The Architecture of a Modern Push-moraine at Svalbard as Inferred from Ground-penetrating Radar Measurements

Abstract

A modern moraine complex in front of a small subpolar valley glacier in Svalbard, the Scott Turnerbreen glacier, has been investigated by ground-penetrating radar (GPR) (pulseEKKO™IV system). The proglacial area is characterized by low relief ridges, which are concentric about the present ice front, and locally dissected by meltwater channels. Exposures suggest that the moraine sediments consist of mud-rich, debris-flow deposits with outsized clasts (reworked “till”). A profile, oriented parallel with the direction of ice-flow, was measured with 50 and 200 MHz antennae, affording depth penetration of 400 ns TWT (ca. 30 m) and 170 ns TWT (ca. 13 m), respectively. The high resolution of these continuous subsurface radar-profiles (distance between each trace is 50 cm), clearly displays the architecture of the moraine. Three sets of reflectors are observed and interpreted as (1) primary bedding, dipping towards the northeast (downvalley), (2) buried ice-blocks, and (3) numerous thrust faults. The faults, truncating both sediment and ice-blocks, postdate the burying of the ice, and are attributed to proglacial shear by the Scott Turnerbreen glacier. Thus, the present-day morphology of this low-relief moraine is controlled primarily by zones of intense thrust faults and secondarily by the position of the ice blocks.