scholarly journals On the Role of Mechanical Energy in Maintaining Subglacial Water Conduits at Atmospheric Pressure

1984 ◽  
Vol 30 (105) ◽  
pp. 180-187 ◽  
Author(s):  
Roger Leb. Hooke
Keyword(s):  
Atmospheric Pressure ◽  
Flow Direction ◽  
Mechanical Energy ◽  
Glacier Surface ◽  
Ice Flow ◽  
Small Perturbations ◽  
Point Pressure ◽  
Ice Velocity ◽  
Glacial Landforms

AbstractRecent theoretical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady-state conditions. This, however, is not necessarily the case. Where discharges are larger than a few tens of liters per second and the down-glacier slope of the bed is more than a few degrees, the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice. As a result, the pressure in such tunnels may normally be atmospheric, or possibly even at the triple-point pressure if there is no open connection to the glacier surface. Simple calculations suggest that such pressures in subglacial conduits may be more common than heretofore anticipated.The positions of such “open” conduits may be unstable to small perturbations in discharge or ice velocity. This is because the mechanical energy available in excess of that needed to balance closure can instead offset the general flow of the ice. Conduits can thus trend diagonally across the direction of ice flow. If an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of the conduit, more mechanical energy will become available, resulting in a positive feedback process.Subglacial channels at atmospheric pressure may influence the origin and morphology of certain glacial landforms, such as eskers and “plastically-molded” features.

scholarly journals On the Role of Mechanical Energy in Maintaining Subglacial Water Conduits at Atmospheric Pressure

1984 ◽  
Vol 30 (105) ◽  
pp. 180-187 ◽  
Author(s):  
Roger Leb. Hooke
Keyword(s):  
Atmospheric Pressure ◽  
Flow Direction ◽  
Mechanical Energy ◽  
Glacier Surface ◽  
Ice Flow ◽  
Small Perturbations ◽  
Point Pressure ◽  
Ice Velocity ◽  
Glacial Landforms

AbstractRecent theoretical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady-state conditions. This, however, is not necessarily the case. Where discharges are larger than a few tens of liters per second and the down-glacier slope of the bed is more than a few degrees, the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice. As a result, the pressure in such tunnels may normally be atmospheric, or possibly even at the triple-point pressure if there is no open connection to the glacier surface. Simple calculations suggest that such pressures in subglacial conduits may be more common than heretofore anticipated.The positions of such “open” conduits may be unstable to small perturbations in discharge or ice velocity. This is because the mechanical energy available in excess of that needed to balance closure can instead offset the general flow of the ice. Conduits can thus trend diagonally across the direction of ice flow. If an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of the conduit, more mechanical energy will become available, resulting in a positive feedback process.Subglacial channels at atmospheric pressure may influence the origin and morphology of certain glacial landforms, such as eskers and “plastically-molded” features.

scholarly journals Using Sequential Photography to Estimate Ice Velocity at the Terminus of Columbia Glacier, Alaska

1986 ◽  
Vol 8 ◽  
pp. 117-123 ◽  
Author(s):  
R.M. Krimmel ◽  
L.A. Rasmussen
Keyword(s):  
Time Resolution ◽  
Principal Direction ◽  
Film Plane ◽  
Time Sequence ◽  
Line Of Sight ◽  
Glacier Surface ◽  
Ice Flow ◽  
Straight Line ◽  
Camera Orientation ◽  
Ice Velocity

The terminus of Columbia Glacier, Alaska, was observed with a single automatic 35 mm camera to determine velocity with a time resolution in the order of a day. The photographic coordinates of the image of a target were then transformed linearly into the direction numbers of the line of sight from the camera to the target. The camera orientation was determined from the film-plane locations of known landmark points by using an adaption of vertical photogrammetry techniques. The line of sight, when intersected with some mathematically-defined glacier surface, defines the true space coordinates of a target, The time sequence of a target’s position was smoothed, first in horizontal x, y space to a straight line, then in y (the principal direction of ice flow) and time with a smoothing cubic spline, and then the x-component was computed from the y-component by considering the inclination of the straight line. This allows daily velocities (about 8 m/day) to be measured at a distance of 5 km, using a 105 mm lens. Errors in daily displacements were estimated to be 1 m. The terminus configuration was also measured using the same photo set.

scholarly journals Modelling mass balance using photogrammetric and geophysical data: a pilot study at Griesgletscher, Swiss Alps

