[PDF] Flow Dynamics Of A Soft Bedded Glacier In Southeast Iceland During Basal Sliding Events eBook

Author : Julie T. Markus
Publisher :
Page : pages
File Size : 16,40 MB
Release : 2011
Category :
ISBN :

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Abstract: The purpose of this study is to determine how glacier motion and stresses vary spatially and temporally in order to clarify weaknesses in current understanding of soft-bedded glacier motion using data collected from Breiðamerkurjökull, Iceland. The dynamics of ice motion are the most substantial source of uncertainty in current models of future ice sheet mass-loss and resulting sea level rise. Currently, there is a general lack of quantitative understanding of how glacial basal conditions, such as the hydrology and till rheology at the bed, control ice motion. This study focuses on the examination of high spatial and temporal resolution surface velocities retrieved from a 12-station GPS grid in the melt seasons of 2009 and 2010 to evaluate the variation of glacial motion and strain rates over time on Breiðamerkurjökull. The first specific objective is to identify any short-term velocity variations. The second is to use the surface motion data to calculate strain rates and other components of the force budget. The third objective is to explain the variations in velocity and force budget components while taking into account glaciomorphic features of the bed. Results reveal five distinct periods of increased surface motion, termed sliding events, corresponding to periods of rainfall and/or increased temperatures during the 2009 and 2010 melt seasons. Along-flow strain rates show extension upglacier and compression downglacier during sliding events. The force budget solution indicates that upglacier, basal drag decreases substantially during speed-up events and cannot resist the local driving stress, most likely indicating pressurization of a distributed subglacial drainage system. The excess driving stress is then transferred downglacier, through gradients in longitudinal stress, to a more efficiently draining terminus where water pressures are lower and basal drag is sufficient to support the excess stress. The results demonstrate that the till at the terminus accommodates the excess stress, possibly through extensive grain bridging and dilatant hardening or by a relocation of stress to bedrock bumps during sliding events. This buttressing role of the till-bedded margin in resisting increased upglacier sliding, likely over bedrock, is novel and counter to the prevailing view of soft beds, with implications for simulating the evolution of past and current ice masses.

Author : Ralf Greve
Publisher : Springer Science & Business Media
Page : 300 pages
File Size : 41,4 MB
Release : 2009-08-07
Category : Science
ISBN : 3642034152

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Dynamics of Ice Sheets and Glaciers presents an introduction to the dynamics and thermodynamics of flowing ice masses on Earth. Based on an outline of general continuum mechanics, the different initial-boundary-value problems for the flow of ice sheets, ice shelves, ice caps and glaciers are systematically derived. Special emphasis is put on developing hierarchies of approximations for the different systems, and suitable numerical solution techniques are discussed. A separate chapter is devoted to glacial isostasy. The book is appropriate for graduate courses in glaciology, cryospheric sciences, environmental sciences, geophysics and related fields. Standard undergraduate knowledge of mathematics (calculus, linear algebra) and physics (classical mechanics, thermodynamics) provide a sufficient background for successfully studying the text.

Author : C.J. van der Veen
Publisher : CRC Press
Page : 407 pages
File Size : 50,69 MB
Release : 2013-03-26
Category : Science
ISBN : 1439835667

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Measuring, monitoring, and modeling technologies and methods changed the field of glaciology significantly in the 14 years since the publication of the first edition of Fundamentals of Glacier Dynamics. Designed to help readers achieve the basic level of understanding required to describe and model the flow and dynamics of glaciers, this second edition provides a theoretical framework for quantitatively interpreting glacier changes and for developing models of glacier flow. See What’s New in the Second Edition: Streamlined organization focusing on theory, model development, and data interpretation Introductory chapter reviews the most important mathematical tools used throughout the remainder of the book New chapter on fracture mechanics and iceberg calving Consolidated chapter covers applications of the force-budget technique using measurements of surface velocity to locate mechanical controls on glacier flow The latest developments in theory and modeling, including the addition of a discussion of exact time-dependent similarity solutions that can be used for verification of numerical models The book emphasizes developing procedures and presents derivations leading to frequently used equations step by step to allow readers to grasp the mathematical details as well as physical approximations involved without having to consult the original works. As a result, readers will have gained the understanding needed to apply similar techniques to somewhat different applications. Extensively updated with new material and focusing more on presenting the theoretical foundations of glacier flow, the book provides the tools for model validation in the form of analytical steady-state and time-evolving solutions. It provides the necessary background and theoretical foundation for developing more realistic ice-sheet models, which is essential for better integration of data and observations as well as for better model development.

