Jökull - 31.12.2001, Side 41

Ice core drilling on Hofsjökull
perate ice and the core catchers function properly. Ex-
periments in varying the rotation speed of the drill
head were carried out at Hofsjökull, but this did not
seem to make any difference in the penetration abil-
ities of the drill. The maximum rotation rate of 150
rpm was normally used.
5. Experiments with pumping of water out of a drill
hole should be continued. One possibility to be con-
sidered would be to drill a hole with a hot water drill
in the immediate vicinity of the borehole and pump
water continuously out of that hole, to lower the wa-
ter level at the drilling site and keep it below the level
of core drilling each time. Even though this would
not improve the ice coring, it could provide important
information related to ice-cap hydraulics.
Recommendations for further work
The successful continuation of ice core drilling and re-
search in Iceland will mainly rely on the development
of both 1) reliable drilling techniques and 2) accurate
dating methods. Work is in progress by the authors
in both fields. Using a combination of engineering-
design ideas from the conventional AWI-type drill and
the Bárðarbunga drill. as described above, seems to
hold promise. Before considering deeper drillings,
thorough annual-layer detection and recognition stud-
ies should be made on snow/firn cores (10-30 m) and
shallow ice cores drilled to depths of 100-200 m. Re-
search should focus primarily on improving the accu-
racy of dust concentration measurements, visual in-
spection and quantification of stratigraphy, and detec-
tion, recognition and geochemical/petrological analy-
sis of tephra layers. In addition to the summit of Hofs-
jökull, the following two sites can be recommended
for future investigations to test these criteria:
Grímsvötn. The winter accumulation has been
measured on the ice shelf covering the Grímsvötn sub-
glacial lake during a period of 50 years (Björnsson,
1985). Such a data set would be invaluable for com-
parison with studies of annual layering in an ice core
drilled on the ice shelf, which locally exceeds 250 m
in thickness. In addition, measurements of ice-core
particles and ice chemistry could provide information
on the atmospheric input of dust and chemical impuri-
ties into lake Grímsvötn and thus would aid geochem-
ical studies of the subglacial lake.
Langjökull. The ice thickness at the northern
dome of Langjökull is only 220 m (Finnur Pálsson,
pers. comm.) Rapid thinning of annual layers with
depth is expected at such a location, and the develop-
ment of dating methods could probably benefit signifi-
cantly from the study of an ice core drilled to bedrock
there.
For deeper drilling, sites which have the potential
to contain the highest possible ages of the ice near
bedrock should be given the highest priority. These
would be mainly sites where ice thickness is great
and accumulation is relatively low. Information on
the subglacial terrain and ice-flow patterns must also
be taken into account. The ice-filled calderas within
Hofsjökull, Bárðarbunga, and the Kverkfjöll massif
clearly seem to be among the most promising sites.
Acknowledgments
Funding for this work was provided by the Icelandic
Research Council (RANNÍS) and by the US National
Geographic Society, Committee for Research and Ex-
ploration. Support by the Icelandic Glaciological So-
ciety, the Alfred Wegener Institute, the Reykjavík unit
of the Hjálparsveit Skáta Rescue Corps, the National
Power Company and the Public Roads Administration
was crucial for the implementation of fieldwork. We
thank technicians Sölvi Oddsson, Hlynur Skagfjörð
Pálsson and Jóhannes Rögnvaldsson for their impor-
tant contributions during drilling operations in the
field.
ÁGRIP
Borun ískjarna á hábungu Hofsjökuls
Borun ískjarna á jöklum landsins er nú hafin á ný eftir
langt hlé. Fyrstu tilraunir voru gerðar fyrir 1970 og
415 m kjarni var boraður í jaðri Bárðarbungu surnar-
ið 1972 með bor sem smíðaður var hérlendis. Arið
1997 var kjarnabor fenginn til landsins frá Alfred
Wegener stofnuninni (AWI) í Bremerhaven og náð-
ist með honum 70 m kjarni úr Langjökli í apríl 1997.
Endurbætt gerð þessa sama bors var notuð við borun
lOOm ískjarna á hábungu Hofsjökuls sumarið 2001
og er tæknilegum hliðum þeirrar borunar lýst í þess-
ari grein. Borstaðurinn er í 1790 m hæð yfir sjávar-
máli og ísþykkt er þar um 300 m. Hábungan er yfir
austurbarmi hinnar miklu gosöskju, sem liggur undir
JÖKULL No. 51 39