What Type of Volcano Is Mount Fuji? Geology & Eruption History

What Type of Volcano Is Mount Fuji?

Mount Fuji (富士山) is a stratovolcano, also called a composite volcano (成層火山). This classification means it was built up over thousands of years by alternating layers of hardened lava, volcanic ash, and rock debris — producing the steep, symmetrical cone that makes Fuji instantly recognizable.

According to the Japan Meteorological Agency (JMA), Mount Fuji is classified as an active volcano. In Japan, "active" means a volcano that has erupted within approximately the last 10,000 years or currently shows volcanic activity such as fumaroles or seismic swarms. This does not mean an eruption is imminent — Fuji has been quiet since 1707.

At 3,776 meters (12,389 feet), Fuji is Japan's highest peak and one of the world's most iconic stratovolcanoes, alongside Mt. Rainier in Washington State and Mt. Vesuvius in Italy. Its near-perfect conical shape, visible from Tokyo on clear days, is a direct result of its volcanic construction. This article explores Fuji's geology and eruption history as part of our Yamanashi volcanic landscape coverage.

How Mount Fuji Formed: Three Volcanoes in One

Old Fuji, New Fuji, and the Layers Beneath

The mountain you see today is actually the most recent in a series of volcanic constructions on the same site. Geologists identify three distinct phases:

1. Komitake (小御岳) — the oldest volcano, formed several hundred thousand years ago. Its remnants are buried beneath the current cone
2. Old Fuji (古富士) — built on top of Komitake roughly 100,000 years ago through repeated eruptions
3. New Fuji (新富士) — the current cone, which began forming approximately 10,000 years ago and produced the shape we recognize today

Each layer added height and mass. The transition from Old Fuji to New Fuji involved a shift from explosive eruptions (producing ash and pumice) to more effusive eruptions (producing lava flows), which contributed to the smooth profile of the upper slopes.

Why Fuji's Shape Is So Symmetrical

Fuji's unusually symmetrical cone results from eruptions occurring from a central vent rather than from multiple side vents. While many stratovolcanoes develop irregular profiles from lateral eruptions, Fuji's eruptions were predominantly vertical, building layers evenly around the summit. The 1707 Hōei eruption was a notable exception — it created a secondary crater on the southeast flank that slightly disrupts the symmetry when viewed from certain angles.

The 1707 Hōei Eruption: Fuji's Last Explosion

What Happened During the Eruption

The Hōei eruption (宝永噴火) began on December 16, 1707, and continued into January 1708. According to JMA records and Yamanashi Prefecture documentation, the eruption was explosive rather than effusive — it produced massive amounts of volcanic ash and pumice rather than lava flows.

The eruption opened a new crater on Fuji's southeast slope, and volcanic ash fell across a wide area. Ash deposits reached Edo (modern-day Tokyo), approximately 100 km to the east, disrupting daily life and agriculture. The eruption was triggered in part by a massive earthquake (the Hōei earthquake, magnitude 8.7) that struck just 49 days earlier.

The Hōei eruption was significant but not catastrophic in terms of casualties. The primary damage was agricultural — ash blanketed farmland across the Kantō plain, ruining crops and contaminating water supplies.

The Hōei Crater You Can Visit Today

The Hōei Crater is a visible scar on Fuji's southeast flank, creating the mountain's only major asymmetry. From the Yamanashi (north) side, the crater is less prominent, but from the Shizuoka (south) side and from many viewpoints along the Tōkaidō Shinkansen line, the secondary cone (Hōei-zan, 宝永山, 2,693m) is clearly visible.

A hiking trail from the Fujinomiya 5th Station on the Shizuoka side leads to the Hōei Crater rim at approximately 3,100 meters. This is accessible during the climbing season (July to September) and offers an up-close look at the volcanic geology without requiring a summit attempt.

Japan's Volcano Monitoring System for Mount Fuji

The 5-Level Alert System Explained

JMA operates a 5-level volcanic alert system (噴火警戒レベル) for all active volcanoes in Japan, including Mount Fuji:

Level	Status	Meaning
1	Normal	Background volcanic activity, safe for normal access
2	Near-crater warning	Restricted access near crater
3	Mountain restriction	No climbing, surrounding areas on alert
4	Evacuation preparation	Prepare to evacuate surrounding areas
5	Evacuation	Evacuate immediately

As of 2026, Mount Fuji is at Level 1 (normal). It has remained at Level 1 continuously. JMA monitors the mountain 24/7 using seismometers, GPS positioning stations, tilt meters, and observation cameras installed around the crater and slopes.

