Ground penetrating radar investigations of open system pingos, Adventdalen, Svalbard

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Abstract
Ground penetrating radar (GPR) investigations conducted on two open system pingos, Innerhytte pingo and Riverbed pingo, in Adventdalen, Svalbard, are described. The surveys were undertaken at frequencies of 50 and 100 Mhz, and are used in an interpretation of the internal structure, origins and evolution of these landforms. Surface exposures suggest that both pingos are largely formed in weak Jurassic shales. Little evidence for the presence of large bodies of massive ice was found. Strong subsurface reflections within the core of both pingos are interpreted as representing either the presence of alternating shale and ice units, or variations in the chemistry, ice crystal properties or air content of pingo ice. Steeply dipping reflections are most pronounced on the flanks of the pingos and are orientated sub-parallel to the pingo surface. Variability in the depth of signal penetration is attributed to variability in subsurface properties, particularly ice content, and the attenuation of the signal by fine grained shales. The internal structure of Innerhytte pingo indicates that the point of sub-pingo groundwater injection has migrated southwards. Lack of evidence for ground ice beneath the north-eastern zone of this landform suggests that at least part of the landform is an erosional remnant of bedrock caused by fluvial incision of Janssonhaugen, with pingo development occurring only in the area proximal to the upper apex of the feature. Both Innerhytte and Riverbed are characterized by conspicuous surface icings, with groundwater flow to the surface in late winter, prior to initiation of active-layer thawing, suggesting derivation from a deep groundwater source.

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