Jökull - 01.12.1982, Page 45

Fig. 4. Hypsographic curves
of volume and area against
depth for Jökulsárlón.
Mynd 4. Rúmmál og flatarmál
J'ókulsárlóns sem fall af dýpi.
We estimate resolution of distance between reflec-
tors to be 2 m. 26 km of profiles were run in the lake.
Positions were fixed by sextant, but the slow speed
required for high resolution by our system and the
presence of numerous icebergs compared with
1975, necessitated numerous course corrections,
and led to much greater errors compared with the
bathymetric survey. The locations of these profiles
were adjusted wherever possible so that depths at
profile crossings points agreed, and there was rea-
sonable agreement with the 1975 bathymetric surv-
ey. We estimate that there may be errors in profile
location in the middle of the lake of up to approxi-
mately 200 m.
In our results we distinguish four principle seis-
mic textures, all of which are illustrated in Fig. 6.
They are: —
a) A strong surface reflector with numerous hyp-
erbolic reflections, but lacking internal coher-
ency. Grab samplingsuggests that much ofthis
is till, and similar acoustic signatures have been
obtained from known tills in several areas. (e.g.
Bugge et al. 1974; Holtedahl et al. 1974; Boulton,
Chroston andJarvis 1979). However, it primarily
Fig. 5. Successive ice front
positions in Tökulsárlón since
1894.
Mynd 5. Lega ísjaðars viðjökuls-
árlón frá árinu 1894.
JÖKULL 32. ÁR 41