How to make an ice stream

Fast-flowing ice streams drain most of the inland ice from the Antarctic and Greenland ice sheets. Despite their critical role, the formation mechanisms of ice streams and their shear margins remain controversial. We present a three-dimensional full-Stokes model of an analogue to the over 500 km long Northeast Greenland Ice Stream. We show that ice streams and their shear margins can form solely due to the anisotropic rheology of ice and evolving crystallographic orientations. A fully developed, fast-flowing ice stream can form in only 1000–2000 years by internal ice anisotropy, even without external forcing such as basal melting. This stresses the importance of evolving ice anisotropy on ice-sheet mass balance and sea-level rise during global climate change.