scholarly journals Some Comments on Glacier Flow

1950 ◽  
Vol 1 (7) ◽  
pp. 383-388
Author(s):  
Richard Finsterwalder
Keyword(s):  
Shear Stress ◽  
Shear Plane ◽  
Critical Value ◽  
Ice Flow ◽  
Crystalline Materials ◽  
Fundamental Point ◽  
Glacier Ice ◽  
Slow Moving ◽  
Glacier Flow ◽  
Streaming Flow

AbstractDrs. Orowan and Perutz have shown that glacier ice does not behave as a viscous fluid but is plastic like all crystalline materials. The present author discusses two observed types of ice flow:—(1) the normal, regular streaming flow in slow-moving glaciers; (2) Block-Schollen movement in swiftly flowing ice. Mention is made of the shear plane or laminar flow theory of Philipp. lt appears that Orowan s thesis is also applicable to Block-Schollen flow. The author agrees with Orowan on the fundamental point that when ice is subjected to shear stress a critical value of the shear stress exists beyond which the ice alters its consistency. But the author disagrees with Orowan in that he believes that below this critical value ice behaves as a viscous material, and he supports this view by reference to many phenomena, measurements and calculations.

scholarly journals Some Comments on Glacier Flow

1950 ◽  
Vol 1 (07) ◽  
pp. 383-388 ◽  
Author(s):  
Richard Finsterwalder
Keyword(s):  
Shear Stress ◽  
Shear Plane ◽  
Critical Value ◽  
Ice Flow ◽  
Crystalline Materials ◽  
Fundamental Point ◽  
Glacier Ice ◽  
Slow Moving ◽  
Glacier Flow ◽  
Streaming Flow

Abstract Drs. Orowan and Perutz have shown that glacier ice does not behave as a viscous fluid but is plastic like all crystalline materials. The present author discusses two observed types of ice flow:—(1) the normal, regular streaming flow in slow-moving glaciers; (2) Block-Schollen * movement in swiftly flowing ice. Mention is made of the shear plane or laminar flow theory of Philipp. lt appears that Orowan s thesis is also applicable to Block-Schollen flow. The author agrees with Orowan on the fundamental point that when ice is subjected to shear stress a critical value of the shear stress exists beyond which the ice alters its consistency. But the author disagrees with Orowan in that he believes that below this critical value ice behaves as a viscous material, and he supports this view by reference to many phenomena, measurements and calculations.

Distribution and origin of patterned ground on Mullins Valley debris-covered glacier, Antarctica: the roles of ice flow and sublimation

2006 ◽  
Vol 18 (3) ◽  
pp. 385-397 ◽  
Author(s):  
Joseph S. Levy ◽  
David R. Marchant ◽  
James W. Head
Keyword(s):  
Patterned Ground ◽  
Ice Flow ◽  
Victoria Land ◽  
Material Weaknesses ◽  
Rapid Flow ◽  
Glacier Ice ◽  
Ice Velocity ◽  
Formation And Evolution ◽  
Structural Stresses ◽  
Glacier Flow

We map polygonally patterned ground formed in sublimation tills that overlie debris-covered glaciers in Mullins Valley and central Beacon Valley, in southern Victoria Land, Antarctica, and distinguish five morphological zones. Where the Mullins Valley debris-covered glacier debouches into Beacon Valley, polygonal patterning transitions from radial (orthogonal) intersections to non-oriented (hexagonal) intersections, providing a time-series of polygon evolution within a single microclimate. We offer the following model for polygon formation and evolution in the Mullins Valley system. Near-vertical cracks that ultimately outline polygons are produced by thermal contraction in the glacier ice. Some of these cracks may initially be oriented radial to maximum surface velocities by pre-existing structural stresses and material weaknesses in the glacier ice. In areas of relatively rapid flow, polygons are oriented down-valley forming an overall fan pattern radial to maximum ice velocity. As glacier flow moves the cracks down-valley, minor variations in flow rate deform polygons, giving rise to deformed radial polygons. Non-oriented (largely hexagonal) polygons commonly form in regions of stagnant and/or near-stagnant ice. We propose that orientation and morphology of contraction-crack polygons in sublimation tills can thus be used as an indicator of rates of subsurface ice flow.

