Crater Lake Kipyashchee in the Caldera of Golovnin Volcano: Water and Gas Geochemistry, Output of Magmatic Volatiles (Kunashir Island)

Lake Kipyashchee similar to 4.6 ha in area whose greatest depth is 25 m fills an explosion crater near an extrusive dome in the Golovnin caldera. The lake water is ultra acid (pH 2.2-2.5), is of the chloride-sulfate type with a salinity of 2.0-2.2 g/L. The water temperature varies between 30 and 100 degrees C at the surface, with the mean value being 37 degrees C. The lake emptied itself via Protoka into Lake Goryachee at a rate of 120 L/s in August 2021. The hydrothermal drainage of magmatic Cl and S (in the form SO4) from Lake Kipyashchee is 10 and 5.4 t/day, respectively. The first ever estimate of the total diffusion output of carbon dioxide from the surface of Lake Kipyashchee is over 5.4 t/day. The geochemical data acquired during the 2020-2021 field surveys indicate an increase (compared with 2015) in the hydrothermal activity in the Golovnin caldera.