Jökull - 01.01.2009, Side 29

Chemical and mechanical fluvial denudation in cold environments
tors causing high sediment delivery rates from the
slope systems into the main channels during heavy
rainfalls. Heavy rainfalls in the Hrafndalur catch-
ment trigger debris flows and cause slope wash pro-
cesses and lead to high channel discharges, suspended
sediment and bedload transport rates (Beylich and
Kneisel, 2009).
In both Kidisjoki and Latnjavagge restricted sedi-
ment availability is a major controlling factor for sed-
iment transport by snowmelt-generated runoff peaks.
Runoff peaks are necessary to mobilise accumulated
material by breaking up channel debris pavements or
by channel bank erosion. In Latnjavagge, also slush
flows and ground avalanches can cause relevant sed-
iment transfers into the channels as well as a mobil-
isation of material during snowmelt. Stable vegeta-
tion cover in the Latnjavagge catchment and stable
slope systems buffer peak runoff (Beylich and Gintz,
2004; Beylich et al., 2006a). Similar conditions as de-
scribed for the Kidisjoki and Latnjavagge catchments,
with snowmelt-generated runoff peaks having a major
quantitative importance for annual sediment transport,
have also been reported from other cold environments,
e. g. from Spitsbergen (Barsch et al., 1994; Gude and
Scherer, 1999) or from northern Siberia (Beylich and
Gintz, 2004; Gintz and Schmidt, 2000).
CONCLUSIONS
The Hrafndalur catchment is characterised by rela-
tively high denudation rates with mechanical denuda-
tion dominating over chemical denudation. About
80% of the annual yield of suspended sediments is
transported during few days with rainfall-generated
runoff peaks over 40 mm d−1. High mechanical de-
nudation in this steep catchment can be explained
by high mechanical weathering rates of rhyolites
and by limited vegetation cover. Rainfall-generated
runoff peaks are of higher importance than snowmelt-
generated peak runoff, triggering debris flows and in-
creased slope wash processes and thus high sediment
delivery rates from the slope systems into the main
channels. Both the Kidisjoki and the Latnjavagge
catchments are characterised by clearly lower denuda-
tion rates. Chemical denudation dominates over sus-
pended sediment yields in both areas. In Latnjavagge
the low intensity of mechanical fluvial denudation is
mainly due to the closed vegetation cover. The low-
relief area of Kidisjoki is characterised by very low
mechanical fluvial denudation rates.
This study confirms the importance of seasonal
runoff peaks for annual fluvial sediment transport and
denudation rates. About 80–90% of the annual sus-
pended sediment transport and connected denudation
occurs within a few days during rainfall- (Hrafndalur)
or snowmelt-generated (Kidisjoki, Latnjavagge) peak
runoff. In Kidisjoki and Latnjavagge restricted sedi-
ment availability is a major controlling factor for sed-
iment transport dynamics.
These results are in agreement with a number of
other studies stating that chemical denudation is a
comparatively important denudative process in cold
environments. More quantitative studies on both
chemical and mechanical fluvial denudation are how-
ever needed to obtain more knowledge on the relative
importance and mutual relationship of both denuda-
tive processes under different environmental condi-
tions as well as on the varying quantitative importance
of seasonal snowmelt- and rainfall-generated runoff
peaks. Future studies in a wide range of cold environ-
ments will further contribute to our understanding of
the internal differentiation of such environments (see
Barsch, 1984; 1986; Beylich, 2000; 2008; Beylich
and Kneisel, 2009; Beylich et al., 2008).
ACKNOWLEDGEMENTS
Research was funded by the German Exchange
Service (DAAD) (1999–2001, grant to Achim A.
Beylich), the German Science Foundation (DFG)
(2002–2004, grant to Achim A. Beylich), FP5 EU
LAPBIAT (field work Kevo, 2003, to Achim A.
Beylich) and the Geological Survey of Norway
(NGU) (since 2004). The logistic support and hos-
pitality of the Kevo Subarctic Research Station, the
Abisko Scientific Research Station and the Latnja-
jaure Field Station are greatly acknowledged. Special
thanks go to Seppo Neuvonen and Ulf Molau for
the fruitful collaboration and for scientific discus-
sions. Great thanks go to the following assistants for
their work in field and/or in the laboratory as well
as for other technical support: Karin Luthbom, Sarah
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