This award is for support of a numerical modeling study to investigate processes and mechanisms that lead to the onset and demise of ice streams. The stability of the West Antarctic ice streams to changes in climate and perturbations at the ice shelf boundary will also be assessed. The project involves development of a two- dimensional map-view model of an ice stream. Processes to be incorporated into the model include calculation of basal temperatures, basal sliding, deformation of sub-glacial till, and the ice shelf/ice stream interaction. By imposing perturbations and/or special basal conditions, and computing the time evolution of the model ice sheet, the importance of each mechanism, as well as their mutual interactions, can be assessed.