Jökull - 01.12.1969, Síða 9

reaches the Húnaflói area in a wide sense. This
has occurred practically every year except dur-
ing the period 1930—1950. Winds, or possibly
an eddy at the boundary of the Polar Current
and the Irminger Current, or icethrust from
the northeast, are probably the main causes of
this ice approach. Sea transport is hampered a
little by this class.
Class B (North-ice). Prolonged SW-winds be-
tween Iceland and Greenland rnove the margin
of the compact pack nearer to much of North-
ern Iceland than is usual. Winds tear up the
margin and drive open pack towards land.
Blockage of most of the northern coast results.
Sea transport ancl fisheries very difficult or
impossible.
Class C (East-ice). This can probably be con-
tidered as such an intensification of the causes
of Class B that a tongue of compact ice is
extended into the East Iceland Current, to be
carried by this ancl other currents even as far
as the Faxa Bay in the most severe ice years.
But slight ice-years in this class may occur with-
out North-ice.
The extreme ice-years are due to ice appro-
aches of classes B and/or C.
Attempts to interpret ice years in Iceland in
terms of climate go back to the beginning of
this century, using Thoroddsen’s data as a basis.
We consider liere the treatments of Koch and
Hovmöller (Koch 1945). Koch uses the time
during which ice contactecl Iceland as a mea-
sure of severity. He finds (1. c., p. 227) this
result: 1880—1899: 67 iccmonths; 1900—1919:
48 icemonths; 1920—1939: 17 icemonths. This
shows a relationship with the amelioration of
climate.
As a further step, Hovmöller takes the pro-
duct of the duration of contact and the length
of the coast affected, as a measure of the ice-
severity. Running 10-years averages give a curve
(Koch, I. c., fig. 107) showing decline of severity
since the beginning of this century.
Now it must be obvious that the connection
between such figures on one hand, and climate
in such a wide region as partook in the changes
of climate in this century, on the other, is both
indirect and very obscure. Many factors, in no
immediate connection witli the climate, mav
affect the time ancl the length of the ice con-
tact with land. The real meaning of Hovmöll-
er’s diagram is then actually a measure of how
the ice that reached Iceland, affected Iceland
itself, its coastal traffic, its fisheries, and to
some degree the local climate.
We conclucled above that certain weather
conditions in the neighbourhood of Iceland are
the main cause of ice approach to Iceland.
Then it must be these conditions which have
changed with the climate. It is suggested that
the Icelandic material on ice years can be used
in the following way to throw more light on
the changes of the critical weather factors:
Each case of ice approach in Class A in-
dicates that the respective causative conditions
were once fulfilled. Whether the contact with
Fig. 5.
Number of ice
years per decade
in the classes A,
B, and C.
JÖKULL 19, ÁR 5
20
30