Journal articles: 'Devensian ice flow directions'

1

Davies, Bethan J., David H. Roberts, David R. Bridgland, and Colm Ó. Cofaigh. "Dynamic Devensian ice flow in NE England: a sedimentological reconstruction." Boreas 41, no. 3 (December 1, 2011): 337–36. http://dx.doi.org/10.1111/j.1502-3885.2011.00237.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Roman, Małgorzata. "Ice-flow directions of the last Scandinavian Ice Sheet in central Poland." Quaternary International 501 (January 2019): 4–20. http://dx.doi.org/10.1016/j.quaint.2017.11.035.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Joughin, Ian R., Mark A. Fahnestock, and Jonathan L. Bamber. "Ice flow in the northeast Greenland ice stream." Annals of Glaciology 31 (2000): 141–46. http://dx.doi.org/10.3189/172756400781820002.

Full text

Abstract:

AbstractWe have measured ice flow and detailed topography in northeastern Greenland using satellite-based synthetic-aperture radar (SAR) interferometry. The subject of this study is the large ice stream that drains this quadrant of the ice sheet. A single SAR interferogram allows the measurement of one component of motion over a several-day-long interval. We have used a set of such measurements from multiple look directions to produce a mosaic of ice-flow velocity. The resulting flow field is tied to an estimated balance-velocity distribution in slow-moving areas and assumes flow to be locally surface-parallel. The velocity field is the most detailed, consistent data-set available over a flow feature of this size. It compares with global positioning system surveyed velocity measurements at the 5 m a–1 level In the process of mapping ice-flow velocity an enhanced elevation model of the ice stream was produced. The elevation model is based on a blend of interferometrically measured short-wavelength topography and radar-altimetry-determined longer-wavelength topography. This enhanced model has improved information on local surface slope, which is useful for estimating the horizontal components of the velocity field.

APA, Harvard, Vancouver, ISO, and other styles

4

Roberts, Jason L., Roland C. Warner, and Adam Treverrow. "Inferring ice-flow directions from single ice-sheet surface images using the Radon transform." Journal of Glaciology 59, no. 213 (2013): 129–36. http://dx.doi.org/10.3189/2013jog12j042.

Full text

Abstract:

AbstractWe present a new method for extracting the direction of surface flow for ice sheets, based on the detection of flow-induced features that are visible in satellite imagery. The orientation of linear features is determined using a Radon transform and only requires a single image. The technique is demonstrated by applying it to the RADARSAT mosaic of Antarctica, over the Lambert Glacier–Amery Ice Shelf region of East Antarctica. Comparisons with both existing flow-direction fields and traced streamlines over the same area provide an evaluation of the method. We also illustrate its application to Landsat 7 imagery.

APA, Harvard, Vancouver, ISO, and other styles

5

Gemmell, Campbell, Dominic Smart, and David Sugden. "Striae and Former Ice-Flow Directions in Snowdonia, North Wales." Geographical Journal 152, no. 1 (March 1986): 19. http://dx.doi.org/10.2307/632935.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Godin, Laurent, Richard L. Brown, Aleksis Dreimanis, Gail M. Atkinson, and Derek K. Armstrong. "Analysis and reinterpretation of deformation features in the Rouge River valley, Scarborough, Ontario." Canadian Journal of Earth Sciences 39, no. 9 (September 1, 2002): 1373–91. http://dx.doi.org/10.1139/e02-059.

Full text

Abstract:

Geometry and timing of deformation affecting Ordovician bedrock and overlying Pleistocene sediments in the Rouge River valley near Scarborough, Ontario, are analysed to evaluate whether or not the structures are a result of glacial action or neotectonic activity. Extensive data on local and regional ice-flow directions are used to evaluate the kinematic compatibility between the observed faults and folds and the local ice-flow directions. Jointing and multiple episodes of faulting affect both the Ordovician bedrock and the overlying Pleistocene sediments. At one site, the bedrock is displaced by a normal fault by a minimum of 1.2 m. Crosscutting relationships constrain the majority of the faulting in the Rouge River valley as being coeval with deposition of the lower Bowmanville till during the Nissouri phase (ca. 2315 ka), and possibly younger at one locality. The youngest regional ice-flow direction is northwestward; however, local ice-flow directions are highly variable. This can be explained by local perturbation enhanced by the presence of drumlinoid features in the area. Most deformation features are compatible with local and regional ice-flow directions. Glaciotectonic ice-push and ice-thrust deformation affected the Thorncliffe Formation after about 23 ka. Although some faults appear to be kinematically incompatible with ice-flow directions, six boreholes drilled to 52 m depth revealed only minor vertical offsets of bedrock strata in the uppermost 20 m, and an absence of obvious fault offsets deeper, precluding the possibility that the faults observed in the surface exposures were caused by deep-seated neotectonic stresses.

APA, Harvard, Vancouver, ISO, and other styles

7

Gipp, Michael R. "Lift-off moraines: markers of last ice-flow directions on the Scotian Shelf." Canadian Journal of Earth Sciences 37, no. 12 (December 1, 2000): 1723–34. http://dx.doi.org/10.1139/e00-066.

Full text

Abstract:

Lift-off moraines are acoustically incoherent, subparallel ridges observed on sidescan sonograms and high-resolution reflection seismic profiles on the southeastern continental margin of Canada. They are up to 3 m high, 2080 m wide, and are commonly overlain by stratified proglacial sediments. Although little is known about them, detailed study of high-resolution seismic profiles from the Emerald Basin and the LaHave Basin, on the Scotian Shelf, show that their height:width ratio varies with the sounderseabed separation, suggesting that the ridges may be narrower than they appear. Their morphology is similar to DeGeer moraines or cross-valley moraines, which form perpendicular to ice-flow direction. As their orientations can be estimated at the intersection of seismic lines, they can be used to estimate ice-flow directions. Since proglacial sediments are draped directly over top of them, they are assumed to record the direction of last ice flow. This directional data suggests that ice retreated not only northward (to Nova Scotia), but also toward local topographic highs on the continental shelf, which acted as anchoring points for ice rises around both the Emerald and LaHave Basins. This pattern of ice-flow directions suggests that ice flowed from the high ground of banks, converging into basin deeps, suggesting that small moraines within the basins are probably of interlobate origin.

APA, Harvard, Vancouver, ISO, and other styles

8

Robert, Barry L. "Modeling the Cordilleran Ice Sheet." Géographie physique et Quaternaire 45, no. 3 (December 13, 2007): 287–99. http://dx.doi.org/10.7202/032876ar.

Full text

Abstract:

ABSTRACT A time-dependent ice flow model is used to provide detailed reconstructions of ice growth and retreat for the southern portion of the Late Wisconsinan Cordilleran Ice Sheet. The two-dimensional, time-dependent model provides ice surface elevations and flow directions at a grid spacing of 15 km. Input to the model includes subglacial topography, a net mass balance function, and two ice flow parameters. The net mass balance function uses a polynomial equation to estimate equilibrium line altitude (ELA) across the study area. A quadratic equation is then used to provide net mass balance values as a function of elevation relative to the ELA. Late Wisconsinan glacial conditions are simulated by systematically lowering the ELA. The general timing of the model ice advance and retreat is tested against radiocarbon dated localities which place limits on the ice sheet's areal extent for different times during the Late Wisconsinan glaciation. In addition, glacial-geologic evidence directly attributable to the latest Cordilleran Ice Sheet is used in assessing the model reconstructions. Results from these experiments show that an ice growth and retreat chronology consistent with the limiting radiocarbon dates can be generated using the model, and provide information on flow directions and ice growth and retreat patterns.

