Jökull - 31.12.2001, Blaðsíða 32

Thorsteinsson et al.
Depth (m)
Figure 4. Length of ice core drilled in each run. - Kjarnalengd í hverrifœru.
Table 1. Drilling progress at Hofsjökull - Gangur borunar á Hofsjökli
Day Dagur Date Dags. Total drilling time Heildarbortími Number of runs Fjöldi fœra Total core length drilled Dagleg borun Average core length per run Meðalkjarnalengd ífœru Comments Athugasemdir
1 1.8. 6.5 h 41 40.61 m 0.99 m Water table at 35 m depth
2 2.8. 6 h 28 10.19 m 0.36 m Motor exchange, tests with isopropyl alcohol
3 3.8. - - - - Drill maintenance
4 4.8. 5.5 h 28 8.31 m 0.30 m Drill motor exchanged twice
5 5.8. 6 h 26 6.41 m 0.25 m
6 6.8. 12 h 45 10.10 m 0.22 m Core barrel modifications
7 7.8. 11 h 40 9.84 m 0.25 m
8 8.8. 7 h 26 7.76 m 0.30 m Water pumped out of hole
9 9.8. 10 h 29 6.98 m 0.24 m
Total 64 h 263 100.20 m 0.38 m
terials. The fact that the electric motor worked al-
most normally after filling with water indicates that
the water in the ice cap is very clean and nearly free of
conducting ions. The motor was thoroughly cleaned
and dried out at the end of each day of drilling.
3. As is evident from Figure 4, much shorter cores
were obtained below the water table. The average core
length in the interval 40-100 m was only 0.27 m. Each
run was then either automatically terminated as rota-
tion of the drill head and barrel became more difficult
and the motor current limit was exceeded, or drilling
had to be stopped due to penetration problems.
In the firn part of the ice cap (0-35 m depth) a
tendency of the chips to stick together on the spiral
section was observed, but chip collection through the
open hatches into the upper part of the barrel (Fig-
ure 3a) seemed to be normal. Below the water table,
chips transport upwards along the spirals did not ap-
30 JÖKULLNo. 51