Jökull - 01.12.1974, Page 35

Fig. 4. Suspended sediment concentration of
coarse silt and fine silt in Skeidará at different
locations from the glacier to the sea.
Mynd 4. Upphrœrður aurburður af mó og
mélu í Skeiðará á ýmsum stöðum frá jökli til
sjávar.
8 Útfall - Skaftafellsbrekkur-garðar
+ Brúasfœði
• y • •
Skeiðóra / * \J
Y \ +
yu v brúars lœði

16 18 20 22 24 26 28
/ >;•
Gi gja » /
- 1 ' •

16 18 20 22 24 26 28
Dagor marzmdnaðar 1972
Days in March /972
Fig. 5. The variations in coarse silt/fine silt
ratio in Skeidará and Gígja.
Mynd 5. Breytileiki mós/mélu hlutfallsins í
Skeiðará og Gígju.
CHANGF.S IN FLOOD CHANNELS
From the observations made during the jökul-
hlaup and an ERTS-1 image of Vatnajökull
taken on January 31 st 1973 (Williams and
Thorarinsson, 1973) a map of the flood chan-
nels has been made. The area of the flood
channels according to this map is approximately
240 km2. At Skeidará the flood channel was
covered by a layer of sand and silt, layer 1,
which coulcl be very easily discerned from the
underlying much coarser material. Studies on
the quantity and composition of this layer are
rnostly limited to the upper reach of the rhan-
nels and as the majority of the areal is in the
lower reach, there is substantial uncertainity as
to the total quantity of the layer. In any case
the quantity of coarse silt to be found on the
sand is approximately half the total load of
suspended coarse silt. That of sand is about
50% more than calculated from the amount in
glacier ice.
This layer of black sand, designated layer 1,
is not stable as it was sorted by wind and water
and disappeared in a few months from the
sandur. Tlie sandur underneath did not con-
tain any such layer. Layers containing silt are
absent at least in the upper part of the sanclur.
The sand in layer 1 can be of two sources, i. e.
from the glacier or washed out of the under-
lying layer.
Underlying the black layer is layer 2. Its
Fig. 6. The jökulhlaup
at Skaftafellsbrekkur near
peak discharge on March
23rd.
Mynd 6. Slieiðarárhlaup-
ið við Skaftafellsbrekhur
nœrri hámarksrennsli 23.
mars.
JÖKULL 24. ÁR 33