Task 3.2: 1992-1998 deformation of the Krafla volcano

The Krafla fissure swarm, in the North Iceland rift zone, last underwent rifting between 1975 and 1984. Activity mostly concentrated at the Krafla volcano although it occurred all along the fissure swarm. We formed interferograms of ERS-SAR scenes (Figure 40) covering the area of Krafla with time span values of up to six years (1992-1998). This long period interferograms have been revealed steady rate of deformation at Krafla volcano, N-Iceland. The deformation rate at Krafla and within the fissure swarm, has values reaching +2.1 cm/year in the ground to satellite direction, at the volcano. The area affected by deformation extends 20 km both north and south of the volcano. The best fit dislocation model consists of sills, to the north and south of the volcano, and a magma chamber, located below the volcano, all of them undergoing contraction. The contraction of the magma chamber induced a subsidence that has been constant in rate during all of the studied period (Figure 41).

 

Figure 40: Model geometry in cross section (A) and plan view (B), best fit model for the 6 year interferogram (C) and residual interferogram, i.e. model minus 6 year interferogram, (D) for the 6 year interferogram (after Henriot et al. 2000). Model elements represented in (A) and (B) are the northern sill (1), the magma chamber (2) and the southern sill (3). The model element dimensions represent their real geometries. The thickness of the lines in the cross-section (A) is proportional to the amount of contraction applied to the discontinuity in the model. The scale for the contraction in the 6 year interferogram model is given in (4).

 

Figure 41: Deformation at Leirhnjúkur, in the ground to satellite direction, with respect to the time span of the corresponding interferogram (after Henriot et al. 2000). The error is a function of the visual quality (Q) of the interferogram, 0 for no readability, 9 for perfect readability. It has been estimated as 1/Q of a fringe.