Detection and Characterization of Discontinuous Motion on Thompson Glacier, Canadian High Arctic, Using Synthetic Aperture Radar Speckle Tracking and Ice-Flow Modeling

We use speckle tracking of high resolution synthetic aperture radar (SAR) images, along with an intensity-rescaling scheme designed to improve accuracy, to investigate discontinuous motion on Thompson Glacier, Umingmat Nunaat, Arctic Canada. The rescaling scheme is developed using simulated SAR images with a known motion field and results in ~25% improvement in speckle tracking accuracy. InSAR and speckle tracking using high resolution RADARSAT-2 data indicate velocity discontinuities of up to 1 cm/d across deep and longitudinally extensive supraglacial channels on Thompson Glacier. We use a cross-sectional finite-element ice-flow model to determine the conditions under which velocity discontinuities of the observed magnitude and signature are possible. The modeling suggests that discontinuous motion across (long and straight) supraglacial channels can occur without ice fracture and under a wide variety of glacier thermal structures, including in fully temperate glaciers. Despite the wide range of conditions conducive to discontinuous motion, the form we observe requires that the associated channels be deep, longitudinally extensive and located in regions of lateral shearing. We speculate that these combined conditions are rare except on polythermal glaciers, where drainage features such as moulins are comparatively scarce and lower deformation rates allow channels to incise consistently and persist over many years.