scholarly journals Modelling glacier-bed overdeepenings and possible future lakes for the glaciers in the Himalaya—Karakoram region

2016 ◽  
Vol 57 (71) ◽  
pp. 119-130 ◽  
Author(s):  
A. Linsbauer ◽  
H. Frey ◽  
W. Haeberli ◽  
H. Machguth ◽  
M.F. Azam ◽  
...  
Keyword(s):  
Ice Thickness ◽  
Surface Slope ◽  
Bed Topography ◽  
Bed Elevation ◽  
Digital Elevation ◽  
Surface Slopes ◽  
Lake Formation ◽  
Topography Model ◽  
Basal Shear ◽  
The Himalaya

AbstractSurface digital elevation models (DEMs) and slope-related estimates of glacier thickness enable modelling of glacier-bed topographies over large ice-covered areas. Due to the erosive power of glaciers, such bed topographies can contain numerous overdeepenings, which when exposed following glacier retreat may fill with water and form new lakes. In this study, the bed overdeepenings for ~28 000 glaciers (40 775 km2) of the Himalaya-Karakoram region are modelled using GlabTop2 (Glacier Bed Topography model version 2), in which ice thickness is inferred from surface slope by parameterizing basal shear stress as a function of elevation range for each glacier. The modelled ice thicknesses are uncertain (±30%), but spatial patterns of ice thickness and bed elevation primarily depend on surface slopes as derived from the DEM and, hence, are more robust. About 16 000 overdeepenings larger than 104m2 were detected in the modelled glacier beds, covering an area of ~2200 km2 and having a volume of ~120km3 (3-4% of present-day glacier volume). About 5000 of these overdeepenings (1800 km2) have a volume larger than 106m3. The results presented here are useful for anticipating landscape evolution and potential future lake formation with associated opportunities (tourism, hydropower) and risks (lake outbursts).

scholarly journals A multi-level strategy for anticipating future glacier lake formation and associated hazard potentials

2010 ◽  
Vol 10 (2) ◽  
pp. 339-352 ◽  
Author(s):  
H. Frey ◽  
W. Haeberli ◽  
A. Linsbauer ◽  
C. Huggel ◽  
F. Paul
Keyword(s):  
Swiss Alps ◽  
Bed Topography ◽  
Aster Gdem ◽  
Digital Elevation ◽  
Lake Formation ◽  
Level 3 ◽  
Multi Level ◽  
Four Levels ◽  
Elevation Model

Abstract. In the course of glacier retreat, new glacier lakes can develop. As such lakes can be a source of natural hazards, strategies for predicting future glacier lake formation are important for an early planning of safety measures. In this article, a multi-level strategy for the identification of overdeepened parts of the glacier beds and, hence, sites with potential future lake formation, is presented. At the first two of the four levels of this strategy, glacier bed overdeepenings are estimated qualitatively and over large regions based on a digital elevation model (DEM) and digital glacier outlines. On level 3, more detailed and laborious models are applied for modeling the glacier bed topography over smaller regions; and on level 4, special situations must be investigated in-situ with detailed measurements such as geophysical soundings. The approaches of the strategy are validated using historical data from Trift Glacier, where a lake formed over the past decade. Scenarios of future glacier lakes are shown for the two test regions Aletsch and Bernina in the Swiss Alps. In the Bernina region, potential future lake outbursts are modeled, using a GIS-based hydrological flow routing model. As shown by a corresponding test, the ASTER GDEM and the SRTM DEM are both suitable to be used within the proposed strategy. Application of this strategy in other mountain regions of the world is therefore possible as well.

scholarly journals A new bed elevation dataset for Greenland

2013 ◽  
Vol 7 (2) ◽  
pp. 499-510 ◽  
Author(s):  
J. L. Bamber ◽  
J. A. Griggs ◽  
R. T. W. L. Hurkmans ◽  
J. A. Dowdeswell ◽  
S. P. Gogineni ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Surface Elevation ◽  
The Arctic ◽  
Ice Thickness ◽  
Data Sampling ◽  
Ice Dynamics ◽  
Bed Elevation ◽  
Digital Elevation ◽  
Arctic Ice ◽  
Elevation Model

