Náttúrufræðingurinn - 1986, Blaðsíða 52

HEIMILDIR
Björn J. Blöndal. 1975. Norðurá fegurst
áa. — Bókaútgáfa Guðjónsó, Reykja-
vík. 221 bls.
Bragi Árnason. 1976. Groundwater sys-
tems in Iceland traced by deuterium. —
Vísindafélag íslendinga 42: 9—236.
Sigurjón Rist. 1969. Mývatnsísar. — Bls.
470-478 í Markús Á. Einarsson
(ritstj.): Hafísinn. Almenna bókafé-
lagið, Reykjavík.
SUMMARY
The ice cover of Lake
Þingvallavatn
by
Sigurjón Rist
National Energy Authority
and
Guðmann Ólafsson
Skálabrekka
Þingvallasveit
Lake Þingvallavatn is the largest lake in
Iceland. Its surface area is 83 km2, mean
depth 34 m and maximum depth 114
m. Almost 9/10 of the inflow is through
subaquatic springs at about 3°C. The out-
flow is very stable at about 100 m’/s and its
temperature may reach 8—13°C during the
summer. In late summer or early autumn
the midsummer thermocline is destroyed
by wind. At the end of October the surface
temperature is usually near 4°C.
Ice normally forms on the lake in Janu-
ary and lasts until March-April (Table 1).
Mean duration of ice cover is 85 days. The
article describes ice phenomena such as
icefolds, cracks and openings.
258