Jökull - 01.12.1982, Page 19

°r less in the Eyvindará andSeyðisfjörðurareas. An
estimated total of 2000 km! has been eroded from
above the 850 m surface.
THE 650 M EROSION SURFACE
A 650 m erosion surface is developed on the
gently undulating plateau of Fljótsdalsheiði bet-
ween Fljótsdalur and Jökuldalur (Fig. 4) rising
above 700 m at only one point. The large rivers flow
across the area in deep glaciated valleys, and isolat-
ed mountains of accumulation such as Snaefell,
built by intraglacial eruptions, rise well above the
650 m surface.
A 650 m summit level is poorly developed on the
ridges near the eastern fringes of the Austfirðir, for
example on either side of Borgarfjörður, north of
Seyðisfjörður, and near Viðfjörður. In addition a
few ílat-topped ridges and mountainside benches
are seen in the middle of Austfirðir, notably Fossár-
fell (west of the head of Berufjörður) and west of
Seyðisfjörður.
The total amount of downcutting to the 650 m
surface was 1000 m west of Berufjörður, 800 m at
Viðfjörður and Breiðdalsvík, 600 m at Seyðisfjörð-
ur, about 400 m at the Lagarfljót and 100 m at the
western limit of the map, and the total rock eroded
from above it is estimated at2800 km!.
LOWER SURFACES
Between the lower parts of Fljótsdalur and Jökul-
dalur the 650 m surface descends rather abruptly to
an ill-defined undulating surface at about 200 m, a
similar surface is found west of the Smjörfjall, and a
bench at about 200 m is often found in the Austfirðir
especially at or near the seaward end of a promont-
ory as at Djúpivogur. These may be remnants of
an ill-defined 200 m surface.
A prominent postglacial raised beach is encount-
ered at 40 to 50 m above sea level as a terrace at the
head ofeach fjord, and as deltas where side streams
enter fjords. The broad terrace at Breiðdalsvík was
Fig. 5. Geomorphology
of a typical section of
the Austfirðir, that
around the head of
Reyðarfjörður.
Mynd 5. Landmótun á
dœmigerðum hluta
AustJjarða.
Alluvium
Raised beach gravels
■ Probable river course
on 650 m. surface
Wind gap resulbing
from river capture
■ Land above 650 m.
> 650 m'
i 850 m.
i ilOO m.
Remnants o-f
■ erosion
surfaces
'w'
«25
Corrie
Glacier
Moraine
j ð K Ð U R
JÖKULL 32. ÁR 17