An Investigation of the Hydrological System of a Debris-Covered Glacier [Catriona Fyffe]

An Investigation of the

Hydrological System of a Debris-

Covered Glacier

Catriona Fyffe University of Dundee

Ben Brock, Martin Kirkbride and Doug Mair

The Miage Glacier

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

-1

-0.5

0

0.5

1

1.5

2

2.5

158 159 160 161 162 163 164 165 166 167 168 169

Julian Day

Dif

fere

nce f

rom

mean

velo

cit

y (

cm

d-1

)

4

5

6

7

8

9

10

11

12

Tem

pera

ture

(˚C

)

Difference from mean velocity

Temperature

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 tracing from Moulin 11, 4030 m from

gauging station

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

13

43

13

48

13

53

13

58

14

03

14

08

14

13

14

18

14

23

14

28

14

33

14

38

14

43

14

48

14

53

14

58

Time

Dy

e c

on

ce

ntr

ati

on

(pp

b)

Dye tracing into englacial conduit, 2650m from gauging station

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

13

19

13

29

13

39

13

49

13

59

14

09

14

19

14

29

14

39

14

49

14

59

15

09

15

19

Time

Dye c

on

cen

trati

on

(p

pb

)

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 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 hourly stage and temperatures

0.370.3750.38

0.3850.39

0.3950.4

0.4050.41

0.4150.42

100

300

500

700

900

1100

1300

1500

1700

1900

2100

2300

Time

Sta

ge (

ma S

D)

0

2

4

6

8

10

12

14

16

Te

mp

era

ture

(˚C)Stage

Air Temperature at lower AWS

• 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

Average 10 min temperature through the debris

profile at LOMET during 2005

0

5

10

15

20

25

30

35

10 210

410

610

810

1010

1210

1410

1610

1810

2010

2210

Time

Te

mp

era

ture

(?

C)

0 cm

24 cm

48 cm

72 cm

(°C

)

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!