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  • Cambridge University Press (CUP)  (10)
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  • Cambridge University Press (CUP)  (10)
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  • 1
    Online Resource
    Online Resource
    Normal modes of an ice sheet
    Cambridge University Press (CUP) ; 1997
    In:  Journal of Fluid Mechanics Vol. 335 ( 1997-03-25), p. 393-413
    Details
    In: Journal of Fluid Mechanics, Cambridge University Press (CUP), Vol. 335 ( 1997-03-25), p. 393-413
    Abstract: A linearized perturbation about the Vialov–Nye fixed-span solution for a steady-state ice sheet yields a Sturm-Liouville problem. The numerical eigenvalue problem is solved and the resulting normal modes are used to compute Green's and influence functions for perturbations to the accumulation rate, the rate factor and for long-wavelength basal topography. The eigenvalue for the slowest mode is approximately the same as that predicted by the zero-dimensional theory. It is found that the sensitivity of the steady profile to accumulation is greatest in the central area of the ice sheet, while the sensitivity to rate factor is greatest near the margin. The antisymmetric perturbation provides information about the relaxation time for divide motion and spatial variation in the sensitivity of divide deviation from the ice-sheet centre to accumulation rate variations. The use of the method for model initialization is considered. Forcing deviations of 30% give relative errors in the perturbation of about 10%.
    Type of Medium: Online Resource
    ISSN: 0022-1120 , 1469-7645
    URL: Article
    DOI: 10.1017/S0022112096004612
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1997
    detail.hit.zdb_id: 1472346-3
    detail.hit.zdb_id: 218334-1
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  • 2
    Online Resource
    Online Resource
    Evidence for a large surface ablation zone in central East Antarctica during the last Ice Age
    Cambridge University Press (CUP) ; 2003
    In:  Quaternary Research Vol. 59, No. 1 ( 2003-01), p. 114-121
    Details
    In: Quaternary Research, Cambridge University Press (CUP), Vol. 59, No. 1 ( 2003-01), p. 114-121
    Abstract: Internal isochronous ice sheet layers, recorded by airborne ice-penetrating radar, were measured along an ice flowline across a large ( 〉 1 km high) subglacial hill in the foreground of the Transantarctic Mountains. The layers, dated through an existing stratigraphic link with the Vostok ice core, converge with the ice surface as ice flows over the hill without noticeable change to their separation with each other or the ice base. A two-dimensional ice flow model that calculates isochrons and particle flowpaths and accounts for ice flow over the hill under steady-state conditions requires net ablation (via sublimation) over the stoss face for the predicted isochrons to match the measured internal layers. Satellite remote sensing data show no sign of exposed ancient ice at this site, however. Given the lack of exposed glacial ice, surface balance conditions must have changed recently from the net ablation that is predicted at this site for the last 85,000 years to accumulation.
    Type of Medium: Online Resource
    ISSN: 0033-5894 , 1096-0287
    URL: Article
    DOI: 10.1016/S0033-5894(02)00014-5
    RVK:
    RA 1000
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2003
    detail.hit.zdb_id: 1471589-2
    detail.hit.zdb_id: 205711-6
    SSG: 13
    SSG: 14
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  • 3
    Online Resource
    Online Resource
    Drumlinization and drumlin-forming instabilities: viscous till mechanisms
    Cambridge University Press (CUP) ; 1998
    In:  Journal of Glaciology Vol. 44, No. 147 ( 1998), p. 293-314
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 44, No. 147 ( 1998), p. 293-314
    Abstract: Glacially induced flow naturally tends to thin and extended till cover through shock formation, even in the absence of longitudinal gradients in the applied stress. Thicker till cover has an increased effective pressure at its surface and base, a lower sliding velocity or deformation rate and above a critical thickness, a decrease in wave velocity with thickness, leading to reverse-facing shocks moving downstream. For sliding and for some theologies of internal deformation, a decrease in sediment flux with thickness occurs, implying backward-moving kinematic waves and reverse-facing, reverse-moving shock. Downstream-facing shocks are also formed which move upstream if the till is sliding and downstream if the till is deforming internally. Eventually, shocks coalesce, leaving an upstream-lacing shock for sliding and a downstream-facing shock for internal deformation. It is observed that some drumlins have downstream blunt ends only. Fairly realistic three-dimensional drumlin shapes can be produced from symmetric sediment bodies and barchan shapes can be produced from linear forms perpendicular to the ice-sheet flow. The fact that viscous theories produce drumlinoid forms suggests that on this scale till behaves viscously and the the lower length scale for drumlins represents the plastic/viscous transition scale.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/S002214300000263X
