The entry of a liquid such as water into a permeable solid such as snow or firn, and, more loosely, the percolation of the liquid through the void spaces of the solid. In general, two forces govern in
filtration gravity and capillary tension. The latter allows the solid to draw in the liquid and is determined by adhesive molecular forces, which can be substantial in materials with very small pores. The rate of infiltration of a liquid into a permeable solid is determined by the porosity and liquid content of the solid and by its hydraulic conductivity.
In Russian-language usage, ice derived from the refreezing of meltwater that has saturated the void spaces in snow or firn. See congelation, recrystallization, superimposed ice.
A term in Russian-language usage referring to the lower percolation zone, where enough meltwater is produced at the surface to percolate out of the snow and into the firn. See zone. In the 'cold infil
tration-recrystallization zone', generally at higher elevation and sometimes called the 'cold firn zone', the meltwater refreezes in the firn because the temperature is below the freezing point. This refreezing is the dominant mechanism for the formation of glacier ice. In the 'warm infiltration-recrystallization zone', generally at lower elevation and sometimes called the 'warm firn zone', the temperature is at or near the freezing point and refreezing makes a lesser contribution to the formation of ice. The runoff limit may lie within the warm firn zone, or within the cold firn zone where slopes are steep.
In the Russian-language literature, part of the lower percolation zone where meltwater is abundant in the snow and firn, but the firn is either a survival from previous years of more positive mass bal
ance or is advected by the glacier flow from higher elevations. See zone. The infiltration zone is sometimes also referred to as the 'firn-ice zone'.