• Solving the  momentum equations for all stress components can be difficult and time-consuming, so it is advantageous to know when simpler approximations can be used. The Shallow Ice Approximation (SIA) allows us to assess when and if variouos stress terms are negligible.

Particle paths and isochrones (internal layers) must be calculated for a number of applications.  Representing the velocities with shape functions often provides a convenient way to calculate particle paths and layers, particularly when the ice-sheet surface evolution also assume shape functions.