Unzen Pyroclastic Flow Day

What Is Unzen Pyroclastic Flow Day?

Every June 3rd is "Unzen Fugen-dake Prayer Day" (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, and Japanese firefighters, journalists, and local government officials who had moved closer to the mountain to observe and document the eruption. The disaster claimed the lives of some of the world's most distinguished volcanologists in a single catastrophic event.

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 a catastrophic eruption and associated tsunami killed approximately 15,000 people in the deadliest volcanic disaster in Japanese history. 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: The Shimabara Peninsula (島原半島) in Nagasaki — where Unzen's eruptions have periodically shaped the landscape — has been designated a UNESCO Global Geopark 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, Gansokun) in Shimabara City uses multimedia exhibits to educate visitors about the 1991-1995 eruption and the principles of volcanic disaster preparedness — one of Japan's most effective natural disaster interpretation facilities.