Náttúrufræðingurinn

Volume

Náttúrufræðingurinn - 1966, Page 35

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

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