 More than twenty craters are distributed on the plateau, sometimes forming chains, with diameters ranging from a few meters to 180 m. Most of these volcanic depressions are partially filled by lakes or marshes.Today, hydrothermal activity is maintained in and around the caldera of Mount Akita-Yakeyama in the form of fumaroles, the circulation of water from hot springs and, in places, boiling puddles of mud and sulfur deposits.In the common era, more than eight eruptions of Mount Akita-Yakeyama were recorded, notably in 1678, three in the nineteenth century, and five in the twentieth century, but no eruptions of Mount Hachimantai itself.