Jökull - 01.12.1990, Page 59

Figure 7: Glacial directional features in the
Sprengisandur area. For legend, see Fig. 2. — Skrið-
stefna jökuls og jaðarmyndanir á Sprengisandi. Sjá
skýringar á mynd 2.
ull (Kaldal 1978; 1982), and mark an ice lobe, which
moved to the north and NE in the Sprengisandur area.
The general ground surface slope towards the re-
treating ice front in this area resulted in formation of
'mpressive ice contact sandur plains in front of the
glacier. As the subglacial rivers lost their transport-
lng capacity, prominent eskers were built up behind
the end moraines. Some of the eskers can be traced
°ver 14 km and terminate in proglacial sandur plains.
Fluted moraine in front of Þjórsárjökull indicates some
glacial input from the Hofsjökull area at this time.
The area between Þjórsá and Kaldakvísl rivers
— The oldest indication of glacier movement is to-
wards the SW as in the other areas (Fig. 6). Youngest
striae show movement towards west and NW, shift-
ing progressively to the north as the glacier retreated.
Few, but prominent, end moraines have been found in
this area. An end moraine can be traced for 10 km
along the Búðarháls ridge (Kaldal, 1984; Kaldal and
Vilmundardóttir, 1986). When the glacier margin was
at the southem slope of the ridge, a subglacial erup-
tion took place, producing large amounts of ash and
pumice, found as terraces in connection with the end
moraine. The same tephra is found mixed with till at
many places inside the former glacier margin. A short
end moraine is at the northem end of Kjalvötn (Kaldal
et al., 1990), possibly of similar age as the Búðarháls
end moraine.
Tungnaárörœfi — In the area between Kaldakvísl
and Tungnaá, information about the ice recession is
lacking, because extensive areas are covered with
postglacial lava or tephra. The bedrock consists of
hyaloclastites, which preserve striae badly. The striae
found, confirm the theory mentioned before, that ice
movement in this area shifted progressively towards
north. No traces of former ice margins can be found
until to the north of Jökulheimar near Tungnaárjökull
(Fig. 6), where small proglacial lakes were formed to
the north of the glacier margin. With help from several
successive shorelines and terraces, one can reconstruct
the local recession of the glacier.
The area between Tungnaá and Skaftá rivers —
Few glacial movement indications have been found in
this area, but mapping is not finished yet. The bedrock
consists mostly of hyaloclastites and all depressions
are filled with tephra. Nevertheless it seems clear that
the ice divide of the last remnants of the main ice
was situated here. To the north of Grænifjallgarður
(Fig. 6) striae show movement towards the NNW but
in the Langisjór depression striae point towards SE.
OTHER HIGHLAND AREAS
Correlation to other parts of the interior highland
is fairly difficult since adjacent areas have not been
mapped yet.
East Iceland Highlands — Aðalsteinsson (1987)
mapped glacial features in an area to the north of
Vatnajökull, extending from the Vopnafjörður high-
lands to the glacier snout of Brúarjökull. End moraines
show that a broad ice lobe has repeatedly surged to-
wards north during the deglaciation period, resembling
JÖKULL, No. 40, 1990 57