From Hot Springs to Deep-seated Fluids: History of Hot Spring Studies from the Viewpoints of Energy and Material Circulations in the Solid Earth

The history of hot spring studies and research in Japan is reviewed mainly from the view-point of Earth science. Studies on the geochemistry of hot spring waters started with geochemical analyses of hot spring water in the 1830s. The relationships between the issuing mechanisms of hot springs and volcanism, active faults, and earthquakes have been studied since around 1910. These studies reveal sources and recycling paths of waters and dissolved materials in the Earth's crust and the upper mantle in relation to plate tectonics and subsequent volcanism. Microbio-logical studies on living organisms, such as algae, bacteria, and archaea, living in hot springs, began in the late 1880s, and have contributed to documenting the origins and evolution of life. Combined with mineralogical studies, minor and trace element analyses of hot spring water have contributed to an understanding of the formation mechanisms of ore deposits. Studies on hot spring waters triggered an understanding of the essential role of water in the Earth and its evolution.