Talus thickness along a steep slope derived from airborne geoscanning to design land slide warning system to protect rail and road in Flåmsdalen

Introduction

Norway’s geology and post-glacial topography poses in part a substantial natural hazard for people and infrastructure. A costly, detailed study of potential sliding mechanisms is typically necessary to manage these risks. Within the framework of a research project connected to municipal mapping funds, we assess the value of airborne electromagnetics (AEM) for efficient structural mapping. Based on airborne- and ground geophysics we produced a 3D model in a fraction of time and funds needed for conventional investigations. A first drilling based on this model found artesian water, the most likely driving mechanism of the investigated creeping landslide. Preliminary monitoring data shows the correlation between precipitation and pore pressure.

Discussion

The Flåm valley project gave us the opportunity to study the potential of semi-regional geophysical mapping in the early phase of a monitoring and warning project. Especially in our setting with a large unstable, creeping area that is difficult to assess and that appears to be driven by a partially fairly deep seated sliding mechanism it may have taken years and tens to hundreds of millions Norwegian kroner until one would have found a sliding plane within the reach of instrumented boreholes. The AEM survey provided us with the planning basis in a matter of weeks at a fraction of these costs.

With a limited ground geophysics program, we zoomed in on the potential drilling sites and have gained first confirmations of the geophysical assumptions. The Flåm valley project is now going ahead towards further instrumentation and establishing a database that after sufficient learning time shall be used to manage this risk for both railway, road and local residents.

Acknowledgements

Aurland municipality and E-CO energy funded the 2014 AEM survey. The 2015 ERT follow up was part of the EWS research project funded by The Regional Research Fund, Vestlandet (RFF). We further acknowledge SkyTEM (Denmark) for acquiring excellent AEM data in a challenging terrain. Shane Gribben (Queens University Belfast) and Aurland municipality helped acquiring the ERT data.

References

The full paper can be requested through the download link above or found directly at www.researchgate.net.

Anschütz, A., Pfaffhuber, A. A., Domaas, U., & Rosenvold, B. S. (2015). Combined airborne and ground geophysics as a first phase towards a landslide warning system—A Norwegian case study. Osterr. Ing. Und Archit. Z, 160, 215-219.