Greinar (Vísindafélag Íslendinga) - 01.01.1977, Síða 46

44
orary high volcano, on which an icecap was formed, and from
which glacial water or glacial tongues reached the surrounding
lower ground, an extremely common phenomenon in higher-
latitude volcanic areas, which nobody takes to be a proof of
Pleistocene age. We have pointed out, in this chapter, the origin
of even high heaps of tuffbreccias in river courses and/or
lakes. In the first chapter we have pointed out the importance
of the Hólsfjöll tuffbreccia mountain chain for the glaciation
of Eastern Iceland in Older Dryas time. In the upper basalts
at Hvalfjörður there are many obvious cases of the formation
of tuffbreccia in a lake which was due to a glaciation (lake
deposits over glacial vestiges). This correlation is very sug-
gestive, although the mountain itself is only found as a plate,
sometimes a very thick one. This indicated mountain might
leave intercalated glacial vestiges at a little higher level, and
create a lake in which a new glacier-bearing tuffbreccia heap
might form, and so on. By glacial erosion in the beginning, and
later by weathering in lower Tertiary climate, each such moun-
tain would rather soon be reduced to such a plate and then
be covered by lava flows. The glacial vestiges are not found
in the lower parts of the basalt pile, where the common lignite
beds indicate a climate about 10 °C warmer than the present
one at sea-level in Iceland today, and most probably an Eocene
age. This climate corresponds about to the climate of southern
Middle Europe today. And even the Alps are not high enough
to produce now such glaciers, the signs of which can be ex-
pected to be found after the peneplanation of the Alps. Vol-
canoes of the height of the Alps or higher were unlikely to
form in Eocene Iceland for reasons, which we shall explain.
The basaltic lavas of the postglacial time in Iceland have
had such a shallow origin, order of 25-30 km, as evidenced
i.a. by earthquakes under Heimaey during the 1973 erup-
tion, that the litho-hydrostatic pressure only allows them to
rise to the neighbourhood of 1500 m (the physical exposition
of this connection is given in my Textbook in Icelandic (16)
if it should not be obvious to the reader). It seems reason-