The firn line elevation was determined according to the Hefer method (Tsomaia and Drobishev, 1977) and ablation area was calculated through the hypsometry curve (Racoviteanu et al., 2008).
According to the Hefer method the elevation of the firn line is the average of the firn line basin height and the elevation of the glacier tongue. The average of the values of the highest peak elevation (two or more peaks) around the glacier basin is determined and the value of the elevation of glacier tongue is added. Finally value of the firn line elevation is the average of these two values.
Glacier accumulation area can be determined using hypsometric curve. Glacier accumulation area is the value of one pixel area multiplied by the total number of pixels on hypsometric curve from the firn line elevation till the highest height of the glacier. Glacier ablation area is the value of one pixel area multiplied by the total number of pixels on hypsometric curve from the firn line elevation till the lowest height of the glacier. The sum of the glacier accumulation and ablation areas makes a total glacier area.
In Fig. 5 the 3D visualization of Gergeti glacier is shown. Blue contour corresponds to the Gergeti glacier contour from GLIMS database. By red one is shown Gergeti glacier adjusted contour using satellite remote sensing. The green line shows the areas free of debris. It is natural that green line differs from the blue line in the lower part of the glacier as the upper part is free of debris.