Jökull - 01.12.1961, Síða 32

special attention for the emphasis of the physi-
cal aspects of the geothermal phenomena.
2. GEOLOGY.
Iceland is a member of the Brito-Arlic basalt
province. The total series of flood basalt in Ice-
land is believecl to reach a thickness of several
kilometers.
According to the results of the seismic refract-
ion studies of the Swedish-Icelandic expeditions
in 1959 (Bath, 1960) and 1960 (Báth and
Tryggvason, 1961), the section through the
upper crust, from Reykjavík in the South-West
to Tjörnes in the North-East, appears to be as
shown in the sketch in FIGURE I. Formations
A and B are flood basalts. Formation C does not
outcrop but may be composecl of basalts of a
relatively early origin. The composition of D
and E is unknown. The Moho-discontinuity
appears to be at a depth of 28 km.
The flood basalts are relatively inhomogene-
ous and the average nature of the figures is
therefore to be emphasized. A striking feature is
the practical absence of a continental structure.
The Tertiary basalt plateau is the predominant
surface formation in the North-West, the Nortli
and East of the country. Quaternary volcanics
cover only small parts of these districts. The
central, southern and south-western parts are,
on the other hand, covered by Quaternary lava
flows and tuffs. The Tertiary plateau appears
to underlie these formations. Post-Glacial vol-
canism is confined to the Quaternary disiricts
as shown in FIGURE II. The shaded areas indi-
cate roughly the extent of the Neo-Volcanic Zone
of Iceland.
3. TYPES, MAGNITUDE AND DISTRIBUT-
ION OF THERMAL AREAS
(a) Relation between type ancl subsnrface
temperatures.
Two main types of thermal areas can be dist-
inguished in Iceland. Firstly, the areas with hot-
water springs and a relatively low degree of
thermal metamorphism. Seconclly, the large are-
as with natural-steam holes and a high degree of
0 100 £00 300 tu» 400
Fi.g. I. Crustal Structure of Iceland in a Section SW-NE according to Báth and Tryggvason (1961).
30