The Izu Islands are a group of volcanic islands stretching south and east from the Izu Peninsula of Honshū, Japan. Miyakejima island rests atop an active volcanic chain that has erupted six times in the last century. However, the danger isn’t just from volcanic eruptions, but from the highest concentrations of poisonous gasses (primarily sulfur) in the world regularly leaking up through the ground. Residents were evacuated from the islands in 2000 due to volcanic activity and dangerously high levels of gas. The people returned in 2005 but are now required to carry gas masks with them at all times in case gas levels rise unexpectedly.