Jökull - 01.12.1981, Blaðsíða 19

Particle Size Analysis
ROUNDNESS samples
F'g- 3. Results of roundness and particle size
analyses.
Mynd 3. Niðurstöður athugana á kornastærð.
western side of the valley and 42, 50, 51,56, 57
and 59 on the eastern side.
For logistical reasons only nine samples
were collected and brought back for particle
size analysis in the laboratory. The locations
from which the samples were taken are shown
on the map (Fig. 2), and the particle size dis-
tributions are presented both graphically (Fig.
3) and in summary tabulation (Table 3).
Sample no. 1 was taken from the subglacial
dirt in transport in the glacier sole, about 1 m
back from the snout edge, no. 7 from the
morainic cover of an ice-cored ridge, and the
remaining seven from the crests of ridges or
mounds. Samples no. 2 and 3 were taken
respectively from the proximal and distal
flanks of ridge 17, about 1 m below the crest.
All of the ridge samples were taken at a depth
of c. 20 cm beneath the ground surface. 'Fhe
samples were analysed by a combination of
sieving and sedimentation techniques, the
latter by X-ray transmission using a Sedi-
graph 5000 D particle size analyser.
ft is not possible to draw major conclusions
from such a small number of samples, but the
two particle size curves that most clearly differ
from the rest, numbers 7 and 1, are the only
ones not to come from the relict moraine
ridges. The samples from the latter all have
small but significant amounts of clay (2.8 —
9.0% of the total sample, and 3.5—14.3% of
the matrix) and high proportions of silt
(20.7 — 32.8% and 27.8-46.3%). Sample no. 1
(glacier sole) differs from the relict morainic
ridge samples only in having very little clay
(0.7% and 1.0%), though this is offset by a
higher proportion of silt, so that the silt + clay
proportion (37.9% and 53.3%) is in keeping
with those of the ridge samples (24.1—37.2%
and 31.9 — 57.8%). The sample from the ice-
cored ridge morainic cover (7) is pre-
dominantly of sand and gravel, the proportion
of silt and clay being only 2.2% of the total
sample (5.9% of the matrix).
The main conclusion to be drawn from
these data is that the material in the relict
morainic ridges sampled is similar to that in
the glacier sole, whereas the morainic cover of
JÖKULL 31. ÁR 17