Displacements and ground motions near volcanoes are one of the warning signs of volcanic eruptions. One of the most important tools to detect such movements is the technology provided by GNSS permanent stations network.\nThis paper studies the use of GNSS techniques for the determination of the spatial and temporal displacements caused by 1803-02 underwater volcano that erupted on the south coast of El Hierro island, in the Canary Islands, on 10 October 2011. \nThe paper also analyses and quantifies the ground displacements that occurred before the eruption.