scholarly journals A ten-year record of supraglacial lake evolution and rapid drainage in West Greenland using an automated processing algorithm for multispectral imagery

2013 ◽  
Vol 7 (4) ◽  
pp. 3543-3565 ◽  
Author(s):  
B. F. Morriss ◽  
R. L. Hawley ◽  
J. W. Chipman ◽  
L. C. Andrews ◽  
G. A. Catania ◽  
...  
Keyword(s):  
Surface Velocity ◽  
Lake Area ◽  
Ice Flow ◽  
Outlet Glacier ◽  
West Greenland ◽  
Subglacial Environment ◽  
Supraglacial Lakes ◽  
Automated Method ◽  
Modis Imagery ◽  
Glacier Flow

Abstract. The rapid drainage of supraglacial lakes introduces large pulses of meltwater to the subglacial environment and creates moulins, surface-to-bed conduits for future melt. Introduction of water to the subglacial system has been shown to affect ice flow, and modeling suggests that variability in water supply and delivery to the subsurface play an important role in the development of the subglacial hydrologic system and its ability to enhance or mitigate ice flow. We developed a fully automated method for tracking meltwater and rapid drainages in 78 large, perennial lakes along an outlet glacier flow band in West Greenland from 2002 to 2011 using ETM+ and MODIS imagery. Results indicate interannual variability in maximum coverage and spatial evolution of total lake area. We identify 238 rapid drainage events, occurring most often at low and middle elevations during periods of net filling or peak lake coverage. We observe a general progression of both lake filling and draining from lower to higher elevations but note that the timing of filling onset, peak coverage, and dissipation are also variable. While lake coverage is sensitive to air temperature, warm years exhibit greater variability in both coverage evolution and rapid drainage. Mid elevation drainages in 2011 coincide with large surface velocity increases at nearby GPS sites, though the relationships between iceshed-scale dynamics and meltwater input are still unclear.

scholarly journals A ten-year record of supraglacial lake evolution and rapid drainage in West Greenland using an automated processing algorithm for multispectral imagery

2013 ◽  
Vol 7 (6) ◽  
pp. 1869-1877 ◽  
Author(s):  
B. F. Morriss ◽  
R. L. Hawley ◽  
J. W. Chipman ◽  
L. C. Andrews ◽  
G. A. Catania ◽  
...  
Keyword(s):  
Surface Velocity ◽  
Lake Area ◽  
Ice Flow ◽  
Outlet Glacier ◽  
West Greenland ◽  
Subglacial Environment ◽  
Supraglacial Lakes ◽  
Automated Method ◽  
Modis Imagery ◽  
Glacier Flow

Abstract. The rapid drainage of supraglacial lakes introduces large pulses of meltwater to the subglacial environment and creates moulins, surface-to-bed conduits for future melt. Introduction of water to the subglacial system has been shown to affect ice flow, and modeling suggests that variability in water supply and delivery to the subsurface play an important role in the development of the subglacial hydrologic system and its ability to enhance or mitigate ice flow. We developed a fully automated method for tracking meltwater and rapid drainages in large (> 0.125 km2) perennial lakes and applied it to a 10 yr time series of ETM+ and MODIS imagery of an outlet glacier flow band in West Greenland. Results indicate interannual variability in maximum coverage and spatial evolution of total lake area. We identify 238 rapid drainage events, occurring most often at low (< 900 m) and middle (900–1200 m) elevations during periods of net filling or peak lake coverage. We observe a general progression of both lake filling and draining from lower to higher elevations but note that the timing of filling onset, peak coverage, and dissipation are also variable. Lake coverage is sensitive to air temperature, and warm years exhibit greater variability in both coverage evolution and rapid drainage. Mid-elevation drainages in 2011 coincide with large surface velocity increases at nearby GPS sites, though the relationships between ice-shed-scale dynamics and meltwater input are still unclear.

scholarly journals Jakobshavns Isbræ, West Greenland: Seasonal Variations in Velocity - or Lack Thereof