Abstract. We present a new bed elevation dataset for Greenland derived from a combination of multiple airborne ice thickness surveys undertaken between the 1970s and 2012. Around 420 000 line kilometres of airborne data were used, with roughly 70% of this having been collected since the year 2000, when the last comprehensive compilation was undertaken. The airborne data were combined with satellite-derived elevations for non-glaciated terrain to produce a consistent bed digital elevation model (DEM) over the entire island including across the glaciated–ice free boundary. The DEM was extended to the continental margin with the aid of bathymetric data, primarily from a compilation for the Arctic. Ice thickness was determined where an ice shelf exists from a combination of surface elevation and radar soundings. The across-track spacing between flight lines warranted interpolation at 1 km postings for significant sectors of the ice sheet. Grids of ice surface elevation, error estimates for the DEM, ice thickness and data sampling density were also produced alongside a mask of land/ocean/grounded ice/floating ice. Errors in bed elevation range from a minimum of ±10 m to about ±300 m, as a function of distance from an observation and local topographic variability. A comparison with the compilation published in 2001 highlights the improvement in resolution afforded by the new datasets, particularly along the ice sheet margin, where ice velocity is highest and changes in ice dynamics most marked. We estimate that the volume of ice included in our land-ice mask would raise mean sea level by 7.36 m, excluding any solid earth effects that would take place during ice sheet decay.

scholarly journals Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland

1996 ◽  
Vol 42 (141) ◽  
pp. 219-232 ◽  
Author(s):  
Ted S. Clarke ◽  
Keiih Echelmeyer
Keyword(s):  
Seismic Reflection ◽  
Dominant Role ◽  
Ice Thickness ◽  
Shear Stresses ◽  
Outlet Glacier ◽  
West Greenland ◽  
Ice Stream ◽  
Surface Slopes ◽  
Radio Echo Sounding ◽  
Basal Shear

AbstractSeismic-reflection methods were used to determine the ice thickness and basal topography of Jakobshavns Isbræ, a large, fast-moving ice stream/outlet glacier in West Greenland. A method of data analysis was developed which involves the pointwise migration of data from a linear seismic array and a single explosive source; the method yields the depth, horizontal position and slope of the basal reflector. A deep U-shaped subglacial trough was found beneath the entire length of the well-defined ice stream. The trough is incised up to 1500 m into bedrock, and its base lies 1200–1500 m below sea level for at least 70 km inland. Center-line ice thickness along most of the channel is about 2500 m, or about 2.5 times that of the surrounding ice sheet. This prominent bedrock trough was not apparent in existing radio-echo-sounding data. Reflection coefficients indicate that much of the basal interface is probably underlain by compacted, non-deforming sediment. The large ice thickness, coupled with relatively steep surface slopes, leads to high basal shear stresses (200–300 k Pa) along the ice stream. The large shear stresses and lack of a deformable bed imply that internal deformation plays a dominant role in the dynamics of Jakobshavns Isbræ.

scholarly journals On the Relationship of Ice-Surface Topography to Bed Topography on the South Polar Plateau

1966 ◽  
Vol 6 (43) ◽  
pp. 43-54 ◽  
Author(s):  
Edwin S. Robinson
Keyword(s):  
Shear Stress ◽  
Standard Deviation ◽  
Wave Length ◽  
Surface Slope ◽  
The South ◽  
Surface Features ◽  
Bed Topography ◽  
Ice Surface ◽  
The Mean ◽  
Basal Shear

AbstractIce-surface and isopachous maps, and rock-elevation maps, were prepared for the area between the South Pole and the Horlick Mountains from seismic and gravimetric measurements. Basal shear-stress was calculated from these data and surface-slope measurements at 25 sites. The mean is 0.8 bar with an areal standard deviation of 0.5 bar. Forty-five values of average basal shear stress were computed from consecutive 30 km. segments along flow lines. The mean is 0.4 bar with an areal standard deviation of 0.1 bar. These variations are too large for accurate estimates of ice-thickness variations to be made from surface-slope data alone, following Nye’s suggestion that basal shear-stress be treated as constant. From theoretical considerations Nye demonstrated that surface features of wave-length less than 40 km. should disappear within a few months unless related to bed topography. Ice and rock profiles along a 220 km. line do not show an expected theoretical relationship. Surface-elevation measurements, repeated after a 2 yr. interval. showed the surface features with wave-lengths between 5 and 40 km. to be essentially unchanged in amplitude and position. Hence these features are not adequately explained by existing theory.

