The Volcanoes of Shimabara and the Birth of Mt. Heisei Shinzan
The Shimabara Peninsula you see today is the result of more than four million years of volcanic and tectonic activity. To understand its history—and the origins of its newest mountain, Heisei Shinzan—is to glimpse how geologic forces shape human habitation.
Deep beneath Tachibana Bay to the west is a large magma chamber from which lava and gas escape to the surface through cracks in the earth. The gas mixes with groundwater, which creates the peninsula’s many hot springs. But if pressure on the magma beneath the peninsula becomes too great, volcanoes will suddenly erupt.
This is further complicated by the Unzen Graben which is the central part of the Shimabara Peninsula. It is slowly sinking as parallel faults pull the region apart. In addition, earthquakes commonly happen before, during, and after eruptions, heightening the danger of living here.
Yet life on the Shimabara Peninsula is rich in history and culture. Fertile volcanic soil creates the perfect environment for a wide variety of crops, and the many igneous rocks are perfect for building walls and terraced farms. The hot springs of Obama, Unzen, and Shimabara have soothed local residents and visitors alike for centuries with their health-bringing waters. Even the catastrophic collapse of Mt. Mayuyama (819 m) in 1792 created an excellent environment for fishing in the Ariake Sea to the east.
The Heisei Eruptions of 1990–1995 are just the latest chapter in the story of the Shimabara Peninsula. When Mt. Fugen (1,359 m) reawakened in November 1990, the town of Shimabara was not fully prepared for the destruction that would come. Five years of earthquakes and landslides claimed 43 lives, destroyed hundreds of homes, and disrupted the lives of thousands, but today the community is stronger than ever. The town was rebuilt with preparedness in mind, and new research stations closely monitor the mountain. Meanwhile, the Shimabara Peninsula has an impressive new peak—the 1,483-meter-tall Mt. Heisei Shinzan.