Evolution of glacial flow and drainage during the ablation season

doi:10.1016/j.jhydrol.2006.04.031

Journal of Hydrology

Volume 330, Issues 3–4, 15 November 2006, Pages 663-671

https://doi.org/10.1016/j.jhydrol.2006.04.031 Get rights and content

Summary

Proglacial discharge is controlled by the geometry of the glacial drainage network and by meltwater processes. The glacial drainage systems of some alpine glaciers have been characterised using a model based on a proglacial discharge analysis. In this paper, we apply high frequency systemic analysis to data collected from the Baounet Glacier (French Alps) during two successive ablation seasons. Our approach is based on an analysis of the evolution of daily recession curves during the ablation period. The observed data are fitted by a single 〈β〉-coefficient dependant recession law. Changes in 〈β〉 are compared to variations in the daily discharge amplitude and the time lag between air temperature and proglacial discharge. The changes in the 〈β〉 values do not appear to be related to changes in the time lag and the amplitude of the daily discharge. There were significant variations in the 〈β〉-coefficient during the two ablation periods studied here even if there was no time lag or the daily discharge amplitude change. High values of 〈β〉 correspond to high drainage velocities; therefore increases in 〈β〉 values can be used as an indicator of the evolution of the glacier’s internal drainage network.

Introduction

Many studies have been carried out on temperate glaciers to calculate annual mass balances and to record climatic changes (Six et al., 2001, Vincent et al., 2004, Dyurgerov, 2003), or to investigate the link between the mass balance and the impact of the glacial water supply on downstream river discharge (Ribstein et al., 1995, Wagnon et al., 1999).

Studies of the Haut Glacier d’Arolla have looked at the hydrodynamic functioning of glaciers as aquifers (Richards et al., 1996, Nienow et al., 1998). Variations in proglacial discharge are dependent on snow meltwater and ice meltwater flows and the evolution of the glacial drainage system. Glacial sediment evacuation (Swift et al., 2002), dye tracer tests (Hasnain et al., 2001) and borehole water pressure measurements (Hubbard and Nienow, 1997) have confirmed the existence of more or less efficient drainage networks. One of the main characteristics of glacial drainage systems is the rapidity of their reorganisation during the ablation season (Gordon et al., 1998).

The subglacial channels in many glaciers are linked-cavity systems (Paterson, 1994) that show significant seasonal variations in the interconnections between cavities. The increasing efficiency of the links between supra-glacial sources and proglacial pathways modifies the movement of water through the glacier (Swift et al., 2005). Variations in the amplitude and timing of diurnal discharge fluctuations through the ablation season can be used to divide the season into periods with homogenous discharge patterns (Gurnell and Clark, 1987). Swift et al. (2005) have recently proposed a system for characterizing the different periods based on the form of the diurnal hydrograph.

Studies that take a systemic approach to the investigation of glacial hydrological responses must take into account the intensity of the melting processes and the evolution of the glacial flow structure (Benn and Evans, 1998, Hock and Hooke, 1993). Similarities between karsts and glaciers, in terms of morphology and hydrological circulation, have been described by Leszkiewicz and Pulina (1997) and an analogy can be made between the evolution of glacial drainage systems on an annual time scale and the development of karsts over a geological time scale.

Recession curve analysis can be used to characterise the evolution of the glacial drainage network. By using a two reservoirs model based on recession curve adjustments, Richards et al. (1996) concluded that a model with a more distributed and dynamic structure is required to describe glacier hydrology. In this paper, we use a different approach based on a single β-coefficient that integrates the input flow intensity to describe the evolution of the structure of the glacial drainage network. The β-coefficient is obtained by fitting a single model for all the daily recessions during the ablation period. This model has already been applied in studies of karstic recession curves during the spring (Drogue, 1972). We applied this method to data from the Baounet Glacier (French Alps) recorded during the 2002/2003 and 2003/2004 melt seasons. In order to describe the evolution of the drainage network during the main melt season phases, we compared the β-coefficient with the variations in the daily discharge amplitude and the daily time lag between air temperature and proglacial discharge.

Section snippets

Field site and monitoring

This case study was carried out on the Baounet Glacier, a small valley glacier on the French side (département of Savoie) of the ridge that forms the border with Italy (Fig. 1). The main glacier faces north-west and occupies the south-eastern part of a 6 km² topographic basin that culminates at an altitude of 3550 m a.s.l. The glacier is situated between 2800 m and 3300 m a.s.l. and covers an area of 2.5 km². The hydrometric station is situated below the main glacier. The slopes to the north-east of

Raw data analysis

Continuous recording data were taken during the 2003 and 2004 melt season. Data from the 2004 cycle were chosen to illustrate the evolution of the measured parameters. Similar patterns were observed during the 2003 cycle, but they started earlier in the season. The raw data were plotted on a graph in order to reveal stages in the evolution of the system (Fig. 2). Air temperature and irradiance values showed daily oscillations. Precipitation inputs to the glacial system were random. As would be

Discussions

A comparative analysis of the two ablation seasons (Fig. 7) showed similarities in the evolution of the daily discharge. For both years, four similar periods were defined according to the schematic curve break points and trends in the daily discharge amplitude (see periods I to IV, Fig. 7). For each of the periods in the ablation season it was possible to associate and interpret the evolution of the time lag (k_t) and the β-coefficient.

Period I is characterised by low and stable daily discharge

Conclusion

Application of our method to the data recorded at the Baounet Glacier during two successive ablation seasons permits to follow the relationship between the evolution of 〈β〉, the daily discharge and the time delay. This method, based on high frequency systemic analysis, can be used to describe changes in glacial drainage networks caused by snow and ice meltwater processes, hence it can be used to compare the behaviour of one glacier over a number of years, or of several glaciers during one

Acknowledgements

Access to the field site was granted by Bessans District Council. We would also like to thank the numerous people who assisted with the installation of the automatic recording station and the taking of field measurements. We are very grateful to Paul Henderson for his help in preparing the English version of the manuscript. The comments made by W.H. Theakstone and D.M. Rippin have resulted in considerable improvements being made to this article.

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Evolution of glacial flow and drainage during the ablation season

Summary

Introduction

Section snippets

Field site and monitoring

Raw data analysis

Discussions

Conclusion

Acknowledgements

J. Hydrol.

J. Hydrol.

J. Hydrol.

J. Hydrol.

Quatern. Sci. Rev.

J. Hydrol.

J. Hydrol.

J. Hydrol.

C.R. Acad. Sci., Paris, Earth Planetary Sci.

Sediment. Geol.

J. Hydrol.

Global Planetary Change

Glaciers and Glaciation