Efficiency prediction for storage chambers using computational fluid dynamics

1996 ◽  
Vol 33 (9) ◽  
pp. 163-170 ◽  
Author(s):  
Virginia R. Stovin ◽  
Adrian J. Saul
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Shear Stress ◽  
Particle Tracking ◽  
Critical Value ◽  
Complex Geometries ◽  
Bed Shear Stress ◽  
Breadth Ratio ◽  
Computational Fluid Dynamics Cfd ◽  
Simulated Flow

Research was undertaken in order to identify possible methodologies for the prediction of sedimentation in storage chambers based on computational fluid dynamics (CFD). The Fluent CFD software was used to establish a numerical model of the flow field, on which further analysis was undertaken. Sedimentation was estimated from the simulated flow fields by two different methods. The first approach used the simulation to predict the bed shear stress distribution, with deposition being assumed for areas where the bed shear stress fell below a critical value (τcd). The value of τcd had previously been determined in the laboratory. Efficiency was then calculated as a function of the proportion of the chamber bed for which deposition had been predicted. The second method used the particle tracking facility in Fluent and efficiency was calculated from the proportion of particles that remained within the chamber. The results from the two techniques for efficiency are compared to data collected in a laboratory chamber. Three further simulations were then undertaken in order to investigate the influence of length to breadth ratio on chamber performance. The methodology presented here could be applied to complex geometries and full scale installations.

scholarly journals Design of plate and screw anchors in dense sand: failure mechanism, capacity and deformation

2019 ◽  
Vol 92 ◽  
pp. 16010
Author(s):  
Benjamin Cerfontaine ◽  
Jonathan Knappett ◽  
Michael Brown ◽  
Aaron Bradshaw
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Failure Mechanism ◽  
Progressive Failure ◽  
Vertical Direction ◽  
Shear Plane ◽  
Design Methods ◽  
Embedment Depth ◽  
Limiting State ◽  
Dense Sand

Plate and screw anchors provide a significant uplift capacity and have multiple applications in both onshore and offshore geotechnical engineering. Uplift design methods are mostly based on semi-empirical approaches assuming a failure mechanism, a normal and a shear stress distribution at failure and empirical factors back-calculated against experimental data. However, these design methods are shown to under- or overpredict most of the existing larger scale experimental tests. Numerical FE simulations are undertaken to provide new insight into the failure mechanism and stress distribution which should be considered in anchor design in dense sand. Results show that a conical shallow wedge whose inclination to the vertical direction is equal to the dilation angle is a good approximation of the failure mechanism in sand. This shallow mechanism has been observed in each case for relative embedment ratios (depth/diameter) ranging from 1 to 9. However, the stress distribution varies non-linearly with depth, due to the soil deformability and progressive failure. A sharp peak of normal and shear stress can be identified close to the anchor edge, before a gradual decrease with increasing distance along the shear plane. The peak stress magnitude increases almost linearly with embedment depth at larger relative embedment ratios. Although further research is necessary, these results lay the basis for the development of a new generation of design criteria for determining anchor capacity at the ultimate limiting state.

scholarly journals Three-dimensional deformation time series of glacier motion from multiple-aperture DInSAR observation

2019 ◽  
Vol 93 (12) ◽  
pp. 2651-2660 ◽  
Author(s):  
Sergey Samsonov
Keyword(s):  
Time Series ◽  
Surface Deformation ◽  
Ground Deformation ◽  
Three Dimensional ◽  
Data Sets ◽  
Ice Flow ◽  
The North ◽  
Glacier Ice ◽  
Deformation Component ◽  
3D Deformation

AbstractThe previously presented Multidimensional Small Baseline Subset (MSBAS-2D) technique computes two-dimensional (2D), east and vertical, ground deformation time series from two or more ascending and descending Differential Interferometric Synthetic Aperture Radar (DInSAR) data sets by assuming that the contribution of the north deformation component is negligible. DInSAR data sets can be acquired with different temporal and spatial resolutions, viewing geometries and wavelengths. The MSBAS-2D technique has previously been used for mapping deformation due to mining, urban development, carbon sequestration, permafrost aggradation and pingo growth, and volcanic activities. In the case of glacier ice flow, the north deformation component is often too large to be negligible. Historically, the surface-parallel flow (SPF) constraint was used to compute the static three-dimensional (3D) velocity field at various glaciers. A novel MSBAS-3D technique has been developed for computing 3D deformation time series where the SPF constraint is utilized. This technique is used for mapping 3D deformation at the Barnes Ice Cap, Baffin Island, Nunavut, Canada, during January–March 2015, and the MSBAS-2D and MSBAS-3D solutions are compared. The MSBAS-3D technique can be used for studying glacier ice flow at other glaciers and other surface deformation processes with large north deformation component, such as landslides. The software implementation of MSBAS-3D technique can be downloaded from http://insar.ca/.

