Campbell, Fay MA

Campbell, Fay M.A. (2007) The role of supraglacial snowpack hydrology in mediating meltwater delivery to glacier systems. PhD thesis. http://theses.gla.ac.uk/2871/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] DEPARTMENT of GEOGRAPHICAL and EARTH SCIENCES The role of supraglacial snowpack hydrology in mediating meltwater delivery to glacier systems Fay M. A. Campbell Submitted to the Faculty of Physical Sciences for the degree of Doctor of Philosophy January 2007 © Fay M. A. Campbell, 2007 Abstract This thesis investigates the role that supraglacial snowpack hydrology plays in mediating meltwater delivery to glacier systems. The movement of water through glaciers is of fundamental importance as a control on proglacial hydrograph amplitude and timing, subglacial and proglacial geomorphic processes, the hydrochemistry of glacial runoff, and glacier dynamics, and as such has been the subject of considerable research effort. Although studies in non-glacial environments have shown that meltwater waves are both dampened and delayed by passage through snow, the role of supraglacial snowcover in mediating water inputs to the rest of the glacier system has received limited attention in studies of glacier hydrology to date. It has been suggested, however, that the varying thickness, and ultimately removal, of the supraglacial snowpack may play a role in controlling the timing and magnitude of ice velocity events. Despite this suggested importance there have been few field observations of the hydrological behaviour of supraglacial snowpacks or of the way in which this behaviour evolves during the melt season. A thorough assessment of the linkages between supraglacial snowpack conditions and glacier dynamic events has therefore not been possible. This study helps fill this gap in our knowledge by explicitly investigating the hydrological behaviour of the supraglacial snowpack at an alpine glacier and its evolution during the summer melt season. Field data was collected during two summer field seasons (2003 and 2004) at Haut Glacier d’Arolla, Valais, Switzerland. Dye tracing experiments were used as the primary method of obtaining information about water flow through the snowpack. Dye was used both qualitatively, to give a visual impression of flow patterns through the snowpack, and quantitatively, with return curves detected by a fluorometer providing detailed information about rates of dye movement and dispersion through the snowpack. Physically-based modelling representations of water flow through snow also informed consideration of the characteristics of snowpack runoff. Experiments were designed to determine: i) the nature of water flow through the supraglacial snowpack; ii) if, and in what way, this evolves over the course of the melt season; and iii) what factors control water movement, and the importance of their roles. In order that links between supraglacial snowpack hydrology and other parts of the glacier system could be considered, season-long records of glacier dynamics, proglacial meltwater discharge, and water quality parameters indicating subglacial conditions were also collected. Observations of the movement of dye-stained water demonstrated the complexity of percolation patterns in snow and the influence of ice layers and preferential flow zones on flow rates. Fluorometric techniques measured percolation velocities of between 0.08 and 0.49 m hr-1, showing the delay that passage through snow will impart on runoff. Corresponding net snowpack permeability values (ranging from 2.02x10-13 to 1.05x10-9 m2) i F.M.A. Campbell Abstract ____________________________________________________________________________________________________________________________________________________________________________________________________________________ are significantly lower than those used in previous modelling studies, thereby indicating a need for future work to be better informed by field-derived measurements of snow permeability. Velocities for water flow in the basal saturated layer were found to be one to two orders of magnitude greater than for percolation (ranging from 1.35 to 18.48 m hr-1), and this part of snowpack runoff therefore plays a lesser role than percolation in altering runoff timing. The velocity and dispersion of flow through both snowpack flow regimes, however, indicate the marked difference in runoff that will occur across a snow-covered as opposed to bare-ice glacier surface. Records of runoff through the saturated layer at the base of the snowpack confirm the net delaying and attenuating effect of the snowpack, revealing lag times of up to 20 hours between peak surface melt input and peak runoff and almost total dampening of diurnal runoff cycles in the early melt season. The hydrological influence of the supraglacial snowpack must therefore be accounted for in order for runoff through the supraglacial environment and meltwater delivery to the subglacial drainage system to be correctly predicted. In addition, the hydrological behaviour of the snowpack was observed to evolve through time. In particular, it is shown here that increasing net snowpack permeability can reduce the delay and attenuation of runoff, and permeability values measured in the field were observed to increase through the 2004 melt season. The influence of this increase in permeability on runoff can be equivalent to that of decreasing snow depth, but has not been considered in previous studies. Changes in preferential flow organisation and in particular ice layer permeability and number are suggested as factors leading to increased snowpack permeability. Information about hydrological processes operating within the snowpack, and the way in which they evolve through time, is therefore required in order to understand changing runoff patterns. Ice velocity events began around 3rd June 2003 and 10th and 24th June 2004. The glacier remained extensively and thickly snow-covered on these dates, showing that runoff through a supraglacial snowpack can be sufficiently high as to trigger an ice dynamic response despite the delaying and attenuating effects noted above. High surface melt fluxes are the first-order control on the occurrence of such speed-up events, but it is suggested that the hydrological behaviour of the supraglacial snowpack can mediate the magnitude of the glacier’s dynamic response to high melt inputs. An improved understanding of the supraglacial snowpack’s hydrological effect is therefore important not only for our ability to predict runoff timing and magnitude (with implications for the management and use of water resources from glaciated catchments), but also for our understanding of ice dynamic response to melt inputs. ii Contents Abstract.................................................................................................................................... i Contents................................................................................................................................. iii List of Tables......................................................................................................................... ix List of Figures..........................................................................................................................x Acknowledgements ...............................................................................................................xv Declaration.......................................................................................................................... xvii Chapter 1. Introduction to the research..............................................................................1 1.1 Introduction and rationale..................................................................................................1 1.2 Objectives ..........................................................................................................................2 1.3 Thesis structure..................................................................................................................3 Chapter 2. Snow and glacier hydrology: a review..............................................................5 2.1 Introduction .......................................................................................................................5 2.2 Snow hydrology: current knowledge and unresolved issues.............................................5 2.2.1 Physical properties of the seasonal snowcover ........................................................6 2.2.1.1 Snowcover formation and evolution: dry snow processes...........................6 2.2.1.2 The metamorphism of wet snow..................................................................7 2.2.2 Hydrological behaviour of wet snow.......................................................................9 2.2.2.1 The occurrence and movement of liquid water in snow ..............................9 2.2.2.2 Snowpack permeability

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