Rit (Vísindafélag Íslendinga) - 01.06.1967, Side 61

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lidified in water, the latter exploded and chilled on account
of an easy access of water into the eruptive vent.
The lava flows capping the tablemountains were poured
out subaerially after a pile of the former rocks had grown up
above the ice surface or at least above the level of a lake
produced by the melting ice and dammed up against ice
walls on all sides.
This mode of origin is evident for the volcano Leggjabrjót-
ur in central Iceland. The steep sides of this tablemountain
are rather low, about 200 metres, as it was formed in a thin-
ning glacier towards the end of the last glaciation. Contrary
to most other tablemountains Leggjahrjótur was never cover-
ed hy ice. Both its typical lava shield with a great crater on
its top and its steep sides are intact of glacial erosion, and
just therefore the Jatter still bear a series of shore lines due
to the gradually lowering level of ice-dammed lakes (Kjart-
ansson 1964 and 1966).
The theory of intraglacial accumulation of the móberg
mountains lacked actualistic support as repeated subglacial
eruptions in Iceland in the last cenuries do not seem to have
created any mountain. This may be explained in the way
that these eruptions were too small to produce sufficient rock
material.
On the other hand the eruption of Surtsey, beginning in
November 1963 and still going on (May 1967) seems to be
a counterpart of the eruptions that formed the Pleistocene
móberg mountains (Kjartansson 1966). This is true in regard
to (1) the successive stages of activity and (2) the resulting
rock facies and to some degree even (3) landscape forms.
During the eruption of Surtsey about nine craters have so
far been active spread over an area of not less than 9 km2.
Most often the only c.rater was active at the time. The most
productive part, near the centre of the active area became
an island, Surtsey itself, 2,7 km2 and 175m high above sea
level, piled up where the sea was 125—130 metres deep be-
fore the eruption.