The incredible volcanic forces that create the Unzen jigoku do not follow a straight path from beneath the Earth’s crust to the surface.
　Imagine a giant bubble of magma deep beneath the Earth’s surface. This magma chamber exists about 10 kilometers below the bottom of Tachibana Bay to your west. To the east, there are smaller bubbles linked together like chains that run beneath the middle of the peninsula. From these magma bubbles, hot gases rise up through volcanic vents, mixing with groundwater and rainwater as they do. When this mix of water and gas bubbles out onto the surface, hot springs are formed—or in special cases, the incredible jigoku.
　The Unzen jigoku cover an area of only 6 hectares, but the vents and springs change locations over time—much to the frustration of officials in charge of maintaining this area’s walkways and parking lots. Approximately 400 tons of hot water emerge from the jigoku every day. During periods of heavy rain the amount of water gushing from the earth increases, but the water itself is cooler.
While the jigoku may seem timeless, they are always changing over the course of days and centuries.