Geological investigations in South Victoria Land, Antarctica
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Summary Large glaciers derived from the ice plateau cut through the mountain ranges of South Victoria Land to the Ross Sea. In the McMurdo Sound region some glaciers have retreated from portions of their courses leaving almost ice free "dry valleys". The general geology of one such valley, provisionally named here the Victoria Dry Valley, is discussed in detail. The original ice level of this valley was 1,000 ft to 1,200 ft higher than the present remnants of Victoria Glacier. During the summer months meltwater from remnant cirque and glacier ice accumulates as extensive lakes in the depressions of the moraine-strewn valley floor. The basement is exposed in Victoria Drjf Valley as thick uniform sheets of granite, separated by younger dolerite sills. Acidic and basic dykes antedating sill intrusion are associated with the granite basement. The petrology and field relations of the granite, dykes, and dolerite sills resemble those of similar exposures in the Kukri Hills, 30 miles to the south. It is probable that the rocks of Victoria Dry Valley forrti part of thé northern continuation of the basement complex of South Victoria Land.Keywords:
Sill
Basement
Crevasse
Meltwater
Abstract The transfer of surface-generated meltwater to the subglacial drainage system through full ice thickness crevassing may lead to accelerated glacier velocities, with implications for ice motion under future climatic scenarios. Accurate predictions of where surface meltwater accesses the ice/bed interface are therefore needed in fully coupled hydrodynamic ice-sheet models. We present a spatially distributed modelling routine for predicting the location and timing of delivery of surface-derived meltwater to the ice/bed interface through moulins and supraglacial lake drainage. The model is explained as it is applied to the Croker Bay glacial catchment of Devon Ice Cap, Canada. The formation of moulins, drainage of lakes, and the transfer of meltwater through the full ice thickness are modelled for the 2004 and 2006 ablation seasons. Through this case study we assess the model’s sensitivity to degree-day factors, fracture toughness, tensile strength and crevasse width, and confirm that parameters influencing the rate at which water fills a crevasse are the most significant controls on the ability of a crevasse to reach the bed. Increased surface melt production, therefore, has the potential to significantly influence the spatial and temporal transfer of meltwater through surface-to-bed connections in a warmer climate
Meltwater
Crevasse
Glacier ice accumulation
Melt pond
Ice divide
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Inflow
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During the late Wisconsin glaciation, ice flow in west-central Newfoundland was to the north-northeast and northeast, sub-parallel to structural lineations. Constructional forms at this stage included drumlins, drumlinoid forms and ribbed moraine. -- The coast of Halls Bay was deglaciated about 12,000 B.P. in a relatively short period during which glaciomarine deltas were formed at Springdale, Dock Point, White Point, Barney's Brook, West Pond, South Brook and Sugarloaf; the latter three being remnants of a continuous terrace. Subsequent net isostatic and eustatic change positioned the deltas approximately 250 feet (75 meters) above present sea level. -- After the initial coastal stage of deglaciation, ice withdrew inland by stagnating in the valleys and lowlands leaving ridged ablation moraine and kettle topography. -- Ice receded in this manner to a plateau level 19 miles (30 kms.) from the coast, where a pause in retreat occurred. During this stage a series of recessional moraines was built and a zone of eskers formed near Barney's Brook and southeast of Sheffield Hill. Surficial crevasse fillings are also found within this zone. A final, topographically controlled flow into the Kitty's Brook - Chain Lakes valley system followed by stagnation, resulted in the fabrication of a series of recessional-ablation moraines. -- Last ice in the field area was situated to the southwest of Gaff Topsail and is evidenced by an area of hummocky, disintegration moraine.
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Terminal moraine
Wisconsin glaciation
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<p>Surface meltwater is transmitted to the bed of the Greenland Ice Sheet via supraglacial lake drainages, moulins, and crevasses. Of these, comparatively little research has been performed on the melt infiltration occurring in crevasse fields, which are widespread&#160; in fast-flowing, marine-terminating sectors of the ice sheet. Here, we explore the relationships between crevassing, incidence of surface meltwater, and glacier dynamics at a fast-flowing, marine-terminating sector of West Greenland. Data were collected at high spatial resolution from unmanned aerial vehicle (UAV) surveys on Store Glacier, Greenland, in July 2018. Crevasses and surface water were identified using an object-based machine learning classifier, and strain rates and subsequent stress fields were derived from feature-tracked velocities. Contemporaneous observations of&#160; crevasses and surface water on a larger regional scale were made using ArcticDEM and Sentinel-2 data processed in the Google Earth Engine cloud-based geospatial analysis platform, while stress fields are derived from MEaSUREs velocity data. We find that, whilst previous studies have focussed on relationships between crevassing and stress regime through yield criterion such as the Von Mises stress, we can additionally link the observed spatial distribution of surface meltwater over crevasse fields to the mean stress (defined as the arithmetic mean of the maximum and minimum stress). Crevasse fields existing in tensile mean stress regimes were less likely to exhibit ponded meltwater through a melt season, which we interpret as meltwater being able to continuously drain into the englacial system. Conversely, crevasse fields in compressive mean stress regimes were more likely to exhibit ponded meltwater, which we interpret to be as a result of englacial conduit closure. We show that in these compressive regions, water transfer takes place via intermittent drainage events (i.e. hydrofracture), as envisaged in linear elastic fracture mechanics (LEFM) models. Hence, stress regime can inform spatially heterogeneous styles of crevasse drainage across the ablation zone of an ice sheet: a continuous, low-intensity mode in extensional regimes, in contrast to an episodic, high-intensity mode in compressional regimes. These processes may have distinctly different impacts on basal processes, including subglacial drainage efficiency, diurnal variability, and cryo-hydrologic warming.</p>
