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Martin J. Siegert - One of the best experts on this subject based on the ideXlab platform.
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Quantifying subglacial Bed Roughness in Antarctica: implications for ice-sheet dynamics and history
Quaternary Science Reviews, 2009Co-Authors: Robert G. Bingham, Martin J. SiegertAbstract:Glaciated landscapes consist of complex assemblages of landforms resulting from ice flow dynamic regimes and ice-sheet history, superimposed over, and in turn modifying, preglacial topography, lithology and geological structure. insights into the formation of glaciated landscapes can, in principle, be obtained by analysing modem ice-sheet Beds, but terrain analyses beneath modern ice sheets are restricted by the inaccessibility of the Bed. It is, however, possible to quantify Roughness, the vertical variation of the subglacial interface with horizontal distance, along two-dimensional images of the Bed obtained from radio-echo sounding (RES). Here we collate several case studies from Antarctica, where Roughness calculations have been used as a glaciological tool to infer basal processes and ice-sheet history over large (> 500 km(2)) areas. We present two examples from West Antarctica, which demonstrate the utility of Bed Roughness in determining the presence and extent of subglacial sediments, glacial dynamics and former ice-sheet size. We also present two examples from East Antarctica, which illustrate how Roughness provides knowledge of ice-sheet dynamics in the interior and pre-Quaternary ice-sheet histories. In modem ice-sheet settings, characterising Bed Roughness along RES tracks has the twin advantages of being relatively simple to calculate while producing informative subsurface data, and is especially powerful at furthering understanding when coupled with knowledge of ice flow from field, satellite and modelling investigations. The technique also offers significant potential for the comparison of modern and former ice-sheet terrains, contributing to an improved understanding of the formation and evolution of glaciated landscapes. (C) 2008 Elsevier Ltd. All rights reserved
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Quantifying subglacial Bed Roughness in Antarctica: implications for ice-sheet dynamics and history
Quaternary Science Reviews, 2008Co-Authors: Robert Bingham, Martin J. SiegertAbstract:Abstract Glaciated landscapes consist of complex assemblages of landforms resulting from ice flow dynamic regimes and ice-sheet history, superimposed over, and in turn modifying, preglacial topography, lithology and geological structure. Insights into the formation of glaciated landscapes can, in principle, be obtained by analysing modern ice-sheet Beds, but terrain analyses beneath modern ice sheets are restricted by the inaccessibility of the Bed. It is, however, possible to quantify Roughness, the vertical variation of the subglacial interface with horizontal distance, along two-dimensional images of the Bed obtained from radio-echo sounding (RES). Here we collate several case studies from Antarctica, where Roughness calculations have been used as a glaciological tool to infer basal processes and ice-sheet history over large (>500 km 2 ) areas. We present two examples from West Antarctica, which demonstrate the utility of Bed Roughness in determining the presence and extent of subglacial sediments, glacial dynamics and former ice-sheet size. We also present two examples from East Antarctica, which illustrate how Roughness provides knowledge of ice-sheet dynamics in the interior and pre-Quaternary ice-sheet histories. In modern ice-sheet settings, characterising Bed Roughness along RES tracks has the twin advantages of being relatively simple to calculate while producing informative subsurface data, and is especially powerful at furthering understanding when coupled with knowledge of ice flow from field, satellite and modelling investigations. The technique also offers significant potential for the comparison of modern and former ice-sheet terrains, contributing to an improved understanding of the formation and evolution of glaciated landscapes.
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Radar-derived Bed Roughness characterization of Institute and Möller ice streams, West Antarctica, and comparison with Siple Coast ice streams
Geophysical Research Letters, 2007Co-Authors: Robert Bingham, Martin J. SiegertAbstract:[1] Subglacial Bed conditions exert a significant control on ice stream behavior and evolution, and can be characterized by determining Bed Roughness from FFT analysis of radar-imaged basal reflectors. Here we assess Bed Roughness across Institute and Moller ice streams, West Antarctica, and compare our findings with Bed Roughness determined across the Siple Coast ice streams. We find that variations in Bed Roughness are spatially organized, and attribute this to the varying efficacy of subglacial erosion and deposition, with rougher (inland, slow-flowing) regions largely manifesting preglacial topography, and smoother (downstream, fast-flowing) regions evincing significant postglacial modification to the subglacial landscape. The observed similarities between Bed Roughness characteristics of IIS/MIS and the Siple ice streams suggest that IIS and MIS are largely underlain by wet, poorly consolidated sediments, and may therefore be vulnerable to the types of dynamical instabilities experienced by the Siple ice streams.
