Jökull - 31.12.2001, Blaðsíða 3

Reviewed research article
/
Geomorphology of the Odáðahraun semi-desert, NE Iceland;
a Landsat TM - based land cover mapping
Jukka Kayhkö*, Petteri Alho, Johan P. M. Hendriks and Matti J. Rossi
Department of Geography, University ofTurku, 20014 Turku, Finland; jukkay@utu.fi
Abstract - This research reports investigations on land degradation processes in the Odáðahraun region,
northeastern Iceland, using land cover classification based on Landsat TM satellite data andfield studies. The
main objective is to increase understanding ofthe geomorphologicalfeatures and processes, and their relation
to land degradation in the study region. A floating Landsat TM quarter scene from July 1992, covering an area
from the northern margin of Dyngjujökull to Öxarfjörður, was subjected to unsupervised Isodata clustering.
Extensive field checks with detailed descriptions ofvarious land-cover types allowed subsequent analyses ofthe
classification resulting in 19 land cover classes in three surface categories: lavas, sediments and miscellaneous
(including vegetation, snow, ice, etc.). The image interpretation also revealed several sediment bodies, which
may indicate the characteristics of the geomorphological processes operating in the region: 1) the elongated
SSW-NNE oriented aeolian sand stretches in the western half of the study area, and 2) the distinctive flood
deposits along the Jökulsá á Fjöllum course, demonstrating the magnitude ofthe past catastropliic jökulhlaups
(glacial outburst floods). The presented land cover classification will serve as the basis for planning and
focusing future investigations on the past and present geoecological processes operating in the region.
INTRODUCTION
Soil erosion is a major environmental problem in Ice-
land (e.g. Arnalds, 1987; Arnalds et al., 1997; Arn-
alds, 2000). Studies across Iceland have demonstrated
that soil erosion rates increased substantially after set-
tlement ca. 874 AD, in the form of a 4- to 8-fold in-
crease in the deposition rate of aeolian and tephra ma-
terials in soil profiles (e.g. Þórarinsson, 1961). More
generally, Iceland has suffered for centuries from loss
of forest cover, resulting in only 1% woodland cover-
age at present.
Along the Northern Volcanic Rift Zone, north of
the Vatnajökull ice cap, vast deposits of gravel, ae-
olian sand and loess blanket an otherwise barren,
severely eroded landscape characterized by abundant
lava fields (Figure 1). At the margin of this degraded
region, advancing fronts of windblown sediments de-
stroy vegetated land cover, threatening pasturelands
and human settlements. Substantial national efforts
have been made for decades to halt the degradation
process.
Unfortunately, the environmental factors that
maintain and expand this barren semi-desert are still
poorly understood (Arnalds, 2000). Human activity,
in the form of deforestation and grazing by sheep and
horses, is one explanation for this continuing degrada-
tion, and a link between land degradation and human
impact has been indisputably documented in several
studies in the coastal areas of Iceland (cf. Dugmore
and Buckland, 1991; Einarsson, 1994; Simpson et al.,
2001). An additional explanation for this degradation
is the influence of natural processes, namely, volcanic
eruptions, tephra falls, glacial outburst floods and cli-
* Formerly at: Postgraduate Research Institute for Sedimentology, University of Reading, United Kingdom
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