Åknes is an active complex large rockslide of approximately 30?40
Mm3 located within the Proterozoic gneisses of western Norway. The
observed surface displacements indicate that this rockslide is divided
into several blocks moving in different directions at velocities
of between 3 and 10 cm year?1. Because of regional safety issues
and economic interests this rockslide has been extensively monitored
since 2004.
The understanding of the deformation mechanism is crucial for the
implementation of a viable monitoring system. Detailed field investigations
and the analysis of a digital elevation model (DEM) indicate that
the movements and the block geometry are controlled by the main schistosity
(S1) in gneisses, folds, joints and regional faults. Such complex
slope deformations use pre-existing structures, but also result in
new failure surfaces and deformation zones, like preferential rupture
in fold-hinge zones.
Our interpretation provides a consistent conceptual three-dimensional
(3D) model for the movements measured by various methods that is
crucial for numerical stability modelling. In addition, this reinterpretation
of the morphology confirms that in the past several rockslides occurred
from the Åknes slope. They may be related to scars propagating along
the vertical foliation in folds hinges. Finally, a model of the evolution
of the Åknes slope is presented.