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Macro-scale Bed Roughness of the Siple Coast ice streams in West Antarctica
Earth Surface Processes and Landforms, 2004Co-Authors: Martin J. Siegert, J. Taylor, Antony J. Payne, Bryn HubbardAbstract:Subglacial Bed conditions are key to understanding ice stream behaviour and evolution, with Bed Roughness reflecting substrate composition and flow resistance. Here we present an analysis of Bed Roughness in the Siple Coast region of West Antarctica from airborne radio-echo sounding data. The ice streams are associated generally with low Bed Roughness values, which decrease downstream. The Bed of the slow-flowing Ice Stream C (∼10 000 km2) is also characterized by being smooth at all scales (wavelengths ranging from 5 km to in excess of 40 km). Furthermore, the Bed is smooth either side of Ice Stream C. This suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by Bed morphology. If the ice stream were encouraged to migrate laterally, when active, there would be little resistance offered by the subglacial morphology. Other inter-ice stream regions are rough, however, indicating a subglacial topographic influence on ice stream position. Bed Roughness increases up-flow of ice streams, which, unless the Bed is modified, may limit the inland migration of these systems. Copyright © 2004 John Wiley & Sons, Ltd.
Robert Bingham - One of the best experts on this subject based on the ideXlab platform.
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Quantifying subglacial Bed Roughness in Antarctica: implications for ice-sheet dynamics and history
Quaternary Science Reviews, 2008Co-Authors: Robert Bingham, Martin J. SiegertAbstract:Abstract Glaciated landscapes consist of complex assemblages of landforms resulting from ice flow dynamic regimes and ice-sheet history, superimposed over, and in turn modifying, preglacial topography, lithology and geological structure. Insights into the formation of glaciated landscapes can, in principle, be obtained by analysing modern ice-sheet Beds, but terrain analyses beneath modern ice sheets are restricted by the inaccessibility of the Bed. It is, however, possible to quantify Roughness, the vertical variation of the subglacial interface with horizontal distance, along two-dimensional images of the Bed obtained from radio-echo sounding (RES). Here we collate several case studies from Antarctica, where Roughness calculations have been used as a glaciological tool to infer basal processes and ice-sheet history over large (>500 km 2 ) areas. We present two examples from West Antarctica, which demonstrate the utility of Bed Roughness in determining the presence and extent of subglacial sediments, glacial dynamics and former ice-sheet size. We also present two examples from East Antarctica, which illustrate how Roughness provides knowledge of ice-sheet dynamics in the interior and pre-Quaternary ice-sheet histories. In modern ice-sheet settings, characterising Bed Roughness along RES tracks has the twin advantages of being relatively simple to calculate while producing informative subsurface data, and is especially powerful at furthering understanding when coupled with knowledge of ice flow from field, satellite and modelling investigations. The technique also offers significant potential for the comparison of modern and former ice-sheet terrains, contributing to an improved understanding of the formation and evolution of glaciated landscapes.
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Radar-derived Bed Roughness characterization of Institute and Möller ice streams, West Antarctica, and comparison with Siple Coast ice streams
Geophysical Research Letters, 2007Co-Authors: Robert Bingham, Martin J. SiegertAbstract:[1] Subglacial Bed conditions exert a significant control on ice stream behavior and evolution, and can be characterized by determining Bed Roughness from FFT analysis of radar-imaged basal reflectors. Here we assess Bed Roughness across Institute and Moller ice streams, West Antarctica, and compare our findings with Bed Roughness determined across the Siple Coast ice streams. We find that variations in Bed Roughness are spatially organized, and attribute this to the varying efficacy of subglacial erosion and deposition, with rougher (inland, slow-flowing) regions largely manifesting preglacial topography, and smoother (downstream, fast-flowing) regions evincing significant postglacial modification to the subglacial landscape. The observed similarities between Bed Roughness characteristics of IIS/MIS and the Siple ice streams suggest that IIS and MIS are largely underlain by wet, poorly consolidated sediments, and may therefore be vulnerable to the types of dynamical instabilities experienced by the Siple ice streams.
Bryn Hubbard - One of the best experts on this subject based on the ideXlab platform.
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Macro-scale Bed Roughness of the Siple Coast ice streams in West Antarctica
Earth Surface Processes and Landforms, 2004Co-Authors: Martin J. Siegert, J. Taylor, Antony J. Payne, Bryn HubbardAbstract:Subglacial Bed conditions are key to understanding ice stream behaviour and evolution, with Bed Roughness reflecting substrate composition and flow resistance. Here we present an analysis of Bed Roughness in the Siple Coast region of West Antarctica from airborne radio-echo sounding data. The ice streams are associated generally with low Bed Roughness values, which decrease downstream. The Bed of the slow-flowing Ice Stream C (∼10 000 km2) is also characterized by being smooth at all scales (wavelengths ranging from 5 km to in excess of 40 km). Furthermore, the Bed is smooth either side of Ice Stream C. This suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by Bed morphology. If the ice stream were encouraged to migrate laterally, when active, there would be little resistance offered by the subglacial morphology. Other inter-ice stream regions are rough, however, indicating a subglacial topographic influence on ice stream position. Bed Roughness increases up-flow of ice streams, which, unless the Bed is modified, may limit the inland migration of these systems. Copyright © 2004 John Wiley & Sons, Ltd.
