Kujusan (Japan): Recorded Eruptions and Historical Activity

Kujusan is a stratovolcano complex located in Japan, standing at an elevation of 1,791 meters within a subduction zone and continental crust setting exceeding 25 kilometers in thickness. Official records from the Smithsonian Global Volcanism Program document 13 confirmed eruptions spanning from deep prehistory into the late 20th century, with the earliest recorded event taking place around 9160 BCE and the latest structured confirmed eruption beginning on October 11, 1995. The profile lists the last known eruption year as 1996, concluding with activity at the Hosho lava dome on the east flank that ended on March 24, 1996.

Geological Setting and Eruptive Capacity

As a stratovolcano—a type of volcanic landform built up by alternating layers of lava flows, volcanic ash, and cinders—Kujusan sits in a tectonic environment shaped by subduction processes beneath continental crust. Across its recorded history, the volcano has produced explosive events of varying magnitudes, measured using the Volcanic Explosivity Index (VEI). Out of the 13 confirmed eruptions, 9 include VEI observations. The largest recorded VEI in the official record is 4.0, which characterizes several prehistoric explosive events identified through isotopic and tephrochronological methods.

Historical Eruption Timeline

The historical and prehistoric record of Kujusan is established through a combination of calibrated radiocarbon dating, tephrochronology, and direct observation. The earliest recorded eruption began around 9160 BCE with an uncertainty of 1,190 years and a VEI of 4.0. Subsequent prehistoric activity includes events identified across multiple millennia, such as eruptions in the 38th century BCE, 32nd century BCE, 25th century BCE, 18th century BCE, 10th century BCE, 1st century BCE, and the 4th century CE.

In later centuries, confirmed eruptions occurred during the 17th century CE and 20th century CE. The final recorded event in the structured eruption database began on October 11, 1995, at the Hosho lava dome on the east flank, featuring a VEI of 1.0, and concluded on March 24, 1996.

Summary of Eruptive Activity

The table below summarizes selected confirmed eruptions from Kujusan's official record, illustrating the variety of evidence methods, activity areas, and eruption magnitudes documented by the Smithsonian Global Volcanism Program. This selection represents key points across the 13 total confirmed eruptions in the database.