Jökull - 01.12.1978, Blaðsíða 20

The Deglaciation of the Area North and Northeast of
Hofsjökull, Central Iceland
INGIBJÖRG KALDAL
National Energy Authority, Reykjavík, Iceland
ABSTRACT
The recession of the Weichselian ice sheet in the
area to the north and northeast of the Hofsjökull ice
cap in Central Iceland is described. First the retreat
was towards soulheast but later turned more to the
south and southwest east of Hofsjökull. The recession
was interrupted by eight stillslands or readvances,
which are marked by end moraines and proglacial
sandur-plains. Generally the end moraines run per-
pendicular to the present margin of Hofsjökull. This
indicates that the Hofsjökull mountain area became
ice free at an earlier stage.
When the glacier margin was at the northernmost
end moraine, the Raudhólar moraine, a great jökul-
hlaup took place, caused by a subglacial eruption. A
huge. ice-contact sandur-plain was formed in this
jökulhlaup.
Most of the fluvioglacial deposits in the area were
laid down by rivers from the retreating Lateglacial ice
sheet. Rivers from the present Hofsjökull deposit
material only nearest to the glacier. Since meltwater
supply from the present ice cap has never been as great
as after 1920, most of these recent deposits were
formed in the present century.
The possible Búdi (Younger Dryas) age of the
oldest end moraine is discussed.
INTRODUCTION
The area dealt with in this paper is situated
to the north and northeast of the Hofsjökull
ice cap in Central Iceland (Fig. 1). A relatively
flat plateau rises from an approximately 600
m elevation above sea level at the edge of the
deep and narrow Skagafjördur valleys in the
north, and reaches 800—900 m in the south,
where the area is bounded by Hofsjökull. The
topography is characterized by low relief.
However some mountains, especially at the
northern margin of Hofsjökull, rise 150—250
m above the surroundings. The vegetation in
the area is sparse, concentrated along lakes
and rivers, with wide completely barren areas
in between.
The bedrock of the area is mostly covered
by glacial and fluvioglacial deposits. There-
fore, boundaries between the formations are
not always clear. The bedrock belongs to the
early Pleistocene Gray Basalt Formation and
the young Pleistocene Móberg Formation, the
basalts being inter- or supraglacial and the
móberg subglacial (Kjartansson 1965). Most of
the mountains to the north of Hofsjökull were
formed in subglacial eruptions on north-south
trending fissures, probably in late Weichselian
time. To the east of Hofsjökull the direction of
the fissures is northeast-southwest. One table-
mountain, Miklafell, was formed in the
northeast corner of Hofsjökull. The volcanism
has continued into Holocene time, and three
small Postglacial lavas were formed at the
northern margin of Hofsjökull (Kjartansson
1965). Their exact age is unknown.
THE DIRECTION OF
GLACIER MOVEMENT
Glacial striae, fluted surfaces and end mo-
raines show the direction of glacial movement
in the area to the north and northeast of
Hofsjökull (Fig. 1).
Glacial striae are common on lava expo-
sures in the area, except in the southernmost
18 JÖKULL 28. ÁR