Rit (Vísindafélag Íslendinga) - 01.06.1967, Page 67

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Both Jones and the present writer have independentlv of
each other come to the same conclusion from studies of Ice-
landic móherg mountains that pillow-lava is in all prohabi-
lity the typical product of basaltic volcanism in deep water.
Quoting Northrop and Frosch, Jones mentions that the sides
of submarine basaltic volcanoes, presumahly consisting of
pillow-lava, have been found to slope as much as 25°. In my
experience still steeper slopes — 50° or more — are often found
in ridges of pillow-lava in Iceland. Admittedly, their steep-
ness may in some cases be due to supporting ice walls during
their extrusion and to subsequent erosion. But the new sea-
mount Surtla has slopes of no less than 34°, according to the
provisory chart (Fig. 3). We must assume that this steepness
does not exceed the angle of repose for a pile of pillow-lava
in statu nascendi.
Up to the middle of this century all students of móberg
landscapes in Iceland considered its strongly parallel - linear
relief to be due to faulting. Now the ridges of the móberg
belt are generally considered to represent, not horsts, but the
edifices of subglacial linear volcanism. I wonder if this latter
view — mutatis mutandis — is not to a more or less degree
also true of the submarine linear relief on the crest of the
Mid-Atlantic Bidge.
REFERENCES
Bemmelen, R. W. van and M. G. Rutten, 1955: Tablemountains of north-
ern Iceland. Leiden, 217 pp.
Jones, J. G., 1966: Intraglacial volcanoes of south-west Iceland and their
significance in the interpretation of the form of the marine basaltic
volcanoes. Nature 212, 586-588.
Kjartansson, Guðmundur, 1960: The móherg formation. In: On the Geo-
logy and Geophysics of Iceland. Intem. Geol. Congress, XXI Session:
21-28.
— 1964: Isaldarlok og eldfjöll á Kili (The retreat of the last glacial
ice-sheet and some volcanoes in the Kjölur area, central Iceland).
Náttúrufræðingurinn 34: 9-38.
— 1966a: Sur la récession glaciaire et les types volcaniques dans la ré-