APA, Harvard, Vancouver, ISO, and other styles

9

Merritt, Jon W., Maxine C. Akhurst, Ian P. Wilkinson, James B. Riding, Emrys R. Phillips, Richard A. Smith, Andrew Finlayson, and Mark T. Dean. "The Late Pleistocene Afton Lodge Clay Formation, Ayrshire, Scotland: evidence for Early to Middle Devensian climatic changes and Late Devensian onshore ice flow and rafting from the Firth of Clyde." Proceedings of the Geologists' Association 125, no. 2 (March 2014): 195–214. http://dx.doi.org/10.1016/j.pgeola.2013.12.004.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

MERRITT, Jon W., Adrian M. HALL, John E. GORDON, and E. Rodger CONNELL. "Late Pleistocene sediments, landforms and events in Scotland: a review of the terrestrial stratigraphic record." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 110, no. 1-2 (March 2019): 39–91. http://dx.doi.org/10.1017/s1755691018000890.

Full text

Abstract:

ABSTRACTLithostratigraphical studies coupled with the development of new dating methods has led to significant progress in understanding the Late Pleistocene terrestrial record in Scotland. Systematic analysis and re-evaluation of key localities have provided new insights into the complexity of the event stratigraphy in some regions and the timing of Late Pleistocene environmental changes, but few additional critical sites have been described in the past 25 years. The terrestrial stratigraphic record remains important for understanding the timing, sequence and patterns of glaciation and deglaciation during the last glacial/interglacial cycle. Former interpretations of ice-free areas in peripheral areas during the Last Glacial Maximum (LGM) are inconsistent with current stratigraphic and dating evidence. Significant challenges remain to determine events and patterns of glaciation during the Early and Middle Devensian, particularly in the context of offshore evidence and ice sheet modelling that indicate significant build-up of ice throughout much of the period. The terrestrial evidence broadly supports recent reconstructions of a highly dynamic and climate-sensitive British–Irish Ice Sheet (BIIS), which apparently reached its greatest thickness in Scotland between 30 and 27ka, before the global LGM. A thick (relative to topography) integrated ice sheet reaching the shelf edge with a simple ice-divide structure was replaced after the LGM by a much thinner one comprising multiple dispersion centres and a more complex flow structure.

APA, Harvard, Vancouver, ISO, and other styles

11

Beltaos, Spyros. "River ice breakup processes: recent advances and future directions." Canadian Journal of Civil Engineering 34, no. 6 (June 1, 2007): 703–16. http://dx.doi.org/10.1139/l06-021.

Full text

Abstract:

The breakup of the winter ice cover is a brief but seminal event in the regime of northern rivers, and in the life cycle of river and basin ecosystems. Breakup ice jams can cause extreme flood events, with major impacts on riverside communities, aquatic life, infrastructure, navigation, and hydropower generation. Related concerns are underscored by the issue of climate change and the faster warming that is predicted for northern parts of the globe. Advances in knowledge of breakup processes and related topics, achieved over the past 15 years or so, are outlined. They pertain to breakup initiation and ice-jam formation, ice-jam properties and numerical modelling of ice jams, waves generated by ice-jam releases, forecasting and mitigation methods, sediment transport, ecological aspects, and climate-change impacts. Major knowledge gaps are associated with the dynamic interaction of moving ice with the flow and with the stationary ice cover. Increasing computing capacity and remote sensing sophistication are expected to provide effective means for bridging these gaps. Key words: climate, ecology, forecasting, ice jam, modelling, onset, sediment, wave.

APA, Harvard, Vancouver, ISO, and other styles

12

Sutherland, Jenna L., Bethan J. Davies, and Jonathan R. Lee. "A litho-tectonic event stratigraphy from dynamic Late Devensian ice flow of the North Sea Lobe, Tunstall, east Yorkshire, UK." Proceedings of the Geologists' Association 131, no. 2 (April 2020): 168–86. http://dx.doi.org/10.1016/j.pgeola.2020.03.001.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Fujita, Shuji, and Shinji Mae. "Relation between ice sheet internal radio-echo reflections and ice fabric at Mizuho Station, Antarctica." Annals of Glaciology 17 (1993): 269–75. http://dx.doi.org/10.1017/s0260305500012957.

Full text

Abstract:

The relationship between ice fabric and the internal radio-echo reflections was investigated using observation data collected at Mizuho Station, Antarctica. The data were obtained by 179 MHz radio-echo sounding and the ice fabric was measured from 700 m Mizuho ice core. The dielectric permittivity tensor at given depths in the ice sheet was calculated from the ice fabric. The calculated dielectric permittivity tensor showed that the ice sheet at Mizuho Station is a uniaxially birefringent medium. The symmetrical axis of rotation was the same as the flow line. In such a medium, theory predicts that the electric field vectors are allowed only in the two directions parallel and perpendicular to the flow line. The prediction coincided well with the observation: a strong signal was observed only when the transmitting antenna and the receiving antenna, kept parallel to one another, were oriented parallel or perpendicular to the flow line. However, the observed signal strength in these two directions differed from one another at each depth. It is also shown that the power reflection coefficient due to the variation of ice fabric with depth is of approximately the same order as that due to the density change and is large enough to produce the predominant internal radio-echo reflections.

APA, Harvard, Vancouver, ISO, and other styles

14

Fujita, Shuji, and Shinji Mae. "Relation between ice sheet internal radio-echo reflections and ice fabric at Mizuho Station, Antarctica." Annals of Glaciology 17 (1993): 269–75. http://dx.doi.org/10.3189/s0260305500012957.

Full text

Abstract:

The relationship between ice fabric and the internal radio-echo reflections was investigated using observation data collected at Mizuho Station, Antarctica. The data were obtained by 179 MHz radio-echo sounding and the ice fabric was measured from 700 m Mizuho ice core. The dielectric permittivity tensor at given depths in the ice sheet was calculated from the ice fabric.The calculated dielectric permittivity tensor showed that the ice sheet at Mizuho Station is a uniaxially birefringent medium. The symmetrical axis of rotation was the same as the flow line. In such a medium, theory predicts that the electric field vectors are allowed only in the two directions parallel and perpendicular to the flow line. The prediction coincided well with the observation: a strong signal was observed only when the transmitting antenna and the receiving antenna, kept parallel to one another, were oriented parallel or perpendicular to the flow line. However, the observed signal strength in these two directions differed from one another at each depth.It is also shown that the power reflection coefficient due to the variation of ice fabric with depth is of approximately the same order as that due to the density change and is large enough to produce the predominant internal radio-echo reflections.

APA, Harvard, Vancouver, ISO, and other styles

15

Bengtsson, Lars. "Dispersion in Ice-Covered Lakes." Hydrology Research 17, no. 3 (June 1, 1986): 151–70. http://dx.doi.org/10.2166/nh.1986.0010.

