Jökull - 01.12.2007, Side 82

Thorsteinsson et al.
vironments might not grow at all. In addition, the
approach that was used is a culture dependent one,
which means that non-culturable bacteria are not de-
tected at all.
The system was filled with ethanol prior to the
tests described here. One possible concern about
this procedure is a risk of ethanol dissolving sensitive
parts of the high pressure unit and the drilling hose,
but no damage was found to have occurred. During
drilling, disinfection of the external parts of the hose
and drill stem can be achieved by spraying ethanol on
the outer surfaces.
A drilling speed of 50 m/h was achieved in the
tests on Langjökull, but a slower speed is recom-
mended for most operations, especially for drilling in
volcanic regions where tephra layers are embedded in
the ice. Two types of drilling tips were tested; one
with seven 0.8 mm wide holes for the drilling water
and another with a single 1.5 mm wide hole. The pen-
etration speed was similar in both cases, but use of
the multi-nozzlemelting tip appears to create a greater
risk of deviations from a vertical drilling direction.
The current version of the drilling system is well
suited for penetration into the subglacial lakes beneath
the Vatnajökull ice cap, which are currently the prime
targets for hot water drilling in Iceland. Model calcu-
lations indicate that the new drilling system can pro-
duce a 300 m deep borehole with a minimum diame-
ter of 15 cm within 25 hours and a minimum diameter
close to 10 cm in 12 hours, but these results should be
viewed with care due to the lack of accurate informa-
tion on the thermodynamic properties of the drilling
hose and the efficiency of heat transfer at the bottom
of the borehole. Moreover, ash layers and the dynamic
nature of the ice shelves covering the subglacial wa-
ter bodies may cause unforeseen obstructions to the
lowering and hoisting of samplers and other devices
in the boreholes.
Acknowledgments
Funding for the construction of the hot water drill
was provided by the Icelandic Centre for Research
(Tækjasjóður RANNÍS), The Public Roads Admin-
istration (Vegagerðin), The National Power Com-
pany (Landsvirkjun) and the NEA Hydrological Ser-
vice (Vatnamælingar Orkustofnunar). The Icelandic
Glaciological Society provided assistance during the
field test on Langjökull. EG was supported by the Na-
tional Aeronautics and Space Administration through
the NASA Astrobiology Institute under Cooperative
Agreement No. NNA04CC08A issued through the
Office of Space Science.
ÁGRIP
Prófun á nýjum bræðslubor með gerilsneyðingar-
búnaði
Lón undir jökulhvelum er óvíða að finna á jörðinni og
rannsóknir á þeim beinast meðal annars að því að auka
skilning á eðli jökulhlaupa og kanna örverulíf undir ís-
hellum. Bræðsluboranir eru hentug aðferð til að koma
búnaði til sýnatöku og mælinga niður í lónin. Nýr bor
hefur verið smíðaður hérlendis í þessum tilgangi og
var við hönnun hans lögð sérstök áhersla á gerilsneyð-
ingu borvatnsins, til að koma í veg fyrir að lónin og
sýni úr þeim mengist frá yfirborði. Borinn var prófað-
ur á Langjökli og voru þá tekin sýni úr borvatni á ýms-
um stöðum í kerfinu, sem síðan voru sett í ræktun við
7!C og 30!C . Fjöldi ræktanlegra örvera lækkaði mjög
við síun og geislun borvatnsins með útfjólubláu ljósi.
Við frekari tilraunir var þekktu magni E-coli örvera
bætt í borvatnið, sem reyndist dauðhreinsað eftir síun,
geislun og hitun upp undir suðumark. Efnagreining-
ar borvatns sýndu að lítil breyting varð á styrk helstu
sporefna og næringarefna á leið í gegnum borkerfið,
en minni háttar aukning á styrk nokkurra málma. Hiti
borvatns í slöngu fellur úr 90!C í 33!C niður á 300 m
dýpi í þíðjökli, skv. niðurstöðum reikninga og ef bor-
kerfið er keyrt á fullu afli má á 12 klst. bora 300 m
holu sem er hvergi mjórri en 10 cm.
REFERENCES
Ágústsdóttir, A.M. and S.L. Brantley 1994. Volatile fluxes inte-
grated over four centuries at Grímsvötn volcano, Iceland. J.
Geophys. Res. 99, 9505–9522.
Björnsson, H. 1991. Skýrsla um starfsemi Jöklarannsóknafélags
Íslands 1990 (Report on the activities of the Icelandic Glacio-
logical Society 1990). Jökull 41, 105–108.
Björnsson, H. 2002. Subglacial lakes and jökulhlaups in Iceland.
Global and Planetary Change, Special Issue 35, 255–271.
CRC Handbook of Chemistry and Physics: http://www.hbcpnet-
base.com
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