[en] The flux jump in superconductors represents a strong local magnetic instability. The disturbance consists of an abrupt change of the magnetic vortex current density, which can occur in three ways: (1) a fast change in the energy density, (2) a fast change in the vortex density, and (3) a fast change in the vortex velocity. Thermodynamic cross effects of them can appear as well. An irreversible thermodynamic analysis on the case and nature of the flux jump is elaborated, which describes the non-equilibrium, the instability, the non-linearity and the irreversibility. The energy current density, the vortex current density and the total entropy production are determined by irreversible thermodynamic methods. This latter contains not only the spontaneous terms, but those which are originated from the source and cross effects too. (orig.)