Deformation pattern and morphology in the Krafla fissure swarm: the Mófell area (work carried out with Dauteuil and Villemin)

$\\$In the northern part of the rift, the deformation affects an area 60 km wide. In this area most of the active extensional deformation is localized into fissure swarms, 1 to 5 km wide. Major volcanic centers are present along swarm axes. We analyzed the partitioning of extension into a major fissure swarm: the Krafla fissure swarm. The studied area was a 4.5 km², near the Mófell mountain, north of the Krafla volcano and composed of basaltic lava flows younger than 10,000 years.

We used two information sources to estimate the spatial distribution of strain in this area. The first dataset was obtained from detailed mapping structures combining field measurements, SPOT satellite images and aerial photographs. Most faults and fissures trend N010$^{\circ }$-030$^{\circ }$. The fissures width ranges from 10 to 200 cm. The faults have a maximum vertical throw of 20 m. The second dataset used is a network of more than 450 geodetic points providing an accurate record of topography within the fissure swarm. This allows us to determine exactly the amount of tilt blocks (less than 2 ees), in an area with a weak extensive rate since 10,000 years. This network was used to define blocks with planar upper surface. The plunge and the trend of each plane were estimated and analyzed in compared to the fault network. The plunge values vary from 0.2$^{\circ }$ to 3$^{\circ }$, with trend comprised between N030$^{\circ }$ and N100$^{\circ }$. The tilt of the blocks was used to estimate the stretching accommodated by the block rotations.

A balance of the extension accommodated by block tilting and fissure dilation is discussed along E-W profiles and on maps. Assuming that the whole area is affected by the same stretching amount, important variations are thus highlighted inside the system.