scholarly journals Spatial and temporal evolution of rapid basal sliding on Bench Glacier, Alaska, USA

2005 ◽  
Vol 51 (172) ◽  
pp. 49-63 ◽  
Author(s):  
Kelly R. Macgregor ◽  
Catherine A. Riihimaki ◽  
Robert S. Anderson
Keyword(s):  
Temporal Evolution ◽  
Surface Velocity ◽  
Mean Velocity ◽  
Surface Uplift ◽  
Ice Surface ◽  
Velocity Wave ◽  
Basal Sliding ◽  
Hydrologic System ◽  
Speed Up ◽  
Cavity System

AbstractWe measured the surface velocity field during the summers of 1999 and 2000 on the 7 km long, 185 m thick Bench Glacier, Alaska, USA. In the spring of both years, a short-lived pulse of surface velocity, 2-4 times the annual mean velocity, propagated up-glacier from the terminus at a rate of ~200-250md-1. Displacement attributable to rapid sliding is ~5-10% of the annual surface motion, while the high-velocity event comprised 60-95% of annual basal motion. Sliding during the propagating speed-up event peaked at 6-14 cm d-1, with the highest rates in mid-glacier. Continuous horizontal and vertical GPS measurements at one stake showed divergence and then convergence of the ice surface with the bed as the velocity wave passed, with maximum surface uplift of 8-16 cm. High divergence rates coincided with high horizontal velocities, suggesting rapid sliding on the up-glacier side of bedrock steps. Initiation of the annual speed-up event occurred during the peak in englacial water storage, while the glacier was entirely snow-covered. Basal motion during the propagating speed-up event enlarges cavities and connections among them, driving a transition from a poorly connected hydrologic system to a well-connected linked-cavity system. Sliding is probably halted by the development of a conduit system.

scholarly journals Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland

1995 ◽  
Vol 41 (137) ◽  
pp. 161-173 ◽  
Author(s):  
James L. Fastook ◽  
Henry H. Brecher ◽  
Terence J. Hughes
Keyword(s):  
Flow Direction ◽  
Greenland Ice Sheet ◽  
Surface Strain ◽  
Curvilinear Coordinates ◽  
Surface Velocity ◽  
Strain Rates ◽  
Bed Topography ◽  
Ice Surface ◽  
Basal Sliding ◽  
Grid Points

AbstractJakobshavns Isbræ (69 °10′ N, 49 °59′ W) drains about 6.5% of the Greenland ice sheet and is the fastest ice stream known. The Jakobshavns Isbræ basin of about 10 000 km2was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Positions and elevations of several hundred natural features on the ice surface were determined for each epoch by photogrammetric block aerial triangulation, and surface velocity vectors were computed from the positions. The two flights in 1985 yielded the best results and provided most common points (716) for velocity determinations and are therefore used in the modeling studies. The data from these irregularly spaced points were used to calculate ice elevations and velocity vectors at uniformly spaced grid points 3 km apart by interpolation. The field of surface strain rates was then calculated from these gridded data and used to compute the field of surface deviatoric stresses, using the flow law of ice, for rectilinear coordinates,X, Ypointing eastward and northward, and curvilinear coordinates.L, Τpointing longitudinally and transversely to the changing ice-flow direction, Ice-surface elevations and slopes were then used to calculate ice thicknesses and the fraction of the ice velocity due to basal sliding. Our calculated ice thicknesses are in fair agreement with an ice-thickness map based on seismic sounding and supplied to us by K. Echelmeyer. Ice thicknesses were subtracted from measured ice-surface elevations to map bed topography. Our calculation shows that basal sliding is significant only in the 10–15 km before Jakobshavns Isbræ becomes afloat in Jakobshavns Isfjord.

scholarly journals Modeling the WorldView-derived seasonal velocity evolution of Kennicott Glacier, Alaska