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1998
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 4
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    Online Resource
    The stability of a viscous till sheet coupled with ice flow, considered at wavelengths less than the ice thickness
    Cambridge University Press (CUP) ; 1998
    In:  Journal of Glaciology Vol. 44, No. 147 ( 1998), p. 285-292
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 44, No. 147 ( 1998), p. 285-292
    Abstract: A perturbation method is used to analyse the stability of a thin till layer overlain by a deep ice layer. Ice is modelled as a linearly viscous fluid, while the till viscosity has power-law dependence on stress and effective pressure. A linearized set of equations yields descriptions of the coupling of the ice flow with the sediment flow and reveals parameter ranges where the till-perturbation amplitude can grow. This sheet-flow instability is an essential part of any theory of drumlin formation and shows that viscous models of till have the ability to explain typical deforming-bed features. This is of great significance for large-scale ice-sheet modelling.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/S0022143000002628
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1998
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 5
    Online Resource
    Online Resource
    Time-scales and degrees of freedom operating in the evolution of continental ice-sheets
    Cambridge University Press (CUP) ; 1990
    In:  Transactions of the Royal Society of Edinburgh: Earth Sciences Vol. 81, No. 4 ( 1990), p. 371-384
    Details
    In: Transactions of the Royal Society of Edinburgh: Earth Sciences, Cambridge University Press (CUP), Vol. 81, No. 4 ( 1990), p. 371-384
    Abstract: Comprehensible explanations of the operation of earth climate systems should consist of descriptions of the operation of a few degrees of freedoms. Qualitative interpretations of results from large-scale numerical models generally follow this principle, but do not render formal definitions of the precise nature of such degrees of freedom. At its simplest, ice-sheet kinematics requires knowledge of the evolving height and span. Rheology and surface mass-balance impose different requirements upon the co-evolution of these variables, meaning a two-degree of freedom model is over-prescribed. By means of a perturbation expansion about the analytic similarity solution for viscous spreading, eigenfunctions corresponding to degrees of freedom in the ice-sheet profile are obtained, and are used to decompose mass-balance distributions. Only a few eigenfunctions are needed to replicate numerical models, implying that ice-sheets in plane flow may operate with fewer than ten degrees of freedom. Unstable evolution of ice-sheets can occur, when the operation of a very large number of degrees of freedom can be manifested. Previous work is reviewed and new results for the unstable transformation of valley glaciers into ice-sheets are presented. Phasing of initiation may be an unpredictable phenomenon.
    Type of Medium: Online Resource
    ISSN: 0263-5933 , 1473-7116
    URL: Article
    DOI: 10.1017/S0263593300020861
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1990
    detail.hit.zdb_id: 2411260-4
    detail.hit.zdb_id: 2402633-5
    detail.hit.zdb_id: 146835-2
    detail.hit.zdb_id: 2085149-2
    SSG: 13
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  • 6
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    Online Resource
    On the numerical computation of temperature in an ice sheet
    Cambridge University Press (CUP) ; 1999
    In:  Journal of Glaciology Vol. 45, No. 151 ( 1999), p. 568-574
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 45, No. 151 ( 1999), p. 568-574
    Abstract: Quadrature solutions for temperature fields in the central regions of ice sheets where flow is by internal deformation are presented and compared with numerical computations and the European Ice Sheet Modelling Initiative (EISMINT) Benchmark standards. The solution appears to be more accurate than the EISMINT Benchmark standards for thermomechanically uncoupled temperature distributions. The ability of finite-difference and pseudo-spectral methods to reproduce this solution is considered. Errors in the EISMINT Benchmark are larger than expected. The possibility that they could arise from inaccurate evaluation of the vertical velocity is considered, and found to be unlikely. Formulae for computing the vertical velocity in Jenssen's σ coordinate are complicated and may lead to programming errors. A simple form of the heat-transport equation in the σ coordinate for flow by sliding and internal deformation is derived arid presented, and it is shown how this form is particularly suitable for finite-element computations. It is also shown that only two quadratures are necessary to compute the vertical and horizontal heat transport and the ice flux.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/S0022143000001441
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1999
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 7
