Open Session - SWISS GEOSCIENCE MEETINGs

2
Symposium 9: Natural Hazards and Risks
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Sar Interferometric Point Target analysis and interpretation of aerial
photographs for landslides investigations in southern switzerland
Ambrosi Christian*, Strozzi Tazio**
* SUPSI, Istituto Scienze della Terra CP 72, CH 6952 Canobbio (christian.ambrosi@supsi.ch)
** GAMMA Remote Sensing, Worbstrasse 225, CH 3073 Gümligen
(strozzi@gamma-rs.ch)
Information on landslide displacement from SAR Interferometric Point Target Analysis (IPTA) and sketch maps from aerial
photography interpretation are combined for the study of landslides in Ticino, Southern Switzerland. For current ITPA investigations,
ENVISAT and RADARSAT SAR acquisitions over the Swiss territory are used. Numerous unstable phenomena are
considered in this mountainous region, with an elevation range from approximately 200 m a.s.l. to more than 3000 m a.s.l.
The results achieved with IPTA are attractive to complement aerial photographs interpretation for the evaluation of the state
of activity of landslides over villages and in sparsely vegetated areas with numerous exposed rocks. On the other hand, over
vegetated areas (forests and meadows) IPTA failed to retrieve displacement information. Because displacement from InSAR
is recorded along the satellite line-of-sight direction, IPTA cannot be directly use for the determination of the intensity of
landslides in hazard mapping. In general, the actual displacement rate is larger than that recorded with InSAR. Over alpine
areas characterized by sparse vegetation, where snow cover limits the availability of a large number of SAR acquisitions,
conventional InSAR was successfully applied to estimate the motion of rockglaciers and other periglacial phenomena. For
vegetated areas and relatively rapid landslides L-band InSAR (JERS-1 SAR and ALOS PALSAR) has been found to be an efficient
solution.
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Interdisciplinary approaches to recognition, analysis and modelling in
sackung system and large landslides in southern Swiss Alps
Ambrosi Christian*, Pera Sebastian*
* SUPSI, Istituto Scienze della Terra CP 72, CH 6952 Canobbio (christian.ambrosi@supsi.ch)
A very large Deep-Seated Gravitational Slope Deformations and large landslides, affecting the slopes of Swiss Southern Alps,
have been recognised and mapped. Several active rotational and translational deep seated landslides occur in the lower part
of the slopes, often in association with rockslides at different scale. These phenomena show a different stage of evolution
along the flanks of the ridges.
Some of these landslides (Pontirone, Osco, Faido) has been recognised through different techniques. In particular, it has been
characterised by aerial photo interpretation, field surveys, tracer tests and analysis of detailed airborne Lidar DEM.
Rock masses, including poly-deformed orthogneisses, paragneisses and dolostones, are affected by systems of impressive
gravitational morpho-structures including ENE trending open trenches, scarps and counterscarps forming graben-like structures.
Geodetic measurements (optical targets and GPS points) and satellite radar interferometry (DinSAR) data demonstrate the
activity of the gravitational features affecting both the upper and lower part of the slopes.
The analysis of geological, geomorphological, hydrogeological, in situ stress, geodetic and uplift data, have been used to
demonstrate the possible relationships among geological, structural, topographic and gravitational features. Numerical 2D
modelling have been used to evaluate failure in presence of elastic, elasto-plastic materials and groundwater flow. This allow
to verify “model” sensitivity to some factors as slope geometry, structural features, groundwater conditions and to determinate
the triggers factors of these instabilities.
On this basis we discuss the possibility that the geological, tectonic and hydrogeological framework can play an active/passive
role in the onset and development of the sackung system and related landslides.