Mount Unzen: The Fire and the Wave

Mount Unzen (Unzen-dake) is a volcanic group located on the Shimabara Peninsula, east of Nagasaki. It is visually dominant, a brooding mass of peaks that looms over the Ariake Sea. But Unzen is defined less by its height and more by its two dark chapters in history: one in 1792 that birthed a tsunami, and one in 1991 that brought the terrifying power of pyroclastic flows into living rooms around the world.

It is a Decade Volcano, a designation reserved for the world’s most dangerous and scientifically important volcanoes. Today, it serves as a global classroom for disaster prevention and a somber memorial to the fury of the earth.

The 1792 Shimabara Catastrophe

The year 1792 marks the deadliest volcanic disaster in Japanese history. It was not the fire that killed the most people, but the water.

• The Collapse: After months of earthquakes and lava flows from the Fugen-dake peak, a massive earthquake struck on May 21. The shockwave caused the eastern flank of the adjacent Mount Mayuyama to collapse completely.
• The Landslide: An estimated 340 million cubic meters of rock and debris slammed into Shimabara City and plunged into the Ariake Sea.
• The Tsunami: The impact generated a megatsunami that reached heights of up to 55 meters (180 feet) (locally) but averaged 10 meters. It roared across the bay to Kumamoto, then rebounded to strike Shimabara again.
• The Toll: Approximately 15,000 people died—5,000 in the landslide and 10,000 in the tsunami. The phrase “Shimabara taihen Higo meiwaku” (Shimabara’s disaster, Higo’s annoyance) is still used today to describe the event. The scar of the landslide on Mount Mayuyama is still clearly visible, looming over the city like a bitten apple.

The 1990-1995 Eruption: The Monster Awakens

After nearly 200 years of silence, Unzen woke up in November 1990.

• Dome Growth: A sticky, viscous lava dome began to grow at the summit of Fugen-dake. Unlike fluid Hawaiian lava, this lava piled up like toothpaste, becoming unstable.
• Pyroclastic Flows: As the dome grew, chunks would break off, collapsing and creating pyroclastic flows—avalanches of superheated gas, ash, and rock racing down the mountain at 100 km/h. Between 1991 and 1995, over 10,000 small flows were recorded.

The Tragedy of June 3, 1991

This date is etched into volcanology history.

• The Setup: A large lava dome was growing. Journalists, scientists, and taxi drivers gathered at a “fixed point” thought to be safe, about 4 km from the crater, to document the flows.
• The Event: At 4:08 PM, a massive section of the dome collapsed. The resulting pyroclastic flow was larger than expected. It detached from the channel and surged over the ridge where the observers were standing.
• The Victims: 43 people were killed instantly by the heat blast. Among them were Katia and Maurice Krafft, the world-famous French volcanologists who had dedicated their lives to filming eruptions, and Harry Glicken, an American volcanologist who had narrowly survived Mount St. Helens. Their deaths shocked the scientific community and forced a complete rethink of safety zones.

Heisei Shinzan

The eruption continued until 1995. The lava dome continued to grow, eventually forming a new peak. The mountain is now higher than it was before. This new summit was named Heisei Shinzan (New Mountain of the Heisei Era). It stands at 1,486 meters, the highest point in Nagasaki Prefecture.

Tourism: A Geopark of Memory

Today, the Shimabara Peninsula is a UNESCO Global Geopark, recognized for how it integrates its volcanic heritage with tourism and education.

Unzen Onsen and the “Hells”

Located high on the mountain slopes, Unzen Onsen is a hot spring resort that dates back to the Meiji era, when it was a summer retreat for Westerners living in Nagasaki.

• Unzen Jigoku (Hells): The highlight is the “Hell” fields—barren, white expanses of ground where boiling water and steam vent furiously from the earth. Wooden boardwalks allow you to walk safely through the hissing landscape. The smell of sulfur is pervasive.
• Oito Jigoku: One vent is named “Oito” after a woman from legend who was executed for killing her husband; the vent appeared shortly after her death.

The Disaster Memorials

Shimabara does not hide its scars; it teaches from them.

