Thermal structure and drainage system of a small valley glacier (Tellbreen, Svalbard), investigated by ground penetrating radar

Abstract

Abstract. Proglacial icings accumulate in front of many High Arctic glaciers during the winter months, as water escapes from englacial or subglacial storage. Such icings have been interpreted as evidence for warm-based subglacial conditions, but several are now known to occur in front of coldbased glaciers. In this study, we investigate the drainage system of Tellbreen, a 3.5 km long glacier in central Spitsbergen, where a large proglacial icing develops each winter, to determine the location and geometry of storage elements. Digital elevation models (DEMs) of the glacier surface and bed were constructed using maps, differential GPS and ground penetrating radar (GPR). Rates of surface lowering indicate that the glacier has a long-term mass balance of −0.6 ± 0.2 m/year. Englacial and subglacial drainage channels were mapped using GPR, showing that Tellbreen has a diverse drainage system that is capable of storing, transporting and releasing water year round. In the upper part of the glacier, drainage is mainly via supraglacial channels. These transition downglacier into shallow englacial "cut and closure" channels, formed by the incision and roof closure of supraglacial channels. Below thin ice near the terminus, these channels reach the bed and contain stored water throughout the winter months. Even though no signs of temperate ice were detected and the bed is below pressuremelting point, Tellbreen has a surface-fed, channelized subglacial drainage system, which allows significant storage and delayed discharge.

Former dynamic behaviour of a cold-based valley glacier on Svalbard revealed by basal ice and structural glaciology investigations

“…A long-term mass balance of -0.6 AE 0.2 m w.e. a -1 has been calculated over this period (Baelum and Benn, 2011), similar to the average calculated for all Svalbard glaciers (-0.55 m a -1 ; Dowdeswell and others, 1997). Baelum and Benn (2011) found no evidence to suggest Tellbreen had ever undergone surge behaviour.…”

“…Local bedrock comprises sandstones, siltstones and shales of the Van Mijenfjorden and Adventdalen Groups (Dallmann and others, 2002). Ground-penetrating radar (GPR) data indicate that Tellbreen is currently almost entirely coldbased, with possibly only a small isolated area of warm ice below the thickest ($100 m) part of the glacier (Baelum and Benn, 2011). It was suggested by Baelum and Benn (2011) that warm-based ice may have been more extensive at the LIA maximum extent of the glacier, but, based on the minimal evidence for valley erosion or modification, was unlikely to have been widespread or prolonged.…”

“…Tellbreen has an active drainage system characterized by a network of supra-, en-and subglacial conduits formed by cut-and-closure processes (incision followed by roof closure), which even within a cold glacier can route meltwater from the surface to the bed (Baelum and Benn, 2011;Naegeli and others, 2014). For the purposes of this study, the presence of active and abandoned conduits within the lower glacier tongue provided an accessible way to investigate ice facies and glaciological structures when they were largely free of water during spring.…”

“…Open fractures also occur in steep areas of the upper accumulation basins (cf. Baelum and Benn, 2011).…”

Three Decades of Volume Change of a Small Greenlandic Glacier Using Ground Penetrating Radar, Structure from Motion, and Aerial Photogrammetry

“…For the conversion of travel time of the GPR signal to ice thickness, a mean velocity of 0.168 m ns -1 of electromagnetic waves in glacier ice was applied. The value was considered appropriate for a polythermal glacier based on Bogorodsky et al (1985), Baelum and Benn (2011), Pettersson and Holmlund (2003), Cuffey and Paterson (2010), Friedt et al (2013), and Ai et al (2014). The software ReflexW (version 7.1.4) was used for post-processing the GPR profiles and identifying the bedrock.…”