A Multidisciplinary Study of Near-shore Landslides in the Trondheim Harbour, Mid Norway

The geological and historical record in the bay of Trondheim, mid Norway, illustrates that landslides are recurrent phenomena. Recent and ongoing development of the area, including land reclamation and extension of harbour facilities, have increased concerns about the stability of the shoreline slopes and highlighted the need for better understanding of these mass-movement processes. Herein, we summarize previous and ongoing work in the area that shed new light on the origin and development of mass wasting processes in the bay of Trondheim. Intergration of geotechnical and geophysical data (including shear wave reflection profiling) from both on- and off-shore shows that the presence of softer and more sensitive laminated clay-rich beds facilitates translational slope failure, by acting as slip planes. Additional pre-conditioning factors promoting instability include the loading of weaker clay-rich beds by delta progradation, over-steepening from erosion and/or sediment accumulation and artesian groundwater pressure at different stratigraphic levels. For the more recent landslides, anthropogenic factors like embankment fillings and vibrations from construction work are considered the most important triggering mechanisms. Finally, the results presented illustrate the importance of detailed morphological analyses, combined with a geological model including the physical/geotechnical characteristics of sediments on- and off-shore, in order to perform proper shoreline slope stability assessment.