Geoscience Reference
In-Depth Information
Table 2.6
Summary of slope denudation estimates and dominant sedimentary process characteristics in the Kärkevagge catchment
1952-1960. (Based on: Rapp 1960.)
Process
Ton-metres (vertical)*
Sedimentary characteristics
Transportation of salts in
running water
Earth slides and mudflows
136,500
Stream and lake solute loads derived from catchment-wide
chemical weathering
Sources include poorly sorted till deposits and talus material.
Deposition in bouldery mudflow levees, alluvial fans and sheet
deposits (sorted gravel and sand)
Slush avalanches. Transported material ranging in size from fine
silt to boulders up to 5 m in length
Includes: pebble falls, small boulder falls and large boulder falls
(varying in size from 10 to 100 m
3
). Rock-fall debris dominantly
20 -50 cm, largest boulders up to 5 m in length
Stony soil with occasional boulders. Vegetated or partly
vegetated surfaces. Develops solifluction lobe movements
4cmyr
−1
to depths of 50 cm
Coarse, clast-supported openwork surface with fine content
increasing with depth. Poorly sorted surface sediments varying
in size from small pebbles to boulders. Surficial rates up to
10 cm yr
−1
96,375
Dirty avalanches
21,850
Rock falls
19,565
Solifluction
5300
Talus creep
2700
*The tons-metres vertical concept was introduced by Jäckli (1957) and is calculated by multiplying the mass of sediment moved by the vertical
component over which the sediment is transferred.
of sediment fluxes, regardless of the contrasts in
scale, the coarse debris system (rock fall, snow
avalanches and debris flows) is significant, and
fluvial and channel processes are particularly
important (although this was not measured at
Kärkevagge). Slow mass movements tend to be
of far less significance. Drainage-basin scale is
important in determining the relative contribution
of such processes because as basin size increases
valley floor and channel processes become more
significant (Church & Ryder 1972; Church &
Slaymaker 1989).
The sediment transfer processes operating in
the Kärkevagge catchment are similar to those
operating in many mountain areas (Barsch &
Caine 1984) (Table 2.6). The sedimentary char-
acteristics of these processes reflect the source
sediments within the catchment and the process
dynamics that generate the subsequent sedi-
mentation patterns. The overall picture is one
of poorly sorted source sediments distributed
across a heterogeneous landscape. Differenti-
ation of these deposits predominantly occurs as
a result of gravitational sorting by rock fall,
frost sorting of susceptible soil and selective
transport by fluvial processes (Table 2.6).
When evaluating models of this kind it should
be kept in mind that Tables 2.5 and 2.6 and
Fig. 2.9b show average values only for sediment
fluxes and neglect the inherent interannual vari-
ability in such sediment systems and the longer
term dynamics of change that have an impact on
mountain environments. In order to evalaute such
changes longer-term sediment budget models need
to be developed. Such models can be developed
over historical time-scales using archival evid-
ence (Piégay et al. 2004); the late Holocene using
detailed lake sediment records and geochemical
analysis (Slaymaker et al. 2003) and soil geomor-
phology (pedology and weathering) (Birkeland
et al. 2003). Furthermore, previous sediment-
budget studies, such as the two examples provided
in Table 2.5, can provide important baseline
studies for later comparison with further sedi-
ment budgets or predictions of future change.
Such an approach has been developed for Rapp's
(1960) work in Kärkevagge in northern Sweden
by Schlyter et al. (1993).
Although the sediment budget framework is
important for establishing how mountain sedi-
ment systems operate and the relative import-
ance of different sedimentological processes,
