Abstract: The early post-eruptive activity is described on the Third Cone, one of the New Tolbachik volcanoes, formed during the eruption at the Northern Breakthrough during the Great Tolbachik Fissure Eruption, which occurred in Kamchatka in 1975–1976. Changes in temperature, exhalation mineral generation, and rock alteration in the fumarole areas of the northern and southern craters of the Third Cone are characterized.