Ata (Japan): Recorded Eruptions and Historical Activity

Ata is a caldera volcano located in Japan, standing at an elevation of 924 meters within a subduction zone and continental crust setting exceeding 25 kilometers in depth. According to the Smithsonian Global Volcanism Program, the volcano has a confirmed record of 23 eruptions spanning thousands of years, with activity documented from prehistoric eras through the early medieval period.

Overview of Recorded Eruptions

The historical and prehistoric record for Ata spans from its earliest recorded eruption year of 5050 BCE up to its latest recorded eruption in 885 CE. Across this timeline, eruptions have occurred across various activity areas associated with the volcanic system, including the Unagi, Narikawa, and Yamakawa maars, the Ikeda-ko caldera, and Kaimon. Evidence methods used to establish these eruptions range from tephrochronology correlations and uncalibrated radiocarbon isotopic dating to direct historical observations.

The largest recorded eruptions at Ata reached a Volcanic Explosivity Index (VEI) of 5.0. Out of the 23 confirmed eruptions, 20 have associated VEI observations. The latest recorded eruption began on August 29, 0885 CE, and concluded on September 28, 0885 CE, with a VEI of 4.0 based on reported observations.

Chronological Distribution of Activity

Confirmed eruptions at Ata are distributed across multiple centuries, reflecting intermittent volcanic episodes over millennia:

• 51st century BCE: 1 eruption (starting around 5050 BCE)
• 27th century BCE: 1 eruption (starting around 2690 BCE with a 75-year uncertainty)
• 21st century BCE: 1 eruption
• 18th century BCE: 1 eruption
• 17th century BCE: 1 eruption
• 16th century BCE: 1 eruption
• 15th century BCE: 2 eruptions
• 7th century BCE: 2 eruptions
• 3rd century BCE: 1 eruption
• 1st century BCE: 1 eruption
• 1st century CE: 1 eruption
• 2nd century CE: 2 eruptions
• 3rd century CE: 1 eruption
• 6th century CE: 2 eruptions
• 7th century CE: 1 eruption
• 8th century CE: 2 eruptions
• 9th century CE: 2 eruptions (including the latest recorded eruption in 885 CE)

The historical record shows no continuing eruptions. The latest recorded activity concluded in 885 CE, placing the last known eruption centuries in the past.