Rit (Vísindafélag Íslendinga) - 01.06.1967, Síða 37

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of most of the basalt plateau by late Miocene except for Ice-
land, the Faeroes and the basalt areas of Scotland and Green-
land. Thoroddsen considers that volcanic activity was resum-
ed in early Pliocene, but largely confined to a narrow belt
across Iceland from SW to NE, where activity has been
maintained to the present day. Hawkes (1916) and others
supported the view of a North-Atlantic basalt plateau, from
Scotland to Greenland, but Tyrrell (1949) thought the size
of the plateau improbable and suggested that Greenland had
drifted westward after the formation of the basalt pile.
Trausti Einarsson (1954) carried out a gravity survey
which led to an interpretation of the Icelandic basalt pla-
teau quite different from that above (1960,1963). He claims
that in early Tertiary a large North-Atlantic Ocean was al-
ready existent, from the floor of which the Iceland and
Faeroe plateaus grew. A major factor in Einarsson’s hypo-
thesis on the structure and genesis of the Icelandic basalt
pile is the fact that the country is in isostatic equilibrium
unlike most oceanic islands, which tend to subside into the
sea. To explain the state of equilibrium Einarsson suggests
initial submarine volcanic activity at depth of 3 km, build-
ing up a 6 km thick pile of pyroclastic rocks with density 2.2,
extending slightly above sea level. Allowing for no compac-
tion, the submarine pyroclastic pile could maintain a recum-
bent 6 km thick basalt pile 1100 m above sea level.
Our understanding of submarine eruptions has been con-
siderably increased in the last few years, notably by re-
search on Surtsey and on the submerged flanks of the Ha-
waiian Islands. It is now clear that the primary product of
submarine eruptions is pillow-lava. Production of tephra,
scoria or pyroclastic material in general does not begin until
quite near sea level. It therefore appears, that Iceland’s iso-
static equilibrium cannot be accounted for by any hypothesis
assuming a thick basal pile of pyroclastic material. After
the build-up was largely completed, according to Einarsson,
the basalt plateau was tilted and faulted after which follow-
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