Basal processes beneath an Arctic glacier and their geomorphic imprint after a surge, Elisebreen, Svalbard

2005 ◽  
Vol 64 (2) ◽  
pp. 125-137 ◽  
Author(s):  
Poul Christoffersen ◽  
Jan A. Piotrowski ◽  
Nicolaj K. Larsen
Keyword(s):  
Flow Instability ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Water System ◽  
Water Drainage ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Glacier Ice ◽  
Water Saturated ◽  
Arctic Glacier

AbstractThe foreground of Elisebreen, a retreating valley glacier in West Svalbard, exhibits a well-preserved assemblage of subglacial landforms including ice-flow parallel ridges (flutings), ice-flow oblique ridges (crevasse-fill features), and meandering ridges (infill of basal meltwater conduits). Other landforms are thrust-block moraine, hummocky terrain, and drumlinoid hills. We argue in agreement with geomorphological models that this landform assemblage was generated by ice-flow instability, possibly a surge, which took place in the past when the ice was thicker and the bed warmer. The surge likely occurred due to elevated pore-water pressure in a thin layer of thawed and water-saturated till that separated glacier ice from a frozen substratum. Termination may have been caused by a combination of water drainage and loss of lubricating sediment. Sedimentological investigations indicate that key landforms may be formed by weak till oozing into basal cavities and crevasses, opening in response to accelerated ice flow, and into water conduits abandoned during rearrangement of the basal water system. Today, Elisebreen may no longer have surge potential due to its diminished size. The ability to identify ice-flow instability from geomorphological criteria is important in deglaciated terrain as well as in regions where ice dynamics are adapting to climate change.

scholarly journals Crystal Orientation in Glacier and in Experimentally Deformed Ice

1960 ◽  
Vol 3 (27) ◽  
pp. 589-606 ◽  
Author(s):  
George P. Rigsby
Keyword(s):  
Crystal Orientation ◽  
Laboratory Experiments ◽  
Ice Crystals ◽  
Equal Area ◽  
Fine Grained ◽  
Planar Structures ◽  
Glacier Ice ◽  
Glacier Flow ◽  
High Shearing ◽  
Universal Stage

AbstractMore than 8,000 ice crystals have been oriented and measured for crystal fabric studies from widely separated temperate and polar glaciers, using a large universal stage and thin-section techniques. Very strong fabrics have been found and a number of laboratory experiments on deformation and recrystallization of ice were conducted in an attempt to solve some of the perplexing problems raised concerning glacier flow.In polar glaciers the c or optic axes of the ice crystals tend to be perpendicular to the foliation plane (alternating planar structures of bubbly and clear ice). In areas of high shearing stress the preferred orientation of the axes reached 39 per cent in 1 per cent of the area when plotted on a Schmidt equal-area projection. In temperate glaciers the optic axes tend to form three or four strong maxima which also appear related to the foliation.Patterns from ice deformed in the laboratory resemble some of the fabric patterns found in polar glaciers. During deformation of laboratory specimens, large crystals have been observed recrystallizing into many smaller ones, while fine-grained ice, after completion of deformation (both glacier ice and laboratory deformed ice), has been annealed at melting temperature into a few large crystals with different orientations from the original pattern.

scholarly journals Could promontories have restricted sea-glacier penetration into marine embayments during Snow ball Earth events?

2016 ◽  
Author(s):  
Adam J. Campbell ◽  
Betzalel Massarano ◽  
Edwin D. Waddington ◽  
Stephen G. Warren
Keyword(s):  
Flow Model ◽  
Narrow Range ◽  
Global Ocean ◽  
Snowball Earth ◽  
Ice Flow ◽  
Climate Conditions ◽  
Eukaryotic Algae ◽  
Extreme Cold ◽  
Glacier Flow

Abstract. During the Neoproterozoic, Earth experienced several climate excursions of extreme cold, often referred to as the Snowball Earth events. During these periods, thick flowing ice, referred to as sea glaciers, covered the entire planet’s oceans. In addition, there is evidence that photosynthetic eukaryotic algae survived during these periods. With thick sea glaciers covering the oceans, it is uncertain where these organisms survived. One hypothesis is that these algae survived in marine embayments hydrologically connected to the global ocean, where the flow of sea glacier could be resisted. In order for an embayment to act as a refugium, the invading sea glacier must not completely penetrate the embayment. Recent studies have shown that straight-sided, marine embayments could have prevented full sea-glacier penetration under a narrow range of climate conditions suitable for the Snowball Earth events. Here we test whether promontories, i.e. headlands emerging from a side shoreline, could further restrict sea-glacier flow. We use an ice-flow model, suitable for floating ice, to determine the flow of an invading sea glacier. We show that promontories can expand the range of climate conditions allowing refugia by resisting the flow of invading sea glaciers.

