Mount Asama

Mount Asama is an active volcano on Honshu, Japan, straddling Nagano and Gunma prefectures. Its frequent eruptions and explosive history have shaped nearby communities and landscapes.

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Stratovolcano: A steep, cone-shaped volcano built from alternating layers of lava, ash, and other volcanic deposits. Asama’s cone consists of layered deposits produced by repeated eruptions.
Tenmei eruption: The major 1783 eruption of Mount Asama, which devastated nearby areas and contributed to famine in Japan. This eruption is Asama’s most destructive historical event, with extensive impacts beyond the volcano.
Japan Meteorological Agency: Japan’s national agency for weather, climate, earthquake, tsunami, and volcanic monitoring and warnings. The agency monitors Asama and issues volcanic alerts as activity changes.
Onioshidashi Lava Flow: A rugged volcanic deposit on Mount Asama’s northern flank formed during the 1783 Tenmei eruption. It preserves the physical footprint of the eruption and is now a distinctive landscape.
Volcanic eruption: The release of magma, gases, and fragmented material from a volcano. Asama’s activity includes explosive eruptions and emissions of volcanic gases.
Asama eruption of 1108: A large medieval eruption of Mount Asama documented in Japanese historical records. Its deposits and records show that major explosive activity predates modern observation.
Volcanic alert level: A graded public warning system indicating volcanic activity and recommended restrictions or precautions. Japan uses alert levels to communicate changing danger around Asama.
Tenmei famine: A severe famine in Japan during the Tenmei era, intensified by crop failures and other disasters. Ashfall and cooling associated with the 1783 eruption compounded hardships during the famine.
Volcanic ash: Fine fragments of rock, minerals, and volcanic glass blasted into the atmosphere during an eruption. Ash from Asama’s eruptions has fallen across surrounding settlements and farmland.
Asama eruption of 2004: A series of explosive eruptions at Mount Asama in September 2004 that dispersed ash over a wide area. It illustrates the volcano’s capacity for disruptive ashfall during the modern monitoring era.