Subsidence associated with the construction of the 57 kilometres-long Gotthard Base Tunnel in Switzerland on the surface of the metamorphic rock masses has been measured with SAR interferometry. Significant movements with values ranging from 2 to 12 mm/yr were detected with ENVISAT ASAR data between 2003 and 2010 above the tunnel on villages and sparsely vegetated alpine slopes, in areas where no displacement was recorded with ERS-1/2 SAR data between 1992 and 2000. The mechanism contributing to the large-scale surface consolidation is believed to be associated with pore-pressure reduction in the rockmass arising from tunnel drainage.