The Present State and Evolution of the Near-Summit Hydrothermal Activity on Ebeko Volcano from 1951 through 2024 (Paramushir Island, Kuril Islands)

This paper is concerned with the present state of the thermal fields in the near-summit part of the active Ebeko Volcano on Paramushir Island (Kuril Islands). We show the area of occurrence, the discharge, and the chemical composition of the main types of water manifestations (pots, lake, springs). All thermal occurrences on the volcano resulted from interaction between volcanic gases on the one hand and the surface and underground waters circulating at small depths on the other; the thermal occurrences have low pH (<3), Cl–SO₄ (SO₄–Cl) composition in a wide range of temperatures (between 10 and 98°C) and salinity (between 1 and 100 g/L). Based on continuous multiyear observations of the evolution of chemical composition in thermal waters we estimated the response of volcanic events to the state of the hydrothermal system. We showed that changes in the chemical composition of Lake Goryachee are related to changes in the intensity (going as far complete decay) of hydrothermal activity in the Middle Crater. The phreatomagmatic eruption beginning in 2016 might have provoked the resumption of deep fluid flow into the lake, resulting in increased concentrations of Cl^– in the water. The pots in the Northeastern Field are the most sensitive to events occurring on the volcano. All periods of increased activity are recorded in the varying concentrations of \({\text{SO}}_{4}^{{2 - }}\) and Cl^– and in the relationships between the two after the increase in activity began. However, even the largest pots periodically become steam–gas jets, which impedes regular geochemical monitoring.