Greinar (Vísindafélag Íslendinga) - 01.01.1977, Blaðsíða 59

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eruption could be expected in 1953-55. In 1955 a great volume
of water flowed down under the glacier Höfðabrekkujökull
from the Katla area, and there were ring-like fractures and
stepwise subsidences over the subglacial site of the Katla
crater. But there was no eruption, and the “short” interval
has by now, in 1976, become 58 years. Just as in the case of
Hekla, the milder climate after 1918 seems to have weakened
the eruptive mechanism of Katla.
The mild climate came to a slight maximum in 1950—1960,
or about 1955, whereafter a slightly noticeable deterioration
set in. But the eruptive mechanism seems to be even more sensi-
tive to the change than the temperature averages which the
Weather Bureau calculated and publishes.
For, beginning with an Askja eruption in 1961, there has
been an almost continuous activity since then, but on a small
scale, i.e. slow and of small mass production: Surtsey 1963—67;
andesitic eruptions in the flanks of Hekla in 1970; Heimaey
1973, a series of earthquake shocks for months during the
summer of 1974 in the area north of Hvítársíða in the district
Borgarfjörður, i.e. in a volcanically inactive prolongation of
the Snæfellsnes volcanic zone, and finally a miniature eruption
in Leirhnjúkur in December 1975 and months of more or less
continuous small earthquakes in all the area between Mývatn
and Axarf jörður, with some tens of destructive shocks of magni-
tude 5 to 6.5. But there has so far been no such continuation of
volcanic activity as there had been in the severe climate in
the early 18th century.
These data seem to indicate rather clearly that volcanism in
the Eastern zone and heavy seismicity in the strong inter-
mediate area of the Southern Lowlands are related to the
severity of climate. But an analysis of the meteorological re-
cord (which for one station goes back to 1846), to throw more
light on this relationship, could not be completed in connec-
tion with the preparation of this paper. Analyses so far done
by meteorologists (45a and 45b) have mainly been concerned
with averages of temperature.
We shall later consider the Icelandic postglacial evidence,