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 infiltration-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.