P. Nienow et al., SEASONAL-CHANGES IN THE MORPHOLOGY OF THE SUBGLACIAL DRAINAGE SYSTEM,HAUT GLACIER DAROLLA, SWITZERLAND, Earth surface processes and landforms, 23(9), 1998, pp. 825-843
Dye tracing techniques were used to investigate the glacier-wide patte
rn of change in the englacial/subglacial drainage system of Haut Glaci
er d'Arolla during the ablation seasons of 1990 and 1991. Analysis of
breakthrough curve characteristics indicate that over the course of a
melt season, a system of major channels developed by headward growth a
t the expense of a hydraulically inefficient distributed system. By th
e end of the melt season, this channel system extended at least 3.3 km
from the snout of the 4 km long glacier and drained the bulk of supra
glacially derived meltwater passing through the glacier. The upper lim
it of the channel system closely followed the retreating snowline up-g
lacier. Rates of headward channel growth reached c. 65 md(-1), althoug
h these rates decreased in the upper 1 km of the glacier where snowlin
e retreat exposed a patchy firn aquifer. It appears that the removal o
f snow (with its high albedo and significant water storage capacity) f
rom the glacier surface resulted in a dramatic increase in the volume
of runoff into moulins, and in the peakedness of daily runoff cycles.
This induced transient high water pressures within the distributed dra
inage system, which caused it to evolve rapidly into a channelised sys
tem. It is therefore likely that, at a local scale, channel growth occ
urred down-glacier from moulins, and that the overall up-glacier-direc
ted pattern of channel formation was caused by the retreating snowline
exposing new moulins and crevasses to inputs of ice-derived meltwater
. Damping of diurnal melt inputs by storage in the firn aquifer accoun
ts for the slowing of channel growth in the upper glacier. (C) 1998 Jo
hn Wiley & Sons, Ltd.