Jökull - 01.12.1967, Side 17

The time of beginning of the rockslide was
determined by an earth tremor registered on
the seismograph at Kirkjubæjarklaustur, 75 km
east of Steinsholt. Ragnar Stefánsson, seismo-
logist at the Geophysical Section of the Meteoro-
logical Office, Reykjavík, has informed the
author that this tremor consisted of microseis-
mic surface waves of unusual character, beginn-
ing at 13 h. 47 min. 55 sec. (Icelandic Mean
Time) and lasting for 2 minutes. The time of
the tremor is in such a good agreement with
the timing by eyewitnesses of a later phase of
the hlaup, namely the flood in Markarfljót
(see Table 1), that it is concluded that the
tremor was svnchronous with, and was caused
hy, the rockslide in Steinsholt.
The scar left by the rockslide on the moun-
tain side has at its head a 975 m long scarp,
running almost straight north-south for most
of its length and rising up to 320 m above the
surface of the glacier. This scarp has a smooth
face. In profile it is curved, almost vertical some
100 m down from the top and then with gra-
dually decreasing slope towards its foot, where
it disappears under the vast heap of debris.
This form of the profile indicates a plane on
which the mass of rock slid down (Fig. 4).
Near the southern, or right, margin of the
Fig. 3. Map of the area affected by the rockslide (cf. Fig. 2), drawn by Á. Bödvarsson after
aerial photographs taken by the Icelandic Survey Department on 27th September, 1967.
3. mynd. Kort af Innstahaus og Steinsholtsjökli eftir hrunið (sbr. 2. mynd). Agúst Böðvarsson
teiknaði eftir flugmyndum Landmcelinga Islands frá 27. september 1967.
JÖKULL 17. ÁR 251