Full text

Abstract:

Dispersion studies in three ice-covered lakes are presented. One of the lakes has a large river through-flow. In the other two lakes, small seiche-induced currents are generated through wind action on the ice cover. Dispersion coefficients are computed from five dye experiments lasting from ½ day to 16 days. These coefficients are related to measured current velocities. The turbulence in the river-flow dominated lake is found to be very low with disperision coefficients less than 1 cm2/s in directions transverse to the flow. In the lakes where the turbulence is generated by shear from the seiche-induced currents the horizontal dispersion coefficients are two orders of magnitude higher, being almost as high as in ice-free lakes.

APA, Harvard, Vancouver, ISO, and other styles

16

Lavoie, C., E. W. Domack, E. C. Pettit, T. A. Scambos, R. D. Larter, H. W. Schenke, K. C. Yoo, et al. "Paleo-ice flow directions of the Northern Antarctic Peninsula ice sheet based upon a new synthesis of seabed imagery." Cryosphere Discussions 8, no. 5 (October 15, 2014): 5321–60. http://dx.doi.org/10.5194/tcd-8-5321-2014.

Full text

Abstract:

Abstract. We present a new seafloor map for the northern Antarctic Peninsula (AP), including swath multibeam data sets from five national programs. Our map allows for the examination and interpretation of Last Glacial Maximum (LGM) paleo-ice sheet/stream flow directions developed upon the seafloor from the preservation of: mega-scale glacial lineations, drumlinized features, and selective linear erosion. We combine this with terrestrial observations of flow direction to place constraints on ice divides and accumulation centers (ice domes) on the AP continental shelf. The results show a flow bifurcation as ice exits the Larsen-B embayment. Flow emanating off the Seal Nunataks (including Robertson Island) is directed toward the southeast, then eastward as the flow transits toward the Robertson Trough. A second, stronger "streaming flow" is directed toward the southeast then southward, as ice overflowed the tip of the Jason Peninsula to reach the southern perimeter of the embayment. Our reconstruction also refines the extent of at least five other distinct paleo-ice stream systems which, in turn, serve to delineate seven broad regions where contemporaneous ice domes must have been centered on the continental shelf during the LGM time interval. Our reconstruction is more detailed than other recent compilations because we followed specific flow indicators and have kept tributary flow paths parallel.

APA, Harvard, Vancouver, ISO, and other styles

17

Coughlan, Mark, Zsuzsanna TÓth, Katrien J. J. Van Landeghem, Stephen Mccarron, and Andrew J. Wheeler. "Formational history of the Wicklow Trough: a marine‐transgressed tunnel valley revealing ice flow velocity and retreat rates for the largest ice stream draining the late‐Devensian British–Irish Ice Sheet." Journal of Quaternary Science 35, no. 7 (August 27, 2020): 907–19. http://dx.doi.org/10.1002/jqs.3234.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Rea, Brice R., David J. A. Evans, Tom S. Dixon, and W. Brian Whalley. "Contemporaneous, localized, basal ice-flow variations: implications for bedrock erosion and the origin of p-forms." Journal of Glaciology 46, no. 154 (2000): 470–76. http://dx.doi.org/10.3189/172756500781833197.

Full text

Abstract:

AbstractA detailed study of a proglacial bedrock site and a subglacial cavity of an outlet of Øksfjordjøkelen, Norway, is presented together with observations from the foreland of Konowbreen, Spitsbergen. Striation directions and subglacial observations indicate that local ice-flow paths were highly variable, deviating at angles of approximately 90° from the main ice-flow direction. Stepped bedrock topography appears conducive to the production of highly variable ice-flow paths, because the high bed roughness creates a locally variable stress regime within the ice, including low-pressure, lee-side areas into which ice can flow. If ice flow is sustained along a specific path and the ice contains debris, then abrasion should produce an erosional bedform. Models are proposed whereby locally variable ice-flow patterns could produce erosional bedforms, which would be described as p-forms, purely through mechanical abrasion.

APA, Harvard, Vancouver, ISO, and other styles

19

Lagerlund, E. "Unexpected ice flow directions and transport of rocks in the south Peribaltic area." GFF 118, sup004 (October 1996): 77. http://dx.doi.org/10.1080/11035899609546373.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Broster, B. E., M. D. Munn, and A. G. Pronk. "Inferences on glacial flow from till clast dispersal, Waterford area, New Brunswick." Géographie physique et Quaternaire 51, no. 1 (October 2, 2002): 29–39. http://dx.doi.org/10.7202/004773ar.

Full text

Abstract:

Abstract Dispersal patterns for till clasts from the Waterford area, New Brunswick, are compared to source outcrops and used to confirm dominant ice-flow directions in a region reported to show multiple and conflicting striae directions. The results demonstrate that the last glaciation produced elongated south and eastward trending dispersal patterns, indicative of the dominant ice-flow directions. Clasts have been derived locally. Train lengths generally vary from 4 km to about 10 km for material in basal till, but can achieve distances up to 26 km because of transport in englacial positions. Felsic and intermediate metavolcanic and intrusive clasts occur in till at locations north of outcropping plutons on the Central Plateau. The till overlies part of the Carboniferous Basin and has been derived in part, from underlying conglomerate bedrock. Since these conglomerate units contain fragments from the surrounding areas including the Central Plateau, they provided a secondary source for some lithologies during glaciation. Glacial erosion of underlying conglomerate units may account for occurrences of distinctive till clasts found at other areas of the New Brunswick lowlands, previously thought to imply northward glacial transport.

APA, Harvard, Vancouver, ISO, and other styles

21

Fudge, T. J., H. Conway, G. Catania, D. D. Blankenship, K. Christianson, I. Joughin, B. Smith, S. D. Kempf, D. A. Young, and S. Anandakrishnan. "Identifying flowlines and limitations of flux analyses in the interior of Thwaites Glacier, Antarctica." Annals of Glaciology 55, no. 67 (2014): 107–14. http://dx.doi.org/10.3189/2014aog67a033.

Full text

Abstract:

AbstractPatterns in radar-detected internal layers in glaciers and ice streams can be tracked hundreds of kilometers downstream. We use distinctive patterns to delineate flowbands of Thwaites Glacier in the Amundsen Sea sector of West Antarctica. Flowbands contain information for the past century to millennium, the approximate time for ice to flow through the study region. GPS-detected flow directions (acquired in 2007/08) agree within uncertainty (~4°) with the radar-detected flowlines, indicating that the flow direction has not changed significantly in recent centuries. In contrast, InSAR-detected directions (from 1996) differ from the radar- and GPS-detected flowlines in all but the middle tributary, indicating caution is needed when using InSAR velocities to define flow directions. There is agreement between all three datasets in the middle tributary. We use two radar-detected flowlines to define a 95 km long flowband and perform a flux balance analysis using InSAR-derived velocities, radar-detected ice thickness, and estimates of the accumulation rate. Inferred thinning of 0.49 ± 0.34 m a–1 is consistent with satellite altimetry measurements, but has higher uncertainty due mainly to the velocity uncertainty. The uncertainty is underestimated because InSAR velocities often differ from GPS velocities by more than the stated uncertainties.

