Jökull - 01.12.1999, Blaðsíða 78

Table 1. Composition of dimensions (L, W, D), azimuths of the axes of length (L), width (W) and of other morphometric
indexes of 16 kettles, —Mismunandi stœrðarhlutföll jökulkerjanna.
dimensions of kettles azimuth of axes morphometric indexes
no. L (m) W (m) D (m) L ° W° D/L 2D/L+W L+W/2D L/W-l
i 28.0 26.0 4.7 140 65 0.16 0.174 5.74 0.077
2 26.8 15.0 3.8 260 198 0.14 0.182 5.50 0.0786
3 7.2 5.5 1.0 220 130 0.14 0.157 6.35 0.309
4 12.0 6.0 2.5 202 130 0.20 0.278 3.60 1.000
5 14.6 10.0 1.2 210 350 0.08 0.097 10.25 0.460
7 8.0 7.6 1.8 108 18 0.23 0.231 4.33 0.052
8 5.6 4.2 0.4 216 284 0.07 0.081 12.25 0.333
9 12.4 4.6 2.2 140 240 0.18 0.259 3.86 1.695
10 13.0 11.4 3.4 134 40 0.28 0.278 3.59 0.140
11 6.0 2.7 0.7 140 235 0.12 0.161 6.21 1.608
12 9.2 6.4 2.5 150 260 0.27 0.318 3.14 0.415
14 6.0 2.4 2.5 92 198 0.41 0.595 1.68 1.500
15 8.0 6.5 1.2 110 190 0.15 0.165 6.04 0.230
16 23.0 18.0 2.2 248 4 0.15 0.156 6.41 0.277
17 3.4 2.6 1.2 192 55 0.35 0.400 2.50 0.307
18 7.0 4.0 1.0 258 352 0.14 0.181 5.50 0.750
D/L - relative depth, (2D/L+W) - isometricality, (L+W/2D - flatness, (L/W-l) elongation.
Kettles 6 and 13 were too damaged to be measured.
along a local erosional cleft. Five such kettles were
formed, whose average dimensions are 7.9*6.1*2.3m.
In contrast, the three largest kettles (no. 1, 2 and 16)
are situated in the peripheral-western part of the kettle
field. Their average dimensions are 25.9*19.7*3.9m.
The main track of the 1918 jökulhlaup lies just
west of the kettle field (Figure 1). Thus, if the ice
blocks forming the kettles were transported there dur-
ing the jökulhlaup, it is likely that the largest and
heaviest icebergs, containing the greatest amount of
moraine material would be the first to be deposited at
the edge of the floodpath. The largest and deepest ket-
tles we observe in the western part of the kettle field
could be formed this way.
The fact that the flattest kettles are located in the
northern and southern peripheries of the kettle field
(Figure 5B: 3-4) and the eight least elongated kettles
in the western and central part of the area (Figure 5C:
1-2, av. L/W-1: 0.216) is also in agreement with the
assumption that the ice blocks were transported into
the area during jökulhlaup, meaning that they were
deposited on a secondary bed.
Juxtaposing the indexes of relative depth (D/L)
and flatness (L+W/2D) brought to light five groups of
Table 2. Juxtaposed indices of relative depth (D/L) and
flatness (L+W/2D). — Stœrðarhlutföll jökulkerja.
No | groups: A/B nos of kettles av. D/L av. L+W/2D|
1 | A4/B1 14, 17 0.38 2.09 |
2 A3/B2 7, 10, 12 0.26 3.69 |
3 A2/B2 4,9 0.19 3.73 j
4 A2/B3 1-3, 11, 15, 16, 18 0.14 5.05
5 A1/B4 5,8 0.075 11.25 |
kettles (Figure 5D and Table 2). Kettles with the max-
imum relative depth and minimum flatness (groups 1-
2) occur in the central-eastern part of the area, in the
vicinity of the erosional cleft. Meanwhile, the oppos-
ing forms (groups 4-5) occupy a peripheral area sur-
rounding groups 1-2.
Morphographic analyses
The shape of the kettle-holes was defined on the ha-
sis of precise morphometric data and also on their
appearance. First, we analysed the ratios of the di-
mensions of the kettle axes, W/L and D/W (Figure 6),
adopting Zingg's square method. The diagram shows
the predominance (50%) of kettles with an oval, shal-
lowly flat shape, i.e. with average index values W/L:
76 JÖKULL, No. 47