Jökull - 01.12.1957, Blaðsíða 26

Fig. 3. The main outlet of the
hlaup from Kötlukvos on June
25th 1955.
Aðalútfall hlaupsins frá Kötlu-
kxios.
Photo S. Thorarinsson
July 3rd 1955.
mind it seems to me that with our present
knowledge of the topography of the Katla area
and of the thickness of the ice in that area
it is no longer very problematic how a volume
of water big enough to cause the tremendous
maximum discharge of the Kötluhlaups, can be
stored there subglacially. The Table shows the
difference in height between the surface of the
stored water at the beginning of the jökul-
hlaups mentioned in the paper, and the outlets
of respective hlaups at the glacier margins. I
liave assumed that the thickness of the ice above
the stored water in Kötlukvos and Skaftárkvos
was ab. 200 m at the beginning of the hlaups,
which of course is a rough estimate. Further the
Table shows the horizontal distance between
the storage areas and the outlets of the hlaups
at the glacier margins, i.e. it shows the distance
the hlaup has to force its way under ice. It
seems to me justified to draw the conclusion
that the bigger the vertical difference is, com-
pared with the horizontal distance, the bigger
is, ceteris paribus, the maximum discharge of
the hlaup compared with the total volume of
the discharged water. The thickness of the
ice under which the water has to force its way,
the absolute length of the subglacial route of
the hlaup and the volume and depth of the
water in the reservoir also influence the lilaup-
type (cf. the difference between the 1934 and
1954 Grímsvötn graphs). The subglacial topo-
graphy also plays some role. From these con-
siderations one would conclude that hlaups
caused by eruptions in Oræfajökull should be
decidedly of the Katla type. An eye-witness’ de-
scription of the 1727-hlaup ancl that little we
know about the hlaup in 1362 rather supports
that conclusion.
Height difference: surface of stored water/outlet at ice margin m Horizontal distance: storage area/outlet m Height difference: horizontal distance
Kötlukvos - 900 14 000 1: 16
Grímsvötn 1330 50 000 1: 38
Skaftárkvos ^ 650 42 000 1: 65
Grænalón 500 20 000 1: 40
Gjánúpsvatn 80 3 800 1: 47
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