scholarly journals Response of glacier flow and structure to proglacial lake development and climate at Fjallsjökull, south-east Iceland

2019 ◽  
Vol 65 (250) ◽  
pp. 321-336 ◽  
Author(s):  
REBECCA DELL ◽  
RACHEL CARR ◽  
EMRYS PHILLIPS ◽  
ANDREW J. RUSSELL
Keyword(s):  
Satellite Imagery ◽  
Surface Velocity ◽  
Outlet Glacier ◽  
Lake Development ◽  
Glacier Terminus ◽  
Air Temperatures ◽  
Glacier Dynamics ◽  
Proglacial Lake ◽  
Glacier Flow ◽  
Structural Architecture

ABSTRACTOver recent decades, the number of outlet glaciers terminating in lakes in Iceland has increased in line with climate warming. The mass-balance changes of these lake-terminating outlet glaciers are sensitive to rising air temperatures, due to altered glacier dynamics and increased surface melt. This study aims to better understand the relationship between proglacial lake development, climate, glacier dynamics and glacier structure at Fjallsjökull, a large, lake-terminating outlet glacier in south-east Iceland. We used satellite imagery to map glacier terminus position and lake extent between 1973 and 2016, and a combination of aerial and satellite imagery to map the structural architecture of the glacier's terminus in 1982, 1994 and 2011. The temporal evolution of ice surface velocities between 1990 and 2018 was calculated using feature tracking. Statistically significant increases in the rate of terminus retreat and lake expansion were identified in 2001, 2009 and 2011. Our surface velocity and structural datasets revealed the development of localised flow ‘corridors’ over time, which conveyed relatively faster flow towards the glacier's terminus. We attribute the overall changes in dynamics and structural architecture at Fjallsjökull to rising air temperatures, but argue that the spatial complexities are driven by glacier specific factors, such as basal topography.

scholarly journals Mapping tide-water glacier dynamics in East Greenland using Landsat data

1995 ◽  
Vol 41 (139) ◽  
pp. 584-595 ◽  
Author(s):  
John L. Dwyer
Keyword(s):  
Cross Correlation ◽  
Drainage Basin ◽  
Surface Velocity ◽  
Key Factors ◽  
Remotely Sensed Data ◽  
East Greenland ◽  
Ice Surface ◽  
Glacier Terminus ◽  
Glacier Dynamics ◽  
Continuous Presence

AbstractLandsat multispectral scanner and thematic mapper images were co-registered For the Kangerdlugssuaq Fjord region in East Greenland and were used to map glacier drainage-basin areas, changes in the positions of tide-water glacier termini and to estimate surface velocities of the larger tide-water glaciers. Statistics were compiled to document distance and area changes to glacier termini. The methodologies developed in this study are broadly applicable to the investigation of tide-water glaciers in other areas. The number of images available for consecutive years and the accuracy with which images are co-registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data.Three domains of glacier state were interpreted: net increase in terminus area in the southern part of the study area, net loss of terminus area for glaciers in upper Kangerdlugssuaq Fjord and a slight loss of glacier terminus area northward from Ryberg Fjord. Local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions Ice-surface velocity estimates were derived for several glaciers using automated image cross-correlation techniques The velocity determined for Kangerdlugssuaq Gletscher is approximately 5.0 km a−1and that for Kong Christian IV Gletscher is 0.9 km a−1. The continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice-front calving.

scholarly journals Modelled glacier dynamics over the last quarter of a century at Jakobshavn Isbræ

2016 ◽  
Vol 10 (2) ◽  
pp. 597-611 ◽  
Author(s):  
Ioana S. Muresan ◽  
Shfaqat A. Khan ◽  
Andy Aschwanden ◽  
Constantine Khroulev ◽  
Tonie Van Dam ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Significant Progress ◽  
Outlet Glacier ◽  
The Past ◽  
Glacier Terminus ◽  
Subsequent Response ◽  
Glacier Dynamics ◽  
Speed Up ◽  
Break Up ◽  
Bed Slope

Abstract. Observations over the past 2 decades show substantial ice loss associated with the speed-up of marine-terminating glaciers in Greenland. Here we use a regional three-dimensional outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in western Greenland. Our approach is to model and understand the recent behaviour of JI with a physical process-based model. Using atmospheric forcing and an ocean parametrization we tune our model to reproduce observed frontal changes of JI during 1990–2014. In our simulations, most of the JI retreat during 1990–2014 is driven by the ocean parametrization used and the glacier's subsequent response, which is largely governed by bed geometry. In general, the study shows significant progress in modelling the temporal variability of the flow at JI. Our results suggest that the overall variability in modelled horizontal velocities is a response to variations in terminus position. The model simulates two major accelerations that are consistent with observations of changes in glacier terminus. The first event occurred in 1998 and was triggered by a retreat of the front and moderate thinning of JI prior to 1998. The second event, which started in 2003 and peaked in the summer 2004, was triggered by the final break-up of the floating tongue. This break-up reduced the buttressing at the JI terminus that resulted in further thinning. As the terminus retreated over a reverse bed slope into deeper water, sustained high velocities over the last decade have been observed at JI. Our model provides evidence that the 1998 and 2003 flow accelerations are most likely initiated by the ocean parametrization used but JI's subsequent dynamic response was governed by its own bed geometry. We are unable to reproduce the observed 2010–2012 terminus retreat in our simulations. We attribute this limitation to either inaccuracies in basal topography or to misrepresentations of the climatic forcings that were applied. Nevertheless, the model is able to simulate the previously observed increase in mass loss through 2014.

