Greinar (Vísindafélag Íslendinga) - 01.01.1977, Qupperneq 57

55
Fig. 7. A simplified picture of climatic (i.e. temperature-) changes during
historic time in Iceland. (After S. Þórarinsson, 1969, cf. Saga Islands (1974),
p. 37. Ed. Sig. Líndal).
orical temperature minimum just after 1700 A.D. In 1724 we
then get the great fissure eruption of Leirhnjúkur, and a
series of smaller fissure eruptions in the neighbouring area
during the next years. Then, in the southern part of the
Eastern volcanic zone, we get 1783 A.D. the 25 km long Laki-
fissure eruption, producing an immense quantity of basaltic
lava. This is considered to be the greatest historic lava flow
on the whole earth.
In the volcanically inactive, “strong” lowland area between
the Eastern and Median volcanic zones, and south of the Hrepp-
ar mountains, the strongest earthquakes in Iceland occur in-
stead as an expression of activity. In 1784 there occurred here
one or two of the strongest historic earthquakes in Iceland. Re-
cent estimates lead to magnitudes of 7.5 to 8 on the Richter
scale (42). In a subsequent swarm in 1789 subsidence by about
0.6 m took place at the northern end of Þingvellir Lake, but
neither in the Snæfellsnes zone nor in the subaerial Median
zone is any volcanic activity on record. On the other hand,
a volcanic eruption formed a provisory island of tuffbreccia
southwest of Reykjanes, an easy prey of the surf.
The temperature remained rather low during the 19th cen-
tury on to 1918. In 1878 there was a small basaltic eruption