Unzen Pyroclastic Flow Day

What Is Unzen Pyroclastic Flow Day?

Every June 3rd is "Unzen Fugen-dake Prayer Day" (also called "Inori no Hi") (雲仙普賢岳祈りの日, Unzen Fugen-dake Inori no Hi) in Japan. On June 3, 1991, a massive pyroclastic flow (火砕流, kasairyū) from Mt. Fugen (普賢岳) on the Unzen volcanic complex in Nagasaki Prefecture killed 43 people — including renowned French volcanologists Maurice and Katia Krafft, American volcanologist Harry Glicken, as well as Japanese journalists, volunteer firefighters, police officers, taxi drivers, and local residents. Shimabara City has designated June 3rd as "Inori no Hi" (Day of Prayer), and since 1998 has worked to keep the lessons of the disaster alive. At 4:08 p.m., the time the pyroclastic flow occurred, sirens sound across the city for a moment of silence.

The 1991 Unzen Eruption

Mt. Fugen on the Unzen volcanic complex began erupting in November 1990 after nearly 200 years of dormancy — its first eruption since 1792, when an eruption was followed by the collapse of Mt. Mayuyama and a tsunami that killed about 15,000 people -- Japan's deadliest volcano-related disaster. The 1990-1995 eruption produced lava dome growth, pyroclastic flows, and lahars (volcanic mudflows) that repeatedly threatened communities in the Shimabara area of Nagasaki Prefecture. The June 3, 1991 pyroclastic flow — which expanded significantly beyond its predicted path — caught observers who believed they were at a safe distance.

The Kraffts' Legacy

Maurice and Katia Krafft were French volcanologists who spent their careers documenting volcanic activity through photographs and film — creating an extraordinary archive of footage that has educated millions about volcanism. Their deaths at Unzen alongside fellow scientist Harry Glicken gave the June 3 date a global resonance in the volcanology community beyond its Japanese significance. Their footage, compiled in documentary films including "Fire of Love" (2022), continues to be shown to students of earth science worldwide.

Fun Facts

• Shimabara Peninsula: In 2009, the Shimabara Peninsula (島原半島) in Nagasaki became, together with Toya-Usu and Itoigawa, one of the first areas in Japan certified as a Global Geopark (a UNESCO Global Geopark since 2015) recognizing its extraordinary geological heritage, including the 1792 tsunami deposits, the 1990-95 lava dome remnants, and hot spring landscapes created by volcanic activity.
• Disaster prevention museums: The Unzen Disaster Memorial Hall (雲仙岳災害記念館, nicknamed "Gamadas Dome") in Shimabara City uses exhibits to educate visitors about the 1990-1995 eruption and volcanic disaster preparedness. Nearby, houses buried by volcanic mudflows are preserved as they were.