scholarly journals Variations in the Sliding of a Temperate Glacier

1974 ◽  
Vol 13 (69) ◽  
pp. 349-369 ◽  
Author(s):  
Steven M. Hodge
Keyword(s):  
Water Discharge ◽  
Ice Flow ◽  
Sliding Speed ◽  
Temporary Storage ◽  
State Of Stress ◽  
Basal Sliding ◽  
Internal Deformation ◽  
Pressure Melting ◽  
Glacier Flow ◽  
Basal Shear

Detailed measurements of the positions of stakes along the center-line of the lower Nisqually Glacier were made over a period of two years. Variations in the basal sliding speed were calculated from the measured changes in surface speed, surface slope, and thickness, using the glacier flow model of Nye (1952) and allowing for the effect of the valley walls, longitudinal stress gradients, and uncertainties in the flow law of ice. The flow is predominantly by basal sliding and has a pronounced seasonal variation of approximately ±25%. Internal deformation contributes progressively less to the total motion with distance up-glacier. Neither the phase nor the magnitude of the seasonal velocity fluctuations can be accounted for by seasonal variations in the state of stress within the ice or at the bed, and the variations do not correlate directly with the melt-water discharge from the terminus. A seasonal wave in the ice flow travels down the glacier at a speed too high for propagation by internal deformation or the pressure melting/enhanced creep mechanism of basal sliding.The rate of sliding appears to be determined primarily by the amount of water in temporary storage in the glacier. The peak in sliding speed occurs, on the average, at the same time as the maximum liquid water storage of the South Cascade Glacier. The data support the idea that glaciers store water in the fall, winter and spring and then release it in the summer. This temporary storage may be greatest near the equilibrium line. The amount of stored water may increase over a period of years and be released catastrophically as a jökulhlaup. Any dependence of sliding on the basal shear stress is probably masked by the effect of variations in the hydrostatic pressure of water having access to the bed.

scholarly journals Present dynamics and future prognosis of a slowly surging glacier

2011 ◽  
Vol 5 (1) ◽  
pp. 299-313 ◽  
Author(s):  
G. E. Flowers ◽  
N. Roux ◽  
S. Pimentel ◽  
C. G. Schoof
Keyword(s):  
Mass Balance ◽  
Force Balance ◽  
Surface Velocity ◽  
Internal Dynamic ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Ice Surface ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Negative Balance

Abstract. Glacier surges are a well-known example of an internal dynamic oscillation whose occurrence is not a direct response to the external climate forcing, but whose character (i.e. period, amplitude, mechanism) may depend on the glacier's environmental or climate setting. We examine the dynamics of a small (∼5 km2) valley glacier in Yukon, Canada, where two previous surges have been photographically documented and an unusually slow surge is currently underway. To characterize the dynamics of the present surge, and to speculate on the future of this glacier, we employ a higher-order flowband model of ice dynamics with a regularized Coulomb-friction sliding law in both diagnostic and prognostic simulations. Diagnostic (force balance) calculations capture the measured ice-surface velocity profile only when non-zero basal water pressures are prescribed over the central region of the glacier, coincident with where evidence of the surge has been identified. This leads to sliding accounting for 50–100% of the total surface motion in this region. Prognostic simulations, where the glacier geometry evolves in response to a prescribed surface mass balance, reveal a significant role played by a bedrock ridge beneath the current equilibrium line of the glacier. Ice thickening occurs above the ridge in our simulations, until the net mass balance reaches sufficiently negative values. We suggest that the bedrock ridge may contribute to the propensity for surges in this glacier by promoting the development of the reservoir area during quiescence, and may permit surges to occur under more negative balance conditions than would otherwise be possible. Collectively, these results corroborate our interpretation of the current glacier flow regime as indicative of a slow surge that has been ongoing for some time, and support a relationship between surge incidence or character and the net mass balance. Our results also highlight the importance of glacier bed topography in controlling ice dynamics, as observed in many other glacier systems.

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