Using bed-roughness signatures to characterise glacial landform assemblages beneath palaeo-ice sheets

Palaeo-glacial landforms can give insights into bed roughness that currently cannot be captured underneath contemporary-ice streams. A few studies have measured bed roughness of palaeo-ice streams but the bed roughness of specific landform assemblages has not been assessed. If glacial landform assemblages have a characteristic bed-roughness signature, this could potentially be used to constrain where certain landform assemblages exist underneath contemporary-ice sheets. To test this, bed roughness was calculated along 5 m × 5 m resolution transects (NEXTMap DTM, 5 m resolution), which were placed over glacial landform assemblages (e.g. drumlins) in the UK. We find that a combination of total roughness and anisotropy of roughness can be used to define characteristic roughness signatures of glacial landform assemblages. The results show that different window sizes are required to determine the characteristic roughness for a wide range of landform types and to produce bed-roughness signatures of these. Mega scale glacial lineations on average have the lowest bed-roughness values and are the most anisotropic landform assemblage.

Submarine landforms on the Weddell Sea shelf imaged at high resolution using AUVs

<p>Multibeam echo-sounders were deployed from Autonomous Underwater Vehicles (AUVs) flying close to the seafloor of the Weddell Sea shelf in order to investiagte the glacial landforms there with a view to understanding processes and patterns associated with deglaciation from the Last Glacial Maximum on the eastern side of the Antarctic Peninsula. A horizontal resolution of 0.5 m (using conventional mulitbeam systems), and in some cases 0.05 m (using interferometric multibeam equipment), allowed delicate seafloor landforms to be mapped in several areas of the shelf beyond the Larsen C and former Larsen A and B ice shelves. A number of glacial landform assemblages were observed, including suites of delicate ridges associated with grounding-zone wedges and the grounding of icebergs on the shelf. These landforms are probably related to the action of tides moving the ice up and down through a series of tidal cycles. At the highest spatial resolution, individual dropstones derived from rain-out during the melting of floating ice were imaged clearly. Imaging the seafloor at such high resolution allows both very detailed descriptions of submarine landform morphology and also the complexity of such landforms and landform assemblages to be better understood, aiding the interpretation of the glacial and related processes that led to their formation.</p>

CONDITIONS OF KAME FORMATION NEAR VILLAGE OF MASHIV (VOLHYNIAN POLISSIA)

Kames located in the Volhynian Polissya remain the most widespread and the least studied type of relict glacial landform. The article is focused on the specific conditions of kames creation within the peripheral parts of the Volhynian Polissya glacial bed elevation and their significant role in the formation of fissure net in the zones of deadened ice compression inherited from the stages of their inactivity. These compression zones were predetermined by the general planned configuration of the glacial bed landform climaxes. The presented reservoir is located to the north of the village of Mashiv and belongs to a complex of similar glacial accumulations crowed at the culmination of pre-glacial relief and placed at a considerable distance from the marginal formations of the maximum stage of the Dnieper glaciation. The morphological and geological structure of the form is analyzed to explain the conditions of its formation. It is revealed that its structure is dominated by fine-grained sediments; textural and structural features of them allow distinguishing two lithofacial complexes. The basis of the form is loamy sandy and sandy lake-ice deposits covered by a complex of fine-medium-grained sandy fluvioglacial sediments. The morphology of the form, its correlation with the elements of buried pre-glacial relief and the textural peculiarities of the described section deposits, allow to state that the accumulation of the material occurred within a semi-flowing or stagnant during certain periods basin filled with sediments of a small convey water-glacial outcasts; they were accumulated by activity of low energy melt water flows within the peripheral part of the ice glade. The glade was formed on the fracture zone line of the inactive (dead) ice, laid above the glacial bed landform climaxes. The textural and structural features of the form give reason to identify it as kame. Key words: Volhynian Polissia, deglaciation, kames, sedimentation, lithofacies analysis, glaciolacustrine and glaciofluvial sediments.

Ice-sheet scale distribution and morphometry of triangular-shaped hummocks (murtoos): a subglacial landform produced during rapid retreat of the Scandinavian Ice Sheet

High-resolution digital elevation models of Finland and Sweden based on LiDAR (Light Detection and Ranging) reveal subglacial landforms in great detail. We describe the ice-sheet scale distribution and morphometric characteristics of a glacial landform that is distinctive in morphology and occurs commonly in the central parts of the former Scandinavian Ice Sheet, especially up-ice of the Younger Dryas end moraine zone. We refer to these triangular or V-shaped landforms as murtoos (singular, ‘murtoo’). Murtoos are typically 30–200 m in length and 30–200 m in width with a relief of commonly <5 m. Murtoos have straight and steep edges, a triangular tip oriented parallel to ice-flow direction, and an asymmetric longitudinal profile with a shorter, but steeper down-ice slope. The spatial distribution of murtoos and their geomorphic relation to other landforms indicate that they formed subglacially during times of climate warming and rapid retreat of the Scandinavian Ice Sheet when large amounts of meltwater were delivered to the bed. Murtoos are formed under warm-based ice and may be associated with a non-channelized subglacial hydraulic system that evacuated large discharges of subglacial water.

Pingo development in Grøndalen, West Spitsbergen

Pingos are common features in permafrost regions that form by subsurface massive-ice aggradation and create hill-like landforms. Pingos on Spitsbergen have been previously studied to explore their structure, formation timing, connection to springs as well as their role in post-glacial landform evolution. However, detailed hydrochemical and stable-isotope studies of massive ice samples recovered by drilling has yet to be used to study the origin and freezing conditions in pingos. Our core record of 20.7 m thick massive pingo ice from Grøndalen differentiates into four units: two characterised by decreasing δ18O and δD and increasing d (units I and III), and two others show the opposite trend (units II and IV). These delineate changes between episodes of closed-system freezing with only slight recharge inversions of the water reservoir, and more complicated episodes of groundwater freezing under semi-closed conditions when the reservoir got recharged. The water source for pingo formation shows similarity to spring water data from the valley with prevalent Na+ and HCO3- ions. The sub-permafrost groundwater originates from subglacial meltwater that most probably followed the fault structures of Grøndalen and Bøhmdalen. Today the pingo of Grøndalen is relict and degrading due to warming surface temperatures. The state of pingos on Spitsbergen depends on complex interaction of climate, permafrost and groundwater hydrology conditions, and is thus highly sensitive to climate warming.