What "Active Volcano" Actually Means in Japan

Japan's Coordinating Committee for Prediction of Volcanic Eruptions (火山噴火予知連絡会) classifies 111 volcanoes as "active" across the country. The definition is broad — any volcano that has erupted within the past 10,000 years qualifies. This means "active" in the Japanese classification does not imply imminent danger.

For context, Fuji last erupted over 300 years ago. The monitoring infrastructure exists precisely because Japan takes volcanic risk seriously, not because an eruption is expected soon. Many visitors on Reddit and TripAdvisor ask whether Fuji is safe — the answer is that Japan's monitoring system is among the most advanced in the world, and any change in volcanic activity would trigger alerts well before reaching dangerous levels.

Seeing Fuji's Volcanic Features Up Close

Hōei Crater Hike from the 5th Station

During the climbing season (approximately July 1 to September 10), the Hōei Crater trail is accessible from the Fujinomiya 5th Station on the Shizuoka side. The trail leads to the crater rim and Hōei-zan peak (2,693m) and takes approximately 2-3 hours round trip. This is a moderate hike that offers dramatic volcanic scenery — exposed rock, ash fields, and views into the crater interior — without the commitment of a full summit climb.

Note that the Yamanashi-side 5th Station (Subashiri and Yoshida routes) does not provide direct access to the Hōei Crater. If this is your primary goal, approach from the Shizuoka side.

Mt. Fuji Panorama Ropeway from Kawaguchiko

For a non-hiking volcanic viewpoint, the Mt. Fuji Panorama Ropeway near Lake Kawaguchiko offers panoramic views of Fuji's volcanic cone and the surrounding landscape. The ropeway operates 9:00-17:00 (seasonally adjusted) and costs ¥1,500 (~$10) roundtrip for adults and ¥750 (~$5) for children. It is closed from late November through early April for maintenance.

From the observation deck, you can see Fuji's full profile including the Hōei Crater scar, the summit crater, and the layered geological structure that defines a stratovolcano. Clear winter days offer the sharpest views.

Visiting Mount Fuji: Access and Practical Info

From Tokyo: Highway buses run from Tokyo Station and Shinjuku to Kawaguchiko Station in approximately 2 hours, costing around ¥2,000 (~$13) one way. The Fuji Kyuko Railway connects to the JR Chuo Line.

Kawaguchiko area: Kawaguchiko Station is the main gateway on the Yamanashi side. From here, buses run to the 5th Station during climbing season (approximately ¥2,100 roundtrip). The Panorama Ropeway station is accessible by local bus or taxi.

Climbing season: The official climbing season runs approximately July 1 to September 10. A ¥2,000 (~$13) cooperation fee is requested from climbers. Outside this window, the mountain is officially closed to climbers due to extreme weather and lack of mountain hut services.

Best viewing conditions: Winter (December-February) offers the clearest skies for viewing Fuji from the Yamanashi side. Summer heat haze frequently obscures the mountain, particularly in the afternoon. Early morning views are consistently the best year-round.

Frequently Asked Questions

Is Mount Fuji safe to climb if it's an active volcano?

Yes. Mount Fuji is currently at JMA alert Level 1 (normal activity) and has not erupted since 1707 — over 300 years ago. The mountain is monitored 24/7 with seismometers, GPS, and tilt meters. The climbing season (July-September) has full safety infrastructure including mountain huts, trail markers, and rescue services. Any change in volcanic activity would trigger public alerts well in advance.

What would happen if Mount Fuji erupted today?

Government hazard maps predict volcanic ash falling on Tokyo within hours of a major eruption, similar to the 1707 Hōei event. Yamanashi and Shizuoka Prefectures would face lava flows, pyroclastic material, and mudflows. Comprehensive evacuation plans exist for surrounding towns. Currently there are no signs of imminent eruption, and JMA's monitoring network would detect precursors weeks to months in advance.

Can you see the Hōei Crater without climbing to the summit?

Yes. The Hōei Crater is visible from many viewpoints in both Yamanashi and Shizuoka Prefectures. For a close-up look, a trail from the Fujinomiya 5th Station (Shizuoka side) reaches the crater rim at approximately 3,100 meters in 2-3 hours round trip. The Mt. Fuji Panorama Ropeway near Kawaguchiko (¥1,500 roundtrip) provides a distant but clear view of the crater scar on Fuji's southeast flank.

How much does it cost to visit Mount Fuji's volcanic viewpoints?

The Mt. Fuji Panorama Ropeway costs ¥1,500 (~$10) roundtrip for adults. Bus access to the 5th Station costs approximately ¥2,100 (~$14) roundtrip from Kawaguchiko. During climbing season, a ¥2,000 (~$13) cooperation fee is requested from climbers. The Fuji Volcano Monitoring Center is free to visit (closed Mondays).