# Blatter-Pattyn model

From Interactive System for Ice sheet Simulation

The starting point for the Blatter-Pattyn model is the full Stokes equations

,

where *P* is the pressure and τ is the deviatoric stress tensor. The latter is given by

,

where σ is the full stress tensor.

There are a number of ways to argue that because of the "shallowness" of ice sheets - that is because the ratio of *H*/*L*, where *H* is the thickness and *L* is a relevant horizontal length scale, is small - the equations above can be reduced to the following "first-order approximation"