Temperate ice permeability, stability of water veins and percolation of internal meltwater
Abstract In temperate glacier ice, in situ, besides water veins, there are water lenses, on grain boundaries more or less perpendicular to the direction of maximum pressure p 1 (at the grain scale). Geometry of veins is developed. Grains are modelled as equal tetrakaidecahedra. The stress and temper...
Published in: | Journal of Glaciology |
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Main Author: | |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Cambridge University Press (CUP)
1996
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Subjects: | |
Online Access: | http://dx.doi.org/10.1017/s0022143000004068 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000004068 |
Summary: | Abstract In temperate glacier ice, in situ, besides water veins, there are water lenses, on grain boundaries more or less perpendicular to the direction of maximum pressure p 1 (at the grain scale). Geometry of veins is developed. Grains are modelled as equal tetrakaidecahedra. The stress and temperature fields around a vein at a smaller, microscopic scale are estimated and the water discharge by a Vein is calculated. The time-derivative of the cross-sectional area S of a vein is governed neither by energy dissipation in the water nor by plasticity, but by capillarity effects and salinity. A “vasodilator threshold” p d for water pressure p w in the veins is defined. Normally, P w < P d , then S has a stable value, the same for any orientation of the vein, and the microscopic temperature is uniform. The coefficient of permeability is proportional to ( P d - p w ) −4 , and thus a true Darcy law does not hold. As an application, the percolation of internal meltwater is studied; in an upper boundary layer about 2 m thick this meltwater flows upwards, because in the bulk of the glacier p w is very close to P 1 , whereas it is zero at the surface. When, exceptionally, p w > p d , S increases irreversibly. Whether it leads to the formation of “worm-holes” is discussed. |
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