APA, Harvard, Vancouver, ISO, and other styles

22

Hvidberg, Christine Schøtt, Kristian Keller, and Niels S. Gundestrup. "Mass balance and ice flow along the north-northwest ridge of the Greenland ice sheet at NorthGRIP." Annals of Glaciology 35 (2002): 521–26. http://dx.doi.org/10.3189/172756402781816500.

Full text

Abstract:

AbstractThe North Greenland Icecore Project (NorthGRIP) deep drilling site (75˚05’47’’N, 42˚19’42’’ W) is located at the north-northwest ridge of the Greenland ice sheet, 320 km from Summit. A strain net has been established around the NorthGRIP site and surveyed with global positioning system. Our results show that ice flows with a horizontal surface velocity of 1.329 ±0.015ma–1 along the ridge. Estimated principal surface strain rates at NorthGRIP are and in the directions along and transverse to the north-northwest ridge, respectively, i.e. ice is compressed along the ridge but stretched transverse to the ridge. Possible implications of the observed flow pattern for the stratigraphy are discussed. the average thickening rate in the strain-net area is found to be ∂H/∂t = 0.00 ±0.04ma– 1, in agreement with previous estimates of mass balance in high-elevation areas of Greenland.

APA, Harvard, Vancouver, ISO, and other styles

23

Rempel, Alan. "Englacial phase changes and intergranular flow above subglacial lakes." Annals of Glaciology 40 (2005): 191–94. http://dx.doi.org/10.3189/172756405781813564.

Full text

Abstract:

AbstractGlaciers are permeated by liquid veins that line the triple junctions between ice grains and act as conduits for material transport. The density difference between water and ice produces a hydraulic gradient that drives liquid flow down towards the glacier bed. We investigate how variations in this transport rate are manifest in the lower regions of a glacier that floats on a subglacial reservoir. When the temperature rises towards the glacier bed, the associated permeability increase leads to more rapid fluid transport; internal melting supplies the changing flow. A reduction in hydraulic gradient results from surface energy effects, and causes a decreasing transport rate near the base; hence, freezing occurs within the polycrystalline ice. For representative values of the heat flux, soluble impurity loading and grain-size, the downward flux peaks at approximately 1–100mma–1 several tens of centimeters above the glacier bed. Beneath this level, the effects of surface energy control the fluid transport and cause the flow to reverse directions, pulling liquid upwards into the polycrystalline ice so that the flow does not introduce glacial material into the underlying reservoir.

APA, Harvard, Vancouver, ISO, and other styles

24

Veillette, J. J. "Former southwesterly ice flows in the Abitibi–Timiskaming region: implications for the configuration of the late Wisconsinan ice sheet." Canadian Journal of Earth Sciences 23, no. 11 (November 1, 1986): 1724–41. http://dx.doi.org/10.1139/e86-159.

Full text

Abstract:

Measurements at some 300 cross-striated sites in the Abitibi–Timiskaming area of Quebec and Ontario revealed two former directions of ice flow: an older west-southwest one (230–270°) in the extreme western part of the area, and a younger, widespread south-southwest one (180–220°) in the region west of the Harricana – Lake McConnell glaciofluvial complex. These sets of older striae, whether one or both on the same outcrop, are almost everywhere crossed by marks of a younger ubiquitous flow to the south-southeast (130–170°). On the basis of striae directions measured below an older till and of three dates obtained from intertill (below the surficial till) nonglacial sediments in the Timmins and Matheson areas in Ontario and the Selbaie mine area in Quebec, the oldest west-southwest (230–270°) striae are tentatively associated with the west-southwest flow that deposited this lowermost till in early to mid-Wisconsinan time or earlier.The Harricana – Lake McConnell glaciofluvial system extends from James Bay to the vicinity of North Bay Ontario and probably continues farther south to the Lake Simcoe area. It is strictly an interlobate deglaciation feature and does not result from the converging flows of two coalescing glaciers. At the last glacial maximum the dominant ice-flow direction in the area was probably toward the southwest, across the space occupied by this glaciofluvial system, confirming the flow lines shown by most models of the late Wisconsinan ice sheet. Because none of the cross-striated outcrops showing marks of the former south-southwest (180–220°) and of the last south-southeast (130–170°) movements show evidence of differential weathering and because glacial transport was due to the former southwest movement at several locations, it is proposed that the cross-striations result from the same ice mass subjected to (1) a general change in flow direction from the southwest to the southeast and (2) a complete scission that led ultimately to the deposition of the Harricana – Lake McConnell glaciofluvial system in the interlobate position.

APA, Harvard, Vancouver, ISO, and other styles

25

Meean, Robert T. "Directions of ice flow during the last glaciation in counties Meath, Westmeath and Cavan." Irish Geography 32, no. 1 (January 1999): 26–51. http://dx.doi.org/10.1080/00750779909478614.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Nye, J. F. "The topology of ice-sheet centres." Journal of Glaciology 37, no. 126 (1991): 220–27. http://dx.doi.org/10.1017/s0022143000007231.

Full text

Abstract:

AbstractAn ice sheet will, in general, possess points where the horizontal component of velocity is zero, and some of these will be ice centres, occurring close to summits. The paper examines the possible flow patterns near such points. The corresponding horizontal strain-rate pattern is studied by considering an ice sheet which initially has perfect circular symmetry about a vertical axis. Before perturbation there is an isotropic point for the horizontal surface strain rate at the centre. It may be shown, on purely topological grounds and without any reference to the mechanism of flow, that, when the symmetry is broken, this point, being degenerate and structurally unstable, breaks up into two structurally stable components. The breakup always occurs in essentially the same way. Around the two component points the trajectories of principal strain-rate directions always have the lemon pattern. The contours of equal principal strain rate around them are usually hyperbolic; however, if the unperturbed flow pattern had a very pronounced spiral character, they would be elliptic. This behaviour is in contrast to that of the ice centre itself, which remains unsplit.

APA, Harvard, Vancouver, ISO, and other styles

27

Nye, J. F. "The topology of ice-sheet centres." Journal of Glaciology 37, no. 126 (1991): 220–27. http://dx.doi.org/10.3189/s0022143000007231.

Full text

Abstract:

AbstractAn ice sheet will, in general, possess points where the horizontal component of velocity is zero, and some of these will be ice centres, occurring close to summits. The paper examines the possible flow patterns near such points. The corresponding horizontal strain-rate pattern is studied by considering an ice sheet which initially has perfect circular symmetry about a vertical axis. Before perturbation there is an isotropic point for the horizontal surface strain rate at the centre. It may be shown, on purely topological grounds and without any reference to the mechanism of flow, that, when the symmetry is broken, this point, being degenerate and structurally unstable, breaks up into two structurally stable components. The breakup always occurs in essentially the same way. Around the two component points the trajectories of principal strain-rate directions always have the lemon pattern. The contours of equal principal strain rate around them are usually hyperbolic; however, if the unperturbed flow pattern had a very pronounced spiral character, they would be elliptic. This behaviour is in contrast to that of the ice centre itself, which remains unsplit.

APA, Harvard, Vancouver, ISO, and other styles

28

Brocklehurst, Paul, Alexander Korobkin, and Emilian I. Părău. "Hydroelastic wave diffraction by a vertical cylinder." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369, no. 1947 (July 28, 2011): 2832–51. http://dx.doi.org/10.1098/rsta.2011.0110.