Bijoy S. Mazumder - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of the saltation process of Bed materials by video imaging under altered Bed Roughness
Earth Surface Processes and Landforms, 2013Co-Authors: Anindita Bhattacharyya, Satya P. Ojha, Bijoy S. MazumderAbstract:The purpose of this paper is to examine the nature of particle saltation and movement over the Beds of fixed Roughness from flume experiments. A series of experiments are carried out to study the saltation of individual sand particles of different sizes over rough Beds under different flow conditions. A 3-D acoustic Doppler velocimeter is used to record the fluid velocity components; subsequently, under different flow conditions, the images of released sand particles are recorded using high-speed video imaging technique. Systematic analysis is made with regard to the forces acting on the grains and the variation of their magnitudes along the saltation trajectories of the grains. Relations between the saltation parameters, flow intensity and Bed Roughness are developed. The distributions of the angle of orientations during a single saltation follows almost a Gaussian distribution. The shape of the Gaussian distribution depends on the particle size and Bed Roughness. Particle collisions with rough Beds and the resulting coefficients of restitution are also discussed. A theoretical framework is developed to compute the mean particle velocity considering the spin in the energy balance equation. Results of the detailed analysis using the imaging technique are much better than in previously reported studies. Copyright © 2013 John Wiley & Sons, Ltd.
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Influence of Bed Roughness on sediment suspension: experimental and theoretical studies
Journal of Hydraulic Research, 2005Co-Authors: Bijoy S. Mazumder, Koeli Ghoshal, D.c. DalalAbstract:Flume experiments with five Beds of heterogeneous sediment mixtures having different values of Bed Roughness show that for fixed height and velocity the amount of suspension concentration increases up to a certain value with increase of Bed Roughness and then decreases with further increase of Bed Roughness. This indicates depletion of concentration in suspension due to increase of coarse sediment in the Bed. Some sort of “critical Bed Roughness” together with sediment entrapment acting on the sediment Beds due to further increase of Bed Roughness prevent grain sizes from lifting into suspension from the Beds. Mathematical models for computation of actual amount (g/l) and size distribution of suspended materials over different sediment Beds, based on Hunt's diffusion equations for sediments and water, have been developed in this work. Models give results which compare well with the observed values of actual amount and grain-size distributions comprising the wide range of grain sizes. In this study, the pa...
Marwan A. Hassan - One of the best experts on this subject based on the ideXlab platform.
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Co-evolution of coarse grain structuring and Bed Roughness in response to episodic sediment supply in an experimental aggrading channel
Earth Surface Processes and Landforms, 2020Co-Authors: Marwan A. Hassan, Matteo Saletti, Chendi Zhang, Carles Ferrer-boix, Joel P. L. Johnson, Tobias Müller, Claudia Von FlotowAbstract:This is the accepted version of the following article: [Hassan, M. A., Saletti, M., Zhang, C., Ferrer‐Boix, C., Johnson, J. P. L., Muller, T., and von Flotow, C. ( 2020) Co‐evolution of coarse grain structuring and Bed Roughness in response to episodic sediment supply in an experimental aggrading channel. Earth Surf. Process. Landforms, 45: 948– 961. https://doi.org/10.1002/esp.4788], which has been published in final form at https://onlinelibrary.wiley.com/doi/abs/10.1002/esp.4788
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The influence of microform Bed Roughness elements on flow and sediment transport in gravel Bed rivers: A reply
Earth Surface Processes and Landforms, 1992Co-Authors: Ian Reid, Marwan A. HassanAbstract:Clifford et al. (1992) argue that differences in hydraulic conditions at the moment of sediment entrainment in Turkey Brook, flood by flood, are attributable to variations in the form drag that arises from cluster microforms. While not denying the possibility of variable cluster concentration, we show that the time-dependent Bed consolidation and cementation that arises as a function of interstitial matrix development can also account for variation in the traction threshold. Clifford et al. further postulate that the growth of pebble clusters just prior to Bedload entrainment is a cause of the observed differences in traction thresholds at the start and finish of Bedload during a flood event. This merits further examination. However, we point out that clusters are not only observed at low flow and, therefore, already present and able to contribute significant form drag as the next Bedload generating flood waxes, but that they are known both to survive more or less intact and to entrap mobile particles during Bed disturbing events. The revelation by Clifford et al. that flow structure in the River Quarme reflects differences in Bed rugosity between riffles and pools and that it relates in scale to Bed Roughness elements (perhaps clusters) is not surprising. There is, however, some difficulty in distinguishing the precedence of chicken and egg when using this data set to elucidate the cause of cluster spacing. Nevertheless, the inference that flow and form are dynamically linked is in sympathy with our own conclusions that cluster spacing is an equilibrium condition governed by the interplay of flow resistance and sediment transport.