Interferometric analysis of Synthetic Aperture Radar images acquired by the RADARSAT-1 satellite of Piton de la Fournaise volcano, show that an eruptive fissure which opened on 9th of March 1998 caused asymmetric deformation, with displacement and bulging of the volcanic edifice on the seaward side of the fissure. Up to 50 cm ground-to-satellite range change occurred in a 3-km wide area, in response to a shallow (< 1-km-deep) inclined dike that opened by up to 60 cm. The erupted magma was transported from more than 7-km-depth below sea level, causing no observable volcano-wide co-eruptive deflation. A series of pre-eruption interferograms show also that no significant inflation occurred prior to the eruption. The dike injection slightly reduced the stability of the volcano seaward flank.