1999 ◽  
Vol 45 (151) ◽  
pp. 575-583 ◽  
Author(s):  
Andreas Kääb ◽  
Martin Funk
Keyword(s):  
Pilot Study ◽  
Mass Balance ◽  
Surface Strain ◽  
Swiss Alps ◽  
Surface Velocity ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Ice Flow ◽  
Applied Model ◽  
Ice Velocity

AbstractThe kinematic boundary condition al the glacier surface can be used to give glacier mass balance at a point as a function of changes in the surface elevation, and of the horizontal and vertical velocities. Vertical velocity can in turn be estimated from basal slope, basal ice velocity and surface strain. In a pilot study on the tongue of Griesgletscher, Swiss Alps, the applicability of the relation for modelling area-wide ice flow and mass-balance distribution is tested. The key input of the calculations, i.e. the area-wide surface velocity field, is obtained using a newly developed photogrammetric technique. Ice thickness is derived from radar-echo soundings. Error estimates and comparisons with stake measurements show an average accuracy of approximately ±0.3 ma-1for the calculated vertical ice velocity at the surface and ±0.7 ma-1for the calculated mass balance. Due to photogrammetric restrictions and model-inherent sensitivities the applied model appeared to be most suitable for determining area-wide mass balance and ice flow on flat-lying ablation areas, but is so far not very well suited for steep ablation areas and most parts of accumulation areas. Nevertheless, the study on Griesgletscher opens a new and promising perspective for the monitoring of spatial and temporal glacier mass-balance variations.

Glacier movement, ice structures, and medial moraine form at a glacier confluence, Berendon Glacier, British Columbia, Canada

1977 ◽  
Vol 14 (12) ◽  
pp. 2807-2816 ◽  
Author(s):  
N. Eyles ◽  
R. J. Rogerson
Keyword(s):  
British Columbia ◽  
Strain Rate ◽  
Lateral Compression ◽  
Ice Streams ◽  
Glacier Surface ◽  
Ice Flow ◽  
Contact Plane ◽  
Confluence Zone ◽  
Ice Velocity ◽  
Surface Ice

On Berendon Glacier, Canada, at the asymmetric Y junction of two large valley glaciers, observations of ice velocity, strain rate, and ice structures indicate that the form of a medial moraine is determined by severe lateral compression between the two ice streams. Debris of the moraine is recycled along complex transport paths determined by ice structures. For example, supraglacial debris is precipitated into the confluence zone between the two glaciers forming a subglacial debris reservoir. Debris is evacuated from the reservoir by shearing between the two glaciers and is revealed on the glacier surface as debris dykes and melt-out tills along the contact plane. Important implications regarding the sedimentology of the moraine can be stated. Elsewhere debris is precipitated into transverse crevasses subsequently resulting in transverse till ridges at the glacier surface.Annually-formed wave ogives, bulges in surface ice, and overriding along the glacier contacts result from severe lateral compresssion, and add further diversity to the moraine.Downglacier, confluence ice structures are destroyed by ablation, the pattern of ice flow becomes less complex, unified flow between the two glaciers is established, and a distinct structurally-determined moraine morphology is replaced by one dependent upon the differential ablation of debris covered and clean ice.

scholarly journals Anisotropic radio-wave scattering from englacial water regimes, Mýrdalsjökull, Iceland

2007 ◽  
Vol 53 (182) ◽  
pp. 473-478 ◽  
Author(s):  
Kenichi Matsuoka ◽  
Throstur Thorsteinsson ◽  
Helgi Björnsson ◽  
Edwin D. Waddington
Keyword(s):  
Radio Wave ◽  
Wave Scattering ◽  
Flow Direction ◽  
Low Frequency ◽  
Radio Waves ◽  
Glacier Surface ◽  
Ice Flow ◽  
Scattering Model ◽  
Water Regimes ◽  
Strong Scattering

AbstractColinear-polarized 5 MHz radar profiling data were obtained on Mýrdalsjökull, a temperate glacier in Iceland. Radar transects, and therefore polarization planes, were aligned approximately parallel, transverse and oblique to the ice flow direction. Echoes from the shallower half to two-thirds of the ice were 10–20dB stronger on the oblique and longitudinal transects than those on the transverse transects. Anisotropy as a function of depth is clearly seen at the sites where the transects cross. Strong scattering on longitudinal transects apparently caused extinction of a radar-reflecting layer that was continuously profiled on the transverse transects. A radio-wave scattering model shows that scattering from a longitudinal water-filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo. We conclude that low-frequency (~MHz) radio waves can help to characterize englacial water regimes.

