A System to Combine Stratigraphic and Annual Mass-Balance Systems: A Contribution to the International Hydrological Decade

Abstract Mass-balance quantities at specific points on a glacier as defined in IHD (1970) relate either to annual maxima or minima in ice mass at that point (the stratigraphic system ), or to values at the beginning and end of a hydrologic year (the annual or fixed-date system ). Most quantities measured in the field relate to summer surfaces, which correspond to the annual minima at the measurement points. When stratigraphic system point values are integrated over a whole glacier, the result may be meaningless because annual maxima and minima and summer surfaces may form at different times at different places. The combined system utilizes several kinds of data to derive meaningful area-average results that can be directly related to other hydrologic and meteorologic information. Measurements to summer surfaces at certain specific times, including the beginning and end of a hydrologic year, are added together with proper recognition of the types of material involved: old firn and ice, snow and superimposed ice of the year under study, new firn formed during that year, and late snow deposited toward the end of the year. Other “balance increment” terms relate values at the beginning and end of a hydrologic year to corresponding area-average balance minima. As a result, two types of “net balance” and many other terms are given precise meaning for a glacier as a whole. The scheme is sufficiently versatile to be used on any glacier, although the terms relating to summer surfaces are not defined on a glacier in which ablation or accumulation is continuous throughout a year.