Toya (Japan): Recorded Eruptions and Historical Activity

Toya is a stratovolcano located in Japan, standing at an elevation of 733.0 meters with a tectonic setting characterized by a subduction zone and continental crust exceeding 25 km in thickness. Maintained in the official records of the Smithsonian Global Volcanism Program (volcano number 285030), the volcano has a documented history comprising 13 confirmed eruptions. These events span from early radiocarbon-dated activity through historical observations up to the year 2000, with a profile last-known eruption year noted as 2001 based on ending dates.

Overview of Recorded Eruptions

The confirmed eruption record for Toya contains 13 events identified through varying methods, ranging from calibrated radiocarbon isotopic analysis for prehistoric occurrences to direct historical reports for later centuries. Across the full structured record, the Smithsonian Global Volcanism Program records 8 eruptions with a measured Volcanic Explosivity Index (VEI). The largest recorded VEI in this dataset is 5.0.

Because the available collection includes representative records alongside derived totals, the known activity is distributed across multiple centuries and distinct local activity areas, such as Usu and Ko-Usu.

Chronological Distribution of Activity

The confirmed eruption count is distributed across several centuries BCE and CE:

• 66th century BCE: 1 eruption
• 46th century BCE: 1 eruption (with a start year uncertainty of 1,500 years, beginning around 6550 BCE)
• 17th century CE: 4 eruptions
• 18th century CE: 1 eruption
• 19th century CE: 2 eruptions
• 20th century CE: 4 eruptions

Selected Historical and Prehistoric Eruptions

The official record captures distinct eruptive phases across different centuries:

• Prehistoric Activity: An early confirmed eruption is recorded starting around 6550 BCE (with a start year uncertainty of 1,500 years) in the Usu activity area, determined via calibrated 14C isotopic evidence.
• 17th Century Events: Activity includes a reported eruption starting on July 25, 1638, followed by a larger event in the Usu activity area that began on August 16, 1663, and ended on September 5, 1663, reaching a VEI of 5.0.
• 18th Century Activity: A reported eruption occurred in the Ko-Usu activity area starting on January 23, 1769, with a VEI of 4.0.
• Recent Activity: An eruption began on the Usu north flank (Kompira-yama and western Nishi-yama) on March 31, 2000, with a VEI of 2.0, and concluded on September 15, 2001. None of these historical records are characterized as continuing in the source data.