The Krafla fissure swarm (KFS) has been very active during the last rifting episode (1975-1984). This 80 km long and 10 km wide swarm includes numerous tension fractures and normal faults. Most of them has been reactivated during the last volcano-tectonic episode. Part of them elongated and we noticed the creation of new fissures. A complete mapping of the swarm before and after the rifting episode has been made from aerial photos. If we assume that the deformation along a transverse section increases with the number of fractures encountered through the section we observe an evolution of the dilation along the swarm strike. This could be related to an unique dyke present at a small depth which controlled the surface fracturing. A comparison between the two mapped states (1960 and 1990) permits us to distinguish between reactivated and new fractures. If we assume that the growth process has not changed since the swarm creation a limited number (<10) of tectonic episodes occurred on the KFS. This implies that the volcanic episodes are not necessary associated with dilation along the whole swarm. The Þeistareykir swarm (TFS) lies 20 km west of the Krafla fissure swarm and is connected with the transform zone in its northern end. A complete mapping of the fissure swarm has also been made from aerial photos by T. Villemin and O. Henriot. The western boundary faults consist in high scarps where both active normal and strike slip faulting has been characterized during the 1998 field trip. In addition displacement profiles has been measured by kinematic GPS on a set of 8 en-echelon normal faults just where the Húsavík fault meets the TFS. No clear evidence for a continuation at depth of the Húsavík lineament can be found on these profiles.