Glacier surge mechanisms inferred from ground-penetrating radar: Kongsvegen, Svalbard

Deformational structures at the surge-type glacier Kongsvegen, Svalbard, are displayed at the glacier surface and on a grounded cliff section at the terminus. A 300 m × 65 m grid of 200 MHz ground-penetrating radar (GPR) profiles has been collected adjacent to the cliff section in order to identify englacial structure. Two sub-horizontal reflectors have been imaged; the upper is interpreted as the glacier bed, and represents a transition between glacier ice and frozen subglacial sediments; while the lower is interpreted as a transition between frozen and unfrozen subglacial sediment. Dipping reflectors, corresponding to sediment-filled features on the cliff and glacier surface, do not cross the glacier bed. A small number of reflectors, interpreted as thrust faults, are visible below the bed reflector. A model is developed for structural development, which suggests that ice built up in a reservoir zone during quiescence. During the surge, ice propagated rapidly from this reservoir, creating a zone of compression which resulted in thrusting. Subsequently an extensional flow regime resulted in extensive fracture of the ice. We suggest dilated sediment was evacuated into these extensional crevasses from the glacier bed, accelerating surge termination.