Full text

Abstract:

A linear three-dimensional problem of hydroelastic wave diffraction by a bottom-mounted circular cylinder is analysed. The fluid is of finite depth and is covered by an ice sheet, which is clamped to the cylinder surface. The ice stretches from the cylinder to infinity in all lateral directions. The hydroelastic behaviour of the ice sheet is described by linear elastic plate theory, and the fluid flow by a potential flow model. The two-dimensional incident wave is regular and has small amplitude. An analytical solution of the coupled problem of hydroelasticity is found by using a Weber transform. We determine the ice deflection and the vertical and horizontal forces acting on the cylinder and analyse the strain in the ice sheet caused by the incident wave.

APA, Harvard, Vancouver, ISO, and other styles

29

Hibler, W. D., and Erland M. Schulson. "On modeling sea-ice fracture and flow in numerical investigations of climate." Annals of Glaciology 25 (1997): 26–32. http://dx.doi.org/10.3189/s0260305500190019.

Full text

Abstract:

Sea ice on the large scale is characterized by leads and ridges that typically have a given orientation. Because of various flaws, we would expect that the ice will form oriented leads and ice-thickness characteristics that control the heat and moisture fluxes into the atmosphere. Prediction of these oriented leads, ridges and slip lines is relevant to understanding the role of ice mechanics in global climate change as they can play a significant role in the ice-thickness distribution.In this paper we develop a model for the dynamical treatment of leads and oriented flaws in large-scale sea-ice models. Two particular isotropic realizations of this model relevant to climate studies are examined: (a) an isotropic composite with oriented leads in all directions imbedded in thick ice, and (b) a simple "strain hardening" isotropic model where only oriented leads having the potential to open rapidly are allowed. Under applied stress both models yield preferential deformation along a symmetric pair of intersecting leads or ridges with the intersection angles dependent on the confinement stress. The "uniform-orientation" model results in a yield curve that approximates a sine lens, while the "strain hardening" model has a teardrop-like yield curve. How the resulting fracture-based yield curves and non-normal flow rules may be cast in a form usable in numerical investigations of climate is discussed.

APA, Harvard, Vancouver, ISO, and other styles

30

Clark, Peter. "A note on the glacial geology and postglacial emergence of the Lake Harbour region, Baffin Island, N.W.T." Canadian Journal of Earth Sciences 22, no. 12 (December 1, 1985): 1864–71. http://dx.doi.org/10.1139/e85-197.

Full text

Abstract:

Ice-flow indicators in the Lake Harbour region of northern Hudson Strait define two flow directions affecting this area during the late Wisconsinan glaciation. A pronounced southward flow direction indicated by medium- and large-scale erosional and depositional features represents ice flow from an ice dome centered to the north, perhaps Foxe Basin and (or) Amadjuak Lake. Carbonate-rich till and striations represent eastward–southeastward ice flow down the axis of Hudson Strait. Convergence of ice-sheet flow with a rapidly moving ice stream has been observed and modelled for West Antarctic ice streams and involves sharp bending of flow lines at the point of convergence. A similar scenario is proposed for the Lake Harbour region to explain the two contrasting ice-flow patterns. Impingement of an ice stream in Hudson Strait onto the southern coast of Baffin Island suggests the influence of northerly flowing ice, perhaps from the Ungava plateau.Radiocarbon dates on marine shells and archeological samples are used to reconstruct the postglacial emergence of the Lake Harbour region. The marine limit (90 m aht) and deglaciation are dated by extrapolation at ca. 8300 years BP. Postglacial emergence is characterized by an initial uplift rate of 4.4 m/100 years, which decreased to 0.2 m/100 years over the last 3900 years. The initial rate (4.4 m/100 years) is nearly 50% lower than rates calculated elsewhere in the Hudson Strait region and is interpreted to reflect the influence of an ice load centered over Amadjuak Lake directly north of the Lake Harbour region.

APA, Harvard, Vancouver, ISO, and other styles

31

Schaetzl, Randall J. "LATE PLEISTOCENE ICE-FLOW DIRECTIONS AND THE AGE OF GLACIAL LANDSCAPES IN NORTHERN LOWER MICHIGAN." Physical Geography 22, no. 1 (January 2001): 28–41. http://dx.doi.org/10.1080/02723646.2001.10642728.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Wu, Xiaolan, and Kenneth C. Jezek. "Antarctic ice-sheet balance velocities from merged point and vector data." Journal of Glaciology 50, no. 169 (2004): 219–30. http://dx.doi.org/10.3189/172756504781830042.

Full text

Abstract:

AbstractWe estimate Antarctic ice-flow balance velocities, which are the average speeds that ice must flow downslope through a volume assuming that there are equal amounts of ice entering and leaving the ice volume. We use the OSU (Ohio State University) digital elevation model of Antarctica, recent ice accumulation rate data and the BEDMAP ice-thickness data compilations for Antarctica to characterize the physical properties of the ice sheet that are included in the balance-velocity calculation. We adapt a flux algorithm from the hydrology literature that enables us to calculate the flux distribution from any cell in any order. Flux from one cell to its neighbors is partitioned as a simple function of surface slope direction. Digitized flow-stripe directions from satellite images minimize errors in flow direction where surface slopes are low or complex. We estimate errors in balance velocity arising from errors in the data and show semi-quantitatively how properties of the algorithm bias the balance-velocity result. We find a favorable comparison between our model and observed velocity data as well as the balance-velocity patterns reported by other researchers.

APA, Harvard, Vancouver, ISO, and other styles

33

Hulton, N. R. J., and M. J. Mineter. "Modelling self-organization in ice streams." Annals of Glaciology 30 (2000): 127–36. http://dx.doi.org/10.3189/172756400781820561.

Full text

Abstract:

AbstractThe EISMINT II experiments revealed the tendency for idealized model ice sheets to produce spatially variable flow under certain uniform thermal, mass-balance and topographic boundary conditions. Warm, fast-flowing streams with enhanced creep were separated by zones of colder, slower flow. Similar but different spatial patterns of differentiated flow were produced by all authors. We present further experiments that explore the formation and function of such ice streams at higher modelled resolutions. These are explored by the use of flat, but stochastically rough (10 m amplitude) beds, idealized, parallel-sided model ice sheets and models of finer (12.5 and 5 km) resolutions. Ice streams self-organize irregularly, but with consistent typical spacings which vary with thermal and miss-balance boundary conditions. More radial features are produced at finer scales indicating a dependency on the grid resolution used although this is not linear; at finer resolutions streams occupy increasingly more gridcells. This variation in scale may be related to the finer resolution of the warm/cold streaming/non-streaming boundary. The numerical solution of the thermodynamic ice equation is also highly sensitive to the orthogonality of the model grid. A major deficiency is that the numerical solution appears to fail where the flow is parallel to the grid axes, suggesting that artificial diffusion in the numerical scheme helps to smooth streams lying across the axes directions. The inclusion of sliding produces fewer, more concentrated, flow features, but these also display a level of scale-dependent organization. The spatial arrangement of such streams adjusts in response to the global mass flux of the ice sheet between "warm" and "cold" flow end-member. The results point to a mechanism in which ice sheets respond to climate by altering the large-scale arrangement of their flow patterns.

