Jökull - 01.10.1998, Síða 32

Jónsson, 1995). Variations of surge-type glaciers are
not directly induced by climate changes in the same
way as for non-surging glaciers. Surge-type glaciers
may, however, be expected to reflect climate changes
on time-scales longer than the interval between surges,
since accumulated mass balance changes over long
time intervals do affect the total size of the glaciers
significantly. Figure 3b shows the advance and retreat
of Múlajökull (cover photograph), which is a surge-
type outlet glacier from the ice cap Hofsjökull, central
Iceland (Fig. 2). Múlajökull has in recent decades
surged with irregular 7 to 18 year intervals. The surge
events in 1954, 1972, 1986 and 1992-1993 are, of
course, the most prominent features of the record from
Múlajökull, but the longer term variations on a time-
scale of several decades are qualitatively similar to the
variations of Sólheimajökull in Figure 3a.
Figure 4 shows the relative number of advancing
and retreating non-surging glacier termini in Iceland
from 1930/31 to 1994/95. The figure is based on mea-
surements at 19 locations at the following 18 glaciers
(Fig. 3 shows the location of the main ice caps;
Sigurðsson, this volume, includes location maps of
the individual glacier tongues):
• Outlet glaciers from Öræfajökull, SE-Iceland:
Svínafellsjökull, Virkisjökull, Falljökull, Kvíárjökull,
Hrútárjökull, Fjallsjökull.
• Outlet glaciers from Vatnajökull, SE-Iceland:
Morsárjökull, Skaftafellsjökull, Brókarjökull, Skála-
fellsjökull, Heinabergsjökull, Fláajökull (two loca-
tions), Svínafellsjökull in Hornafjörður.
• Other glaciers: Gígjökull in Eyjafjallajökull (S-
Iceland), Gljúfurárjökull (N-Iceland), Hymingsjökull
in Snæfellsjökull (W-Iceland), Nauthagajökull in
Hofsjökull (central Iceland), Sólheimajökull in Mýr-
dalsjökull (S-Iceland).
Only termini which have been measured for sev-
eral decades are included in the figure. Monitoring
did not start until 1932 or 1933 at many locations and
the figure is therefore based on somewhat fewer data
series before 1935 (8 to 14 series) than after this time
(15 to 19 series). The measurement periods for the in-
dividual glaciers are given in Table 1 in Sigurðsson
(this volume). Measurements from glaciers which are
known to surge are not included because terminus
variations of surging glaciers are typically not con-
trolled by climate changes. Data from mixed type
glaciers, which are affected by surge events, but also
seem to react to decadal variations in climate, are not
included either due to difficulties in the interpretation
of such records. Data from Skeiðarárjökull and
Breiðamerkurjökull in Vatnajökull are not included
for this reason.
The glaciers represented in Figure 4 have lengths
varying from 2 to 29 km and vertical elevation ranges
from 740 to over 2000 m. They fall in categories 2
and 3 as defined by Haeberli (1995):
1. “The smallest, somewhat static, low-shear-
O i--'---1--'---1--'---1---■--1---'--1---'--1—
1930 1940 1950 1960 1970 1980 1990
a Years
\ J M úlajökull
'==□¥= ctú T[fu-|~iJLr
1930 1940 1950 1960 1970 1980 1990
Years
Fig. 3. Yearly advance and retreat of Sólheimajökull, “vesturtunga” (a), and Múlajökull, “suður”, (b) from 1930/31 to 1994/95
(histograms) and the cumulative advance/retreat of the glaciers since 1930 (dashed curves). The ticks on the x-axis indicate the
beginning/end of the measurement intervals (i.e. the tick marked 1960 is at the end of the interval 1959/60 and at the beginning
of the interval 1960/61 which is in the fall of 1960).
- Breytingar á Sólheimajökli, „vesturtunga" (a) og Múlajökli, „suður“ (b), á tímabilinu 1930131 til 1994195 (stöplarit) og
heildarbreyting á stöðu jökulsporðanna síðan 1930 (slitnir ferlar). Hökin á x-ásnum sýna upphaf og endi mœlitímabilanna
(þ.e. hakið sem merkt er 1960 sýnir endi mœliársins 1959/60 og upphaf mæliársins 1960/61 haustið 1960).
30
JOKULL, No. 45, 1998