Jökull - 31.12.2001, Blaðsíða 5

Geomorphology of Ódáðahraun
mate change. Determining whether present-day ero-
sion is a natural or human-induced process has clear
implications for decision-making and soil protection
measures.
Systematic research in the study region, how-
ever, is severely hindered by a lack of detailed
land cover maps depicting the distribution of various
geomorphological features and sedimentary deposits.
The national mapping of the land degradation (Arn-
alds et al., 1997), and the Geological Map of Ice-
land 1:500 000 (Jóhannesson and Sæmundsson, 1998)
have been the principal sources of information for the
region as a whole.
THE OBJECTIVE
As the Odáðahraun area is remote and difficult to ac-
cess, very few systematic studies have been conducted
in this region. Too little is therefore known about the
history of these landscapes and their erosion processes
to allow conclusive statements about the relative im-
portance of anthropogenic or endogenous forces in
this area. Based on pilot studies in the region (Káyhkö
and Worsley, 1997; Kayhkö, 2000), and recently pub-
lished literature (e.g. Arnalds et al„ 1997) we argue
that more comprehensive studies on the distribution
of sediments and the adjacent geomorphological pro-
cesses in the Odáðahraun region are needed in order
to unravel the past and present land degradation pro-
cesses.
In this paper we report a study of the geomor-
phology of the Odáðahraun area using a Landsat The-
matic Mapper (TM) land cover classification and de-
tailed field studies. Our primary objective was to in-
crease our understanding of the region’s geomorpho-
logical features and processes, and their relation to
land degradation.
CHARACTERISTICS OF THE STUDY
AREA
The Ódáðahraun area consists of barren lava flow
fields and loose surface sediments with scanty patches
of vegetation, and is bordered to the south by Dyngju-
jökull, an outlet glacier of the Vatnajökull ice cap. The
glacially fed river Jökulsá á Fjöllum runs from the
ice cap along the eastern margin of the area towards
the north, where it drains into the Atlantic Ocean at
Öxarfjörður. Five volcanic systems are located in or
near to the study area (cf. Figure 1). Lake Mývatn,
situated in the north-west of the study area, marks
the westem border of the Ódáðahraun lava forma-
tion. At present, the advancing northern margin of
the Ódáðahraun semi-desert is located near the road
no. 1 between Reykjahlíð and Grímsstaðir.
Climate
The area north of Vatnajökull has been characterised
by Hallgrímsson (1969) as the most continental of the
climate regions in Iceland, with relatively low precip-
itation, a large annual temperature range, and short
spring and autumn seasons. Limited long-term cli-
matic statistics are available for the interior of Iceland
and the current study area. The mean annual precipita-
tion for 1931-1960 at Grímsstaðir was a mere 355 mm
(cf. Ashwell, 1986); and for 1961-1990 at Reykja-
hlíð, 435 mmyr_1(Einarsson, 1994). The mean an-
nual temperature in the Ódáðahraun area was 0°C for
1931-1960, and 0.7°C for 1961-1990.
Southwesterly winds prevail in Iceland. Ashwell
(1986) has demonstrated that the Vatnajökull ice cap
has a profound regional influence on wind direction,
generating a high-pressure field and thus katabatic
winds. Ashwell (1986) has also observed that the
wind direction varies from southwest to west near
the ice cap margin, and from south to southeast fur-
ther north. Observations made during this study of
ventifact orientation generally demonstrate the same
pattern of dominantly southwesterly winds. A local,
southeastern anomaly in ventifact orientation, how-
ever, was observed on the summit plateau of Dyngju-
fjöll ytri.
Tectonic processes
The study area is located at an extensional plate
boundary. During rifting events, such as the rifting
eþisode in 1975-1984 at Krafla, widening at these
boundaries results in fractures and faults that often oc-
cur in swarms and intensively alter the landscape. Our
study area covers four en echelon tectonic swarms be-
longing to the volcanic systems of Kverkfjöll, Askja,
Fremrinámar and Krafla (Björnsson, 1985). The
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