The temporal stability and activity of landslides in Europe with ž ...

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Moreover, they do not give the quantitative characteristics
and physical background of the temporal
moving pattern in the past nor they reliably indicate
future patterns of activity. Methods are available to
distinguish between active and inactive landslides,
but a larger number of mutually supportive and
complementary methods are required to assess the
past, present and possible future patterns of behaviour.
A detailed diagnosis for activity requires
more detailed geological–stratigraphical data and
field observations and especially more elaborate
methods of modelling and analysis. Earth sciences,
hydrological sciences and geotechnics have methods
and models suitable to carry out these tasks.
One major task of the temporal stability and
activity of landslides in Europe with respect to climatic
change Ž TESLEC. project was to combine the
resources of these disciplines by focusing them on
the solution to this problem. A further task of the
TESLEC project was the identification of the temporal
stability condition of landslides which serves as a
necessary calibration to assess the future slide behaviour
under a changed climate. The results are
supposed to improve the predictability of future
landslide activities by means of a better understanding,
firstly, of the climatically caused fluctuations in
slope stability and, secondly, of the dominant parameters
which control the activity of landslides.
The purpose of this paper is to summarise the
objectives, methodologies and achievements of the
TESLEC project. It will identify the constraints and
opportunities that have arisen in the course of the
research. In addition, the value of the results will be
discussed and directions for further research will be
identified. Different landslide test sites in Europe
have been selected in order to achieve the aims of
the project. The main criteria for the selection of the
test sites were related to: Ž. 1 the existence of ongoing
research with landslide monitoring andror historical
data, Ž. 2 site specific hazard potential, Ž. 3
high recent landslide activity, and Ž. 4 the requirement
that different landslide types be included. Thus,
research was focused on site specific scales, which
means that the representativeness of each particular
site was not the major objective of site selection.
Depending on the test site, the temporal scale of the
research covered a wide range including historical
events as well as present activity.
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R. Dikau, L. SchrottrGeomorphology 30 1999 1–12
Key questions related to climatic signals in landslide
processes were discussed on the European Science
Foundation workshop ‘‘Rapid mass movement
and climatic variation during the Holocene’’ at the
Academy of Sciences, Mainz, Germany in 1993
Ž Matthews et al., 1997 . . The discussion was focused
on the climatic controls on rapid mass movements
during the Holocene. The general conclusions show
that despite many landslide data sets available, too
few high quality records are able to give a continuous
picture even of single sites. It has been further
shown that while the data records contain a climatic
signal, non-climatic factors Žgeology,
geomorphology,
human impact. significantly influence the climatic
signal. It was stated that more work has to be
done in correlating precipitation proxy data with
rapid mass movement records including rainfall
threshold models for regions with similar climate. A
further aspect concerning the character of the climatic
signal itself and its change in time has been
stressed by Thornes Ž 1987. and Crozier Ž 1986, 1997 . .
Thornes Ž 1987. discussed the problem of changing
behaviour of state variables in dynamical systems.
Applied to landslide response and rainfall triggers
the different types of behaviour that could help in
understanding the character of change as follows:
– damped behaviour, when landslide activity declines,
e.g., because of decreasing material
availability Ž Crozier and Preston, 1998 . ;
– gradual behaviour, when landslide activity increases,
e.g., because of a decrease of the factor
of safety in time Ž Popescu, 1996 . ;
– explosive behaviour, when a progressive increase
of landslide activity occurs Že.g.,
due to
deforestation, Crozier and Preston, 1998 . ;
– periodic behaviour; and
– unsystematic behaviour.
Crozier Ž 1997. discussed different climatic signal
types responsible for the triggering of landslides
including Ž. 1 frequency, Ž. 2 magnitude, and Ž. 3 duration
of rainfall and emphasised different changing
climatic conditions responsible for a change in these
rainfall attributes. This means that at least for periods
for which rainfall records are available Žapproxi-
mately 1850 to the present . , trend analysis of precipitation
data Ž Schonwiese ¨
and Birrong, 1990. is a