Author : Laura Kehrl
Publisher :
Page : 130 pages
File Size : 21,27 MB
Release : 2018
Category :
ISBN :

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Mass loss from the world’s ice sheets is one of the largest sources of uncertainty in sea-level rise projections for the 21st century. One way to improve sea-level rise projections is to better understand the processes driving past ice-sheet mass loss. This dissertation investigates past changes in ice flow for two regions: (1) Helheim and Kangerlussuaq Glaciers, two fast-flowing tidewater glaciers in Southeast Greenland, and (2) the Allan Hills Blue Ice Area, a slow-flowing blue ice area in East Antarctica. For both regions, I constrain changes in ice-sheet dynamics using geophysical observations and interpret those changes using numerical ice-flow models. At Helheim and Kangerlussuaq, I examine seasonal and interannual variations in surface velocity, elevation, and terminus position from 2001 to 2016. I show that glacier dynamics depend on the extent of floating ice near the terminus. Helheim’s grounded terminus calved small, nontabular icebergs, while Kangerlussuaq’s floating ice tongue calved large, tabular icebergs. Furthermore, terminus-driven, seasonal speedups and dynamic thinning were generally larger at Helheim than at Kangerlussuaq, likely due to its grounded rather than floating ice tongue. To interpret the observed changes at Helheim and Kangerlussuaq, I use inverse methods to investigate changes in basal conditions under the two glaciers. The basal shear stress under Helheim and Kangerlussuaq decreased or remained relatively constant during terminus-driven speedup events, suggesting that changes in the stress balance were generally supported outside of the region of fast flow. Finally, I use the inferred basal shear stresses to help constrain the form of the basal sliding law. At the Allan Hills Blue Ice Area, I combine ice-penetrating radar data, an ice-flow model, and age constraints to determine a potential site to drill a million-year-old ice core. I also show that thickness anomalies in the englacial stratigraphy suggest that glacier velocity was 30% of present-day values during the last glaciation. While the dynamics of the Allan Hills Blue Ice Area are likely unimportant for sea-level rise projections, an ice core from the region could provide insight into the past stability of the Ross Sea Sector and West Antarctic Ice Sheet.

Author : C.J.van der Veen
Publisher : CRC Press
Page : 472 pages
File Size : 36,33 MB
Release : 1999-01-01
Category : Science
ISBN : 9789054104711

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Fundamentals of Glacier Dynamics presents an introduction to modelling the flow and dynamics of glaciers. The emphasis is more on developing and outlining procedures than on providing a complete overview of all aspects of glacier dynamics. Derivations leading to frequently-used equations are presented step-by-step to allow the reader to grasp the mathematical details and approximations involved and gain the understanding needed to apply similar concepts to different applications. The first four chapters discuss the background and theory needed for glacier modelling. The central part of the book discusses simple analytical solutions and time-evolving numerical models that are used to study general aspects of glacier dynamics and important feedback mechanisms. The final three chapters discuss applications specific to smaller mountain glaciers, the Greenland Ice Sheet, and the Antarctic Ice Sheet, respectively. This book will be suitable for graduate courses in geophysics and will also serve as a reference volume for scientists active in all aspects of glaciology and related research. Standard undergraduate mathematics and physics are sufficient background for studying the text.

Author : Dougal Douglas Omar Hansen
Publisher :
Page : 0 pages
File Size : 34,7 MB
Release : 2022
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ISBN :

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Ice mass flux for many of the world's most active glaciers and ice streams arises from glacier ice slipping over a lubricated substrate of bedrock or sediment. The physics controlling this "basal slip" fundamentally control glacier dynamics and drive the rapid denudation of alpine landscapes. Many tenets in the field of glaciology related to these processes currently lack a solid empirical basis, yet are repeatedly applied in theory or models of glacier dynamics and landscape evolution. Until these assumptions are thoroughly vetted, our understanding of glacier processes will be limited by this uncertainty. Here, I employ a range of novel experimental techniques to test long-standing hypotheses regarding the mechanics of hard and soft glacier beds. Specifically, I focus on questions related to subglacial rock friction/abrasion, which increases drag at the ice-bed interface and drives erosion, and till deformation, a first-order control on glacier dynamics, landform generation, and erosion. In chapter one, I constrain the influence of two fundamental controls on subglacial sediment transport during till deformation-effective stress and slip speed. Using digital image correlation to quantify flux rates from a photographic time series of the till bed, I demonstrate that sediment flux scales nearly linearly with slip speed when ice and till are coupled, but flux varies non-monotonically with effective stress, contradicting prior assumptions. In chapter two, I test physical controls on subglacial friction for hard-bedded glaciers under drained hydrologic conditions. Using a modified direct shear apparatus with an insulating sample chamber, I slid limestone slabs beneath slabs of debris-laden ice and assessed the relative influence of basal melt rate, effective stress and ice temperature on frictional resistance during slip. I show that basal drag scales linearly with both melt rate and normal stress in these experiments, confirming they influence the contact force in the presence of efficient drainage. Lastly in chapter three, I examine physical expression of rock-on-rock friction at glacier beds-subglacial abrasion-and use these observations to test the validity of the basal-power abrasion law. Using a novel cryogenic ring shear device in concert with the direct shear, I produce the most realistic simulations of abrasion to date, estimate abrasion rates from high-resolution 3D models of the eroded surface, and then quantify the energy dissipated through this process during slip. For planar rock beds, I show that i) average rock-frictional shear force at the bed increases linearly with abraded volume (per unit area), ii) abrasion rates increase linearly with basal power, and iii) percentage of slip energy expended through abrasion is one-two orders of magnitude lower than prior estimates