Jökull - 01.12.1988, Side 34

Fluctuations of Gljúfurárjökull,
Northem Iceland 1983-1987
C. J. CASELDINE
Department of Geography, University ofExeter,
Amory Building, Rennes Drive, Exeter EX4 4RJ, U.K.
ABSTRACT
Detailed survey of the marginal position of
Gljúfurárjökull, Northern Iceland between 1983 and
1986 has shown a considerable slowing and prob-
able cessation of the advance recorded since the
mid-1970‘s. This is confirmed by independent obser-
vations in 1987. During the same period there has
also been a reduction in the velocity of ice move-
ment in the snout area, from 25.3 ma~' between
1979 and 1981 to an average value of23.2 ma“' for
the more recent period.
GLACIER SURVEY AND MEASUREMENTS
Visits to Gljúfurárjökull in 1986 by the author as
part of the Exeter University North Iceland Expedi-
tion and in 1987 by Hans Stötter of the University of
Munich (pers. comm.) have provided continuing
evidence of the status and position of the glacier in
its snout area. These complement regular observa-
tions begun in 1979 (Caseldine and Cullingford,
1981; Caseldine, 1983, 1985a). Themarginal area of
the snout of Gljúfurárjökull in 1986 is shown in Fig.
1 based on accurate survey using a Wild T1000
electronic theodolite and Distomat D14L distance
measurer, and using fixed stations established during
earlier surveys. Survey was extended over the gla-
cier ice approximately 600 m onto the glacier so that
all ice contours represent the 1986 ice surface.
Measurements using this survey demonstrate that
Gljúfurárjökull advanced 22.5 m between 1983 and
1986, an average rate of 7.5 ma“'. Earlier in the
decade higher average annual rates of advance were
observed (21-22 ma_1 between 1979-1981, and 12.5
ma_1 between 1981-1983) and it thus appears that
this continued reduction in the annual average
represents a cessation of advance and probably even
a slight retreat in 1986. In 1987 Stötter observed
three closely-spaced, parallel moraine ridges on the
westem margin of the glacier. One of these appeared
to be in process of formation and the other two he
tentatively assigned to frontal positions in 1985 and
1986 (pers. comm.). Such an interpretation would
imply retreat from 1985 but should perhaps be con-
sidered with caution as Gljúfurárjökull had been
advancing over ground last covered in the 1950‘s on
which could be found occasional remnants of earlier
ridges which had not become vegetated. Measure-
ment of the distance from the crest of the proximal
ridge to a fixed point near the snout showed a margi-
nal position in 1987 ridge ca. 5 m inside that
identified in 1986. Although not the result of accu-
rate survey this observation confirms the conclusion
made earlier that retreat had indeed begun by 1987
at the latest. Caseldine (1985b), based on the work
of Björnsson (1971) at Baegisárjökull, has argued
that there is a close link between summer tempera-
tures and glacier response for Gljúfurárjökull with
an approximate 10 year lag between temperature
deterioration and glacial advance. Observations of
the temperature records form Akureyri point to a
similar lag time between amelioration and retreat.
Mean temperatures for the summer months (May to
September) increased in the late 1970‘s and early
1980‘s at Akureyri generally rising above 8 °C.
32 JÖKULL, No. 38, 1988