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 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 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 Structures and Ice Deformation in the White Glacier, Axel Heiberg Island, Northwest Territories, Canada

1978 ◽  
Vol 20 (82) ◽  
pp. 41-66 ◽  
Author(s):  
M.J. Hambrey ◽  
F. Müller
Keyword(s):  
Strain Rate ◽  
Compressive Strain ◽  
Source Area ◽  
Strain Rates ◽  
Glacier Surface ◽  
Ice Flow ◽  
Passive Deformation ◽  
Differential Flow ◽  
Shearing Strain ◽  
Prominent Ridge

AbstractThe major structures in the long, narrow tongue of a sub-polar valley glacier are described: namely, longitudinal foliation, crevasses, clear-ice layers related to crevasses, debris-rich layers (frequently referred to as thrust or shear planes in the past), and folds. The foliation is vertical, is as well-developed in the centre of the glacier as at the margins, and does not, apparently, form perpendicular to the principal compressive strain-rate axis, nor exactly parallel to a line of maximum shearing strain-rate, although it sometimes approximately coincides with the latter. The intensity of foliation development is not related to the magnitude of the strain-rates, but the structure consistently lies parallel to flow lines through the glacier. There is no critical extending strain-rate, as such, associated with the development of new crevasses. Some crevasses have formed where the principal extending strain-rate is as low as 0.004 a-1while, in other areas, extending strain-rates of 0.163 a-1have not always resulted in fracturing. Prominent clear-ice layers, referred to as crevasse traces as displayed at the glacier surface, have formed in crevasse belts parallel to the main fracture directions. These are interpreted either as tensional veins or as the result of the freezing of water in crevasses. Extension parallel to the layering occurs during flow and, near the snout, the surface dip decreases rapidly. The fact that the crevasse traces can be followed to the snout implies that fracture occurs almost to the bottom of the glacier in the source area of the traces. Near the snout, debris-rich layers have developed parallel to the crevasse traces; frequently these are marked by prominent ridge-like ice-cored moraines. It is suggested that these structures are formed by a combination of basal freezing and thrusting. Isoclinal and tight similar folds on all scales are present. Some may be formed by the passive deformation of clear-ice layers as a result of differential flow; others may arise from the lateral compression of the original stratification in areas where ice flow becomes constricted by the narrowing of the valley. An axial plane foliation sometimes is associated with these folds.

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.

Processing and analysis of dense ice velocity time series to reconstruct seasonal fluctuations of 3 greenlandic glaciers : Russell Gletscher, Upernavik Isstrom, Petermann Gletscher.

2020 ◽  
Author(s):  
Anna Derkacheva ◽  
Jeremie Mouginot ◽  
Romain Millan ◽  
Fabien Gillet-Chaulet
Keyword(s):  
Time Series ◽  
Seasonal Variations ◽  
Seasonal Changes ◽  
High Temporal Resolution ◽  
Landsat 8 ◽  
Post Processing ◽  
Seasonal Fluctuations ◽  
Ice Flow ◽  
Ice Velocity ◽  
Surface Ice

<p>Significant seasonal changes in ice flow have been reported for outlet glaciers in Greenland. Understanding the mechanisms that control these rapid intra-annual changes in dynamics could potentially help to clarify Greenland's long-term evolution and climate change response.</p><p>In this study, we investigate seasonal changes in ice flow velocity in order to better understand the processes controlling them. We focus on 3 Greenlandic glaciers of different types: Russell which is a land-terminating glacier with speed ranging from 50 to 350 m/yr,  Upernavik Isstrøm which is a marine-terminating tidewater glacier with speeds up to 4 km/yr, and Petermann Gletscher that has a large ice shelf and with speed at the order of 1 km/yr. Since 2014, the number of spaceborne observations over the ice sheet has increased dramatically with the launch of Landsat-8, Sentinel-1 and -2, providing almost continuous monitoring of glacier dynamics.</p><p>Here, we develop an automatic processing chain to derive dense time series of surface ice flow from radar sensors, Sentinel -1a/b, and optical sensors, Landsat-7/8 and Sentinel-2, using speckle or feature tracking algorithms. We construct a post-processing analysis based on local polynomial regression to filter our multi-sensor time series and create a velocity database with high temporal resolution and reduced noise. The database allows us to reconstruct the continuous evolution of surface ice velocity with frequency intervals ranging from monthly for the entire glacial basin to weekly for the downstream parts. </p><p>Using this methodology, we obtain velocity fields for 4 years between 2015 and 2019 of the entire basins of Russell, Upernavik and Petermann glaciers. Our results clearly show the seasonal variations in flow to which these glaciers are subjected. We analyze the average seasonal fluctuations during the 4 years, as well as particular behavior in different years. These results are then compared and discussed in relation to potential external forcings such as subglacial hydrology (change in basal friction), fluctuations in the ice front or grounding line positions (change in buttressing) and the presence of sea ice or ice melange in front of the glaciers. </p><p>Finally, we conclude on the benefits of our post-processing approach for the analysis of dense ice flow time series and provide first insights on the causes of seasonal variations observed on these 3 glaciers.</p>

scholarly journals Fabric Analysis of Surface Ice near Casey Range, East Antarctica

1969 ◽  
Vol 8 (54) ◽  
pp. 375-383 ◽  
Author(s):  
Koshiro Kizaki
Keyword(s):  
Strain Rate ◽  
Grain Growth ◽  
Ice Sheet ◽  
East Antarctica ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
Single Maximum ◽  
Fabric Analysis ◽  
Surface Ice ◽  
The Antarctic

