The Antarctic Ice Sheet is one of the two polar ice packs of the Earth that holds about 61% of all fresh water and is thus a crucial component in climate models. Several pieces of evidence indicate that Antarctica is warming, with most of the mass loss occurring in West Antarctica. The principal drainage routes for the inland ice are the West Antarctic ice streams - regions of several km width and hundreds of km length in which the ice flows more than an order of magnitude faster than in the surrounding ice ridges.Unfortunately, the reasons for the differences in flow regime between ice streams and the rest of the ice sheet are still largely unknown. The goal of this project is to shed some new light on the thermal and fluid-dynamical processes that determine the width and flow speed of ice streams. We explore the hypothesis that the width of ice streams is controlled primarily by internal melting within the ice sheet margins. Since the flow speed in ice streams is usually attributed to basal processes, we focus particularly on meltwater generation and distribution at the base of the ice stream.