Automating the implementation of an equilibrium profile model for glacier reconstruction and Equilibrium Line Altitude calculation in a GIS environment

Reconstruction of glacier equilibrium line altitudes (ELAs) associated with advance stages of former ice masses is widely used as a tool for palaeoclimatic studies. This requires an accurate reconstruction of palaeo-glacier surface hypsometry, based on geomorphological evidence. Classically, the approach used to define ice-surface elevations follows the ‘cartographic method’, whereby contours are estimated based on an ‘understanding’ of the typical surface form of contemporary ice masses. This method introduces inherent uncertainties in the palaeoclimatic interpretation of reconstructed ELAs, especially where the upper limits of glaciation are less well constrained and/or the age of such features in relation to terminal moraine sequences is unknown. An alternative approach is to use equilibrium profile models to define ice surface elevations. Such models are tuned, generally using basal shear stress, in order to generate an ice surface that reaches ‘target elevations’ defined by geomorphology. In areas where there are no geomorphological constraints for the former ice surface, the reconstruction is undertaken using glaciologically representative values for basal shear stress. Numerical reconstructions have been shown to produce glaciologically “realistic” ice surface geometries, allowing for more objective and robust comparative studies at local to regional scales.