Hydrothermal Systems of the Shiashkotan Island (Kuril Islands, Russia)

Abstract

Two hydrothermal systems are distinguished in the Shiashkotan Island - North-Shiashkotan and Kuntomintar, whose thermal power makes 3800 and 4500 kcal/sec, correspondingly. These systems are located in the interior of Sinarka and Kuntomintar volcanoes. The volcanoes have composite edifices of Somma-Vesuvius type, heavily destroyed by seismic-tectonic processes. Specific development history of the volcanoes in the Holocene period conditioned the formation of two different hydrogeological environments in the northern and southern parts of the island, in which two different hydrothermal systems formed. The North-Shiashkotan hydrothermal system is a typical example of the island-arc type hydrothermal system associated with active andesite volcanism. Surface thermal manifestations of the system are distributed over 5-8 km of the outflow area and show typical vertical hydrochemical zoning. The Kuntomintar hydrothermal system belongs to the local type. Its surface manifestations are constrained by two thermal fields. The conducted geochemical studies have demonstrated that Kuntomintar volcano gasses are of magmatic origin. Their final composition has formed as a result of slow fluid ascent to the surface and due to significant dilution by meteoric waters under the near-surface conditions. High vent temperature of the gasses and a number of elevated prognostic ratios of S/Cl, S/C, CO2/H2 in their composition are indicative of possible intensification of the volcano fumarole activity.