1990 ◽  
Vol 36 (122) ◽  
pp. 82-88 ◽  
Author(s):  
Keith Echelmeyer ◽  
William D. Harrison
Keyword(s):  
Drainage Basin ◽  
Surface Velocity ◽  
West Greenland ◽  
Supraglacial Lakes ◽  
Ice Stream ◽  
Significant Seasonal Variation ◽  
Melt Water ◽  
Basal Sliding ◽  
Seasonal Basis ◽  
Made In

AbstractThe lower 80 km of the fast-moving Jakobshavns Isbræ, West Greenland, is subject to significant melting during the summer season. The melt water drains into large supraglacial rivers which pour into moulins or feed into beautiful supraglacial lakes, some of which are observed to drain periodically. Except for a few streams that drain directly off the margins of the ice sheet within the drainage basin of this glacier, the fate of this melt water is unknown. However, a localized upwelling of highly turbid water is often observed during the melt season in the fjord adjacent Io the terminal cliff of the glacier, indicating that water from some source does move along the glacier bed.As part of an investigation on the mechanisms of rapid flow on Jakobshavns Isbræ, measurements of surface velocity at several (∼25) locations along the ice stream at and below the equilibrium line were made in order to investigate the effects of this seasonally varying input of melt water on the speed of the glacier.No significant seasonal variation in speed was found at any location. This indicates that, unlike many other sub-polar and temperate glaciers, surface melt-water production does not affect the motion of this glacier on a seasonal basis, and, thus, does not cause a significant temporal variation in basal sliding. This finding has important ramifications on the mechanisms of flow for this ice stream.

scholarly journals Glacier disequilibrium in the Convoy Range, Transantarctic Mountains, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 269-276 ◽  
Author(s):  
T.J. Chinn
Keyword(s):  
Field Work ◽  
Snow Accumulation ◽  
Low Velocity ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Regime Changes ◽  
Positive Balance ◽  
Geological Map ◽  
Glacier Flow ◽  
Surficial Deposits

Field work for a geological map of the Convoy Range included mapping glaciers, moraines and surficial deposits. A range of glaciological indicators, including supraglacial and other moraines and margin morphology, has been used to assess the present equilibrium of the glaciers. Fields of rafted supraglacial moraine have accumulated over long periods of time at specific low-gradient, low-velocity locations. As the glacier regime changes, the shape of the moraine field distorts, signalling a change in flow pattern. By reversing the ice flow vectors directed at the moraine field, the directions from whence the debris came are shown. Unsorting the contortions of supraglacial moraine fields reveals the nature of the changes in glacier regime. Moraine-field configurations all suggest that local glaciers are expanding in response to higher local precipitation, estimated to have occurred between 2000 and 8000 year BP, most likely coincident with the world-wide “climatic optimum” of about 6000 year BP.Ice-cliff morphology, fresh terminal moraines and boulder trains indicate that larger local glaciers are currently receding from a Holocene maximum, while the margin of the large Mackay Ice Sheet outlet glacier shows no evidence of recent recession and is probably close to its Holocene maximum. In contrast, areas of present snow cover are expanding, superimposing a recent positive balance (decades to hundreds of years), which has yet to reverse a general recession of mid- to high-altitude glaciers. Local hollows in some névé areas imply that glacier flow is not in equilibrium with snow accumulation.

Calving Front Machine (CALFIN): Automated Calving Front Dataset and Deep Learning Methodology for East/West Greenland, 1972-2019

2020 ◽  
Author(s):  
Daniel Cheng ◽  
Yara Mohajerani ◽  
Michael Wood ◽  
Eric Larour ◽  
Wayne Hayes ◽  
...  
Keyword(s):  
Deep Learning ◽  
West Greenland ◽  
Automated Method ◽  
Current State ◽  
Time Period ◽  
Current Implementation ◽  
Landsat 7 ◽  
Modis Imagery ◽  
Processing Techniques ◽  
East West