APA, Harvard, Vancouver, ISO, and other styles

34

Napieralski, Jacob, Alun Hubbard, Yingkui Li, Jon Harbor, Arjen P. Stroeven, Johan Kleman, Göran Alm, and Krister N. Jansson. "Towards a GIS assessment of numerical ice-sheet model performance using geomorphological data." Journal of Glaciology 53, no. 180 (2007): 71–83. http://dx.doi.org/10.3189/172756507781833884.

Full text

Abstract:

AbstractA major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.

APA, Harvard, Vancouver, ISO, and other styles

35

Burton-Johnson, Alex, Ricarda Dziadek, and Carlos Martin. "Review article: Geothermal heat flow in Antarctica: current and future directions." Cryosphere 14, no. 11 (November 10, 2020): 3843–73. http://dx.doi.org/10.5194/tc-14-3843-2020.

Full text

Abstract:

Abstract. Antarctic geothermal heat flow (GHF) affects the temperature of the ice sheet, determining its ability to slide and internally deform, as well as the behaviour of the continental crust. However, GHF remains poorly constrained, with few and sparse local, borehole-derived estimates and large discrepancies in the magnitude and distribution of existing continent-scale estimates from geophysical models. We review the methods to estimate GHF, discussing the strengths and limitations of each approach; compile borehole and probe-derived estimates from measured temperature profiles; and recommend the following future directions. (1) Obtain more borehole-derived estimates from the subglacial bedrock and englacial temperature profiles. (2) Estimate GHF from inverse glaciological modelling, constrained by evidence for basal melting and englacial temperatures (e.g. using microwave emissivity). (3) Revise geophysically derived GHF estimates using a combination of Curie depth, seismic, and thermal isostasy models. (4) Integrate in these geophysical approaches a more accurate model of the structure and distribution of heat production elements within the crust and considering heterogeneities in the underlying mantle. (5) Continue international interdisciplinary communication and data access.

APA, Harvard, Vancouver, ISO, and other styles

36

Wesche, Christine, Olaf Eisen, Hans Oerter, Daniel Schulte, and Daniel Steinhage. "Surface topography and ice flow in the vicinity of the EDML deep-drilling site, Antarctica." Journal of Glaciology 53, no. 182 (2007): 442–48. http://dx.doi.org/10.3189/002214307783258512.

Full text

Abstract:

AbstractInterpretation of ice-core records requires accurate knowledge of the past and present surface topography and stress–strain fields. The European Project for Ice Coring in Antarctica (EPICA) drilling site (75.0025° S, 0.0684° E; 2891.7 m) in Dronning Maud Land, Antarctica, is located in the immediate vicinity of a transient and forking ice divide. A digital elevation model is determined from the combination of kinematic GPS measurements with the GLAS12 datasets from the ICESat. Based on a network of stakes, surveyed with static GPS, the velocity field around the drilling site is calculated. The annual mean velocity magnitude of 12 survey points amounts to 0.74 m a–1. Flow directions mainly vary according to their distance from the ice divide. Surface strain rates are determined from a pentagonshaped stake network with one center point close to the drilling site. The strain field is characterized by along-flow compression, lateral dilatation and vertical layer thinning.

APA, Harvard, Vancouver, ISO, and other styles

37

Möller, D., and B. Ritter. "Glacial Geodetic Contributions to the Mass Balance and Dynamics of Ice Shelves." Annals of Glaciology 11 (1988): 89–94. http://dx.doi.org/10.1017/s0260305500006388.

Full text

Abstract:

The glacial geodetic contribution to the mass balance and dynamics of ice shelves includes repeated determinations of the absolute position (ϕ,λ,Η) of selected points (using satellite methods), the establishment of relative positions (y,x,Δh) in deformation figures, and height measurements. The results are used to establish ice-flow velocities and directions, strain and rotation rates, and changes in height. Modelling of deformation parameters at a few points over a large ice shelf is made possible by the collocation method. Results of these observations and analysis of Ekström Ice Shelf for the period 1979–87 are reported.

APA, Harvard, Vancouver, ISO, and other styles

38

Möller, D., and B. Ritter. "Glacial Geodetic Contributions to the Mass Balance and Dynamics of Ice Shelves." Annals of Glaciology 11 (1988): 89–94. http://dx.doi.org/10.3189/s0260305500006388.

Full text

Abstract:

The glacial geodetic contribution to the mass balance and dynamics of ice shelves includes repeated determinations of the absolute position (ϕ,λ,Η) of selected points (using satellite methods), the establishment of relative positions (y,x,Δh) in deformation figures, and height measurements. The results are used to establish ice-flow velocities and directions, strain and rotation rates, and changes in height. Modelling of deformation parameters at a few points over a large ice shelf is made possible by the collocation method. Results of these observations and analysis of Ekström Ice Shelf for the period 1979–87 are reported.

APA, Harvard, Vancouver, ISO, and other styles

39

Christ, Andrew J., and Paul R. Bierman. "The local Last Glacial Maximum in McMurdo Sound, Antarctica: Implications for ice-sheet behavior in the Ross Sea Embayment." GSA Bulletin 132, no. 1-2 (May 2, 2019): 31–47. http://dx.doi.org/10.1130/b35139.1.

Full text

Abstract:

AbstractDuring the Last Glacial Maximum (LGM), a grounded ice sheet filled the Ross Sea Embayment in Antarctica and deposited glacial sediments on volcanic islands and peninsulas in McMurdo Sound and coastal regions of the Transantarctic Mountains. The flow geometry and retreat history of this ice are debated, with contrasting views yielding divergent implications for the interaction between and stability of the East and West Antarctic ice sheets during late Quaternary time. Here, we present terrestrial geomorphologic evidence and reconstruct former ice-marginal environments, ice sheet elevations, and ice-flow directions in McMurdo Sound. Fossil algae in ice-marginal sediments provide a coherent radiocarbon chronology of maximum ice extent and deglaciation. We integrate these data with marine records to reconstruct grounded ice dynamics in McMurdo Sound and the western Ross Sea. The combined data set suggests ice flow toward the Transantarctic Mountains in McMurdo Sound during peak glaciation, with thick, grounded ice at or near its maximum position between 19.6 and 12.3 ka. Persistent grounded ice in McMurdo Sound and across the western Ross Sea after Meltwater Pulse 1a (14.0–14.5 ka) suggests that this sector of Antarctica did not significantly contribute to this rapid sea-level rise event. Our data show no significant advance of locally derived ice from the Transantarctic Mountains into McMurdo Sound during the local LGM.

APA, Harvard, Vancouver, ISO, and other styles

40

McClenaghan, M. B., and R. N. W. DiLabio. "Ice-flow history and glacial dispersal patterns, southeastern Cape Breton Island, Nova Scotia: implications for mineral exploration." Canadian Journal of Earth Sciences 33, no. 2 (February 1, 1996): 351–62. http://dx.doi.org/10.1139/e96-026.