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Meltwater
Greenland ice sheet
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AbstractOwing to increased winter balances especially since AD 1988/89, almost all valley outlet glaciers of Jostedalsbreen in western Norway are experiencing the largest advance since that of the early 18th century, the regional "Little Ice Age" maximum. Brigsdalsbreen advanced 441 m between 1987 and 1997. By the end of this period, the glacier had reached the outlet of the proglacial lake Brigsdalsvatnet, ploughing into unfrozen, fine‐grained, water‐soaked glaciolimnic sediments from the lake bottom and forming frontal moraines. These moraines are characterised by a lack of internal structures and preferred fabric. Owing to the strong advance, the moraine morphology is constantly changing, leaving only temporary moraine ridges.Observations made along the glacier front suggest that the formation of these moraines can best be described as "bulldozed moraines", since the term push moraine, commonly associated with advancing glaciers, should be restricted to permafront environments. Different processes involved in moraine formation at frontal and lateral glacier margins result from variations in proglacial sediment properties, microrelief and glacier dynamics. Among these processes, large boulders left in the proglacial areas are pushed forward, forming pressure ridges on the distal side. Some of the largest boulders (c. 80–120 m3) are overturned or rotated by the glacier.Key words: blockstreamsdebris depositsslope processesHigh Drakensberg
Terminal moraine
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Abstract Surface crevasses on the Greenland Ice Sheet (GrIS) capture nearly half of the seasonal runoff, yet their role in transferring meltwater to the bed has received little attention relative to that of supraglacial lakes and moulins. Here, we present observations of crevasse ponding and investigate controls on their hydrological behavior at a fast‐moving, marine‐terminating sector of the GrIS. We map surface meltwater, crevasses, and surface‐parallel stress across a ∼2,700 km 2 region using satellite data and contemporaneous uncrewed aerial vehicle (UAV) surveys. From 2017 to 2019 an average of 26% of the crevassed area exhibited ponding at locations that remained persistent between years despite rapid advection. We find that the spatial distribution of ponded crevasses does not relate to previously proposed controls on the distribution of supraglacial lakes (elevation and topography) or crevasses (von Mises stress thresholds), suggesting the operation of some other physical control(s). Ponded crevasse fields were preferentially located in regions of compressive surface‐parallel mean stress, which we interpret to result from the hydraulic isolation of these systems. This contrasts with unponded crevasse fields, which we suggest are readily able to transport meltwater into the wider supraglacial and englacial network. UAV observations show that ponded crevasses can drain episodically and rapidly, likely through hydrofracture. We therefore propose that the surface stress regime influences a spatially heterogeneous transfer of meltwater through crevasses to the bed of ice sheets, with consequences for processes, such as subglacial drainage and the heating of ice via latent heat release by refreezing meltwater.
Crevasse
Meltwater
Ponding
Greenland ice sheet
Ice divide
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Abstract Please click here to download the map associated with this article. A 1:30,000 scale map poster of the snout and proglacial landscape of the surging Icelandic glacier Brúarjökull, provides a spatial and temporal assessment of the geomorphic impacts of surging in glaciated terrains. Based upon aerial photography from 1998, 1999 and 2000, the map identifies the major landforms that are regarded as diagnostic of glacier surging when viewed in a landsystem framework; specifically, thrust block and push moraines, overridden thrust block moraines, zig-zag eskers, crevasse squeeze ridges, long utings, hummocky moraine and ice-cored, pitted outwash. This landscape imprint, when identi_ed in ancient glaciated terrains, can therefore be used as indicative of surge activity in palaeoglaciological reconstructions.
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Crevasse
Terminal moraine
Landform
Drumlin
Glacial landform
Aerial photography
Glacier terminus
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Abstract. The marine-terminating outlet in Basin 3, Austfonna ice cap, has been accelerating since the mid-1990s. Stepwise multi-annual acceleration associated with seasonal summer speed-up events was observed before the outlet entered the basin-wide surge in autumn 2012. We used multiple numerical models to explore hydrologic activation mechanisms for the surge behaviour. A continuum ice dynamic model was used to invert basal friction coefficient distributions using the control method and observed surface velocity data between April 2012 and July 2014. This has provided input to a discrete element model capable of simulating individual crevasses, with the aim of finding locations where meltwater entered the glacier during the summer and reached the bed. The possible flow paths of surface meltwater reaching the glacier bed as well as those of meltwater produced at the bed were calculated according to the gradient of the hydraulic potential. The inverted friction coefficients show the “unplugging” of the stagnant ice front and expansion of low-friction regions before the surge reached its peak velocity in January 2013. Crevasse distribution reflects the basal friction pattern to a high degree. The meltwater reaches the bed through the crevasses located above the margins of the subglacial valley and the basal melt that is generated mainly by frictional heating flows either to the fast-flowing units or potentially accumulates in an overdeepened region. Based on these results, the mechanisms facilitated by basal meltwater production, crevasse opening and the routing of meltwater to the bed are discussed for the surge in Basin 3.
Crevasse
Meltwater
Glacier ice accumulation
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