The damage induced by 5 MeV oxygen ion implantation in x-cut congruent LiNbO3 has been investigated by Rutherford backscattering spectrometry channeling technique. The dynamics of the damage growth has been described by an analytical formula considering the separate contributions of nuclear and electronic energy deposition. It has been hypothesized that the nuclear damage provides the localization of the energy released to the electronic subsystem necessary for the conversion into atomic displacements. The strong influence of the preexisting defects on the damage pileup, foreseen by the analytical formula, has been experimentally verified by pre-implanting the samples with 500 keV oxygen ions. It has been shown that a subsequent 5 MeV oxygen implantation step gives rise to an impressive damage accumulation, eventually leading to the total amorphization of the surface, even at moderate fluences.