Jökull - 01.12.1976, Page 3

JOKULL
Á R S R I T
J Ö KLARAN N SÓ K NAFÉLAGS ÍSLANDS
26. ÁR REYKJAVÍK 1976
Morphology o£ Upper Lundarreykjadalur,
Western Iceland
IAN ASHWELL,
UNIVERSITY OF SALFORD, ENGLAND
ABSTRACT
Several features in the older part of the valley
indicate that present-day forms are a result of
sub-glacial and englacial drainage through the
valley, part of the system being controlled by
tlie slope of the overlying ice surface, part by
the existing valley drainage. The existence of
material apparently dropped from a floating
ice-shelf at the Lundur farm, near the main
valley heacl, suggests that changes in sea-level
were a controlling factor in the level of tlie sub-
glacial and englacial drainage systems, even 15
km up a narrow valley from tlie coastal plain.
INTRODUCTION
Lundarreykjadalur is one of the longer Borg-
arfjardardalir in Western Iceland, with a total
length of 26 km from the outlet of the Reydar-
vatn lake to the threshold of the valley mouth,
overlooking the Borgarfjörd—Mýrar
The whole western part of the valley is cut in
Tertiary basalts, but younger basalts and erup-
tives form the head of the valley, where the
mountain Thverfell, a Móberg eruptive, block-
ed an original valley head and ponded up
Reydarvatn (S. Thorarinsson, T. Einarsson and
G. Kjartansson (1959), 138, (Fig. 1)).
The Hestháls'channels, connecting the valley
with its southern neighbour, Skorradalur, have
been described by Ashwell (1965). A further
paper (Ashwell, 1975) suggests that many
morphological features in the valley and the
Hestháls channels are the result of water action
resulting from englacial and subglacial drain-
age in the late-glacial ice cover sloping from
east-north-east to west-south-west over the whole
district except the Skardsheidi nunatak. The
coastal section of the ice sheet floated with
rising sea-level at about 12,000 years BP and
deposits of glacial marine drift were dropped
from the base of the ice shelf. This deposit
consists of silt from the subglacial drainage
lowland. 'á; sysfeth 'withltill from the shelf ice.
It is further suggested that signs of this drain-
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JÖKULL 26. ÁR 1