Formation of mega-scale glacial lineations far inland beneath the onset of the Northeast Greenland Ice Stream

Abstract. Rapidly-flowing ice streams drain the interior of the Greenland Ice Sheet, currently accounting for around half of its annual mass loss. The Northeast Greenland Ice Stream (NEGIS) is one of the largest, recognisable almost 600 km inland, and extends close to the central ice divide. Numerical ice sheet models are unable to accurately reproduce the configuration of the NEGIS, but understanding its bed properties and spatial and temporal evolution is critical to predicting its future contribution to sea-level change. Here, we use swath radar imaging to create a high-resolution Digital Elevation Model of the bed close to where the NEGIS initiates. Surprisingly, this reveals a landscape interpreted to include mega-scale glacial lineations (MSGLs) that are often assumed to be indicative of rapid ice stream flow (100s m yr^-1), under present-day flow velocities of only ~60 m yr^-1. Given that MSGLs are thought to form under much higher flow velocities, their presence so far inland at an onset zone raises important questions about their formation and preservation under ice streams, as well as past configurations of the NEGIS. Elongate bedrock landforms outside the current shear margins also suggest that the NEGIS was wider than its present configuration at some point in the past.