Christoph Prager

Deriving 3D displacement vectors from multi-temporal airborne laser scanning data for landslide activity analyses

Information on geometries and kinematics of landslides are necessary to establish geological slope deformation models. We present two complementary geospatial methods to analyze landslide surface changes even in areas affected by strong surface pattern changes, making use of airborne laser scanning (ALS) data. An image correlation method based on shaded relief images with a uniformly diffuse lighting and a feature tracking based on terrain breaklines are applied on a data set of eight ALS flight campaigns analyzing an active deep-seated rockslide in the Eastern Alps (Austria). Both tracking methods are described in detail, including parameter assessment. Additionally, an accuracy assessment of the input data sets has been conducted. 3D vector displacement maps derived from image correlation are well suited for the study of landslides if only slight surface pattern changes occur. The smallest detectable displacements strongly depend on the accuracy of the ALS data and for image correlation results lie within the range of 0.24 and 0.75 m for this study. Displacement vectors derived by breakline tracking only allow to detect displacements greater than 2 m. However, in comparison to image correlation, breakline tracking is not limited to areas with slight surface pattern changes and allows us to detect displacements even in areas with strong surface pattern changes. For a comprehensive interpretation of landslide activity a combination of both methods, with consideration of additional supportive data such as elevation change images and orthoimages, is recommended.

Characterisation and Kinematics of Deep-Seated Rockslides in Foliated Metamorphic Rock Masses

Deep-seated rockslides in the surroundings of a large reservoir were studied to improve the geological and kinematical models. The models form the basis to quantify the impact of reservoir operation on the behaviour of the rockslides and to increase the process understanding of slow to extremely slow moving rockslides in foliated metamorphic rock masses.

Process-based investigations and monitoring of deep-seated landslides

Through the consolidation of alpine settlement areas there have been an increasing number of incidents in recent years related to the activity of landslides in Northern Tyrol (Austria). This has led to humans, buildings, and communication and transportation routes being increasingly threatened. In 1999 a rockfall event in Huben (Otztal, Austria) destroyed a wood mill and cut the main power supply for the inner Otztal. In the same year increased deformation rates at the Eiblschrofen (Schwaz, Austria) induced reoccurring rockfall events. In early summer 2003, parts of the deep-seated Steinlehnen rockslide system (Gries i. Sellrain, Austria) were reactivated, causing an acceleration of a sliding slab (Henzinger 2005). Secondary events in the form of increased rockfall activity were the direct consequence of these slope movements and demanded temporary evacuations and roadblocks as immediate measure. In order to protect the road and settlement area permanently a safety dam was built. After the floods in Tyrol in August 2005, parts of the complex Zintlwald landslide system (Strengen, Austria) accelerated. This was triggered on the one hand by increased water infiltration of the slope and on the other hand by intense fluvial erosion of the slope foot. As a consequence important supra-regional infrastructure such as sections of the Arlberg national road were destroyed. In addition, the possibility was given that a rapid landslide could dam the river Rosanna. Considering that a collapse of this dam would entail a sudden flood event downstream, a monitoring and warning system has been installed.