Jökull - 01.12.1983, Blaðsíða 113

Resurvey of the Margins of Gljúfurárjökull
and the Chronology of recent Deglaciation
C.J. CASELDINE
Department of Geography, University of Exeter,
Amory Building, Rennes Drive, Exeter EX4 4RJ, U.K.
INTRODUCTION
Two of theprincipal aims of the 1981 Joint Universities
(ExeterandSt. Andrews) Norlh IcelandExpeditionwere to
resurvey the margins of Gljúfurárjökull and to test the
chronology proposedfortherecent deglaciation of Gljúfurár-
dalur by Caseldine and Cullingford (1981), on the basis of
work undertaken on the Exeter University North Iceland
Expedition of 1979. This paper describes the results of the
1981 survey work and outlines a histoiy of recent deglaci-
ation based on a lichenometric survey of the sequence of
morainic ridges mapped and described in 1979.
GLACIER SURVEY
The methods used in the survey of the snout area
of Gljúfurárjökull followed those previously de-
scribed (Caseldine 1981, Caseldine and Cullingford
1982), and the mapping was greatly facilitated by
the abundance of well-marked stations from pre-
vious studies. The persistence of snowbeds around
the glacier margin delayed the survey as many stat-
ions were not visible but the presence of a thick
snowbed covering the steep frontal slope of the glac-
ier allowed direct survey of part of the glacier not
adequately surveyed in 1979, allowing the contour-
ing of the ice in 1981 to be based on a better spread
of survey points. Any difference in the trends of the
ice contours may, at least partially, be due to this
better cover.
Overall Gljúfurárjökull has shown a continued
advance since 1979 with the maximum downvalley
extent increasing by 30 m over the two years (Fig.
1). It is diflicult to estimate correctly the degree of
change of the eastern and western margins of the
glacier due to the continued presence of thick snow-
beds masking the true edge of the ice and this
accounts for any apparent inconsistency in the be-
haviour of these margins since 1977. The dead ice
features noted in 1979 immediately in front ofGljúf-
urárjökull were not apparent in 1981 and there was
very little evidence of dead ice and debris con-
centrations in this area as a whole. There seems to
have been little alteration in the slope of the snout
and the large dip in the surface of the centre of the
ice above the snout was still clearly pronounced,
TABLE 1. Net movement of the glacier surface, July 1979 — July 1981.
TAFLA 1. Heildarhreyjing áyfirborði j'ókuls frájúlí 1979 tiljúlí 1981.
Direction of Distance 1979 1981 Altitude
movement moved altitude altitude change
Marker Stefna Tilftersla stiku htsð hteb hæbarbreyting
hreyfingar (m) (m) (m) (m)
I N 9° E 35 688-8 681-6 -7-2
IV N 22° E 50 757-5 748-4 -9.1
VII N 27° E 42-5 780-7 769-5 — 11-2
VIII N 20° E 42-5 772-1 759-8 —12-3
Note — Station II was located but not surveyed in 1979.
— The altitude of Station IV has been omitted in error from Fig. 1.
JÖKULL 33. ÁR 111