White smoker (white hydrothermal emission) was also discovered in the same area. It suggests the increased magma activity at Hatoma Knoll. Several reasons can be hypothesized for the blue color of hydrothermal fluid. Some physicochemical process is assumed to be closely related to the color of the hydrothermal fluid because the color of hydrothermal fluid is closely related with the physical/chemical process of hydrothermal emission. We are going to study the reason further because the observation this time is not sufficient to identify the reason for the blue color.