An Investigation of the Hydrological System of a Debris-Covered Glacier. Presented by Catriona Fyffe at the "Perth II: Global Change and the World's Mountains" conference in Perth, Scotland in September 2010.
Debris-Covered Glaciers Have a mantle of rock debris across at least part of their ablation area Usually from rockfall, mixed rock and snow avalanches, and melt out of englacial debris Where cover thick (on lower parts of the ablation area) ablation reduced due to the insulating nature of the debris Where cover thinner (on the upper glacier, or on ice cliffs) decreased albedo leads to increased ablation
But how does a debris cover influence the glacier’s hydrology? Aims are to….1. Understand the influence of the debris on the structure and evolution of the hydrological drainage network.2. Understand the influence of the debris on the water balance of the glacier.
Methodology To answer 1: Glacier velocity measurements using Leica 1200 System differential GPSs Dye tracing Analysis of proglacial stream water (for suspended sediment concentration, pH, conductivity, temperature, bicarbonate, sulphate and chloride ion concentration) To answer 2: Weather data from two automatic weather stations, with a rain gauge and lysimeter at the lower station Ablation stake measurements Pressure transducer on the proglacial stream
The drainage network and glacier velocity Velocities highest upglacier, around 11 cm d-1, similar on main tongue, and decreasing down glacier to an average of 2.7 cm d-1 on the southern lobe
Velocity variations in June Change from cooler days to more pronounced diurnal cycle, and an increase in discharge, corresponded with an increase in horizontal velocity (average of 0.71 cm d-1) for several points on Julian day 163 C6 had an increased velocity (to 20.6 cm d-1, compared to a mean of 11.3 cm d-1) during the afternoon of day 162 – relating to an increased daily velocity on day 163 for the other points Overall increase on most points small, so probably more a variation than an “event” linked to a change in the hydrological regime Suggests existence of subglacial linked cavity system
Difference from mean velocity and average daily temperature from the lower weather station 2.5 12 Difference from mean velocity Temperature 2 11)-1Difference from mean velocity (cm d 10 1.5 9 Temperature (˚C) 1 8 0.5 7 0 6 -0.5 5 -1 4 158 159 160 161 162 163 164 165 166 167 168 169 Julian Day
Dye tracing Most traces gave pronounced peaks with an average minimum velocity of 0.43 ms-1, and traces were detected within 3 hours = channelised flow One trace from above the snowline into moulin 11 on day 162 had a velocity of 0.69 ms-1 Importantly, the flow was channelized despite it being early in the season, suggesting certain flow paths are never completely closed during the winter
Dye concentration (ppb) -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1343 1348 1353 1358 1403 1408 1413 1418Time 1423 gauging station 1428 1433 1438 1443 Dye tracing from Moulin 11, 4030 m from 1448 1453 1458
Dye tracing into englacial conduit, 2650m from gauging station 0.9 Dye concentration (ppb) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -0.1 1319 1329 1339 1349 1359 1409 1419 1429 1439 1449 1459 1509 1519 Time Dye injected into an englacial conduit between the eastern and central moraines on the 10th of June – drainage clearly channelised Minimum velocity = 0.37 ms-1
Influence of debris? Overall recent thinning of the Miage (Diolaiuti et al., 2009) (debris-covered glaciers tend to thin rather than retreat) may have increased the likelihood of the channelised system remaining over the winter as the preservation of channelised systems is more likely for thinner glaciers (Flowers, 2008) The main supraglacial streams follow the valleys between the medial, and eastern and western moraines => drainage is focused, increasing the inputs into the englacial system
Runoff and Temperature Average hourly stage and temperatures 0.42 16 0.415 14 Temperature (˚C) 0.41 Stage (ma SD) 0.405 12 0.4 10 0.395 8 0.39 6 0.385 4 0.38 Stage 0.375 2 Air Temperature at lower AWS 0.37 0 0 0 0 0 0 00 00 00 00 00 00 00 10 30 50 70 90 11 13 15 17 19 21 23 Time• Average lag time between peak daily temperature and peak daily discharge around 7 hours• The diurnal variation of runoff isn’t as large as on clean glaciers, possibly due to the debris causing different delays on different parts of the glacier
Average 10 min temperature through the debris profile at LOMET during 2005 35 30 0 cm (°C) Temperature (?C) 24 cm 25 48 cm 20 72 cm 15 10 5 0 10 10 10 10 10 10 10 10 0 0 0 0 21 41 61 81 10 12 14 16 18 20 22 Time• Some lag due to the time taken for temperature cycle peak to reach the ice/debris interface (at an average debris thickness ~ 0.25 m, takes ~ 6 hrs for the rising temperature at the surface to reach the ice/debris interface)• May also be due to the percolation of water through the debris
Conclusions Majority of dye traces indicated efficient and channelised drainage, preferential flow paths don’t close completely over the winter Suggests combination of cavity system which is only slightly influenced by changes in input, linked to a preserved conduit system that transfers the majority of water Large lag between temperature and discharge, and small diurnal amplitude of discharge fluctuations imply debris increases and varies the time taken for water to reach the proglacial stream
References Diolaiuti, G., D’Agata, C., Meazza, A., Zanutta, A. and Smiraglia, C. (2009) Recent (1975-2003) changes in the Miage debris-covered glacier tongue (Mont Blanc, Italy) from analysis of aerial photos and maps, Geografia Fisica e Dinamica Quaternaria (32) 117-127 Flowers, G. E. (2008) Subglacial modulation of the hydrograph from glacierized basins, Hydrological Processes (22) 3903-3918
Acknowledgements The Geography and Environmental Science department at the University of Dundee for their studentship Several dissertation students for help in the field Dr Tim Reid for assistance with fieldwork and equipment Prof. Joe Holden for the loan of the flourometer NERC Geohphysical Equipment Facility in Edinburgh for the loan of two dGPS rovers Milan University for the use of their stake network Marco Vagliasindi from the Fondazione Montagna Sicura, La Palud, for logistical support Doug Mair for the loan of a Kovax ice drill Scottish Crop Research Institute for the loan of a Campbell logger My supervisors!