Náttúrufræðingurinn - 1966, Page 35

NÁTTÚRUFRÆÐINGURINN
181
hyaloclastites, pillow lava and lava. As regards structure and build up Surtsey
is thus a striking parallell to the Icelandic tablemountains or the tuyas of
British Columbia, tlie socles of which also were built up under water (melt-
water) within the Pleistocene ice sheets according to the view of G. Kjartansson,
W. H. Mathews and others, now generally accepted. Tlie main difference one
may expect between oceanic and glacial tablemountains is that airborne pyro-
clasts (tephra) constitute a proportionately greater part of the oceanic ones
as they are piled up in an open and often stormy sea wliicli is likely to prolong
the explosive (phreatic) activity wliereas the glacial tablemountains were piled
up in calm water. Capelinhos in the Azores was built up 1957/58 in a similar
way as Surtsey although its effusive activity did not forrn a real lava shield.
Surtsey is in many ways very interesting from a geomorphological point of
view. Exogenic agencies, especially marine abrasion and wind erosion, work
tliere with an astonishingly great speed and one can there study their effect
on a landscape of a known initial stage. Especially remarkable are the rapid
changes of the coastline because of erosion in some places, deposition in other.
Pl. II a and b and Pl. III a show three stages in the development of the lava
shore on the south side of the island. The rounding of gravel and blocks has
also been remarkably rapid.
Guðmundur E. Sigvaldason:
Um rannsóknir á gosefnum
í grein þessari segir £rá því starl'i, sem unnið hefur verið af jarð-
fræðingum Atvinnudeildar Háskólans í sambandi við Surtseyjar-
gosið. Tilgangur greinarinnar er ekki sá að gi'eina frá niðurstöðum
rannsókna, en öllu fremur reynt að skýra í almennu yfirliti hvað
Irefur verið gert og hversvegna. Þeir sem unnið liafa að þessu starfi
liafa skipt með sér verkum þannig, að Gunnlaugur Elíasson hefur,
ásarnt höfundi þessarar greinar, safnað lofttegundum og athugað
efnasamsetningu þeirra og útfellinga á yfirborði hrauna. Sigurður
Steinjrórsson hefur framkvæmt rannsóknir á efnasamsetningu og
bergfræði ösku og hrauns. Þá hefur Haraldur Sigurðsson unnið að