2016 ◽  
Vol 62 (234) ◽  
pp. 763-777 ◽  
Author(s):  
W. H. ARMSTRONG ◽  
R. S. ANDERSON ◽  
JEFFERY ALLEN ◽  
H. RAJARAM
Keyword(s):  
Stress Gradient ◽  
Surface Expression ◽  
Surface Velocity ◽  
Cross Sectional ◽  
Ice Surface ◽  
Hydrologic System ◽  
Glacier Velocity ◽  
Glacier Flow ◽  
Insight Into ◽  
Gaining Insight

ABSTRACTGlacier basal motion generates diurnal to multi-annual fluctuations in glacier velocity and mass flux. Understanding these fluctuations is important for prediction of future sea-level rise and for gaining insight into glacier physics and erosion. Here, we derive glacier velocity through cross-correlation of WorldView satellite imagery to document the evolution of ice surface velocity on Kennicott Glacier, Alaska, over the 2013 melt season. The summer speedup is spatially uniform over a ~12 km2 area, over which the spring velocity varies significantly. Velocity increases by 1.4-fold to tenfold across the study domain, with larger values where spring velocities are low. To investigate the cross-glacier distribution of basal motion required to explain the observed surface speedup, we employ a two-dimensional cross-sectional glacier flow model. We find the model is insensitive to the spatial distribution of basal slip because stress gradient ice coupling diffuses the surface expression of the basal velocity field. While the temporal evolution of the subglacial hydrologic system is critical for predicting a glacier's response to meltwater inputs, our work suggests that glacier and ice-sheet models do not require a detailed representation of subglacial hydrology to accurately capture the spatial pattern of glacier speedup.

Surface velocity variations of glaciers on Kenai Peninsula, Alaska, 2014-2019

2021 ◽  
Author(s):  
Ruitang Yang ◽  
Regine Hock ◽  
Shichang Kang ◽  
Donghui Shangguan ◽  
Wanqin Guo
Keyword(s):  
Time Series ◽  
Velocity Profile ◽  
Velocity Fields ◽  
Surface Velocity ◽  
Spatiotemporal Variations ◽  
Outburst Flood ◽  
Mean Velocity ◽  
Kenai Peninsula ◽  
Speed Up ◽  
Offset Tracking

<p>We characterize the spatiotemporal variations surface velocity of glaciers on the Kenai Peninsula, Alaska, using intensity offset tracking on a set of repeat-pass Sentinel-1 data and TerraSAR-X data. We derived 92 velocity fields and generated time-averaged annual and seasonal surface velocity maps for the period October 2014 to December 2019, as well as time series surface velocity profiles along centerlines for individual glaciers. We find considerable spatial and seasonal variations in surface velocity in the study area, especially a pronounced average spring speedup of 50% averagely compared to annual mean velocity. Ice velocities varied systematically between glaciers with different terminus types. Generally, the pixel-averaged velocity of tidewater and lake-terminating glaciers are up to 2 and 1.5 times greater than those of the land-terminating glaciers, respectively. For Bear glacier, with the analysis of surface velocity profile and the terminus change, we state this glacier retreat and accelerate. While the time-series result shows the velocity speed-up of the Bear glacier synchronizes well with the ice-damaged lake outburst flood (GLOF) events.</p>

scholarly journals Assessing the summer water budget of a moulin basin in the Sermeq Avannarleq ablation region, Greenland ice sheet

2011 ◽  
Vol 57 (205) ◽  
pp. 954-964 ◽  
Author(s):  
Daniel McGrath ◽  
William Colgan ◽  
Konrad Steffen ◽  
Phillip Lauffenburger ◽  
James Balog
Keyword(s):  
Water Budget ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Time Lapse ◽  
Balance Model ◽  
Diurnal Variability ◽  
Surface Uplift ◽  
Ice Surface ◽  
Basal Sliding

