The authors of the article published below propose a physical model that explains the mechanism of tsunami formation proceeding from the ideas once elaborated by N.E. Zhukovskii. In the hydrodynamic current diagram, two regions of liquid motion are singled out: the near-surface layer of equal pressure and the deep layer. An equation for primary mathematical analysis is given to indicate the existence of a critical condition in the hydrodynamic description of the sharp water rise process under the formation of tsunami waves.