Estimates of glacier equilibrium line altitudes by the Area×Altitude, the Area×Altitude Balance Ratio and the Area×Altitude Balance Index methods and their validation

Unlike other methods of estimating the Equilibrium Line Altitude of present or former glaciers from morphometric data (as distinct from direct observations of the glacier mass balance), the Area×Altitude, the Area×Altitude Balance Ratio and the Area×Altitude Balance Index methods take explicit account of hypsometric differences between glaciers and thus yield more reliable results. In addition they offer the means of applying various mass balance/altitude relationships of increasing complexity and examining which of these is most correct; the last of these methods is newly developed to permit the application of any desired relationship. Their general adoption has been restricted hitherto by computational problems, but this objection is removed by the easy-to-use spread sheets presented in this paper. By whatever method estimates are derived, it is essential to validate the optional variables used in the computations and methods for doing this are set out.