Zaozan [Zaosan] (Japan): Recorded Eruptions and Historical Activity

Zaozan [Zaosan] is a complex volcano located in Japan at an elevation of 1,841 meters within a subduction zone and continental crust tectonic setting. According to the Smithsonian Global Volcanism Program record, the volcano has a total of 43 confirmed eruptions spanning from 7600 BCE to 1940 CE. The largest recorded eruption magnitude in the official record reached a Volcanic Explosivity Index (VEI) of 4.0.

Geographical and Structural Context

Positioned at latitude 38.1439 and longitude 140.4397, Zaozan [Zaosan] features activity areas documented across distinct zones such as the Goshiki-dake area and Okama. The volcano's structure is classified as a complex type, reflecting diverse eruptive vents and features shaped over millennia of geological activity.

Chronology of Recorded Eruptions

The official record documents 43 confirmed eruptions utilizing various evidence methods, ranging from calibrated radiocarbon isotopic dating for prehistoric events to direct historical observations for later centuries. The earliest recorded eruption in the dataset dates back to 7600 BCE with a year modifier uncertainty, while the latest confirmed eruption concluded on May 18, 1940 CE.

Activity across centuries is unevenly distributed in the historical and geological record. Eruptive phases are documented in multiple centuries spanning BCE and CE eras, including notable clusters in the 17th and 19th centuries CE. Recorded Volcanic Explosivity Index (VEI) values among the observations reach up to 4.0, such as an event dated to 0300 CE (with a 200-year uncertainty), while later historical events—such as those in 1668, 1830, and the 1940 eruption—recorded lower VEI values ranging from 1.0 to 2.0.