Morphology and Specific Features of Formation of Thermal Lake Utinaya Banya (Iturup Island, Southern Kuril Islands)

—This paper describes a set of studies performed at a thermal manifestation (Lake Utinaya Banya) on the Iturup Island (Kuril Islands). These studies include bathymetric survey of the lake basin, geometric leveling across the lake, pitting, sampling of thermal waters from the lake and springs, hydrochemical research, and isotopic analysis of oxygen and hydrogen in the lake water. It is suggested by the shape of the lake basin (close to lenticular with a significant concentric depression), the underwater gas-hydrothermal vents, the bank along the perimeter of the lake basin, and the presence of several layers of clastic deposits at the top of the rampart that the lake was formed by a hydrothermal eruption. The lake temperature has remained constant over the years and ranges on average from 25 to 15 °C, depending on the season. The water of Lake Utinaya Banya is represented by acidic, sulfate calcium, and low-mineralized waters.