AbstractWe provide an assessment of the supraglacial water budget of a moulin basin on the western margin of the Greenland ice sheet for 15 days in August 2009. Meltwater production, the dominant input term to the 1.14 ± 0.06 km2 basin, was determined from in situ ablation measurements. The dominant water-output terms from the basin, accounting for 52% and 48% of output, respectively, were moulin discharge and drainage into crevasses. Moulin discharge exhibits large diurnal variability (0.017–0.54 m3 s−1) with a distinct late-afternoon peak at 16:45 local time. This lags peak meltwater production by ∼2.8 ± 4.2 hours. An Extreme Ice Survey time-lapse photography sequence complements the observations of moulin discharge. We infer, from in situ observations of moulin geometry, previously published borehole water heights and estimates of the temporal lag between meltwater production and observed local ice surface uplift (‘jacking’), that the transfer of surface meltwater to the englacial water table via moulins is nearly instantaneous (<30 min). We employ a simple crevasse mass-balance model to demonstrate that crevasse drainage could significantly dampen the surface meltwater fluctuations reaching the englacial system in comparison to moulin discharge. Thus, unlike crevasses, moulins propagate meltwater pulses to the englacial system that are capable of overwhelming subglacial transmission capacity, resulting in enhanced basal sliding.

scholarly journals Derived bedrock elevations, strain rates and stresses from measured surface elevations and velocities: Jakobshavns Isbræ, Greenland

1995 ◽  
Vol 41 (137) ◽  
pp. 161-173 ◽  
Author(s):  
James L. Fastook ◽  
Henry H. Brecher ◽  
Terence J. Hughes
Keyword(s):  
Flow Direction ◽  
Greenland Ice Sheet ◽  
Surface Strain ◽  
Curvilinear Coordinates ◽  
Surface Velocity ◽  
Strain Rates ◽  
Bed Topography ◽  
Ice Surface ◽  
Basal Sliding ◽  
Grid Points

AbstractJakobshavns Isbræ (69 °10′ N, 49 °59′ W) drains about 6.5% of the Greenland ice sheet and is the fastest ice stream known. The Jakobshavns Isbræ basin of about 10 000 km2 was mapped photogrammetrically from four sets of aerial photography, two taken in July 1985 and two in July 1986. Positions and elevations of several hundred natural features on the ice surface were determined for each epoch by photogrammetric block aerial triangulation, and surface velocity vectors were computed from the positions. The two flights in 1985 yielded the best results and provided most common points (716) for velocity determinations and are therefore used in the modeling studies. The data from these irregularly spaced points were used to calculate ice elevations and velocity vectors at uniformly spaced grid points 3 km apart by interpolation. The field of surface strain rates was then calculated from these gridded data and used to compute the field of surface deviatoric stresses, using the flow law of ice, for rectilinear coordinates, X, Y pointing eastward and northward, and curvilinear coordinates. L, Τ pointing longitudinally and transversely to the changing ice-flow direction, Ice-surface elevations and slopes were then used to calculate ice thicknesses and the fraction of the ice velocity due to basal sliding. Our calculated ice thicknesses are in fair agreement with an ice-thickness map based on seismic sounding and supplied to us by K. Echelmeyer. Ice thicknesses were subtracted from measured ice-surface elevations to map bed topography. Our calculation shows that basal sliding is significant only in the 10–15 km before Jakobshavns Isbræ becomes afloat in Jakobshavns Isfjord.

scholarly journals The flow of a polythermal glacier: McCall Glacier, Alaska, U.S.A.

1997 ◽  
Vol 43 (145) ◽  
pp. 522-536 ◽  
Author(s):  
B.T. Rabus ◽  
K. A. Echelmeyer
Keyword(s):  
Surface Profile ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Longitudinal Stress ◽  
Surface Slope ◽  
Basal Sliding ◽  
Speed Up ◽  
Polythermal Glacier ◽  
Long Term Variations

