Jökull - 01.12.1969, Side 126

Geiteyjarströnd
ReykjahtíO
SKYRINGAR:
Bfl Alltaf autt
Venjulegast autt
Autt í mildri tíð
L:J Lagís
0 I 2km
Joh.S /S.Rist/G
Fig. 2. Open water in the lake Mývatn in winter. Legend: Black: Always open. Double crossed:
Variable ice cover. Most frequently free from ice, only covered with ice in periods of severe frost.
Hatched: Open water in mild winter periods. Shaded: Ice cover.
and warm springs at tlie farm Vogar. Mývatn
only receives surface runoff from Grænavatn.
There the water has a similar mode of origin
as in Mývatn, i.e. springs from surrounding
lava and oozing-water from the lava-bottom,
this flow-patterns keep open pools in the ice.
The discharge of Grænilækur is only 6 m3/sec.
The outflow frorn lake Mývatn is the river
Laxá (Salmon-river), which is one of the most
constant flowing rivers in Icelancl, 30—40 m3/
sec. A power plant was put into operation in
122 JÖKULL 19. ÁR
Laxá in late 1939. It soon became apparent
that ice repeatedly choked up the outlets of
the lake. The outlets were three: Geirastada-
kvisl farthest to north, then Hólskvísl, ancl
Sydstakvísl farthest to the south. The blockage
usually lasted one or two days each time, on
a few occasions a whole week. During the
summer of 1946 the Akureyri Municipal Light
ancl Power Work had a dam constructed in
Sydstakvísl, the purpose being to open gates
in it, when the other two outlets were choked