On the Relationship of Ice-Surface Topography to Bed Topography on the South Polar Plateau

1966 ◽  
Vol 6 (43) ◽  
pp. 43-54 ◽  
Author(s):  
Edwin S. Robinson
Keyword(s):  
Shear Stress ◽  
Standard Deviation ◽  
Wave Length ◽  
Surface Slope ◽  
The South ◽  
Surface Features ◽  
Bed Topography ◽  
Ice Surface ◽  
The Mean ◽  
Basal Shear

AbstractIce-surface and isopachous maps, and rock-elevation maps, were prepared for the area between the South Pole and the Horlick Mountains from seismic and gravimetric measurements. Basal shear-stress was calculated from these data and surface-slope measurements at 25 sites. The mean is 0.8 bar with an areal standard deviation of 0.5 bar. Forty-five values of average basal shear stress were computed from consecutive 30 km. segments along flow lines. The mean is 0.4 bar with an areal standard deviation of 0.1 bar. These variations are too large for accurate estimates of ice-thickness variations to be made from surface-slope data alone, following Nye’s suggestion that basal shear-stress be treated as constant. From theoretical considerations Nye demonstrated that surface features of wave-length less than 40 km. should disappear within a few months unless related to bed topography. Ice and rock profiles along a 220 km. line do not show an expected theoretical relationship. Surface-elevation measurements, repeated after a 2 yr. interval. showed the surface features with wave-lengths between 5 and 40 km. to be essentially unchanged in amplitude and position. Hence these features are not adequately explained by existing theory.

scholarly journals Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland

1996 ◽  
Vol 42 (141) ◽  
pp. 219-232 ◽  
Author(s):  
Ted S. Clarke ◽  
Keiih Echelmeyer
Keyword(s):  
Seismic Reflection ◽  
Dominant Role ◽  
Ice Thickness ◽  
Shear Stresses ◽  
Outlet Glacier ◽  
West Greenland ◽  
Ice Stream ◽  
Surface Slopes ◽  
Radio Echo Sounding ◽  
Basal Shear

AbstractSeismic-reflection methods were used to determine the ice thickness and basal topography of Jakobshavns Isbræ, a large, fast-moving ice stream/outlet glacier in West Greenland. A method of data analysis was developed which involves the pointwise migration of data from a linear seismic array and a single explosive source; the method yields the depth, horizontal position and slope of the basal reflector. A deep U-shaped subglacial trough was found beneath the entire length of the well-defined ice stream. The trough is incised up to 1500 m into bedrock, and its base lies 1200–1500 m below sea level for at least 70 km inland. Center-line ice thickness along most of the channel is about 2500 m, or about 2.5 times that of the surrounding ice sheet. This prominent bedrock trough was not apparent in existing radio-echo-sounding data. Reflection coefficients indicate that much of the basal interface is probably underlain by compacted, non-deforming sediment. The large ice thickness, coupled with relatively steep surface slopes, leads to high basal shear stresses (200–300 k Pa) along the ice stream. The large shear stresses and lack of a deformable bed imply that internal deformation plays a dominant role in the dynamics of Jakobshavns Isbræ.

scholarly journals A Comparison of Surface Slopes Extracted from ICESat Waveform Data and High Resolution DEM

2020 ◽  
Vol 237 ◽  
pp. 01001
Author(s):  
Huan Xie ◽  
Hong Tang ◽  
Wenjia Du ◽  
Xiaohua Tong
Keyword(s):  
High Resolution ◽  
Surface Slope ◽  
Laser Altimeter ◽  
Waveform Data ◽  
Ice Cloud ◽  
Full Waveform ◽  
Digital Elevation ◽  
Surface Slopes ◽  
Sloping Surface ◽  
Elevation Model

Surface slope is an important topographic variable, accurate surface slope can support many research appliacations. Large footprint full waveform data has been used to estimate the surface slope and performes well. In this paper, surface slope within laser footprint is calculated using the Ice, Cloud, and land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) full waveform data and a high resolution Digital Elevation Model (REMA, the Reference Elevation Model of Antarctica). A comparison is done between two extracted surface slopes, the results show that the slopes extracted from full waveform data are close to slopes extracted from DEM, and the width of waveform can be used to extract surface slope in moderately sloping surface.

scholarly journals Bed properties and hydrological conditions underneath McCall Glacier, Alaska, USA

2009 ◽  
Vol 50 (51) ◽  
pp. 80-84 ◽  
Author(s):  
Frank Pattyn ◽  
Charlotte Delcourt ◽  
Denis Samyn ◽  
Bert de Smedt ◽  
Matt Nolan
Keyword(s):  
Potential Gradient ◽  
Ice Thickness ◽  
Central Frequency ◽  
Bed Topography ◽  
Ice Volume ◽  
Arctic Alaska ◽  
Digital Elevation ◽  
Basal Sliding ◽  
Radio Echo Sounding ◽  
Elevation Model

