Jökull - 01.12.1985, Page 20

Fig. 10. The coastal cliff sections 2
and 3 in Haelavík. For legend see
Fig. 8.10. mynd. Strandsnið 2 og 3
í Hœlavík.
likely that zone A in reality represents the true Weichse-
lian maximum position of the ice front outside Adalvík.
Stadarvatn and Thverdalur: At southeastern Adalvík,
glacial striae (direction from 164°) at 140 m altitude on
the west end of the Hvarfnúpur mountain (Figs 6 and
11) show that an actively eroding glacier of at least that
thickness at one time expanded from the mouth of the
Stadarvatn valley. Younger stages of this glacier are
indicated by the following features:
(1) On the southern slopes of the Stadarvatn valley,
about 1 km west of the lake, there is a set of subglacially
engorged eskers (Sugden and John 1976, p. 331) run-
ning perpendicular to the slope (Fig. 11).
(2) Between the west end of Hvarfnúpur and the
mouth of Thverdalur a higher set of lateral deposits are
found between 70 m and 50 m altitude (Fig. 11). The
sediments are a rather coarse supraglacial till with hum-
mocky surface, and with irregular drainage channels
trending down towards the valley.
(3) Directly below follows another set of lateral
deposits, situated approximately between 50 m and 35
m. These are less hummocky, contain more glaciofluvial
material and the drainage channels here run parallel to
the main valley.
(4) These two sets of lateral deposits seem to corre-
spond to a terminal moraine zone, about 500 m wide, at
the mouth of Thverdalur, deposited by a glacier in that
valley and with superimposed drainage channels runn-
ing outwards from Thverdalur. The proximal part of the
moraine zone lies around 70 m and the distal part
between 40 m and 25 m. The distal slope is steep which
could indicate either a deposition against a glacier in the
Stadarvatn valley or erosion by such a glacier.
(5) The final recession of Stadarvatn glacier to behind
the present coastline and to the conspicuous Stadarvatn
moraines, just west of the Iake (Fig. 11), was related to
a sea level about 15 m higher than today. This is
indicated by (a) the altitude of the inner part of a wide
abrasion terrace in front of the Stadarvatn moraines,
coinciding with a change from clearly supramarine till to
a sandy, gravelly cover on and around these ridges, and
(b) a distinct beach cliff below the mouth of Thverdalur.
These features are found between 17 m and 14 m, the
approximate level of the local marine limit.
A section along the stream draining Stadarvatn,
slightly west of the lake (section in Fig. 8, position in
Fig. 11), shows, from bottom and up, a rather sandy till
covered by a bed of glaciofluvial sand and gravel, about
1 m thick. The upper bed is gravelly in its lower and
upper parts, but sandy in the middle. It lies roughly 16—
17 m above present sea level, which corresponds to the
marine limit, and thus sea level probably stood below
the 16—17 m level when the sand/gravel bed was depo-
sited. The glaciofluvial sediments are covered by
another sandy till, about 5 m thick, with large boulders
on its surface. How far the glacier depositing the upper
till reached can not be determined, only that after a
probable initial deglaciation, at a sea level below 16 m,
the Stadarvatn glacier readvanced. There are two alt-
ernative interpretations of the glacial geology here:
(1) That a first retreat of the glacier into the Stadar-
vatn basin took place when sea level stood rather low
(see stratigraphy at Látrar described below). Later the
glacier readvanced across the glaciofluvial deposits on
top of the lower till, without disturbing them, to beyond
the present coastline, forming the lateral terraces at
50-35 m. Probably sea level was rising at the time.
Later the glacier started to disintegrate, the subglacially
engorged eskers were deposited, and the active front of
the glacier retreated to a position immediately west of
18 JÖKULL 35. ÁR