scholarly journals Changes in ice thickness and flow velocity of Yala Glacier, Langtang Himal, Nepal, from 1982 to 2009

2013 ◽  
Vol 54 (64) ◽  
pp. 157-162 ◽  
Author(s):  
Shin Sugiyama ◽  
Kotaro Fukui ◽  
Koji Fujita ◽  
Kenta Tone ◽  
Satoru Yamaguchi
Keyword(s):  
Flow Velocity ◽  
Surface Elevation ◽  
Ice Thickness ◽  
Glacier Surface ◽  
Ice Flow ◽  
Ice Volume ◽  
Glacier Changes ◽  
Ice Velocity ◽  
Ground Penetrating ◽  
Thinning Rate

Abstract To investigate recent glacier changes in the Himalayan region, we carried out GPS and ground-penetrating radar (GPR) measurements at Yala Glacier, a benchmark glacier in Nepal. Glacier surface elevation and ice thickness were surveyed along a 1.5 km profile from the glacier top to the terminus. Ice flow velocity was measured at five locations by surveying stakes for either 1 year or 4 day periods. Obtained surface elevation and ice velocity were compared with those measured in 1982 and 1996. The mean ice thickness along the radar profile was 36 m in 2009 and the ice has been thinning at rates of-0.69 ±0.25 and -0.75 ± 0.24 m a-1 during the periods 1982-96 and 1996-2009, respectively. The thinning rate increases down-glacier, reaching a magnitude up to -1.8 m a-1 near the terminus from 1996 to 2009. The ice velocity has reduced by >70% from 1982 to 2009 in the lower half of the glacier. By assuming a constant driving stress over the glacier, the total ice volume in 2009 was estimated as 0.061 km3. Our results indicate that Yala Glacier has lost ∼40% of its ice volume over the last 27 years and that the rate of the mass loss has accelerated over the last decade.

scholarly journals Basal melting beneath a fast-flowing temperate tidewater glacier

2013 ◽  
Vol 54 (63) ◽  
pp. 265-271 ◽  
Author(s):  
D.J. Alexander ◽  
T.R.H. Davies ◽  
J. Shulmeister
Keyword(s):  
Mass Balance ◽  
Published Data ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Ice Flow ◽  
Tidewater Glaciers ◽  
Tidewater Glacier ◽  
Order Of Magnitude ◽  
Basal Melting

AbstractThe role of melting at the base of temperate tidewater glaciers is rarely discussed, and its potential importance for total glacier mass balance and subglacial dynamics is often overlooked. We use Columbia Glacier, Alaska, USA, as an example of a temperate tidewater glacier to estimate the spatial distribution of basal melt due to friction both before and during the glacier’s well-documented retreat since the early 1980s. Published data on glacier surface and bed profiles, ice-flow velocities and surface melt were collated and used as input data for a two-dimensional basal melt model. We estimate that before the retreat of Columbia Glacier (pre-1980s), mean basal melt amounted to 61 mm a–1, increasing to 129 mma–1 during retreat (post-1980s). According to our calculations, basal melt accounts for 3% and 5% of total glacier melt for the pre-retreat and syn-retreat (i.e. during retreat) glacier profiles, respectively. These calculations of basal melt are an order of magnitude greater than those typically reported in polar glacier settings. Basal melting in temperate tidewater settings may be a non-negligible process affecting glacier mass balance and subglacial dynamics.

scholarly journals Modelling mass balance using photogrammetric and geophysical data: a pilot study at Griesgletscher, Swiss Alps

1999 ◽  
Vol 45 (151) ◽  
pp. 575-583 ◽  
Author(s):  
Andreas Kääb ◽  
Martin Funk
Keyword(s):  
Pilot Study ◽  
Mass Balance ◽  
Surface Strain ◽  
Swiss Alps ◽  
Surface Velocity ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Ice Flow ◽  
Applied Model ◽  
Ice Velocity

AbstractThe kinematic boundary condition al the glacier surface can be used to give glacier mass balance at a point as a function of changes in the surface elevation, and of the horizontal and vertical velocities. Vertical velocity can in turn be estimated from basal slope, basal ice velocity and surface strain. In a pilot study on the tongue of Griesgletscher, Swiss Alps, the applicability of the relation for modelling area-wide ice flow and mass-balance distribution is tested. The key input of the calculations, i.e. the area-wide surface velocity field, is obtained using a newly developed photogrammetric technique. Ice thickness is derived from radar-echo soundings. Error estimates and comparisons with stake measurements show an average accuracy of approximately ±0.3 ma-1 for the calculated vertical ice velocity at the surface and ±0.7 ma-1 for the calculated mass balance. Due to photogrammetric restrictions and model-inherent sensitivities the applied model appeared to be most suitable for determining area-wide mass balance and ice flow on flat-lying ablation areas, but is so far not very well suited for steep ablation areas and most parts of accumulation areas. Nevertheless, the study on Griesgletscher opens a new and promising perspective for the monitoring of spatial and temporal glacier mass-balance variations.

