Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 127

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tuff. The narrow Sveifluháls ridge was formed later by up-
lift of part of these strata. One main fissure producing these
tuffs has been the Vatnshlíð faultline, as evidenced by the
dip of apparently undisturbed tuffs on the west side of Lamb-
hagatjörn and the occurrence of large hombs there.
When the Sveifluháls was formed, hy an uplift of 200 m
or more, many deep parallel fractures resulted, along its crest
and in the slopes, and here volcanic activity was revived at
least two times, producing first a hreccia cover in the east
slope and later a few lava flows. In the following we will refer
the main tuffs of Sveifluháls to a Phase I, the breccia to a
Phase II, and the lavas to a Phase III.
The tuffs of Phase I are finely stratified fine, medium, and
coarse tuff with an occasional coarser layer of homb frag-
ments. Near the summit ridge was found a piece of coarsely
crystallized xenolith included in the tuff.
The stratification in the central ridge is broadly horizontal
although much twisted and faulted, but towards the eastern
side (in the area above Innri Stapi) the strata turn suddenly
over to the vertical. Along the central axis various faults and
dislocations are seen and the weathering has added much to
the rough and often fantastic forms seen here. This is evi-
dence of prolonged weathering which occupied much more
than the post-glacial time. This is also verified by the ah-
sence of glacial vestiges on the ridge while such are found
at lower levels as we shall see.
Along the west coast of Kleifarvatn the tuffs of Phase I
are seen at several places, the main outcrops being the pro-
montories Innri Stapi, Syðri Stapi and an unnamed headland
between them, which here might be called Miðstapi. The pro-
montories show clear evidence of much shore erosion at a
level of about 45 m above the present lake (which is given
as 135 m), cf. Fig. 63. To judge from the remnant of a lava
flow on the abrasion plane of Innri Stapi it seems likely that
the promontories represent remnants of a more general abra-
sion bench. The high level of the lake will be called the Stapi