ABSTRACT
To describe the flow of a particular glacier, the appropriate model needs to be selected first. In some instances, the choice is obvious. For example, the lamellar flow model discussed in Section 4.2 is based on the assumption that the driving stress is balanced by drag at the glacier base. For floating ice shelves, basal drag is zero and the lamellar flow model does not apply. Most often, the choice is less clear. For example, many of the West Antarctic ice shelves have formed in embayments, and lateral drag may provide much, if not all, of the resistance to flow. It is not immediately obvious whether the ice-shelf model described in Section 4.5 applies best or whether the lateral-drag model of Section 4.4 should be used. On the Siple Coast ice streams, the concave surface profile has led some authors to propose that the flow along these drainage routes is primarily controlled by gradients in longitudinal stress and that other resistive stresses may be neglected when modeling these ice streams. Because the selected model determines to a large extent the predicted behavior of the glacier under consideration, it is important to include the major sources of flow resistance. To be on the safe side, one could use a complete model in which all stresses are calculated at depth. Increasingly, higher-order full-Stokes models are being applied to model glacier flow, but this may not always be a very practical solution, especially when trying to model the evolution of an ice sheet over an extended period of time. Therefore, one often seeks simpler models that realistically include the most important physical processes, treating the less important processes in a parameterized way. This means that the relative importance of the potential sources of resistance to flow needs to be known.