Full text

Abstract:

Regional till sampling and stratigraphic studies were completed in southeastern Cape Breton Island, Nova Scotia, in 1990 and 1991 to document the directions and distances that successive ice-flow events have dispersed material and to document regional till geochemical patterns to aid mineral exploration in this heavily drift-covered area. Three major Wisconsinan ice-flow events affected the area: an early eastward flow, followed by a northeastward flow, and finally a southward flow. The shape and magnitude of dispersal trains in the area are the net result of the three ice-flow events, which are variable from north to south. In the north, the northeast ice flow was the dominant erosive and depositional event, producing a large northeast-trending drumlin field. Salmon River porphyry clasts and Pb- and Zn-rich till from the Yava Pb mine were dispersed more than 15 km to the northeast. In the south, eastward ice flow was the dominant erosive and depositional event, producing large east-trending till ridges. Dispersal in this area is difficult to detect because exotic red silty till in the giant till ridges masks underlying mineralized bedrock and dilutes the locally derived glacial debris. Many precious and base metal anomalies and dispersal trains were identified in the regional till samples, several of which are related to unknown mineralized sources.

APA, Harvard, Vancouver, ISO, and other styles

41

Åberg, Annika Katarina, Seija Kultti, Anu Kaakinen, Kari O. Eskola, and Veli-Pekka Salonen. "Weichselian sedimentary record and ice-flow patterns in the Sodankylä area, central Finnish Lapland." Bulletin of the Geological Society of Finland 92, no. 2 (December 15, 2020): 77–98. http://dx.doi.org/10.17741/bgsf/92.2.001.

Full text

Abstract:

Three different till units separated by interstadial fluvial deposits were observed in the Sodankylä area in the River Kitinen valley, northern Finland. The interbedded glaciofluvial sediments and palaeosol were dated by OSL to the Early (79±12 to 67±13 ka) and Middle (41±9 ka) Weichselian. A LiDAR DEM, glacial lineations, the flow direction of till fabrics, esker chains and striations were applied to investigate the glacial flow patterns of the Sodankylä, Kittilä and Salla areas. The analysis revealed that the youngest movement of the Scandinavian Ice Sheet is not visible as DEM lineations within the studied areas. The modern morphology in Kittilä and Salla shows streamlined landforms of various dimensions mainly oriented from the NW and NNW, respectively, corresponding to the Early/Middle Weichselian ice-flow directions inferred from till fabrics. The Late Weichselian ice flow has produced an insignificant imprint on the landforms. This study suggests a northern location for the ice-divide zone during the Early/Middle Weichselian, and a more western–southwestern position during the Late Weichselian. The OSL ages of 14±3.3 ka from the aeolian deposits may indicate ice-free areas during the Bølling–Allerod warm period in the vicinity of the River Kitinen.

APA, Harvard, Vancouver, ISO, and other styles

42

BÖSE, MARGOT. "Reconstruction of ice flow directions south of the Baltic Sea during the Saalian and Weichselian glaciations." Boreas 19, no. 3 (January 16, 2008): 217–26. http://dx.doi.org/10.1111/j.1502-3885.1990.tb00447.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Drews, Reinhard, Carlos Martín, Daniel Steinhage, and Olaf Eisen. "Characterizing the glaciological conditions at Halvfarryggen ice dome, Dronning Maud Land, Antarctica." Journal of Glaciology 59, no. 213 (2013): 9–20. http://dx.doi.org/10.3189/2013jog12j134.

Full text

Abstract:

AbstractWe present a comprehensive approach (including field data, remote sensing and an anisotropic ice-flow model) to characterize Halvfarryggen ice dome in coastal Dronning Maud Land, Antarctica. This is a potential drill site for the International Partnerships in Ice Core Sciences, which has identified the need for ice cores covering atmospheric conditions during the last few millennia. We derive the surface topography, the ice stratigraphy from radar data, and accumulation rates which vary from 400 to 1670 kg m−2 a−1 due to preferred wind directions and changing surface slope. The stratigraphy shows anticlines and synclines beneath the divides. We transfer Dansgaard–Johnsen age–depth scales from the flanks along isochrones to the divide in the upper 20–50% of the ice thickness and show that they compare well with the results of a full-Stokes, anisotropic ice-flow model which predicts (1) 11 ka BP ice at 90% of the ice thickness, (2) a temporally stable divide for at least 2700–4500 years, (3) basal temperatures below the melting point (−12°C to −5°C) and (4) a highly developed crystal orientation fabric (COF). We suggest drilling into the apices of the deep anticlines, providing a good compromise between record length and temporal resolution and also facilitating studies of the interplay of anisotropic COF and ice flow.

APA, Harvard, Vancouver, ISO, and other styles

44

Katz, Richard F., and M. Grae Worster. "Stability of ice-sheet grounding lines." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 466, no. 2118 (January 13, 2010): 1597–620. http://dx.doi.org/10.1098/rspa.2009.0434.

Full text

Abstract:

Recent observations of the West Antarctic Ice Sheet document rapid changes in the mass balance of its component glaciers. These observations raise the question of whether changing climatic conditions have triggered a dynamical instability in the ice-sheet–ice-shelf system. The dynamics of marine ice sheets are sensitive to grounding-line position and variation, characteristics that are poorly captured by most current models. We present a theory for grounding-line dynamics in three spatial dimensions and time. Our theory is based on a balance of forces across the grounding line; it is expressed as a differential equation that is analogous to the canonical Stefan condition. We apply this theory to the question of grounding-line stability under conditions of retrograde bed slope in a suite of calculations with different basal topography. A subset of these have basal topography inspired by the Pine Island glacier, where basal depth varies in both the along-flow and across-flow directions. Our results indicate that unstable retreat of the grounding line over retrograde beds is a robust feature of models that evolve based on force balance at the grounding line. We conclude, based on our simplified model, that unstable grounding-line recession may already be occurring at the Pine Island glacier.

APA, Harvard, Vancouver, ISO, and other styles

45

Rignot, Eric, and Douglas R. MacAyeal. "Ice-shelf dynamics near the front of the Filchner—Ronne Ice Shelf, Antarctica, revealed by SAR interferometry." Journal of Glaciology 44, no. 147 (1998): 405–18. http://dx.doi.org/10.3189/s0022143000002732.

Full text

Abstract:

AbstractFifteen synthetic aperture radar (SAR) images of the Ronne Ice Shelf (also referred to as the Filchner-Ronne Ice Shelf), Antarctica, obtained by the European remote-sensing satellites ERS-1 and -2, are used to study ice-shelf dynamics near two ends of the iceberg-calving front. Interferograms constructed from these SAR images are used to resolve the ice-shelf displacement along several directions in response to both ocean tide and long-term creep flow. Tidal motion is separated from creep flow using differential interferometry, i.e. two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow. Creep-flow velocities thus determined compare well with prior ice-shelf velocity surveys. Using these data, we studied the influence of large-scale rifts, ice rises and coastal separation on the ice-shelf flow. Many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice, ice-shelf debris and wind-blown snow. The interferograms show that this melange tends to deform coherently in response to the ice-shelf flow and has sufficient strength to trap large tabular ice-shelf fragments for several decades before the fragments eventually become icebergs. In many instances, the motion of the tabular fragments is a rigid-body rotation about a vertical axis that is driven by velocity shear within the melange. Tfhe mechanical role of the rift-filling melange may be to bind tabular ice-shelf fragments to the main ice shelf before they calve. This suggests two possible mechanisms by which climate could influence tabular iceberg calving. First, spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and, thus, the location of the iceberg-caking margin. Second, melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice-shelf disintegration.

