Náttúrufræðingurinn

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Náttúrufræðingurinn - 1981, Qupperneq 8

Náttúrufræðingurinn - 1981, Qupperneq 8
Grein þessi er fyrsta yfirlit en ætlunin er síðar að gera nánar grein fyrir athug- unum, sem eru i gangi varöandi þau málefni, sem hér er drepið á. HEIMILDIR Einarsson, Einar II. 1975. Mýrdalur. Árbók F.I. Rcykjavík. Fairbridge, R. & fíourgeois, J. 1978. The Encyclopaedia of Sedimentology. En- cyclopedia of Earth Science Series, Vol. VI., Dowden, Hutchinson & Ross, Inc., Stroudsburg, Penn. Jóhannsson, Guðgeir. 1919. Kötlugosið 1918. Ársæll Árnason, Reykjavík. Jónsson, Jón. 1969. Athuganir varðandi skipulagningu byggðar á sandinum austan við Reynisfjall I Mýrdal. Grein- argerð til skipulagsstjóra, nóvember 1969. — 1975. Um Kötluhlaup og hættu af þeim fyrir Vík í Mýrdal. Greinargerð fyrir Al- mannavarnaráð, desembcr 1974. Loftsson, Markús. 1880. Rit um jarðclda á ís- landi. Reykjavik. Markússon, Kjartan L. 1969. Kötlukletlur. Lesbók Morgunblaðsins, bls. 573. Skýrslur um Kötlugos. Safn til sögu Islands IV. Kaupmannahöfn & Reykjavík 1907-1915. Sveinsson, GLsli. 1919. Kötlugosið 1918 og af- leiðingar þess. Gutenberg, Reykjavík. Sveinsson, Páll. 1930. Kötluför 2. septembcr 1919. Vestur-Skaftafellssýsla og íbúar hennar. Útgefandi Björn O. Björnsson. Thoroddsen, Þorvaídur. 1920. Vulkancn Katla og dens sidste Udbrud 1918. Geografisk Tidsskrift Bd. 25, Kobenhavn. SUMMARY On the nature of Katla floods By Jón Jónsson National Energy A uthority Reykjavík, Iceland The tremendous floods caused by the eruptions of the Katla subglacial volcano in Iceland are commonly termed glacier bursts (Icel. jökulhlaup). This is not quite correct. Thc initial phases of the Katla floods are belter described as Lahars, debris flows or perhaps still more correct as volcano-glacial debris flows (Fairbridge & Bourgeois 1978) as they consist of a mixture of primary vol- canic material, tephra, sand, clay, rocks in all sizes, water, fragmentary glacier ice and larger icebergs. The specific gravity of this mixture is supposed to be 2,6—2,7 or even ntore. This seems to be the only way to explain the facts that, firstly a rock the size of Kötluklettur (Katla rock, see photo) which is estimated to be approx. 1400 metric tons could be trans- ported a distance of at least 15 km in the flood of 12th October 1918, secondly that the coastline was moved out approx. 4 km and out to a depth of 40 m in less than 24 hours and thirdly that the icebergs were carried on top of the flood. The origin of the flood water is supposed to be threefold. 1) from a subglacial lake around the volcanic vent, 2) rapid melting of the ice perhaps several days before the eruption started and 3) tremendous amount of ground water in and around the volcanic vent. 86
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