Jökull - 01.12.1967, Side 33

Fig. 5: A section AB of Hagafellsjökull Eystri (cf.Fig. 1) showing the thickness of the glacier lobe
at different times and the changing level of Hagavatn, where lake level 1 represents the maxim-
um elevation of Hagavatn. Lake level 2 is that before the “jökulhlaup” of 1929, lake level 3
is that before the “jökulhlaup” of 1939 and lake Ievel 4 is that of the present Hagavatn.
Langsnið Ali af Hagafellsjökli eystri (sjá 1. mynd), sem sýnir þykkt jökultungunnar á mismun-
andi tímum og vatnsborðsbreytingar Hagavatns. Valnsborð 1 er hámarkshœð Hagavatns, vatns-
borð 2 er hœð vatnsins fyrir jökulhlaupið 1929, vatnsborð 3 er hœð þess fyrir hlaupið 1939 og
vatnsbprð 4 er núverandi hœð Hagavatns.
area as will be discussed later. Björn Ólafsson
(1929) does not mention any such stream in
his description of the conditions at Hagavatn
prior to the “jökulhlaup” of 1929, but it may
have been caused by leakage through the very
permeable bedrocks in the Sanddalur Col.
Very distinct abancloned zones of shore lines
are to be found in many places in the SW part
of the Hagavatn basin (Fig. 6), but each single
shore line is usually too diffuse for their eleva-
tion to be measured with an accuracy greater
then 1—2 m. Probably the Iake level has been
fluctuating during their formation. The lowest
one of these shore line zones is 10—12 m above
the present lake level (Fig. 6). It is in a good
correlation with the Leynifoss Col, which is 9.5
m above the present lake level. Another zone
of shore lines is at an elevation of 16—18 m
above the lake level (Fig. 6), which is in a
good correlation with the elevation of Haga-
vatn before the “jökulhlaup” of 1929 (Wright
1935, Thorarinsson 1939). In the Brekknafjöll
Range there is no col that can be correlated
with these shore lines, which are 12—14 m lower
than the Sanddalur Col. About 300 m to the
NE of the Sanddalur Col in the NW down-
slopes of Brekknafjöll (Fig. 1) there are very
distinct series of shore line zones (Fig. 6). The
highest one of these is 21—22 m above the
present lake level and 4—5 m higher than the
16—18 m shore line zone, but it is 8—9 m below
the lowest point of the Sanddalur Col, and no
higher shore lines are to be found anywhere
else. There has been no surface outlet from the
Hagavatn basin while the glacier blocked the
Leynifoss Col. There are two possibilities as to
drainage from the lake during that period.
Either, there has been sufficient ground water
drainage through the pervious Lambahraun
lava and the Brekknafjöll Range, or the water
JÖKULL 17. ÁR 267