    Online Resource
    Online Resource
    Thermoviscous stability of ice-sheet flows
    Cambridge University Press (CUP) ; 2004
    In:  Journal of Fluid Mechanics Vol. 502 ( 2004-3-10), p. 17-40
    Details
    In: Journal of Fluid Mechanics, Cambridge University Press (CUP), Vol. 502 ( 2004-3-10), p. 17-40
    Type of Medium: Online Resource
    ISSN: 0022-1120 , 1469-7645
    URL: Article
    DOI: 10.1017/S0022112003007390
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2004
    detail.hit.zdb_id: 1472346-3
    detail.hit.zdb_id: 218334-1
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  • 8
    Online Resource
    Online Resource
    Ice-stream surface texture, sticky spots, waves and breathers: the coupled flow of ice, till and water
    Cambridge University Press (CUP) ; 1998
    In:  Journal of Glaciology Vol. 44, No. 148 ( 1998), p. 589-614
    Details
    In: Journal of Glaciology, Cambridge University Press (CUP), Vol. 44, No. 148 ( 1998), p. 589-614
    Abstract: This paper addresses the coupling of flows of ice, till and water, and the issue of whether such coupling provides mechanisms for meso-scale (kilometres to tens of kilometres) variability in ice-sheet flow and texture. The question of whether effective pressures at the ice-bed interface are statically or hydraulically controlled is examined in this paper. The answer is scale dependent, and has a significant effect on the relationship between ice surface and basal topography. The consequences of these considerations on till flow, coupled ice–till flow and coupled ice, till and water flow are examined. An analysis of till-flow kinematics and shock formation is carried out. The linear stability of coupled long-wavelength ice-till flow is analysed, and regions in parameter space where this flow is unstable, with rather small rate constants are found. Upstream-moving ice surface waves are predicted. The linear stablity of coupled ice–till–water flow is examined, where water flow is modelled using a basal flow system with effective-pressure-dependent properties. Again, regions in parameter space where the system is linearly unstable are found, this time with relatively rapid rate constants. The water pressure exhibits “breather” modes. These analyses assume that there is a substantial basal traction. A problem with models of ice streams wholly restrained at the side is identified: they seem to predict erosion rates which are unfeasibly large. There appears to be sufficient variability in the ice–till– water system to potentially explain texture in ice-stream surfaces, variations in ice-stream thickness of tens of metres not directly relatable to topography, and waves moving upstream or downstream. Most importantly, the ice-stream–bed system is shown to exhibit meso-scale variability simply by coupling ice flow according to the shallow-ice approximation, till flow according to the hydrostatic thin-till approximation and water flow according to an effective-pressure-dependent hydraulics.
    Type of Medium: Online Resource
    ISSN: 0022-1430 , 1727-5652
    URL: Article
    DOI: 10.1017/S0022143000002100
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1998
    detail.hit.zdb_id: 2140541-4
    SSG: 14
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  • 9
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    Online Resource
    G. S. H. Lock 1990. The Growth and Decay of Ice. Studies in Polar Research Series. xvii + 434 pp. Cambridge University Press. Price £65.00, US $100.00 (hard covers). ISBN 0 521 33133 1. - R. P. Sharp 1991. Living Ice. Understanding Glaciers and Glaciation. First paperback edition; first published in 1988. Cambridge University Press. Price £10.95, US $15.95 (paperback). ISBN 0 521 40740 0.
    Cambridge University Press (CUP) ; 1992
    In:  Geological Magazine Vol. 129, No. 3 ( 1992-05), p. 376-377
    Details
    In: Geological Magazine, Cambridge University Press (CUP), Vol. 129, No. 3 ( 1992-05), p. 376-377
    Type of Medium: Online Resource
    ISSN: 0016-7568 , 1469-5081
    URL: Article
    DOI: 10.1017/S0016756800019385
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 1992
    detail.hit.zdb_id: 956405-6
    detail.hit.zdb_id: 1479206-0
    SSG: 13
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  • 10
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    G ARCÍA -G ARCÍA , F., C ISNEROS , G., F ERNÁNDEZ -E GUIARTE , A. & Á LVAREZ , R. (eds) 1997. Numerical Simulations in the Environmental and Earth Sciences . Proceedings of the Second UNAM–CRAY Supercomputing Conference. xiv + 283 pp. Cambridge, New York, Port Chester, Melbourne, Sydney: Cambridge University Press. Price £45.00, US $69.95 (hard covers). ISBN 0 521 58047 1.
    Cambridge University Press (CUP) ; 2000
    In:  Geological Magazine Vol. 137, No. 1 ( 2000-01), p. 97-106
    Details
    In: Geological Magazine, Cambridge University Press (CUP), Vol. 137, No. 1 ( 2000-01), p. 97-106
    Type of Medium: Online Resource
    ISSN: 0016-7568 , 1469-5081
    URL: Article
    DOI: 10.1017/S0016756800353663
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2000
    detail.hit.zdb_id: 956405-6
    detail.hit.zdb_id: 1479206-0
    SSG: 13
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