Jökull - 01.12.1967, Blaðsíða 53

at present were there already, but instead o£
crater rows and lava flows they were separated
by moraine-covered depressions, probably oc-
cupied by a great number of lakes. This pat-
tern did not remain for long unaltered, because
soon immense volcanic eruptions and tectonic
dislocations began to develop. The earliest in-
dication of a volcanic eruption in these parts
in postglacial time is the oldest Tungnaá lava
flow, which is approximately 8.000 years old
according to C14 datings of underlying peat.
During the next 6.000 years a succession of new
lava flows followed from the Tungnaá area.
Altogether ten liave been found in boreholes,
on the surface and in canyons. Besides the lavas
the chief records of these volcanic activities are
a great number of crater rows ancl fault lines.
The tephrochronological classification indi-
cates that lake Stórisjór originated about 4,000
years ago. Then, seven of the Tungnaá lava
flows had already been poured out. The lowest
sample, from the 17 m depth, contains 43%
pumice with characteristics of Tungnaá lava
flows. No diatoms were found in this sample,
indicating that either the tephra has filled up
a former lake, or there was no lake at all prior
to the eruption. On the contrary diatoms are
abundant in the sample from the 16 m depth
indicating tliat by then the basin had become
lakefilled. This lake, which came into existence
almost simultaneously with the tephra layer H4,
then remained up to the year 1783, when fall
of tephra from the Laki eruption filled it up.
Thus a lake has existecl liere for approximately
4,000 years and during nine the first centuries
of human habitation in Iceland. The exact
size of the lake cannot be stated and it may
have been variable. Generally it has been about
1—2 km wide but indented, especially its south-
eastern shore. At the present time some of the
indentations form separate lakes. The length is
more difficult to estimate, but it can be con-
sidered probable that the lake extended south-
west to the point where the course of Tungnaá
narrows just south of Tröllid and north-west
to against Hraunsskard. Thus it has been about
15 km in length and about 25 km2 in area or
similar in size to lake Langisjór. The lake may
have extended farther to the north-west in the
Tungnaá depression, but it is also conceivable
that another lake was situated there. It must
be considered probable that our anchestors at-
tributed this lake a name. A name without a
lake does in fact exist, ancl to ascribe this lost
lake to the preserved name and call it STÓRI-
SJÓR, as has been done liere, seems to be to
the point.
In tales on Stórisjór mention is made of great
shoals and catches of fish. This assertion may
be considered incredible since the Tungnaá
river was flowing througli the lake, but as far
as is known much trout does not live in lakes
contaminated with glacier water. Glacier water
contains very scant amounts of nourishment for
trout, because vegetation must be very sparse
there as the light only penetrates a few cm into
the water owing to silt. Contradicting this is
the fact that the sediments of Stórisjór abound
in remains of a mature diatomaceous flora,
which shows no signs of severe living condi-
tions. This can hardly lead to any other con-
clusion than that Tungnaá was not glacier-fed
while the diatoms lived in Stórisjór. The topo-
graphy is such as to make it impossible for
Tungnaá to liave had a different course at this
time.
In the west bank of Tungnaá ruins of liuts
were discovered a short way from the place
where the drilling was performed, cf. Fig. 1.
They throw some light on the history of Stóri-
sjór. These ruins were dug up and investigated
by G. Gestsson archaeologist and others in the
summer of 1956. (Gcstsson 1956 and 1959). The
digging revealed remains of two huts side by
side which have been built against a hanging
rock wall close to the riverbank. Of implements
little was found except studs of trout nets
made of horse legs. In his description Gestsson
a.o. says: “A lot of scattered bones and pieces
of bones were found in the huts and ash heaps
also show that great quantities of bones had
been burnt... Pieces of sheep bones, dorsal
vertebras, ribs and tigh-bones were most frequ-
ent, but bones of feet or heads were not found.
It is therefore a possibility that all the sheep
bones are remains of travel provisions although
it cannot be proved. Bones of birds are also
quite common, yet there is still more of bones
of fishes, especially in the rubbish .. . Accord-
ing to the size of the huts and other buildings
in the cavern I consider it a natural conclusion
that the huts were inhabited by 2—4 men. They
JÖKULL 17. ÁR 287