AbstractForbes Glacier, one of the outlet ice streams from the Antarctic ice sheet, is located 20 km west of Mawson, Mac.Robertson Land, east Antarctica. In the uppermost part of the glacier near Casey Range, the velocity at the centre of the glacier is 59 m year−1and the strain-rate at seven strain grids ranges from −6.7 to 6.7×10−3year−1on the surface of the glacier. The fabric types of this area are characterized by single-maximum and small-girdle fabrics. It is confirmed that the single-maximum fabric is an original pattern which changes gradually to a small girdle fabric about the maximum compressive axis in association with grain growth. The patterns predicted by Brace (1960) can be adapted to the small-girdle fabrics of this area.

scholarly journals ICE FLOW VELOCITY MAPPING IN EAST ANTARCTICA USING HISTORICAL IMAGES FROM 1960s TO 1980s: RECENT PROGRESS

2021 ◽  
Vol XLIII-B3-2021 ◽  
pp. 491-496
Author(s):  
S. Luo ◽  
Y. Cheng ◽  
Z. Li ◽  
Y. Wang ◽  
K. Wang ◽  
...  
Keyword(s):  
Mass Balance ◽  
Flow Velocity ◽  
East Antarctica ◽  
Input Output ◽  
Velocity Mapping ◽  
Ice Flow ◽  
Optical Images ◽  
Elevation Changes ◽  
Ice Velocity ◽  
Surface Ice

Abstract. Recent research indicates that the estimated elevation changes and associated mass balance in East Antarctica are of some degree of uncertainty; a light accumulation has occurred in its vast inland regions, while mass loss in Wilkes Land appears significant. It is necessary to study the mass change trend in the context of a long period of the East Antarctic Ice Sheet (EAIS). The input-output method based on surface ice flow velocity and ice thickness is one of the most important ways to estimate the mass balance, which can provide longer-term knowledge of mass balance because of the availability of the early satellites in 1960s. In this study, we briefly describe the method of extracting ice velocity based on the historical optical images from 1960s to 1980s. Based on the draft ice velocity map of the EAIS using this method, we conduct a series of validation experiments, including comparisons with in-situ measurement, existing historical maps and rock outcrop dataset. Finally, we use the input-output method to estimate mass balance in some regions of EAIS using the generated velocity map.

scholarly journals Structures and Ice Deformation in the White Glacier, Axel Heiberg Island, Northwest Territories, Canada

1978 ◽  
Vol 20 (82) ◽  
pp. 41-66 ◽  
Author(s):  
M.J. Hambrey ◽  
F. Müller
Keyword(s):  
Strain Rate ◽  
Compressive Strain ◽  
Source Area ◽  
Strain Rates ◽  
Glacier Surface ◽  
Ice Flow ◽  
Passive Deformation ◽  
Differential Flow ◽  
Shearing Strain ◽  
Prominent Ridge

AbstractThe major structures in the long, narrow tongue of a sub-polar valley glacier are described: namely, longitudinal foliation, crevasses, clear-ice layers related to crevasses, debris-rich layers (frequently referred to as thrust or shear planes in the past), and folds. The foliation is vertical, is as well-developed in the centre of the glacier as at the margins, and does not, apparently, form perpendicular to the principal compressive strain-rate axis, nor exactly parallel to a line of maximum shearing strain-rate, although it sometimes approximately coincides with the latter. The intensity of foliation development is not related to the magnitude of the strain-rates, but the structure consistently lies parallel to flow lines through the glacier. There is no critical extending strain-rate, as such, associated with the development of new crevasses. Some crevasses have formed where the principal extending strain-rate is as low as 0.004 a-1while, in other areas, extending strain-rates of 0.163 a-1have not always resulted in fracturing. Prominent clear-ice layers, referred to as crevasse traces as displayed at the glacier surface, have formed in crevasse belts parallel to the main fracture directions. These are interpreted either as tensional veins or as the result of the freezing of water in crevasses. Extension parallel to the layering occurs during flow and, near the snout, the surface dip decreases rapidly. The fact that the crevasse traces can be followed to the snout implies that fracture occurs almost to the bottom of the glacier in the source area of the traces. Near the snout, debris-rich layers have developed parallel to the crevasse traces; frequently these are marked by prominent ridge-like ice-cored moraines. It is suggested that these structures are formed by a combination of basal freezing and thrusting. Isoclinal and tight similar folds on all scales are present. Some may be formed by the passive deformation of clear-ice layers as a result of differential flow; others may arise from the lateral compression of the original stratification in areas where ice flow becomes constricted by the narrowing of the valley. An axial plane foliation sometimes is associated with these folds.

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 An observationally validated theory of viscous flow dynamics at the ice-shelf calving front

2012 ◽  
Vol 58 (208) ◽  
pp. 375-387 ◽  
Author(s):  
Richard C.A. Hindmarsh
Keyword(s):  
Analytical Theory ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Grounding Line ◽  
Interior Flow ◽  
Ice Velocity ◽  
Calving Rate ◽  
The Stability ◽  
Low Sensitivity

AbstractAn analytical theory is developed for ice flow velocity in a boundary layer couplet at the calving front. The theory has simple quantitative characteristics that relate ice front velocity to thickness, strain rate and shelf width, matching one set of empirically derived relationships (Alley and others, 2008) and implying that these relationships predict ice velocity rather than calving rate. The two boundary layers are where longitudinal and transverse flow fields change from the interior flow to patterns consistent with the calving-front stress condition. Numerical simulations confirm the analytical theory. The quantitative predictions of the theory have low sensitivity to unmeasured parameters and to shelf plan aspect ratio, while its robustness arises from its dependence on the scale invariance of the governing equations. The theory provides insights into calving, the stability of ice-shelf calving fronts, the stability of the grounding line of laterally resisted ice streams, and also suggests that the calving front is an instructive dynamical analogue to the grounding line.

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