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A 200-km-long and 10-km-wide linear assemblage of till-filled geometrical ridges on the bed of the Maskwa palaeo-ice stream of the late Wisconsinan southwest Laurentide Ice Sheet are interpreted as crevasse-squeeze ridges (CSR) developed during internal flow unit reorganization, immediately prior to ice stream shutdown. Ridge orientations are predominantly orientated WNW–ESE, with a subordinate WSW–ENE alignment, both indicative of ice fracture development transverse to former ice stream flow, as indicated by NNE–SSW aligned MSGL. Subglacial till injection into basal and/or full depth, mode I and II crevasses occurred at the approximate centreline of the ice stream, in response to extension and fracturing. Landform preservation indicates that this took place during the final stages of ice streaming, immediately prior to ice stream shutdown. This linear zone of ice fracturing therefore likely represents the narrowing of the fast-flowing trunk, similar to the plug flow identified in some surging valley glaciers. Lateral drag between the final active flow unit and the slower moving ice on either side is likely recorded by the up-ice bending of the CSR limbs. The resulting CSR corridor, here related to an individual ice stream flow unit, constitutes a previously unreported style of crevasse infilling and contrasts with two existing CSR patterns: (1) wide arcuate zones of CSRs related to widespread fracturing within glacier surge lobes; and (2) narrow concentric arcs of CSRs and recessional push moraines related to submarginal till deformation at active temperate glacier lobes. [ABSTRACT FROM AUTHOR]

The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75°37.61' N, 35°56.49' W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations. Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11m ice equivalent (i.e.) for the period 1607-2011, although accumulation varied between 0.08 and 0.14mi.e., likely due to flowrelated changes in surface topography. Tracing of RES layers from the NGRIP (North Greenland Ice Core Project) ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice-lithosphere interactions of the Greenland Ice Sheet. [ABSTRACT FROM AUTHOR]

The transition from limited-slip conditions at the base of grounded ice to free-slip conditions beneath floating ice occurs across the few-kilometers-wide grounding zone. This region involves either an elastic flexural transition from bedrock to hydrostatically supported elevations (often tidally influenced), a transition from thicker to thinner ice over a flat bed, or some combination of these two processes. In either case, ice must flow across a changing stress field, often resulting in brittle deformation, manifested as basal crevassing. Thus the position and morphology of basal crevasses reveal important information about the stress state across this transition. Our gridded ground-based radar surveys on Whillans Ice Stream, West Antarctica, indicate a complex pattern of basal crevasses, but most are associated with regions where the surface elevation gradient is steepest. Due to the high reflectivity of sea water, we image many off-nadir crevasses from a corner-reflector geometry involving reflections from the ice/sea-water interface and then from the crevasse, producing echoes with an inverted phase that could be misinterpreted as subglacial returns. Our results indicate that basal crevasses offer a rich dataset for diagnosing stress state and salient processes across grounding zones, and that special care is needed when interpreting subglacial returns in radar data. [ABSTRACT FROM AUTHOR]

There remain large regions of scientific interest in the Antarctic that are not instrumented. These include highly dynamic ice streams and glaciers that are difficult or impossible to reach safely because heavy crevassing impedes an overland trek or an aircraft landing. We have developed an alternative strategy for instrumenting these regions: an aerodynamic sensor that can be dropped from an overflying aircraft. During freefall the sensor accelerates to its terminal velocity of 42 m s-1 before impacting with the glacier. On impact it partially buries itself in the snow while leaving an antenna mast protruding high above the surface to ensure a long operating life. In this paper, we describe the design and results of testing this aircraft-deployable sensor. Finally we present the initial results of two campaigns to instrument inaccessible regions of Pine Island Glacier, West Antarctica, and Scar Inlet, Antarctic Peninsula, with GPS receivers. [ABSTRACT FROM AUTHOR]

The article presents a study regarding the method for figuring the heights of basal crevasses formed at the grounding lines of ice shelves and ice streams. It states that a thin-elastic beam (TEB) formulation and tensional yielding criterion to captivate the physics of flexed ice at grounding lines are applied in the study. Results show the TEB formulation applied at upstream of observed basal crevasses has produces order-of-magnitude crevasse heights.

The flow of several large glaciers draining the Greenland Ice Sheet is accelerating. This change, combined with increased melting, suggests that existing estimates of future sea-level rise are too low. [ABSTRACT FROM AUTHOR]

The article reports on the crack observed to a glacier in the Northern Hemisphere by glaciologist Jason Box and colleagues of the Ohio State University on August 3, 2008. They stress that the breakdown of the glacier will result to a loss of 160 square kilometres and will be considered as the largest ice loss since its last break off of 86 kilometres in 2000-2001. According to a study, the glacier has lost 29 square kilometres from the Petermann glacier between July 10-24 of the same year and 10 square kilometres from the Jakobshavns glacier since the end of the melt season.