High hydrothermal activity is concentrated in the crater of Ushishir volcano which represents an almost closed bay connected with the ocean through a narrow and shallow strait. In their composition the thermal waters can be divided into two groups: (1) thermal waters of sea origin of high mineralization altered as a result of high-temperature interaction with rocks and (2) waters of sea origin heated in the near-surface conditions and mixed with fresh meteoric water. Ion and gas geothermometry as well as mixing plots in Na - 1ма_к and CI - coordinates suggest that these thermal vents are fed by steam-water geothermal reservoir with temperature of about 260°C; mineralization of the fluid in equilibrium zone is 23 g/l, C02 pressure being about 4 bar. Calculations of the equilibrium solution composition in the closed "water-andesite" system indicate that the observed Mg concentration could be formed in a wide temperature range but at low, lower than 0,01, mass rock-water ratios. Reequilibration of the solution at temperatures of 170-200°C in the near-surface conditions is most probable. The main discharge takes place primarily in the intersection zone of the ring-shaped and linear faults. Through the ring-shaped fracture mostly gas and steam-heated waters are discharged.

The origin of diamonds in the lava and ash of the recent Tolbachik eruption of 2012–2013 (Kamchatka) is enigmatic. The mineralogy of the host rocks provides no evidence for the existence of the high pressure that is necessary for diamond formation. The analysis of carbon isotope systematics showed a similarity between the diamonds and dispersed carbon from the Tolbachik lava, which could serve as a primary material for diamond synthesis. There are grounds to believe that the formation of Tolbachik diamonds was related to fluid dynamics. Based on the obtained results, it was suggested that Tolbachik microdiamonds were formed as a result of cavitation during the rapid movement of volcanic fluid. The possibility of cavitation-induced diamond formation was previously theoretically substantiated by us and confirmed experimentally. During cavitation, ultrahigh pressure is generated locally (in collapsing bubbles), while the external pressure is not critical for diamond synthesis. The conditions of the occurrence of cavitation are rather common in geologic processes. Therefore, microdiamonds of such an origin may be much more abundant in nature than was supposed previously.