Jökull - 01.12.1985, Síða 81

Some Observations on the Characteristics
of the Drainage System of Kverkjökull,
Central Iceland
COLIN FENN
Worcester College of Higher Education,
Worcester, WR2 6AJ, England.
IAN ASHWELL
University of Salford, Salford, M5 4WT, England.
ABSTRACT
At the beginning of a glaciological investigation of
Kverkjökull in August 1981, the subglacialstream emerg-
ing from a large cavern in the snout wasfound to be cold.
On August llth, the temperature of the stream rose
rapidly to a maximum of 25.5°C, discharge fell, and
electrical conductivity rose to a maximum of 500 \iS/cm,
10 times that of other nearby outflow streams. A strong
smell of sulphur was noted at a meteorological station
some 23 km. downwind from the Kverkfjöll caldera at
1800h on the same day. This suggests a change in the
geothermal/drainage system in Kverkfjöll.
INTRODUCTION
As part of the scientific programme of the 1981
expedition of the British Schools’ Exploring Society,
based to the north of Vatnajökull, a small party studied
the Kverkjökull outlet glacier which drains the ice-filled
caldera of Kverkfjöll through a breach in its northern
wall. Traces of geothermal activity remain in the caldera
and on its north-western rim (Hveradalur thermal
area), as described by Friedman and others, (1972).
The group's main aim was to study the hydrology of
the supraglacial streams on the outlet lobe of Kverk-
jökull, and the hydrogeomorphology of their proglacial
extensions. The main stream issuing from the large
cavern in the centre of the glacier terminus was con-
sidered too large and swift for safe investigation in the
early stages of the expedition (late July, early August).
Measurements of flow discharge and water quality
were, however, made throughout the study period (27
July to 14 August) on the two outflow streams issuing
from the snout of the glacier approximately 250 m either
side of the main outflow stream. Hourly records of
discharge were determined through velocity-area rating
methods (Fig. 1). Hourly records of turbidity, electrical
conductivity, pH and water temperature were deter-
mined from the analysis of water samples using Horiba
U7 and WPA EVl water quality meters.
OBSERVATIONS ON THE NATURE OF THE
DRAINAGE SYSTEM OF KVERKJÖKULL
The dominant features of the drainage system of the
Kverkjökull outlet tongue are a huge bottom-connected
„moulin“ (Fig. 2) and a well-developed „Röthlisberger
type“, subglacial channel which emerges from a large
semi-circular cavern in the centre of the glacier snout as
the main outflow stream from the glacier (Fig. 3).
The „moulin“ was measured as being some 21.5 m in
diameter and approximately 50 m in depth (as ascer-
tained via a controlled abseil descent). The surface
morphology of the feature closely resembles that of the
active (water-filled) and abandoned (bottom-conn-
ected) supraglacial lakes found on the Gor Garang
group of glaciers in the N.W. Himalaya by Kaul and
others (1982) (compare their Figure 4 with Fig. 2 here),
suggesting that the Kverkjökull „moulin“ may at one
time have been a supraglacial lake which later achieved
a bottom outlet.
The characteristics of the subglacial stream system
were studied during periods of low flow, when it proved
possible to enter the cavern at the glacier snout and
follow the internal drainage system to and beyond the
base of the „moulin" for a distance of some 400 m. The
system remains semi-circular throughout, narrowing
irregularly, being floored mostly in subglacial tills but
occasionally being carved into solid rock. A waterfall
from the roof of the channel was encountered at one
point. A number of dry tributary caverns were also
found.
JÖKULL 35. ÁR 79