Isotopic study links hot spring magmatic water to subducting Pacific Plate

Researchers at the University of Tsukuba have demonstrated that the hot‑spring and volcanic‑gas waters of Kussharo Caldera in Hokkaido originate from the subducting Pacific Plate. By combining numerical simulations with isotopic measurements, the team showed that the magmatic component of the springs and gases is derived from a slab that has descended to a depth of 125 km (78 mi) beneath the Kuril Trench. The study, published in the *Journal of Volcanology and Geothermal Research*, links the hydrothermal system of the caldera directly to the deep subduction zone.

The analysis revealed that meteoric water infiltrating the crust mixes with deeper magmatic fluids before emerging at the surface. The isotopic signatures matched those expected from the subducted Pacific Plate, confirming that the slab’s melt contributes to the geothermal activity at Kussharo. This finding clarifies the source of magmatic water in the region and provides a clearer understanding of the link between plate subduction and surface hydrothermal phenomena.