Náttúrufræðingurinn - 1981, Page 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.
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