Náttúrufræðingurinn - 1977, Page 13

rétt ummæli eins sjónarvottar nærri
upphafi greinarinnar eru úr bók Guð-
jóns Ármanns Eyjólfssonar: Vest-
mannaeyjar, byggð og eldgos (ísafold-
arprentsmiðja 1973).
S U M M A R Y
Tlie eruption fissures of the 1973
Heimaey eruption
by Sigurdur Thorarinsson,
Science Institute, University of Iceland.
On January 23, 1973, a fissure opened
up on Heimaey. This occurred between
die tinies of 0140, when, locally, a rather
strong earthquake shock was felt, and
about 0155, when an eruption started.
About 20 minutes later an almost con-
tinuous wall of lava fountains had been
formed on a 1.5 km long fissure running
N20°E througli eastern Heimaey. Eight
hours later the erupting fissure stretched
some 120 m northwards into the sea. By
1400 hrs on January 24, narrow non-
erupting fissures liad opened up between
the southern end of tlie eruption fissure
and the shore in Bót. That same day a
short ca. 12 m high ridge was built up
on the sea floor 0.9 km NNE of the
continuous Heimaey fissure (cf. Eig. 1)
and on February 0—7 submarine activity
in the same area built up another small
ridge and damaged an electric cable and
one of two pipelines carrying fresh water
from the mainland. Surprisingly, the
second pipeline remained intact although
situated between the two. At noon on
January 26, a small eruption was observ-
ed in the sea at Bót, some 300 m from
the southern end of the fissure. Tlie
Heimaey lissure system liad by then reach-
etl a length of 3.5 km and the submarine
activity of February 6 aclded very little
to that length.
On May 26, 1973, a month before the
end of the Heimaey eruption, signs of
submarine volcánic activity were observ-
ed between Heimaey and the mainland
only 4 km from the mainland. At 1400
hrs that day captain Bogi Finnbogason of
the fishing vessel Ver VE 200, observed
dead fish floating in a dark patch of sim-
mering sea. His echo-sounder registcred
wliat looked like a narrow column rising
from the sea floor at 38—40 fathoms (ca.
70 m) depth to about 18 fathoms below
sea level (Fig. 2). This column appeared
to consist of some scattered material
penetrable to a considerable deptli below
the sea floor.
It is suggested that the echogram re-
gistered lumps of lava and/or rock frag-
ments thrown upwards into the sea from
an eruption fissure and escaping gases
caused the surface to boil. This eruption
was probably of very short duration and
a Coast Guard vessel sounding the area
on June 17, 1977, did not find any ridge
on the sea floor in the area.
The overall length of the fissure system
formed during the Heimaey eruption
thus appears to be about 10 km, and to-
gether with the fissures tliat opened up
cluring the Surtsey eruption 1963—1967 it
forms a 35 km long lefl lateral en echélon
fissure system.
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