Rit (Vísindafélag Íslendinga) - 01.07.1962, Page 128

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Fig. 63. Innri Stapi.
1 — tuff of Phase I; 2 = lava remnant; 3 = consolidated scree;
4 = breccia of Phase II.
level. Other remnants are Lambhagi on the east side of the
lake and a bench on the west side above the south end of
Lambhagatjörn.
Innri Stapi consists mostly of fine tuff but in its outermost
part is coarser stratified breccia and the horizontal surface
cuts variously dipping strata. The remnant of a horizontal
lava, already referred to, has been glacially striated in a
southwesterly direction.
Lambhagi consists of a coarse globular breccia. In a depres-
sion on its surface is preserved a weathering layer, derived
from the breccia, covered by a 3—4m thick succession of
light-brown consolidated stratified clay with clear wave marks.
There is also an occasional layer of debris weathered from
the breccia. Further there are some 5 darker layers of glass
fragments, either ash from eruptions or windblown dust from
the surrounding primary tuff-breccias. These layers, which
reach a height of about 30 m above the lake, have been de-
posited in shallow water; they were most reasonably formed
at the Stapi level of the lake. These rocks are cut off at the
steep western wall of Lambhagi; the wall has in part been
formed by erosion at the present lake level, but the wall falls
in line with a probably tectonic step of 60 m in the floor of
the lake (P. Hannesson 1941) and may therefore be mainly
tectonic. Possibly a median part of the lake bottom subsided
after the Stapi stage and this may even explain the drop of