Characterization of englacial channels by ground‐penetrating radar: An example from austre Brøggerbreen, Svalbard

Abstract

Ground‐penetrating radar profiles at 100 MHz have been collected over an englacial channel system on the cold‐ice glacier austre Brøggerbreen, Svalbard. Analysis and synthetic modeling of the travel times and waveforms of the reflections from the channel have shown that after a near‐vertical drop of ∼45 m in a moulin, the watercourse flows ∼900 m subhorizontally. The size of the conduit varies from a large semicircular channel, ∼5 m wide at its base close to the moulin, to a vertically elongated ∼2.5 m high channel close to the outlet. Variations in the depth of water along the channel have been calculated to be between 14 and 90% of the channel height using detailed analysis of waveforms. The low channel gradient (<2°) and results of dye‐tracing experiments suggest that there is a significant degree of ponding along the channel length. This channel geometry was probably created during a period of increased crevassing from the Little Ice Age. A descent into the moulin provided direct observations of the channel dimensions close to the moulin and helped verify the interpretations and conclusions drawn from the study. Thus radar reflections can be successfully used to determine the depth, dimensions, and water content of englacial watercourses due to the transparency of ice to radar signals and the strong contrast in velocity between water, ice, and air. This technique offers exciting possibilities for the remote monitoring of englacial channels from the glacier surface.