DInSAR, GPS and gravity observation results in La Palma, Canary islands

We review several results from geodetic observations carried out in La Palma Island during the period 1992-2007. A gravity survey was done for structural studies, and InSAR and GPS observations techniques were applied to study the existence of deformation areas in the Island. Gravity anomalies have been inverted using a non-linear three-dimensional gravity inversion approach to obtain the geometry of the anomalous bodies. The main structural feature is a large high density body interpreted as a dense intrusive plutonic body and the pliocene-age uplifted seamount. An elongated minimum is detected below the Cumbre Vieja according to the rift structure. InSAR results show two areas of subsidence, a mild long wavelength signal on the western part of Cumbre Vieja and clear subsidence located on the Teneguia volcano where the last eruption took place in 1971. A GPS network composed by 26 stations covering the island has been defined. Vertical displacements determined by comparing the GPS coordinates obtained in 2007 and in 1994 are consistent with the InSAR results. From the comparison of 2006 and 2007 coordinates we conclude that more time span is needed to obtain clearly significant displacements, but observed trends are also consistent with InSAR results. All the observed significant displacements are at stations located outside of the large high density central body.