AbstractWe have analyzed the flow of polythermal McCall Glacier in Arctic Alaska. Using measurements of surface velocity from the 1970s and 1990s, together with measurements of ice thickness and surface slope, we have investigated both the present flow and seasonal and long-term flow variations. Our analysis of the present flow reveals that (i) longitudinal stress coupling is important along the entire length of the glacier, and (ii) there is significant basal sliding beneath a 2 km long section of the lower glacier. This sliding exists year-round and it accounts for more than 70% of the total motion there. We have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness. Accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up-glacier from it. Both effects are reflected in the observed surface profile of McCall Glacier.The longitudinal stress-coupling length of McCall Glacier is three times the ice thickness, almost twice that typical of temperate glaciers. This is a direct effect of lower strain rates, which themselves are associated with the smaller mass-balance gradients of Arctic and continental glaciers. Long-term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution. This means that long-term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small. Seasonally, Velocities reach their annual minimum in spring and increase during the short summer nick season by up to 75% above mean winter values. However, the extra motion associated with the period of elevated velocities is only about 5% of the total annual motion. The speed-up is due to an increase in basal sliding. This implies that most of the glacier bed is at the melting point. The zone a affected by the melt-season speed-up extends well up-glacier of any moulins or other obvious sources for melt water at the bed.

scholarly journals The flow of a polythermal glacier: McCall Glacier, Alaska, U.S.A.

1997 ◽  
Vol 43 (145) ◽  
pp. 522-536 ◽  
Author(s):  
B.T. Rabus ◽  
K. A. Echelmeyer
Keyword(s):  
Surface Profile ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Longitudinal Stress ◽  
Surface Slope ◽  
Basal Sliding ◽  
Speed Up ◽  
Polythermal Glacier ◽  
Long Term Variations

AbstractWe have analyzed the flow of polythermal McCall Glacier in Arctic Alaska. Using measurements of surface velocity from the 1970s and 1990s, together with measurements of ice thickness and surface slope, we have investigated both the present flow and seasonal and long-term flow variations. Our analysis of the present flow reveals that (i) longitudinal stress coupling is important along the entire length of the glacier, and (ii) there is significant basal sliding beneath a 2 km long section of the lower glacier. This sliding exists year-round and it accounts for more than 70% of the total motion there. We have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness. Accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up-glacier from it. Both effects are reflected in the observed surface profile of McCall Glacier.The longitudinal stress-coupling length of McCall Glacier is three times the ice thickness, almost twice that typical of temperate glaciers. This is a direct effect of lower strain rates, which themselves are associated with the smaller mass-balance gradients of Arctic and continental glaciers. Long-term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution. This means that long-term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small. Seasonally, Velocities reach their annual minimum in spring and increase during the short summer nick season by up to 75% above mean winter values. However, the extra motion associated with the period of elevated velocities is only about 5% of the total annual motion. The speed-up is due to an increase in basal sliding. This implies that most of the glacier bed is at the melting point. The zone a affected by the melt-season speed-up extends well up-glacier of any moulins or other obvious sources for melt water at the bed.

scholarly journals Inversion of a glacier hydrology model

2016 ◽  
Vol 57 (72) ◽  
pp. 84-95 ◽  
Author(s):  
Douglas J. Brinkerhoff ◽  
Colin R. Meyer ◽  
Ed Bueler ◽  
Martin Truffer ◽  
Timothy C. Bartholomaus
Keyword(s):  
Covariance Structure ◽  
Monte Carlo Algorithm ◽  
Surface Velocity ◽  
Stream Discharge ◽  
Ice Surface ◽  
Input Flux ◽  
Outlet Stream ◽  
Hydrologic System ◽  
Parameter Values ◽  
Averaged Model

ABSTRACTThe subglacial hydrologic system exerts strong controls on the dynamics of the overlying ice, yet the parameters that govern the evolution of this system are not widely known or observable. To gain a better understanding of these parameters, we invert a spatially averaged model of subglacial hydrology from observations of ice surface velocity and outlet stream discharge at Kennicott Glacier, Wrangell Mountains, AK, USA. To identify independent parameters, we formally non-dimensionalize the forward model. After specifying suitable prior distributions, we use a Markov-chain Monte Carlo algorithm to sample from the distribution of parameter values conditioned on the available data. This procedure gives us not only the most probable parameter values, but also a rigorous estimate of their covariance structure. We find that the opening of cavities due to sliding over basal topography and turbulent melting are of a similar magnitude during periods of large input flux, though turbulent melting also exhibits the greatest uncertainty. We also find that both the storage of water in the englacial system and the exchange of water between englacial and subglacial systems are necessary in order to explain both surface velocity observations and the relative attenuation in the amplitude of diurnal signals between input and output flux observations.

