Abstract
AbstractStudying subglacial drainage networks is important for understanding the potential relationship between channel dynamics and rapid glacier recession as well as the role of subglacial channels in subglacial sediment evacuation. In order to delineate the planform geometry of snout marginal subglacial channels, densely spaced ground-penetrating radar (GPR) measurements at a frequency of ~70 MHz were carried out over the snout marginal zones of two temperate glaciers in the southwestern Swiss Alps, the Haut Glacier d'Arolla and the Glacier d'Otemma. Three-dimensional (3-D) data processing and amplitude analysis of the GPR reflection along the glacier bed was used to map the channels. At the Haut Glacier d'Arolla, two relatively straight channels of several meters in width were identified. The positions of these channels correspond well with the locations of channel outlets at the glacier terminus, as well as with fractures appearing on the glacier surface one month after the GPR data acquisition. The latter are believed to represent the beginning of ice collapse above the subglacial channels. At the Glacier d'Otemma, a major subglacial conduit was detected with similar dimensions to those identified at the Haut Glacier d'Arolla, but greater sinuosity. The position of this channel was confirmed by drone-based imagery acquired after glacier margin collapse. Our results confirm that high-density 3-D GPR surveys can be used to map subglacial channels near temperate alpine glacier margins.
Highlights
Understanding the hydrology of alpine glaciers, and in particular the geometry and dynamics of the channels that form within and beneath glacier ice, has been an important research interest since at least the 1950s (Fountain and Walder, 1998)
3.1 Haut glacier d’Arolla In Figure 6, we present the results of our analysis of the Haut Glacier d’Arolla (HGdA) ground-penetrating radar (GPR) dataset
Amplitude analysis of the GPR reflection along the glacier bed made it possible to reveal areas with a significant change in bed reflectivity, which allows for the identification of subglacial channels that may otherwise be difficult to detect on individual GPR profiles
Summary
Understanding the hydrology of alpine glaciers, and in particular the geometry and dynamics of the channels that form within and beneath glacier ice, has been an important research interest since at least the 1950s (Fountain and Walder, 1998). If a channel meanders strongly, its shape is likely a result of interactions with the glacier bed such as erosion, deposition, sediment transport and deviation by bedrock outcrops (Alley and others, 1997). Such knowledge is critically important for understanding how glaciers transfer eroded sediment through their marginal zones and for parameterizing models of subglacial sediment export (Beaud and others, 2018; Perolo and others, 2019)
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