Preliminary Experiments on the Formation of Elongated Air Bubbles in Glacier Ice by Stress

Abstract

ABSTRACT. Biaxial compression tests on glacier ice with bubbles revealed that elongated air bubbles were d eveloped with long axes in the direction of free expansion. The elongated bubbles were not only derived from spherical bubbles but also created by the h ealing of cracks that were developed during compression. Formation of elongated bubbles and foliations in natural glacier ice are discussed h ere in the light of results obtained experimentally. RESUME. Experiences preliminaires sur la formation tU bulles de l' air allongees dalls la glace de glacier sous contrainte. Des essais de compression biaxiale sur la glace de glacier contenant des bulles m ontrent que des bulles de l'air a llongees se developpent avec l'axe long dans le sens de l'expansion libre. Les bulles allongees ne se forment pas seulement a partir de bulles spheriques, mais aussi par l'inclusion de fissures form ees au cours de la compression. L es auteurs discute de la formati on des bulles allongees et de la foliation da ns la glace de glacier naturelle a la lumiere des resultats obtenus experimentalement. ZUSAMMENFASSUNG. Vorliiufige Versuche zur Bildung ver/angerter Luftblasen in Gletschereis durch

Conditions for bubble elongation in cold ice-sheet ice

“…We thus reach the simple result that for typical conditions in cold ice, the diffusive strain rate restoring elongated bubbles toward spherical depends on the initial bubble size (large bubbles become elongated more easily; Hooke and Hudleston, 1978; Nakawo and Wakahama, 1981), but is independent of compression of those initial bubbles because of compensating effects of compression on vapor diffusion and on geometric factors. The diffusive restoration increases linearly with elongation initially, but approaches a constant value for large elongations.…”

“…Duval and Lliboutry, 1985), we cannot with confidence assume that the ice theology in the region very close to the bubble is identical to that in the bulk. Furthermore, one set of experiments on rapid laboratory elongation of bubbles found that the viscous model matched observations rather closely (Nakawo and Wakahama, 1981). We thus believe that it is acceptable to use a linear-viscous approximation, although a power-law rheology should be explored in the future.…”

Structural Evolution During Cyclic Glacier Surges: 2. Numerical Modeling

“…A significant role for air bubbles received early attention (Hooke & Hudleston, 1978) and is consistent Journal of Geophysical Research: Earth Surface 10.1029/2018JF004870 with field observations on Trapridge Glacier (Hambrey & Clarke, 2019). This line of thinking raises question concerning the extent to which bubble geometry reflects the geometry of strain ellipsoids (e.g., Alley & Fitzpatrick, 1999;Nakawo & Wakahama, 1981). If the two are similar, then one might imagine that strain ellipsoids that are flattened by horizontal compression, would produce bubbles that, when exposed by surface melting, would favor vertical penetration of meltwater and hence enhanced ice ablation.…”

“…For Trapridge Glacier the S 1 foliation was attributed to enhanced ablation of ice that contained a high density of elongated bubbles. Bubbles have been taken as strain indicators although diffusion processes can complicate this idea (e.g., Alley & Fitzpatrick, 1999;Gay, 1968;Hudleston, 1977;Nakawo & Wakahama, 1981). Our association of the S 1 foliation with the geometry and orientation of strain ellipsoids is contingent on the extent to which the geometry of strain ellipsoids influences the geometry of bubbles and the orientation of ice fabric.…”

Healed cracks in iceberg ice

“…Evidence that a crack can lead to the development of a network of air bubbles was provided by Nakawo and Wakahama (1981). Two mechanisms may be envisaged for the increase in size of gas inclusions in a crystalline matrix (e.g.…”