We report various STM observations which demonstrate that a drastic change of the morphology of a metallic surface can be induced by the tip, at room temperature, even using so-called "standard" tunnelling parameters of about 1 V and 0.5 nA. The results on a 0.75-ML deposit of copper on Cu(100) highlight a strong amplification of the surface diffusion at room temperature. The time scale at which this phenomenon takes place excludes the effect of basic thermal activation. More surprisingly, we show that tip scanning can induce nucleation and growth of monoatomic islands from a bare copper (100) surface.