Mass Movement Processes Under Changing Climatic and Socioeconomic Conditions - Sustainable Development in Mountain Regions: Southeastern Europe - page 21

topography, parent rock material, the genesis of loose material and soil are relevant.
They assign the effects of gravitation (slope angle) and the countering forces (fric-
tion angle). They also affect the water regime (infiltration, water storage capacity).
The varying availability of material in the circle of soil generation, erosion
and transport on slopes and in channels may be appointed as variable disposition
(Fig. 3.1 ) as well as the complex of land use and vegetation, which is often sub-
jected to the turn of seasons. Also road constructions and other building projects as
well as protective measures like drainages or constructions in varying conditions are
important factors.
Triggering effects of spontaneous, shallow landslides are predominantly heavy
precipitation and earthquakes in seismic active zones. Depending on soil properties,
the role of precipitation differs in amount and period. Debris or mud flows may
be triggered by several factor combinations; the role of precipitation intensity and
amount vary accordingly. Usually, they are not directly caused by earthquakes but
they may emerge from seismic triggered landslides.
Except for the factor precipitation, none of these factors includes a time compo-
nent. For this reason, it is hardly feasible to determine the frequency of occurrence
and even less the changes in the frequency-magnitude function caused by climate
change.
3.2.2 The Event of 2005 (Communities of Gasen and Haslau,
Austria)
Between the 20th and 22nd of August 2005, an extreme precipitation event produc-
ing about 200 mm of rainfall within 36 h (>100 years return period) triggered off
several shallow landslides and mud flows (Fig. 3.2 ).
As an additional triggering factor, a high soil moisture content acting as a critical
pre-condition was considered. The conjunction of these adverse climatic conditions
can be assessed as very rare (>>100 years return period, Andrecs et al., 2007 ).
The variable disposition for spontaneous landslides of the area may be consid-
ered all in all as high because of extensive road construction especially for forestry
measures. About 2/3 of the surveyed landslides were triggered (or increased in
magnitude) because of improper road slopes. Debris- or mud-flow events were not
affected that adversely by road construction - in some cases, material deposition on
the roads could even stop or attenuate small debris flows.
In relation to the part of the surface, agricultural areas were affected more seri-
ously by landslides than forestry areas although forestry areas are to be found
predominantly in the steeper parts of the region.
If they are affected, the woody debris will cause quite often problems by
impairing protection measures (Fig. 3.3 ) and jamming channels.
The basic deposition of the area is high due to the lack of glaciation during the
last ice age. Therefore, thick soil and loose material horizons could develop.
Considering long periods, it seems that socioeconomic changes in the area have
led to damages and to an increase of vulnerability, the extent of which had never
been possible before.