The snow-capped cone of Mount Fuji is globally recognized as a symbol of Japan, but beneath its serene appearance lies a complex geological structure. As the country’s highest peak, the mountain is a stratovolcano subject to continuous scientific investigation regarding its potential for renewed activity. Determining whether Mount Fuji is “dormant” or remains a long-term threat requires understanding how geologists classify volcanoes and examining the mountain’s history and current subterranean conditions. Its status is a serious concern for the millions of people living in the greater Tokyo metropolitan area nearby.
Understanding Volcanic Status
Scientists typically use three classifications to describe a volcano’s activity level: active, dormant, and extinct. An active volcano is one that has erupted within the Holocene epoch (the last 11,700 years) or shows signs of ongoing unrest, such as seismic activity or gas emissions. This classification relies on recent geological history, not necessarily a current eruption.
The term “extinct” applies to volcanoes believed to have completely severed their connection to a magma source and are not expected to erupt again. The designation of “dormant” is less formal and often interchangeable with “quiescent.” Quiescent describes an active volcano that is currently quiet but retains the potential to erupt. Mount Fuji’s classification hinges on its historical context, placing it firmly outside the extinct category.
Mount Fuji’s History of Activity
Mount Fuji is geologically structured from three main formations, the most recent being the New Fuji volcano, which has been active for the past 10,000 years. Historical records confirm at least 17 eruptions since 781 CE, establishing it as a cyclically active system. The most recent and consequential event was the Hoei Eruption, which began in December 1707 and lasted until February 1708.
This eruption was a powerful, Plinian-type event that did not produce lava flows but generated immense columns of ash and cinders. The event reached a Volcanic Explosivity Index (VEI) of 5, depositing over 800 million cubic meters of material. Ash reached Edo (present-day Tokyo), over 100 kilometers away. The Hoei eruption is believed to have been triggered by the massive magnitude 8.7 Hoei earthquake that struck 49 days earlier, demonstrating the mountain’s sensitivity to regional tectonic forces. Because its last eruption occurred only about 300 years ago, well within the 11,700-year geological window, Japanese agencies officially classify Mount Fuji as an active volcano.
Current Geological Monitoring and Unrest
Despite its current quiescent state, Mount Fuji is subjected to an intensive, multi-layered monitoring program. The monitoring network includes an array of seismographs, Global Positioning System (GPS) deformation sensors, and tiltmeters installed in deep boreholes around the cone. This equipment continuously tracks subterranean magma movement, ground swelling, and seismic activity.
Signs of “unrest” have appeared periodically, notably an intense swarm of deep low-frequency (DLF) earthquakes beneath the volcano in 2000 and 2001. These deep tremors suggested the movement or accumulation of molten material within the volcano’s plumbing system. Furthermore, the massive 2011 Tohoku earthquake and its subsequent magnitude 5.9 aftershock near Fuji generated significant stress changes on the mountain’s magma chambers.
The 2011 event did not immediately trigger an eruption, but it served as a reminder that major tectonic shifts can affect the pressure balance beneath the volcano. Scientists continue to track subtle changes in ground inflation, which could signal pressurization of the magma reservoir, and fluctuations in gas emissions. The Japanese Meteorological Agency maintains Mount Fuji at Volcanic Alert Level 1, recognizing its potential for impact but noting its current non-eruptive status.