Jökull - 01.12.1967, Blaðsíða 20

Fig. 6. The top of the rockslide scarp. — Photo G. Kjartansson, June 30, 1967.
6. mynd. Brún hrunstálsins i Innstahaus; horft norður.
Ice fragments dominated near the right (east)
side of the glacier whereas rock fragments
dominated to the left (west) side. In June most
of the ice had melted so that the glacier tongue
turned quite dark.
The debris was not confined to the surface
of the glacier, but ice blocks were thrown up
to a distinct height limit on the steep valley
sides. Viewed from distance this limit was
marked with a white stripe, continuous for
about 1200 m, on the right slope of the valley.
Apart from its remarkable height, up to 75 m
above the valley floor, and its undulating form,
this stripe was similar to the high water mark
on a river bank after a great flood with drift-
ing ice (Fig. 10).
But by the time of the hlaup, no adequate
body of water can possibly have been stored
in the track of the hlaup above the glacier
snout. It is therefore assumed that some other
material has transportecl the ice blocks up to
this distinct height limit. Most likely compress-
ed air, trapped by the rock-fall, was responsible.
In front of the glacier the rushing mass,
consisting of a mixture of rock and ice frag-
ments and compressed air, swept along with it
the water of the lake Steinsholtslón. Then.
augmented with this water, the whole mass
travelled at great velocity down the valley of
the Steinsholtsá.
However, the lake was not drained in the
way that its outlet was lowered by erosion. On
the contrary, its level rose some 7 m due to
deposition of hlaup debris in front o£ it. As
254 JÖKULL 17. ÁR