&lt;p&gt;We present Calving Front Machine (CALFIN), an automated method for extracting calving fronts from satellite imagery. We generate results for 66 glaciers along East/West Greenland from 1972 to 2019. We output these results as a dataset, and provide new constraints on glacial evolution over the time period. This method is uniquely robust to clouds, illumination differences, ice m&amp;#233;lange, and Landsat-7 Scan Line Corrector errors. The current implementation offers a new opportunity to explore previous trends, and validate existing models moving forward.&lt;/p&gt;&lt;p&gt;This method utilizes deep learning, in the form of the Google DeeplabV3+ Xception derived CALFIN Neural Network. This approach builds on existing work by Mohajerani et al., Zhang et al., and Baumhoer et al. Additional post-processing techniques allow our method to achieve accurate and useful segmentation of raw images into Shapefile outputs.&amp;#160;&lt;/p&gt;&lt;p&gt;We achieve are often indistinguishable from the manually-curated fronts, deviating from such test data by 1 pixel (about 80 meters) or less XXX% of the time across 162 test images.&lt;/p&gt;&lt;p&gt;CALFIN excels among the current state of the art. We show this by performing a model inter-comparison to evaluate CALFIN's performance against existing methodologies. We also showcase CALFIN's ability to generalize to SAR and MODIS imagery. We achieve a mean error of 2.25 pixels (86.76 meters) from the true front on a diverse set of 162 testing images.&lt;/p&gt;

scholarly journals Elastic deformation plays a non-negligible role in Greenland’s outlet glacier flow

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Julia Christmann ◽  
Veit Helm ◽  
Shfaqat Abbas Khan ◽  
Thomas Kleiner ◽  
Ralf Müller ◽  
...  
Keyword(s):  
Sea Level ◽  
Elastic Deformation ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Fast Ice ◽  
Global Mean Sea Level ◽  
Glacier Flow ◽  
Glacier Motion ◽  
Gps Observations

AbstractFuture projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. Here we study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities.

scholarly journals ERS SAR feature-tracking measurement of outlet glacier velocities on a regional scale in East Greenland

2003 ◽  
Vol 36 ◽  
pp. 129-134 ◽  
Author(s):  
Adrian Luckman ◽  
Tavi Murray ◽  
Hester Jiskoot ◽  
Hamish Pritchard ◽  
Tazio Strozzi
Keyword(s):  
Feature Tracking ◽  
Regional Scale ◽  
Surface Velocity ◽  
Ice Flow ◽  
Outlet Glacier ◽  
East Greenland ◽  
Ice Surface ◽  
Fast Ice ◽  
Regional Basis ◽  
Ice Velocity

AbstractFeature tracking, or patch intensity cross-correlation, is used to derive two-dimensional ice-surface velocity fields from 1day and 35 day repeat-pass European Remote-sensing Satellite (ERS) synthetic aperture radar (SAR) data covering a 500 km by 500 km area of central East Greenland. Over regions of fast ice flow, 35 day tracking yields only a slightly lower density of velocity measurements than 1day tracking, and both are broadly in agreement about the spatial pattern of ice velocity except at the glacier termini where tidal effects may dominate. This study suggests that SAR feature tracking may be used to routinely monitor ice-discharge velocities on a regional basis and thereby inform studies of regional mass balance.

scholarly journals Influence of debris-rich basal ice on flow of a polar glacier

2014 ◽  
Vol 60 (223) ◽  
pp. 989-1006 ◽  
Author(s):  
Erin C. Pettit ◽  
Erin N. Whorton ◽  
Edwin D. Waddington ◽  
Ronald S. Sletten
Keyword(s):  
Low Temperatures ◽  
Ablation Rate ◽  
Surface Velocity ◽  
Inverse Theory ◽  
Limited Data ◽  
Outlet Glacier ◽  
Basal Ice ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Taylor Glacier

