Characterization and monitoring of the Åknes rockslide using terrestrial laser scanning

TLDR

Terrestrial laser scanning provides high‑resolution point clouds for characterizing and monitoring slope movements, and this study focuses on the 35 million m³ Åknes rockslide in Western Norway, one of the most investigated and monitored rockslides worldwide. TLS point clouds were used to analyze the steep, inaccessible main scarp of the Åknes rockslide, with acquisitions from 2006 to 2008 enabling 3‑D displacement mapping across the entire area, and an affine transformation matrix between scans precisely described the displacements, separating translational components such as velocity and direction from rotational components like toppling. The study demonstrates that TLS can reliably capture 3‑D displacement information over a large, unstable area, and proposes an instability model for the upper Åknes rockslide that attributes measured translational and rotational displacements to southward planar sliding along gneiss foliation, gravitational vertical settlement along a complex basal sliding surface, and northward toppling toward the opened graben structure. Abstract.

Abstract

Abstract. Terrestrial laser scanning (TLS) provides high-resolution point clouds of the topography and new TLS instruments with ranges exceeding 300 m or even 1000 m are powerful tools for characterizing and monitoring slope movements. This study focuses on the 35 million m3 Åknes rockslide in Western Norway, which is one of the most investigated and monitored rockslides in the world. The TLS point clouds are used for the structural analysis of the steep, inaccessible main scarp of the rockslide, including an assessment of the discontinuity sets and fold axes. TLS acquisitions in 2006, 2007 and 2008 provide information on 3-D displacements for the entire scanned area and are not restricted like conventional survey instruments to single measurement points. The affine transformation matrix between two TLS acquisitions precisely describes the rockslide displacements and enables their separation into translational components, such as the displacement velocity and direction, and rotational components, like toppling. This study shows the ability of TLS to obtain reliable 3-D displacement information over a large, unstable area. Finally, a possible instability model for the upper part of Åknes rockslide explains the measured translational and rotational displacements by a combination of southward planar sliding along the gneiss foliation, gravitational vertical settlement along the complex, stepped basal sliding surface and northward toppling toward the opened graben structure.