Shikotsu (Japan): Recorded Eruptions and Historical Activity

Shikotsu is a caldera volcano located in Japan at latitude 42.688° N and longitude 141.38° E, with a summit elevation of 1,320 meters. Situated in a subduction zone characterized by continental crust thicker than 25 kilometers, the volcanic complex has a documented eruptive record maintained by the Smithsonian Institution's Global Volcanism Program under volcano number 285040.

Chronology of Recorded Eruptions

Official records document 41 confirmed eruptions at Shikotsu. The documented eruptive history extends from an uncalibrated radiocarbon-dated event in approximately 6950 BCE to the most recent confirmed event on February 27, 1981. Over time, the distribution of confirmed events by era and century includes:

• 70th century BCE: 1 eruption
• 6th century BCE: 1 eruption
• 1st century BCE: 2 eruptions
• 15th century CE: 1 eruption
• 16th century CE: 1 eruption
• 17th century CE: 1 eruption
• 18th century CE: 2 eruptions
• 19th century CE: 9 eruptions
• 20th century CE: 23 eruptions

The concentration of events in the 19th and 20th centuries reflects both the volcano's eruptive frequency and the expansion of continuous direct human observation and written reporting in modern times.

Explosive Magnitude and Key Eruptive Events

The scale of explosive activity at Shikotsu is measured using the Volcanic Explosivity Index (VEI), an open-ended scale ranking explosive power based primarily on ejecta volume and plume height. All 41 confirmed eruptions have assigned VEI ratings, with the largest known events reaching a VEI of 5.0.

Documented eruptive activity in the official catalog includes events centered at post-caldera vents such as Tarumai:

The August 1739 eruption represents one of the largest historically documented explosive events at the complex, rated at VEI 5.0. Twentieth-century activity was characterized primarily by lower-magnitude events, including the VEI 1.0 eruption on February 27, 1981, which concluded on the same day.