AbstractAt Taylor Glacier, a cold-based outlet glacier of the East Antarctic ice sheet, observed surface speeds in the terminus region are 20 times greater than those predicted using Glen’s flow law for cold (–17°C), thin (100 m) ice. Rheological properties of the clean meteoric glacier ice and the underlying deformable debris-rich basal ice can be inferred from surface-velocity and ablation-rate profiles using inverse theory. Here, with limited data, we use a two-layer flowband model to examine two end-member assumptions about the basal-ice properties: (1) uniform softness with spatially variable thickness and (2) uniform thickness with spatially variable softness. We find that the basal ice contributes 85–98% to the observed surface velocity in the terminus region. We also find that the basal-ice layer must be 10–15 m thick and 20–40 times softer than clean Holocene-age glacier ice in order to match the observations. Because significant deformation occurs in the basal ice, our inverse problem is not sensitive to variations in the softness of the meteoric ice. Our results suggest that despite low temperatures, highly deformable basal ice may dominate flow of cold-based glaciers and rheologically distinct layers should be incorporated in models of polar-glacier flow.

scholarly journals Glacier disequilibrium in the Convoy Range, Transantarctic Mountains, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 269-276 ◽  
Author(s):  
T.J. Chinn
Keyword(s):  
Field Work ◽  
Snow Accumulation ◽  
Low Velocity ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Regime Changes ◽  
Positive Balance ◽  
Geological Map ◽  
Glacier Flow ◽  
Surficial Deposits

Field work for a geological map of the Convoy Range included mapping glaciers, moraines and surficial deposits. A range of glaciological indicators, including supraglacial and other moraines and margin morphology, has been used to assess the present equilibrium of the glaciers. Fields of rafted supraglacial moraine have accumulated over long periods of time at specific low-gradient, low-velocity locations. As the glacier regime changes, the shape of the moraine field distorts, signalling a change in flow pattern. By reversing the ice flow vectors directed at the moraine field, the directions from whence the debris came are shown. Unsorting the contortions of supraglacial moraine fields reveals the nature of the changes in glacier regime. Moraine-field configurations all suggest that local glaciers are expanding in response to higher local precipitation, estimated to have occurred between 2000 and 8000 year BP, most likely coincident with the world-wide “climatic optimum” of about 6000 year BP.Ice-cliff morphology, fresh terminal moraines and boulder trains indicate that larger local glaciers are currently receding from a Holocene maximum, while the margin of the large Mackay Ice Sheet outlet glacier shows no evidence of recent recession and is probably close to its Holocene maximum. In contrast, areas of present snow cover are expanding, superimposing a recent positive balance (decades to hundreds of years), which has yet to reverse a general recession of mid- to high-altitude glaciers. Local hollows in some névé areas imply that glacier flow is not in equilibrium with snow accumulation.

scholarly journals Outlet glacier response to forcing over hourly to interannual timescales, Jakobshavn Isbræ, Greenland

2012 ◽  
Vol 58 (212) ◽  
pp. 1212-1226 ◽  
Author(s):  
David Podrasky ◽  
Martin Truffer ◽  
Mark Fahnestock ◽  
Jason M. Amundson ◽  
Ryan Cassotto ◽  
...  
Keyword(s):  
Dual Frequency ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Temperature Index ◽  
Index Model ◽  
Supraglacial Lakes ◽  
Air Temperatures ◽  
Time Period ◽  
Surface Melt ◽  
Global Sea Level

AbstractThe loss of the floating ice tongue on Jakobshavn Isbrӕ, Greenland, in the early 2000s has been concurrent with a pattern of thinning, retreat and acceleration leading to enhanced contribution to global sea level. These changes on decadal timescales have been well documented. Here we identify how the glacier responds to forcings on shorter timescales, such as from variations in surface melt, the drainage of supraglacial lakes and seasonal fluctuations in terminus position. Ice motion and surface melt were monitored intermittently from 2006 to 2008. Dual-frequency GPS were deployed 20–50 km upstream of the terminus along the glacier center line. Gaps in surface melt measurements were filled using a temperature-index model of ablation driven by surface air temperatures recorded during the same time period. Our results corroborate the premise that the primary factors controlling speeds on Jakobshavn Isbrӕ are terminus position and geometry. We also observe that surface speeds demonstrate a complex relationship with meltwater input: on diurnal timescales, velocities closely match changes in water input; however, on seasonal timescales a longer, more intense melt season was observed to effectively reduce the overall ice flow of the glacier for the whole year

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