology
• Online Access: http://dx.doi.org/10.1017/s002214300001474x; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002214300001474X

Abstract Self-consistent, steady, one-dimensional, subsolidus creep models of temperature and velocity are calculated for constant-thickness ice sheets sliding down a bed of constant slope under their own weight. Surface velocities of meters per year together with ice thicknesses of hundreds of meters can be realized by models wherein no melting occurs only if the activation energy for shear deformation E * is relatively small; a value of E * of about 60.7 kJ/mol (14.5 kcal/mol) is satisfactory, but an activation energy twice as large is not. Models which satisfy these constraints always lie close to the critical point which separates subcritical solutions (surface velocity u 0 and basal temperature T b increase with ice thickness h ) from supercritical ones (u 0 T b decrease with h) . All steady states, whether subcritical or supercritical, are stable to perturbations of infinitesimal amplitude. However these ice layers are vulnerable to finite-amplitude frictional-heating instability which may be caused, for example, by sudden increases of glacier thickness. The superexponential growth-rates of such finite-amplitude instabilities may be responsible for the disintegration of large ice sheets in short periods of time. On a calculé pour la température et la vitesse des modèles de fluage cohérents, stables, uni-dimensionnels, quasi-solides pour une épaisseur constante de glace glissant sur un lit de pente constante sous l’effet de son propre poids. Des vitesses de surface de quelques mètres par an liées à des épaisscurs de glace de quelques centaines de mètres ne peuvent être réalisées par des modèles sans fusion que si l’énergie d’activation pour la déformation par cisaillement E * est relativement faible. Une valeur de E * d’environ 60,7 kJ/mol (14,5 kcal/mol) est satisfaisante mais une énergie d’activation double ne l’est pas. Les modéles qui satisfont à ces contraintes demeurent trés proches du point critique qui sépare les solutions sous-critiques (la vitesse de surface u 0 et la température à la base T b ...