Geohistory - Rocks from Continental to Sea Periods
Green tuff, found on theeast coast of Dōgo Island and in Nishinoshima Island, is one of the rocks that help us understand how the Sea of Japan and Japanese Archipelago were formed. This rock, formed 20-15 mln years ago in the lake and the sea, covers a large area on the west coast of Honshū Island. Its colour comes from the chlorine which developed when the minerals in volcanic ash came in contact with hot water. We can thus tell that during the formation of the Sea of Japan, the area between the continent and the islands had many active volcanoes.