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 Reactions of a calving glacier to large changes in water level

1992 ◽  
Vol 16 ◽  
pp. 158-162 ◽  
Author(s):  
Tron Laumann ◽  
Bjørn Wold
Keyword(s):  
Water Level ◽  
Lake Level ◽  
Surface Velocity ◽  
Hydropower Development ◽  
Outlet Glacier ◽  
Glacier Terminus ◽  
Western Norway ◽  
Measured Response ◽  
Good Agreement

Austdalsvatn in western Norway was regulated in 1988 as a reservoir for a hydropower development. From a pre-1988 water level of 1157 m a.s.l. the new water level will vary more or less annually from 1170 to 1200 m a.s.l. The outlet glacier Austdalsbreen calves into this reservoir. About 1600 m up-valley from its terminus the glacier flows over a bedrock riegel that is, at its lowest point, ∼ 15 m above the projected maximum lake level of 1200 m. As a result of the increase in water level, the surface velocity near the front has increased from about 0.07 to 0.13 m d−1.Calculations suggest that the glacier terminus will retreat about 750 m in 50 years. The measured response of the glacier terminus for the first three years is in good agreement with the simulations.

scholarly journals Contrasting thinning patterns between lake- and land-terminating glaciers in the Bhutanese Himalaya

2019 ◽  
Vol 13 (10) ◽  
pp. 2733-2750 ◽  
Author(s):  
Shun Tsutaki ◽  
Koji Fujita ◽  
Takayuki Nuimura ◽  
Akiko Sakai ◽  
Shin Sugiyama ◽  
...  
Keyword(s):  
Numerical Experiments ◽  
Surface Flow ◽  
Ice Dynamics ◽  
Thickness Change ◽  
Surface Mass ◽  
Ablation Area ◽  
Lake Development ◽  
Glacier Terminus ◽  
Proglacial Lake

Abstract. Despite the importance of glacial lake development in ice dynamics and glacier thinning, in situ and satellite-based measurements from lake-terminating glaciers are sparse in the Bhutanese Himalaya, where a number of proglacial lakes exist. We acquired in situ and satellite-based observations across lake- and land-terminating debris-covered glaciers in the Lunana region, Bhutanese Himalaya. A repeated differential global positioning system survey reveals that thickness change of the debris-covered ablation area of the lake-terminating Lugge Glacier (-4.67±0.07 m a−1) is more than 3 times more negative than that of the land-terminating Thorthormi Glacier (-1.40±0.07 m a−1) for the 2004–2011 period. The surface flow velocities decrease down-glacier along Thorthormi Glacier, whereas they increase from the upper part of the ablation area to the terminus of Lugge Glacier. Numerical experiments using a two-dimensional ice flow model demonstrate that the rapid thinning of Lugge Glacier is driven by both a negative surface mass balance and dynamically induced ice thinning. However, the thinning of Thorthormi Glacier is minimised by a longitudinally compressive flow regime. Multiple supraglacial ponds on Thorthormi Glacier have been expanding since 2000 and have merged into a single proglacial lake, with the glacier terminus detaching from its terminal moraine in 2011. Numerical experiments suggest that the thinning of Thorthormi Glacier will accelerate with continued proglacial lake development.

scholarly journals Observation of recent surges of Vatnajökull, Iceland, by means of ERS SAR interferometry

2003 ◽  
Vol 37 ◽  
pp. 69-76 ◽  
Author(s):  
Andrea Fischer ◽  
Helmut Rott ◽  
Helgi Björnsson
Keyword(s):  
Sar Interferometry ◽  
Surface Velocity ◽  
Outlet Glacier ◽  
Ice Cap ◽  
Glacier Terminus ◽  
New Information ◽  
Basal Sliding ◽  
Velocity Changes ◽  
Extended Area ◽  
In The Beginning

AbstractRecent surges of two outlet glaciers of the Vatnajökull ice cap, Iceland, were observed using European Remote-sensing Satellite (ERS) synthetic aperture radar (SAR) tandem interferograms from12 different dates between December 1995 and January 2000. ERS SAR interferometry provided new information on the temporal and spatial variations in surface velocity during surges, after fieldwork became impossible. The area affected by the surge and therefore by increased basal sliding was delineated. Themigration of flow divides on the ice cap during a surge was described. At Sylgjujökull, a western outlet glacier covering an area of 175 km2, the fully developed surge and its abating phase were studied. Over a period of 4 2 years after December 1995, the ice motion decreased steadily, with initially the highest velocities and subsequently the most pronounced decrease in velocity at the glacier terminus. The surge of Dyngjujökull, a northern outlet glacier covering an area of 1040 km2, reached its maximum in 1999/2000. Slow acceleration over an area of about 200 km2 was first observed between March 1996 and January 1997. The interferogram from January 1999 shows a well-developed surge area, covering 210 km2. This area more than doubled by January 2000, with maximum velocities reaching >7 md–1. Between January 1997 and January 2000, the flow divide between Dyngju- and Skeiðararjökull shifted 16 km to the south. The investigations indicate that a surge cycle on these glaciers spans several years, with slowly increasing motion over an extended area in the beginning, and more pronounced velocity changes during the active surge phase lasting 1–2 years.

