Jökull - 01.12.1957, Side 3

JOKULL
Á R S R I T
JÖKLARANNSÓKNAFÉLAGS ÍSLANDS
7. ÁR REYKJAVÍK 1957
Geothermal Effects of the Pleistocene Glaciation in Iceland
BY
GUNNAR BODVARSSON
STATE ELECTRICITY AUTHORITY, REYKJAVIK, ICELAND
ABSTRACT.
The influence of the erosion by Pleistocene
glaciers on the subsurface temperature field in
Iceland is estimated. Temperature data from
three shallow wells are corrected for the effect
of the erosion on the basis of three different
hypotheses about the rate and magnitude of
the erosion. The reduced heat flow is sub-
stantially above the normal and evidence is
presented that the present landscape forms of
Iceland were formed mainly during the latter
half of the Pleistocene Period.
INTRODUCTION
Iceland belongs to the North-Atlantic or
Brito-Arctic basalt province. The main part of
the Brito-Arctic basalts was formed during the
early Tertiary and there are no signs of a late
Tertiary volcanism in most parts of the pro-
vince.
Iceland is an exception. The island and the
surrounding shelf have been subjected to re-
current volcanism after the formation of the
main parts of the Brito-Arctic basalts. Con-
spicuous formations of late Tertiary and Quat-
ernary basalts and basaltic tuffs are found on
the island.
The area of post-Glacial volcanism in Iceland
covers, on the other hand, only about 14 to ]/s
of the total area of the island, as shown in
Figure 1. The coastal areas in the West, North
and East have not been subjected to volcanism
for a considerable period. The basalt plateau
in these regions is cut by a peneplaine and a
number of large and deep erosion valleys and
fiords have been formed.
Immediately under the peneplaine in the
West and the North is a section which reaches
a thickness of 300 to 400 metres and has a
lighter colour than the lower lying basalts. This
section is generally termed as the grey section.
The grey section is undarlain by a sedimen-
tary section having in places a thickness of
several hundred metres. According to Pjeturss
O) the sediments contain conglomerates, which
appear to be of a glacial origin. Pjeturss and
some iater geologists have therefore considered
the grey section as a series of Quaternary lavas.
This result was questioned by Einarsson (2)
partially on the basis of the extremely rapid
denudation and dissection of the basalt plateau
required by Pjeturss’ theory. The peneplaina-
tion and the erosion of fiords and valleys 1 to
2 km deep would have to be the work of the
glaciers in the latter half of the Pleistocene.
Einarsson therefore found a Tertiary age of
the grey section more likely. This would re-
quire a reinterpretation of the nature of the
conglomerates or the assumption of a pre-
Quaternary glaciation in Iceland.
1
LANDSBOKASAFN
214453
ÍSUHIIS