AbstractDuring three summer field seasons (2003, 2005 and 2006) we carried out radio-echo sounding measurements with a 5MHz (central frequency) ice-penetrating radar on McCall Glacier, Arctic Alaska, USA, along the central flowline and 17 cross-profiles. Two-way travel time was, after migration, converted to ice thickness, which, in combination with a recent digital elevation model of the surface of the glaciated area, resulted in a detailed map of the bed topography. This reveals a complex basal topography in the confluence area of the different glacial cirques. The pattern of subglacial water flow following the hydraulic potential gradient was calculated for the whole glacier area and shows a confluence of subglacial water downstream from the confluence of the glacier cirques. From the ice-thickness map the total ice volume was estimated as slightly less than 0.5 km3. Bed reflection power (BRP) was determined for the glacier after correction for ice-thickness dependence. Results reveal a clear relationship between the BRP pattern and basal sliding anomalies along the central flowline.

scholarly journals High-resolution bed topography mapping of Russell Glacier, Greenland, inferred from Operation IceBridge data

2013 ◽  
Vol 59 (218) ◽  
pp. 1015-1023 ◽  
Author(s):  
M. Morlighem ◽  
E. Rignot ◽  
J. Mouginot ◽  
X. Wu ◽  
H. Seroussi ◽  
...  
Keyword(s):  
Mass Conservation ◽  
Radar Data ◽  
Airborne Radar ◽  
Ice Thickness ◽  
Flux Divergence ◽  
Motion Data ◽  
Bed Topography ◽  
Bed Elevation ◽  
Comparable Performance ◽  
Mapping Techniques

AbstractDetailed maps of bed elevation and ice thickness are essential for understanding and projecting the evolution of the ice sheets. Such maps are traditionally obtained using airborne radar-sounding profiler data interpolated onto regular grids using geostatistical tools such as kriging. Here we compare three mapping techniques applied to a dense radar survey of Russell Glacier, West Greenland, by NASA Operation IceBridge: (1) radar tomography (RT) processing of the radar data to map the bed elevation, (2) interpolation of radar-derived thickness by ordinary kriging (KR) and (3) reconstruction of ice thickness based on the principles of mass conservation (MC) combining radar-sounding profiler and ice motion data. RT eliminates ambiguities caused by off-nadir reflections, but is spatially limited. KR yields a standard error in bed elevation of 35 m, but large errors (>300 m a−1) in flux divergence when combined with ice motion data. MC yields a comparable performance in bed elevation mapping, and errors smaller than 1 m a−1 in flux divergence. When the number of radar-sounding tracks is reduced, the performance of KR decreases more rapidly than for MC. Our study site shows that MC is capable of maintaining precision levels of 60 m at 400 m posting with flight tracks separated by 5 km.

scholarly journals Assessment of evolution and risks of glacier lake outbursts in the Djungarskiy Alatau, Central Asia, using Landsat imagery and glacier bed topography modelling

2017 ◽  
Vol 17 (10) ◽  
pp. 1837-1856 ◽  
Author(s):  
Vassiliy Kapitsa ◽  
Maria Shahgedanova ◽  
Horst Machguth ◽  
Igor Severskiy ◽  
Akhmetkal Medeu
Keyword(s):  
Landsat Imagery ◽  
Shuttle Radar Topography Mission ◽  
Ice Thickness ◽  
Srtm Dem ◽  
Hazard Management ◽  
Bed Topography ◽  
Digital Elevation ◽  
Uncertainty Of Measurements ◽  
Subglacial Topography ◽  
Elevation Model

Abstract. Changes in the abundance and area of mountain lakes in the Djungarskiy (Jetysu) Alatau between 2002 and 2014 were investigated using Landsat imagery. The number of lakes increased by 6.2 % from 599 to 636 with a growth rate of 0.51 % a−1. The combined areas were 16.26 ± 0.85 to 17.35 ± 0.92 km2 respectively and the overall change was within the uncertainty of measurements. Fifty lakes, whose potential outburst can damage existing infrastructure, were identified. The glacier bed topography version 2 (GlabTop2) model was applied to simulate ice thickness and subglacial topography using glacier outlines for 2000 and SRTM DEM (Shuttle Radar Topography Mission digital elevation model) as input data achieving realistic patterns of ice thickness. A total of 513 overdeepenings in the modelled glacier beds, presenting potential sites for the development of lakes, were identified with a combined area of 14.7 km2. Morphometric parameters of the modelled overdeepenings were close to those of the existing lakes. A comparison of locations of the overdeepenings and newly formed lakes in the areas de-glacierized in 2000–2014 showed that 67 % of the lakes developed at the sites of the overdeepenings. The rates of increase in areas of new lakes correlated with areas of modelled overdeepenings. Locations where hazardous lakes may develop in the future were identified. The GlabTop2 approach is shown to be a useful tool in hazard management providing data on the potential evolution of future lakes.

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