Mount Fuji, an iconic symbol of Japan, is a majestic stratovolcano renowned for its striking beauty and deep cultural significance. Reaching an elevation of 3,776 meters, it is the highest mountain in Japan. Its almost perfect conical shape has inspired countless artists and been a site of spiritual importance for centuries.
The Hoei Eruption
Mount Fuji’s last confirmed eruption, the Hoei eruption, began on December 16, 1707, and concluded on February 24, 1708. This Plinian eruption ejected pumice, scoria, and ash without significant lava flows. It occurred on the mountain’s southeast flank, creating three new vents known as the Hoei craters.
Ashfall from the Hoei eruption was widespread, blanketing areas up to 100 kilometers away, including Edo (present-day Tokyo). An estimated 800 million cubic meters of volcanic ash were released, causing significant disruption. This heavy ashfall led to agricultural decline, starvation, and subsequent flooding as ash-clogged rivers overflowed. The eruption was preceded by warning signs, including rumbling sounds beginning in 1704 and strong earthquakes, notably the Hoei earthquake 49 days prior.
Mt. Fuji’s Volcanic History
Mount Fuji’s formation evolved through distinct phases of volcanic activity. The earliest stage involved the Komitake volcano, active approximately 700,000 years ago. This was succeeded by Ko-Fuji, or “Old Fuji,” which developed between 100,000 and 10,000 years ago. The current structure, Shin-Fuji or “New Fuji,” began forming about 10,000 years ago and continues to the present.
Throughout its history, Mount Fuji has experienced various eruption styles, from lava flows to explosive ash eruptions. Historical records indicate periods of significant activity, such as the Heian era, which saw twelve eruptions between 800 and 1083 AD. There were also long quiescent periods, including over 400 years without recorded activity between 1083 and 1511.
Current Status and Monitoring
Mount Fuji is classified as an active volcano, despite its inactivity since 1707. Scientific monitoring efforts are underway to detect changes in its behavior. Networks of seismographs are placed to detect earthquakes and volcanic tremors, providing insights into magma movement beneath the surface.
Other monitoring methods include GPS stations that measure ground deformation, indicating swelling or changes in the volcano’s shape. Scientists also analyze gas emissions and temperature changes, which signal subsurface activity. Agencies such as the Japan Meteorological Agency and the multi-prefectural Mt. Fuji Volcano Disaster Prevention Council collaborate to oversee monitoring and manage data.
Understanding Future Activity
While Mount Fuji remains dormant, its active status means future eruptions are possible, though their exact timing and scale cannot be predicted. Potential hazards from a renewed eruption include widespread ashfall, pyroclastic flows, and lava flows. Ashfall, even in small amounts, could disrupt transportation, cause power outages, and pose health risks, particularly in densely populated areas like Tokyo, located about 100 kilometers away.
To mitigate these risks, comprehensive preparedness measures and contingency plans are in place. These include hazard maps and updated evacuation plans, which advise residents to stock essential supplies and, in some scenarios, to seek refuge indoors or evacuate on foot. Authorities regularly conduct drills and simulations to enhance public safety and ensure effective response to renewed volcanic activity.