Fujisan (Japan): Recorded Eruptions and Historical Activity

Overview and Tectonic Setting

Fujisan is a stratovolcano located in Japan with an elevation of 3,776 meters. According to the Smithsonian Global Volcanism Program, its tectonic setting is classified as a subduction zone on continental crust greater than 25 kilometers thick. The official record documents a total of 58 confirmed eruptions, spanning from prehistoric events dated via isotopic and tephrochronological methods to historical activity documented through direct observations.

The earliest recorded eruption year in the official profile is 8540 BCE (with a start year modifier indicating a date earlier than or around that point). The largest recorded eruption in the dataset reached a Volcanic Explosivity Index (VEI) of 5.0. While the structured event list records activity concluding in the early 18th century, the source profile lists the last known eruption year as 1708.

Chronological Eruption History

The confirmed eruption record spans multiple millennia, utilizing various evidence methods ranging from uncalibrated radiocarbon dating and tephrochronology to direct historical reports. The documented activity is distributed across numerous centuries BCE and CE:

• Prehistoric Activity: Early records include events such as an eruption on the south flank (near Mishima) indicated by uncalibrated 14C isotopic evidence starting around 8540 BCE (with a start year modifier >), as well as events indicated by tephrochronology around 2550 BCE (with a start year uncertainty modifier) and 100 BCE (with a 150-year uncertainty range).
• Historical Observations: As records transitioned to direct observations, specific dates and magnitudes were documented. For example, an eruption occurred in July 0781 CE with a recorded VEI of 3.0.
• Latest Recorded Eruptions: The structured record culminates with activity at the southeast flank's Hoei Craters, which began on December 16, 1707 CE, and ended on February 24, 1708 CE, reaching the maximum recorded Volcanic Explosivity Index of 5.0.

Understanding the Record and VEI

The Volcanic Explosivity Index (VEI) is a relative scale used to describe the size of explosive volcanic eruptions based on volume of products, eruption cloud height, and qualitative observations. Of the 58 confirmed eruptions in Fujisan's record, 30 have an associated VEI observation. The historical record relies heavily on a combination of reported human observations for later centuries and scientific dating techniques—such as radiocarbon analysis—for older, prehistoric events.