By combining morphotectonic lineament analysis and digital geological mapping we investigate the significance of the fracture system on Hamarøya, and its relation to the adjacent Hamarøya Fault. Three fracture sets were encountered: (i) NNE–SSW striking, (ii) ENE–WSW striking and (iii) NW–SE striking. These fracture sets, in combination with ductile foliation, define the regional morphotectonic lineament pattern mapped from bathymetry and digital elevation models. The fractures are linked to several stages of pre-breakup rifting and subsequent stress patterns following the opening of the North Atlantic Ocean. The ENE–WSW-trending fractures are interpreted to be the oldest and to have developed as joints during NNW–SSE crustal extension. Locally, this fracture set is reactivated as sinistral shear fractures which act as transfer faults linking the NNE–SSWstriking, right-stepping fracture array.

The latter is interpreted to represent WNW–ESE crustal extension in late Middle Jurassic–Early Cretaceous times related to the development of the Hamarøya Fault, the southeastern boundary fault of the northern part of the Vestfjorden Basin. The NW– SE-trending fracture set is the youngest and developed as a result of NE–SW crustal extension. It is interpreted as neotectonic joints reflecting the present stress regime generally related to ridge-push forces, or at least the stress system prevailing since post-break-up time in the Eocene.