APA, Harvard, Vancouver, ISO, and other styles

46

Rignot, Eric, and Douglas R. MacAyeal. "Ice-shelf dynamics near the front of the Filchner—Ronne Ice Shelf, Antarctica, revealed by SAR interferometry." Journal of Glaciology 44, no. 147 (1998): 405–18. http://dx.doi.org/10.1017/s0022143000002732.

Full text

Abstract:

AbstractFifteen synthetic aperture radar (SAR) images of the Ronne Ice Shelf (also referred to as the Filchner-Ronne Ice Shelf), Antarctica, obtained by the European remote-sensing satellites ERS-1 and -2, are used to study ice-shelf dynamics near two ends of the iceberg-calving front. Interferograms constructed from these SAR images are used to resolve the ice-shelf displacement along several directions in response to both ocean tide and long-term creep flow. Tidal motion is separated from creep flow using differential interferometry, i.e. two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow. Creep-flow velocities thus determined compare well with prior ice-shelf velocity surveys. Using these data, we studied the influence of large-scale rifts, ice rises and coastal separation on the ice-shelf flow. Many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice, ice-shelf debris and wind-blown snow. The interferograms show that this melange tends to deform coherently in response to the ice-shelf flow and has sufficient strength to trap large tabular ice-shelf fragments for several decades before the fragments eventually become icebergs. In many instances, the motion of the tabular fragments is a rigid-body rotation about a vertical axis that is driven by velocity shear within the melange. Tfhe mechanical role of the rift-filling melange may be to bind tabular ice-shelf fragments to the main ice shelf before they calve. This suggests two possible mechanisms by which climate could influence tabular iceberg calving. First, spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and, thus, the location of the iceberg-caking margin. Second, melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice-shelf disintegration.

APA, Harvard, Vancouver, ISO, and other styles

47

Brinkerhoff, D., and J. Johnson. "A stabilized finite element method for calculating balance velocities in ice sheets." Geoscientific Model Development 8, no. 5 (May 4, 2015): 1275–83. http://dx.doi.org/10.5194/gmd-8-1275-2015.

Full text

Abstract:

Abstract. We present a numerical method for calculating vertically averaged velocity fields using a mass conservation approach, commonly known as balance velocities. This allows for an unstructured grid, is not dependent on a heuristic flow routing algorithm, and is both parallelizable and efficient. We apply the method to calculate depth-averaged velocities of the Greenland Ice Sheet, and find that the method produces grid-independent velocity fields for a sufficient parameterization of horizontal plane stresses on flow directions. We show that balance velocity can be used as the forward model for a constrained optimization problem that can be used to fill gaps and smooth strong gradients in InSAR velocity fields.

APA, Harvard, Vancouver, ISO, and other styles

48

Golledge, Nicholas R. "Sedimentology, stratigraphy, and glacier dynamics, western scottish Highlands." Quaternary Research 68, no. 1 (July 2007): 79–95. http://dx.doi.org/10.1016/j.yqres.2007.03.003.

Full text

Abstract:

AbstractGlacial sediments of the western Scottish Highlands are comprehensively described and characterized here for the first time, enabling the first glacial stratigraphy for the area to be proposed. This classification is based on the results of extensive geological mapping and field investigation of sedimentary sequences and their structures, X-ray diffraction and particle size distribution analyses, and comparison with deposits formed in contemporary glaciated environments. These new data are subsequently appraised in terms of their implications for late Pleistocene glacier evolution and dynamics. Together, the data suggest that much of the landscape is palimpsest, and can be attributed to the Weichselian (Late Devensian) glaciation. Subsequent glacier advance during the Younger Dryas did little to modify the area, suggesting that ice flow was dominated by sliding on a meltwater-lubricated rigid bed, with deformation of basal sediments playing a more limited role. Final deglaciation was marked by a significant increase in basal meltwater flux, reflecting the warming climate and increasing precipitation. These new palaeoglaciological and palaeoenvironmental insights advance our understanding of former glacier dynamics in the western Scottish Highlands, improve our knowledge of Pleistocene landscape evolution of this area, and enable comparisons to be made with sedimentary sequences elsewhere.

APA, Harvard, Vancouver, ISO, and other styles

49

Stumpf, Andrew J., Bruce E. Broster, and Victor M. Levson. "Glacial Stratigraphy of the Bulkley River Region: A Depositional Framework for the Late Pleistocene in Central British Columbia*." Glacial History 58, no. 2-3 (July 18, 2006): 217–28. http://dx.doi.org/10.7202/013139ar.

Full text

Abstract:

Abstract A depositional framework for late Pleistocene sediments in central British Columbia was developed from the composite stratigraphy of glacial sediments found in the Bulkley River region. Nonglacial deposits correlated to the Olympia Nonglacial Interval, are overlain in succession by sub-till, ice-advance sediments, Late Wisconsinan (Fraser Glaciation) till, and late-glacial sediments. Due to local erosion and depositional variability, some of the units are not continuous throughout the region and differ locally in their thickness and complexity. At the onset of the Fraser Glaciation, ice advance was marked by rising base levels in rivers, lake ponding, and ice marginal subaqueous deposition. Physiography and glacier dynamics influenced the position of drainage outlets, direction of water flow, and ponding. The region was completely ice covered during this glaciation and ice-flow directions were variable, being dominantly influenced by the migrating position of ice divides. Deglaciation was marked by the widespread deposition of fine-grained sediments in proglacial lakes and glaciofluvial sands and gravels at locations with unrestricted drainage.

APA, Harvard, Vancouver, ISO, and other styles

50

Plouffe, A., J. M. Bednarski, C. A. Huscroft, R. G. Anderson, and S. J. McCuaig. "Late Wisconsinan glacial history in the Bonaparte Lake map area, south-central British Columbia: implications for glacial transport and mineral exploration1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia.2Earth Sciences Sector Contribution Number: 20100093." Canadian Journal of Earth Sciences 48, no. 6 (June 2011): 1091–111. http://dx.doi.org/10.1139/e10-100.

Full text

Abstract:

This study is centred on the Bonaparte Lake map area located in the southern Interior Plateau of south-central British Columbia. The reconstruction of the Late Wisconsinan glacial history of this part of the southern sector of the Cordilleran Ice Sheet incorporates (i) the analysis and interpretation of landforms of various scales, (ii) the sedimentology and stratigraphy of glacial sediments, and (iii) the geochemical and mineralogical composition of till and analysis of regional glacial dispersal of these components. The onset of the last glacial event was initiated by ice advancing westerly and southwesterly into the study area from an alpine source region located in the Cariboo Mountains. As glaciation intensified, ice from the Coast Mountains coalesced with the Cariboo Mountain ice over the Interior Plateau and developed into an ice divide around 52° north latitude, which resulted in ice flow to be diverted to a southerly direction over the study area. The two dominant ice-flow directions produced palimpsest dispersal that was measured by three tracers in till including thorianite grains and terbium concentrations in the heavy mineral fraction, and granitoid pebble percentage. The two main phases of ice flow identified within our study area have significant implications for mineral exploration that uses mineral tracing in glacial sediments, especially in the area underlain by the highly prospective Quesnel Terrane.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Devensian ice flow directions'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles