Jökull - 01.06.2000, Blaðsíða 11

Ice-thickness measurements on Sólheimajökull, southern
Iceland and their relevance to its recent behaviour
Andrew N. Mackintosh1,3, Andrew J. Dugmore1 and Frank M. Jacobsen2.
1. Department of Geography, University of Edinburgh, Drummond St. EH89XP, Scotland.
2. Geophysics Laboratory, Department ofGeology, University ofÁrhus, Finlandsgade 6-8 8200N, Árhus, Denmark.
3. now at Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, Postbus 80.005 3508
TA Utrecht, The Netherlands, email: anm@phys.uu.nl
Abstract — We present a radio-echo sounding and ice elevation survey along a central flowline of Sólheima-
jökull, a 15 km long outlet glacier of the Mýrdalsjökull ice cap. The glacier reaches a maximum thickness of
433 m and occupies an overdeepened parabolic trough. The troughform contrasts with nearby canyons incised
by jökulhlaups, indicating that it has formed predominantly as a result of glacial erosion. The ice sutface
showsfew large undulations and has a consistent decline in altitude, indicating regular iceflow conditions. The
parabolic profile, a gentle, consistently declining bed and ice surface slope, wide accumulation area and long
narrow snout are characteristics of a glacier that is sensitive to climatic change. The recent glacier advance
(1970-1995) is likely to have resulted from a dynamic response to changing mass balance conditions over the
lastfew decades, in line with other maritime glaciers in the North Atlantic.
INTRODU CTION
Sólheimajökull drains from between two domes of the
Mýrdalsjökull ice cap through a valley 1 to 2 km wide
(Figure 1). The ice surface and sub-glacial topograp-
hy of the upper catchment has been surveyed by
Björnsson (in Lawler et al., 1994); however little is
known of the outlet glacier. This paper presents an ice
radar and GPS survey conducted in 1996 and 1997
as part of a wider project that aims to understand the
climatic significance of the fluctuations of Sólheima-
jökull. Sólheimajökull has one of the most detailed
geomorphic records of glacier fluctuations in Iceland
(Dugmore, 1989). Although the Holocene fluctuati-
ons are similar in timing to other glaciers in Ice-
land (Stötter, 1994), suggesting a response to a reg-
ional climate signal, Sólheimajökull is known for its
anomalously large extent during the mid Holocene.
Dugmore and Sugden (1991) suggested that this was
caused by changes in the position of the Mýrdalsjökull
ice divide over time. However, other hypotheses may
be valid. For example, the large extent may reflect a
favourable topographic configuration as the geometry
of the glacier trough can influence a glacier’s respon-
se to a climate signal (Firbish and Andrews, 1984).
Also, Sólheimajökull may have exhibited irregular
flow in the past through the influence of sub-glacial
flood events from the Katla caldera. The ice radar and
bedrock profiles from this study give an opportunity
to constrain some of these alternative hypotheses.
SURVEY METHODS
The survey was located along a central flowline of
the glacier, from the ice-divide to the snout (Figure
1). In addition, two cross profiles were undertaken in
order to determine the trough cross section. Seventy
soundings were made at 250 m intervals (Table 1).
The sounding points were located by differential GPS
(Magellan Promark 10). A base station was establis-
hed at Skógar, 5 km from the glacier and the remote
unit was placed midway between the radar transmitter
JÖKULL No. 48 9