Greenland ice sheet hydrology

2013 ◽  
Vol 38 (1) ◽  
pp. 19-54 ◽  
Author(s):  
Vena W. Chu
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Field Studies ◽  
Ice Dynamics ◽  
Surface Water Hydrology ◽  
Basal Sliding ◽  
Hydrologic System ◽  
Global Sea Level

Understanding Greenland ice sheet (GrIS) hydrology is essential for evaluating response of ice dynamics to a warming climate and future contributions to global sea level rise. Recently observed increases in temperature and melt extent over the GrIS have prompted numerous remote sensing, modeling, and field studies gauging the response of the ice sheet and outlet glaciers to increasing meltwater input, providing a quickly growing body of literature describing seasonal and annual development of the GrIS hydrologic system. This system is characterized by supraglacial streams and lakes that drain through moulins, providing an influx of meltwater into englacial and subglacial environments that increases basal sliding speeds of outlet glaciers in the short term. However, englacial and subglacial drainage systems may adjust to efficiently drain increased meltwater without significant changes to ice dynamics over seasonal and annual scales. Both proglacial rivers originating from land-terminating glaciers and subglacial conduits under marine-terminating glaciers represent direct meltwater outputs in the form of fjord sediment plumes, visible in remotely sensed imagery. This review provides the current state of knowledge on GrIS surface water hydrology, following ice sheet surface meltwater production and transport via supra-, en-, sub-, and proglacial processes to final meltwater export to the ocean. With continued efforts targeting both process-level and systems analysis of the hydrologic system, the larger picture of how future changes in Greenland hydrology will affect ice sheet glacier dynamics and ultimately global sea level rise can be advanced.

scholarly journals The propagation of a surge front on Bering Glacier, Alaska, 2001–2011

2013 ◽  
Vol 54 (63) ◽  
pp. 221-228 ◽  
Author(s):  
James Turrin ◽  
Richard R. Forster ◽  
Chris Larsen ◽  
Jeanne Sauber
Keyword(s):  
Feature Tracking ◽  
Average Rate ◽  
Surface Velocity ◽  
Ablation Zone ◽  
Ice Surface ◽  
Glacier Terminus ◽  
Bering Glacier ◽  
Landsat 7 ◽  
Ice Velocity ◽  
Recent Activity

AbstractBering Glacier, Alaska, USA, has a ∼20 year surge cycle, with its most recent surge reaching the terminus in 2011. To study this most recent activity a time series of ice velocity maps was produced by applying optical feature-tracking methods to Landsat-7 ETM+ imagery spanning 2001-11. The velocity maps show a yearly increase in ice surface velocity associated with the down-glacier movement of a surge front. In 2008/09 the maximum ice surface velocity was 1.5 ±0.017 km a-1 in the mid-ablation zone, which decreased to 1.2 ±0.015 km a-1 in 2009/10 in the lower ablation zone, and then increased to nearly 4.4 ± 0.03 km a-1 in summer 2011 when the surge front reached the glacier terminus. The surge front propagated down-glacier as a kinematic wave at an average rate of 4.4 ±2.0 km a-1 between September 2002 and April 2009, then accelerated to 13.9 ± 2.0 km a-1 as it entered the piedmont lobe between April 2009 and September 2010. The wave seems to have initiated near the confluence of Bering Glacier and Bagley Ice Valley as early as 2001, and the surge was triggered in 2008 further down-glacier in the mid-ablation zone after the wave passed an ice reservoir area.

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