Rit (Vísindafélag Íslendinga) - 01.06.1967, Page 59

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Most numerous are long, sometimes discontinuous, móberg
ridges running parallel with the axis of the young volcanic
belt. But the highest and largest móberg mountains are small
equidimensional or only a little elongated plateaux with ab-
rupt edges. Their steep sides consist of móberg and pillow-
lavas up to a height limit somewhat below the sharp edge,
where they are capped with lavaflows forming the flat or
smoothly convex plateau. Some móberg mountains are inter-
mediate in shape betw'een these two types.
The pronounced linear relief of the móberg mountains
was formerly considered to be of tectonic origin. The ridges
and tablemountains were interpreted as horsts and the inter-
vening valleys as grabens. More recent investigations by
Kjartansson (1943, 1964 and 1966) and Bemmelen and Rut-
ten (1955) and others, have made clear that although verti-
cal displacement is evidently responsible for many minor
features in the young volcanic zone, it was not a general
factor in the formation of the móberg mountains proper. The
view now held by most or all students of the móberg morpho-
logy is that both the ridges and the tablemountains represent
volcanic piles formed súbglacially and intraglacially, the first
from linear, the latter from more central vents.
In some móberg mountains only one of the two types of
rock, móberg or pillow-lava, is visible. More often both occur,
and if so, the pillow-lava is usually exposed most abundant-
ly near the base and the móberg on top of it. The pillow-lava
at the base shows the most perfect pillow structure, every
pillow being coated with a skin of brown glass and there are
usually little or no interstices with other structures in be-
tween them. In addition there may also be found some smal-
ler intercalations of pillow-lava in the móberg, especially at
the contact of the móberg and the lava flows that cap the
tablemountains. But in these intercalations the structure is
usually crude, the pillows, single or in clusters, lying scatter-
ed in a matrix of brecciated lava and móberg.