1. Mt. Unzen Disaster Memorial Hall: A massive, modern museum that uses simulation technology to let visitors experience the terror of a pyroclastic flow and the debris flows (lahars). It focuses on the human stories of evacuation and rebuilding.
2. The Buried Houses: At the Mizunashi-Honjin Deep Blue Park, several houses that were buried to their roofs by lahars have been preserved exactly as they were found. You can see the roofs sticking out of the mud, a chilling reminder of the volume of material that came down the mountain.
3. Former Onokoba Elementary School: This school stands as a ruin. It was hit by a pyroclastic flow on September 15, 1991. The building is a skeletal shell of twisted steel and concrete, preserved to show the heat and force of the flow. Thankfully, it had been evacuated months earlier, so no children died there.

The Hidden History: Christianity and Persecution

Long before the 1792 disaster, Unzen was the stage for another tragedy: the Shimabara Rebellion (1637-1638) and the persecution of Hidden Christians (Kakure Kirishitan).

• The Hells as Torture: In the 17th century, the boiling hot springs of Unzen Jigoku were used by the Tokugawa Shogunate to torture Christians into renouncing their faith. A monument in the “Hells” today commemorates the 33 martyrs who were boiled alive here between 1627 and 1631.
• Shimabara Castle: The rebellion ended with the slaughter of 37,000 rebels at Hara Castle, but Shimabara Castle remains the city’s icon. Today, it houses a museum dedicated to this dark history, linking the violence of man with the violence of the mountain.

The Heisei Shinzan Nature Center

For those who want to understand the science behind the 1991 eruption, the Heisei Shinzan Nature Center is a must-visit.

• Location: It is located near the Taruki Plateau, which was devastated by pyroclastic flows.
• The View: From the observation lounge, you have a direct line of sight to the lava dome. You can use telescopes to observe the jagged rocks and fumaroles of the new peak.
• Education: The center focuses on the mechanism of lava dome growth and the ecological recovery. Children can learn how plants are slowly recolonizing the ash-covered slopes, starting with hardy species like Japanese pampas grass and knotweed.

Hiking Unzen: The Fugen-dake Trail

While Heisei Shinzan is off-limits due to instability, you can hike up the old peak, Fugen-dake (1,359 m).

• The Route: The trail starts from Nita Pass. It takes about 60-90 minutes to reach the summit.
• The Experience: The trail is steep and rocky, passing through wind-twisted azalea bushes.
• The Reward: Standing on Fugen-dake, you are face-to-face with the massive lava dome of Heisei Shinzan, just a few hundred meters away. It is a thrilling and slightly unnerving experience to be so close to Japan’s youngest mountain peak.

Nita Pass and the Ropeway

For standard tourists, the Nita Pass (Nita-toge) offers the best view.

• The Ropeway: A cable car whisks visitors up close to the summit. From the top observatory, you can see the menacing, steaming lava dome of Heisei Shinzan up close. It is a stark, grey monster that contrasts with the colorful azaleas that bloom on the slopes in May and the brilliant autumn leaves in November.

The Taste of Resilience: Guzoni

No trip to Unzen is complete without tasting Guzoni, a soup that is literally the “taste of history.”

• Origins: The dish dates back to the Shimabara Rebellion of 1637. When the Christian rebels were besieged in Hara Castle, their leader, Amakusa Shiro, ordered them to gather all available food—mochi (rice cakes), vegetables, and seafood—and boil it into a nutritious soup to sustain the troops. They fought for months fueled by this meal.
• The Dish Today: Today, Guzoni is the signature dish of Shimabara. It is a dashi-based soup filled with round mochi, eel, lotus root, burdock, egg, and mushrooms. eating it is a way of communing with the region’s defiant past.

Unzen Vidro: The Glass of the West

Because Nagasaki was the only port open to the West during Japan’s isolation (Sakoku), Unzen has a unique tradition of glass-making, known as Vidro (from the Portuguese word vidro).

• The Craft: Local artisans create delicate, blown-glass objects. The most famous is the poppen, a flask-shaped toy that makes a “pop” sound when you blow into it. The fragility of the glass stands in stark contrast to the destructive power of the mountain that looms above the workshops.

Conclusion

Mount Unzen is a sombre giant. It is beautiful, with its seasonal flowers and steaming onsens, but it commands a fearful respect. The people of Shimabara live with the mountain not as an enemy, but as a temperamental neighbor. They have built a culture of resilience, turning their tragedies into lessons for the world, ensuring that the sacrifice of 1792 and 1991 was not in vain.