Eruptive vent on Piton de la Fournaise on Réunion Island, a 'hotspot' volcano that has been extremely active in the last few years. Measuring the extent of local ground deformation occurring in relation to the eruptions helps researchers get an understanding of what processes are taking place underground. InSAR is proving to be an effective means of obtaining this information, and multiple interferograms of Piton de la Fournaise have been produced based on Envisat ASAR data.