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The explosive model of a quick-moving cathode spot ,  allows us to describe many experimental facts qualitatively. However, some details of the model need further physical explanation, in particular because of the analysis of the latest experimental data . Estimations given in this paper show it is possible to include in the framework of the explosive model mass balance in the plasma ball and explain the fact of the appearance of a new spot at the periphery of an old one observed in experiments , . From the physical point of view, solution of this question is connected in the paper with the presence of oxide film on the cathode surface. Besides, it is shown that the discrepancy in erosion, observed in experiments , , can be connected with the difference in the thickness of oxide film.