Deep Seated Landslieds

Assessment of deep-seated landslide distribution in the Alps: Ticino

Student : Andrina Vlasek

Supervisor: Kerry Leith, Andrea Manconi, Engineering Geology, Geological Institute ETH Zurich

Natural hazards such as landslides happen frequently in Switzerland. More than 6% of Switzerland’s area is prone to slope instability (Raetzo, 2002.). Not all landscapes are equally prone to landslide instabilities, but depends on various factors, such as geologic (e.g.  lithology), topographic (e.g. slope steepness) or climatic factors (e.g. length and intensity of rainfalls), which are common to large areas. The aim of this study project is to analyse the distribution of large deep seated gravitational slope deformations (DSGSD) and a possible relationship to river incision. This will be examined in the southern part of the Swiss Alps; more precisely the catchment area of the Lake Maggiore, which consists of a fluvially formed, western part, a central and eastern region which got more glacially shaped. DSGSDs are a widespread phenomenon in mountainous regions. According to Agliardi (Agliardi, 2013 non catastrophic) there is a positive correlation of the degree of valley incision and the abundance of DSGSDs. As the most valleys in the catchment area of Lake Maggiore are fluvially incised nowadays, especially in the western region, this too increases the susceptibility of large slope instabilities. To investigate this subject, the landslides were mapped using a combination of Google Earth (navigation in 3D with satellite pictures and an overlain LiDar hillshade greysacle layer) and QGIS in order to produce a categorised distribution map. The data from this map then could provide input data for an analysis of the association of landslides with river channels. After a selection to only analyse the large deep-seated landslides, the final data was processed in Matlab. The result displays intersections of landslides with river channels, excluding the alluvium (it rather accumulates than incises). The distribution of the landslides and channel intersections shows that they are somewhat clustered in the western, fluvially formed part. In this region at 700m above the alluvium often a knickpoint could be detected. Further up this knickpoints are followed by a flatter part which displays less landslides. The assumption can be made, that there are less landslides on flatter terrains because the erosion force and therefore the incision is weaker there. This supports the thesis, that the landslide distribution is positively correlated with river incision.