A crystallographic investigation of glacier structure and the mechanism of glacier flow

Abstract 1. Introduction (a) The transition of firn into glacier ice; glacier structure Glaciers are divided into two main parts: the accumulation area, firn region or névé where the annual accumulation in the form of snow exceeds the loss by melting, evaporation and wind erosion, and the ablation area or glacier tongue. The dividing line between the two regions is called the Firn Line. Granular, compacted snow called firn covers the accumulation area. Its crystals are rarely larger than 2 mm. in diameter and are mixed with a considerable volume of air, so that the specific gravity is much lower than that of ice. The surface of the tongue consists of blue or glassy ice, more or less covered with rock debris; here the diameter of the ice crystals varies between 1 and 10 cm. or even more; the specific gravity of the ice is never far below 0.90. In summer the tongue has a bluish or grey appearance, while the firn region retains its white or whitish hue.