雲仙の地獄地帯の面積は約6ヘクタール。その一帯を縫うように整備された歩道は、約1.7kmにもおよびます。
　活発な動きを見せる雲仙地獄のエネルギー源は島原半島の西側、千々石湾海底の地下、数10kmにあるマグマだまりだと考えられています。
　　このマグマだまりから発生した高温高圧のガスが岩盤の裂け目を通って上昇し、地下水と混ざり合って温泉となっています。
　雲仙地獄全体では、1日約400トンのお湯が湧き出ていますが、湧き出るお湯の量は降水量に比例しています。
そのため、大雨が降ると湯量は増えますが、お湯の温度は低くなってしまいます。

★ 英語バージョン
　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.