scholarly journals Mapping tide-water glacier dynamics in East Greenland using Landsat data

1995 ◽  
Vol 41 (139) ◽  
pp. 584-595 ◽  
Author(s):  
John L. Dwyer
Keyword(s):  
Cross Correlation ◽  
Drainage Basin ◽  
Surface Velocity ◽  
Key Factors ◽  
Remotely Sensed Data ◽  
East Greenland ◽  
Ice Surface ◽  
Glacier Terminus ◽  
Glacier Dynamics ◽  
Continuous Presence

AbstractLandsat multispectral scanner and thematic mapper images were co-registered For the Kangerdlugssuaq Fjord region in East Greenland and were used to map glacier drainage-basin areas, changes in the positions of tide-water glacier termini and to estimate surface velocities of the larger tide-water glaciers. Statistics were compiled to document distance and area changes to glacier termini. The methodologies developed in this study are broadly applicable to the investigation of tide-water glaciers in other areas. The number of images available for consecutive years and the accuracy with which images are co-registered are key factors that influence the degree to which regional glacier dynamics can be characterized using remotely sensed data.Three domains of glacier state were interpreted: net increase in terminus area in the southern part of the study area, net loss of terminus area for glaciers in upper Kangerdlugssuaq Fjord and a slight loss of glacier terminus area northward from Ryberg Fjord. Local increases in the concentrations of drifting icebergs in the fjords coincide with the observed extension of glacier termini positions Ice-surface velocity estimates were derived for several glaciers using automated image cross-correlation techniques The velocity determined for Kangerdlugssuaq Gletscher is approximately 5.0 km a−1 and that for Kong Christian IV Gletscher is 0.9 km a−1. The continuous presence of icebergs and brash ice in front of these glaciers indicates sustained rates of ice-front calving.

scholarly journals Reactions of a calving glacier to large changes in water level

1992 ◽  
Vol 16 ◽  
pp. 158-162 ◽  
Author(s):  
Tron Laumann ◽  
Bjørn Wold
Keyword(s):  
Water Level ◽  
Lake Level ◽  
Surface Velocity ◽  
Hydropower Development ◽  
Outlet Glacier ◽  
Glacier Terminus ◽  
Western Norway ◽  
Measured Response ◽  
Good Agreement

Austdalsvatn in western Norway was regulated in 1988 as a reservoir for a hydropower development. From a pre-1988 water level of 1157 m a.s.l. the new water level will vary more or less annually from 1170 to 1200 m a.s.l. The outlet glacier Austdalsbreen calves into this reservoir. About 1600 m up-valley from its terminus the glacier flows over a bedrock riegel that is, at its lowest point, ∼ 15 m above the projected maximum lake level of 1200 m. As a result of the increase in water level, the surface velocity near the front has increased from about 0.07 to 0.13 m d−1.Calculations suggest that the glacier terminus will retreat about 750 m in 50 years. The measured response of the glacier terminus for the first three years is in good agreement with the simulations.

scholarly journals Seasonal variations of outlet glacier terminus position in Greenland

2013 ◽  
Vol 59 (216) ◽  
pp. 759-770 ◽  
Author(s):  
Kristin M. Schild ◽  
Gordon S. Hamilton
Keyword(s):  
Seasonal Variations ◽  
Spatial And Temporal Variability ◽  
Simple Relationship ◽  
Environmental Forcing ◽  
Outlet Glacier ◽  
Glacier Terminus ◽  
Air Temperatures ◽  
Spatial Differences ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer

AbstractMany of Greenland’s marine-terminating outlet glaciers have undergone rapid retreat in the past decade, accompanied by accelerated flow and dynamic thinning. Superimposed on this pattern of retreat, these glaciers undergo seasonal variations in terminus position, corresponding roughly to wintertime advance and summertime retreat. We compiled near-daily time series of terminus position for five of Greenland’s largest outlet glaciers (Daugaard Jensen, Kangerdlugssuaq and Helheim glaciers in East Greenland, and Jakobshavn Isbræ and Rink Isbræ in West Greenland) using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. There are spatial differences in the timing of the onset of seasonal retreat among all the glaciers in our study, as well as variability in terminus behavior for individual glaciers from year to year. We examine whether this spatial and temporal variability is linked to above-freezing air temperatures or high sea surface temperatures, but find no simple relationship. Instead, we hypothesize that terminus geometry (ice thickness, subglacial topography, fjord bathymetry) exerts an important control on the response of marine-terminating glaciers to climate perturbations. Models for predicting outlet glacier response to climate change need to include this complex interaction between geometry and environmental forcing.

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.

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