A high-head three-bladed inducer has been equipped with pressure taps along the blade channels to characterize the dynamics of the axial pump in view of a deeper insight of the cavitation-induced instabilities. The spectral analysis of the pressure signals located in both the stationary and rotating frames has allowed to characterize the nature and intensity of the principal flow instabilities detected during the experimental campaign: a sub-synchronous rotating cavitation, a cavitation surge and a high order axial oscillation. A model of the dynamics of the blade channels, that relies on experimental data and on a suitable modelling of the mean flow and cavitating volume oscillations, has been used to estimate, for all the relevant flow coefficients, the intensity of flow oscillations associated to the cavitation surge generated by the rotating cavitation.