Jökull

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Jökull - 31.12.2001, Qupperneq 5

Jökull - 31.12.2001, Qupperneq 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 JÖKULL No. 51 3
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