Craters caused by high voltage ignition discharges on the surface of materials are important features of the erosion processes of electrodes. In this paper, a thermal simulation of the crater formation on a platinum cathode is carried out by means of the finite element method (FEM). The model is based on the modelling of cathode spots and includes phenomena such as ion bombardment, electron emission, vaporization, melting and heat conduction. The surface of the cathode is submitted to various ion power densities (10¹⁰–10¹² W m⁻²) of different durations (0.1, 1 and 10 µs) over a disc of a radius a = 10 µm. By comparing the results of the simulation with experimental data of molten depths and molten volumes, characteristic values of the time, the ion power density and the current involved in the crater formation are determined. These values are related to the electrical characteristic of an ignition discharge, permitting the identification of the phase producing the crater. Furthermore, the contribution of the different heat dissipation mechanisms is evaluated and discussed.