scholarly journals The Causes of Debris-Covered Glacier Thinning: Evidence for the Importance of Ice Dynamics From Kennicott Glacier, Alaska

2021 ◽  
Vol 9 ◽  
Author(s):  
Leif S. Anderson ◽  
William H. Armstrong ◽  
Robert S. Anderson ◽  
Dirk Scherler ◽  
Eric Petersen
Keyword(s):  
Mass Balance ◽  
Flow Direction ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Ice Flow ◽  
Thickness Change ◽  
Air Temperatures ◽  
Compressive Flow ◽  
Wide Range

The cause of debris-covered glacier thinning remains controversial. One hypothesis asserts that melt hotspots (ice cliffs, ponds, or thin debris) increase thinning, while the other posits that declining ice flow leads to dynamic thinning under thick debris. Alaska’s Kennicott Glacier is ideal for testing these hypotheses, as ice cliffs within the debris-covered tongue are abundant and surface velocities decline rapidly downglacier. To explore the cause of patterns in melt hotspots, ice flow, and thinning, we consider their evolution over several decades. We compile a wide range of ice dynamical and mass balance datasets which we cross-correlate and analyze in a step-by-step fashion. We show that an undulating bed that deepens upglacier controls ice flow in the lower 8.5 km of Kennicott Glacier. The imposed velocity pattern strongly affects debris thickness, which in turn leads to annual melt rates that decline towards the terminus. Ice cliff abundance correlates highly with the rate of surface compression, while pond occurrence is strongly negatively correlated with driving stress. A new positive feedback is identified between ice cliffs, streams and surface topography that leads to chaotic topography. As the glacier thinned between 1991 and 2015, surface melt in the study area decreased, despite generally rising air temperatures. Four additional feedbacks relating glacier thinning to melt changes are evident: the debris feedback (negative), the ice cliff feedback (negative), the pond feedback (positive), and the relief feedback (positive). The debris and ice cliff feedbacks, which are tied to the change in surface velocity in time, likely reduced melt rates in time. We show this using a new method to invert for debris thickness change and englacial debris content (∼0.017% by volume) while also revealing that declining speeds and compressive flow led to debris thickening. The expansion of debris on the glacier surface follows changes in flow direction. Ultimately, glacier thinning upvalley from the continuously debris-covered portion of Kennicott Glacier, caused by mass balance changes, led to the reduction of flow into the study area. This caused ice emergence rates to decline rapidly leading to the occurrence of maximum, glacier-wide thinning under thick, insulating debris.

scholarly journals Using Sequential Photography to Estimate Ice Velocity at the Terminus of Columbia Glacier, Alaska

1986 ◽  
Vol 8 ◽  
pp. 117-123 ◽  
Author(s):  
R.M. Krimmel ◽  
L.A. Rasmussen
Keyword(s):  
Time Resolution ◽  
Principal Direction ◽  
Film Plane ◽  
Time Sequence ◽  
Line Of Sight ◽  
Glacier Surface ◽  
Ice Flow ◽  
Straight Line ◽  
Camera Orientation ◽  
Ice Velocity

The terminus of Columbia Glacier, Alaska, was observed with a single automatic 35 mm camera to determine velocity with a time resolution in the order of a day. The photographic coordinates of the image of a target were then transformed linearly into the direction numbers of the line of sight from the camera to the target. The camera orientation was determined from the film-plane locations of known landmark points by using an adaption of vertical photogrammetry techniques. The line of sight, when intersected with some mathematically-defined glacier surface, defines the true space coordinates of a target, The time sequence of a target’s position was smoothed, first in horizontal x, y space to a straight line, then in y (the principal direction of ice flow) and time with a smoothing cubic spline, and then the x-component was computed from the y-component by considering the inclination of the straight line. This allows daily velocities (about 8 m/day) to be measured at a distance of 5 km, using a 105 mm lens. Errors in daily displacements were estimated to be 1 m. The terminus configuration was also measured using the same photo set.

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