Gamanjunni 3 is an unstable rock slope in Manndalen valley, northern Norway that shows active deformation. Structural mapping and analyses of terrestrial laser scans identified many discontinuity sets, but none of those may act as a basal failure surface based on kinematical analysis. Hence, decomposed InSAR data from two different satellite geometries was used to understand the failure mechanism of Gamanjunni 3. This 2D InSAR data allows quantification of all displacement components and the dip of the total displacement vector in an east-west plane and is covering almost the entire surface of the unstable rock slope. At the top of Gamanjunni 3, 2D InSAR data show up to 6 cm displacement per year with a dip angle of 50°. This is in agreement with the displacement measured from differential GNSS. The displacement rate as well as the dip angle decrease gradually downwards towards the toe. The displacement vector at the top of Gamanjunni 3 shows clearly that the uppermost part of the unstable rock slope is a wedge failure along the two rectangular back-scarps. However, the intersection line of these two failure planes does not daylight in the slope. Displacement needs to be transferred to a shallower structure at the lower parts of the unstable rock slope, as for example the sub-horizontal foliation. This is reflected in an approximately horizontal displacement at the toe of Gamanjunni 3. We thus propose a compound biplanar rock slope deformation based on the observed displacement pattern, morphology and structures.