Abstract
Ushishir volcano is located in the middle of the Kuril Arc. The Ushishir crater, a closed bay connected with the ocean by a narrow and shallow strait is characterized by a strong hydrothermal activity. Boiling springs, hot pools, fumaroles and shallow submarine vents are manifestations of a magmatic-seawater hydrothermal system with the discharging solution similar in chemical and isotopic composition to the seafloor hydrothermal fluids. The main features of the Ushishir fluids are: (1) water has close to zero δD and a large oxygen isotopic shift (6 7‰); (2) high boron concentration (~70 ppm); (3) a significant uptake of Ca and Sr from the rock and Ca/Sr higher than that for seawater with 87Sr/86Sr ~0.7037, a bit higher than the rock value (0.7032). The measured onshore discharge of boiling water is ~ 5 kg/s; however, a large plume of the discoloured seawater releasing from the outer submarine slope of the volcano indicates a much higher total mass and heat output.
Highlights
Kuril Island arc between Kamchatka Peninsula and Hokkaido Island in the NW Pacific (Fig. 1a) is a ~1200 km long chain that consists of about 30 islands, each one with one or more active volcanoes
We report new data obtained during the fieldwork in 2016, which include some trace elements, composition of fumarolic gases, isotopic composition of gases and isotopic composition of the dissolved SO4 and Sr
All samples contain a significant proportion of the nonatmospheric nitrogen, which is a common characteristic of volcanic gases of the Kuril Arc [3]. He isotopic composition and ratios CO2/3He and N2,ex/3He in the Ushishir gases are typical for subduction zones
Summary
Kuril Island arc between Kamchatka Peninsula and Hokkaido Island in the NW Pacific (Fig. 1a) is a ~1200 km long chain that consists of about 30 islands, each one with one or more active volcanoes. The island is a small closed bay separated from the ocean by a shallow strait (Fig. 1) and known as hosting an unusual hydrothermal system, more similar to the seafloor magmatic-seawater hydrothermal systems. There are several drainless pools and a small steaming hill to the north of the main thermal water manifestations composed of altered rocks mixed with elemental sulfur. Within this steaming ground there are several weak fumaroles encrusted by sulfur. Other thermal manifestations are open at low tide (sites 2-7 in Fig.1) and discharge diluted warm waters. At sites 8 and 9 at the oceanic coast of the island there are no visible vents but an intense underwater discharge in the small bay of the site 8 is marked by the large plume of discolored water
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