Jökull - 01.12.1979, Page 77

meet in Vatnajökull (8300 km2) which comprises
over 70% of all the glacierized area in Iceland.
Vatnajökull is the largest ice mass in the world after
Antarctica and the Greenland Inland Ice. The
average ice thickness of Vatnajökull is about 420 m.
The ice is 800—900 m thick above the deepest
valleys and the maximum thickness is about 1000
m. The main part of the ice cap is located on top of
a highland plateau at 700—800 m elevation. Only
10% of the rock-bed ranges above the 1100 m ele-
vation which marks the present level of the firn line
in the southern part of Vatnajökull. On the other
hand, about 70% of the glacier surface lies above
the 1100 m elevation.
CLIMATIC CONDITIONS AND GLACIER
ACTIVITY
The climate in Iceland can be described as cold-
temperate. The average temperature for the
warmest summer month is only about 110 C along
the southern coast and 8—9° C at the northern
coast. On the highest parts of the main ice caps the
average temperature is close to or below freezing
throughout the year. The cyclonic activity is at
maximum during the autumn and the winter
months. About 80% of the annual precipitation
falls in the months from September through May.
At higher levels on the glaciers most of the
precipitation falls as snow. The maximum
precipitation (Fig. 2) is found at the southern slopes
of Vatnajökull and Mýrdalsjökull where the firn
line lies at 1100 m above sea level. On Hofsjökull
and the northern outlets of Vatnajökull the firn line
is at about 1300 m, and at 1200 m on Langjökull. In
the precipitation shadow north of Vatnajökull the
annual precipitation is down to 400 mm and the
orographic snow line lies above 1700 m. In the
northern glacier region the snow line has again
fallen down to 900—1000 m on the valley glaciers
in Tröllaskagi and down to the lowest level in Ice-
land of 550—600 m at Drangajökull in the north-
west. At Snæfellsjökull the firn line is at 900—1000
m elevation.
Glaciers in Iceland are dynamically quite active.
The most active glacier outlets flow southwards
from the high plateaus of Mýrdalsjökull and
Vatnajökull. Only one quarter of the accumulation
is melted inside the accumulation areas so enor-
mous amountsof ice are transported by the outlets
JÖKULL 29. ÁR 75