Mount Fuji Geography: Volcanic Status, Geology & Physical Facts

Mount Fuji at a Glance: Key Geographic Facts

Mount Fuji (富士山) stands at 3,776m (12,388ft) on the border of Yamanashi and Shizuoka prefectures, roughly 100km (62 miles) southwest of Tokyo. It is Japan's highest peak and one of the most recognizable mount fuji mountains in the world. As a stratovolcano (成層火山) — a steep-sided cone built from alternating layers of lava and volcanic ash — Fuji is classified as an active volcano by the Japan Meteorological Agency (JMA).

Despite its calm appearance, Fuji last erupted in 1707 and remains under continuous monitoring. For more on elevation facts and current weather conditions or how Japan's highest peak compares to other mountains, see our dedicated guides. You can also browse all Mount Fuji guides for the complete picture.

How Mount Fuji Formed: Four Volcanic Phases

Fuji is not one volcano but four stacked on top of each other. According to the Geological Survey of Japan (GSJ), the mountain evolved through four distinct volcanic phases over roughly 700,000 years. Each phase produced a different cone, and the newest one is what you see today.

For detailed trail maps of the mountain, see our area guide.

Sen-Komitake and Komitake: The Ancient Base (700,000–100,000 Years Ago)

The oldest layer is Sen-Komitake, a volcanic foundation that began forming around 700,000 years ago. On top of it grew Komitake (小御岳), whose remnants are still partially visible on Fuji's north slope near the 5th station. Komitake was a broad, relatively low volcano that provided the platform for everything that followed.

Ko-Fuji (Old Fuji): The Explosive Middle Phase

Starting around 100,000 years ago, Ko-Fuji (古富士, Old Fuji) erupted repeatedly with violent explosions. This phase produced large volumes of volcanic ash and pyroclastic material, building the mountain's height substantially. Ko-Fuji eruptions were more explosive than those of the current cone, sending debris across much of the Kanto plain.

Shin-Fuji (New Fuji): The Mountain You See Today

Approximately 10,000 years ago, Shin-Fuji (新富士, New Fuji) began forming over the older cones. This current phase is characterized by more fluid basaltic lava flows that spread evenly in all directions, gradually building the iconic symmetrical profile. Shin-Fuji has erupted numerous times since its formation, with the most recent being the Hoei eruption of 1707.

Why Mount Fuji Is a Perfect Cone

Visitors often wonder how Fuji achieved its near-perfect symmetry when most volcanoes have irregular shapes. The answer lies in the composition of its lava. According to GSJ data, Fuji's magma ranges from basaltic to dacitic, but the dominant Shin-Fuji eruptions produced basaltic lava — relatively fluid material that flows evenly down all sides of the cone before solidifying.

The mountain's position at a tectonic junction also plays a role. Magma rises through a relatively uniform conduit, and without dominant rift zones pulling lava in one direction, the material distributes symmetrically. The Hoei crater on the southeast flank is one of the few visible breaks in this symmetry, created during the 1707 eruption.

It is worth noting that Fuji's perfect shape is geologically young. The older cones beneath (Ko-Fuji and Komitake) were not symmetrical at all. What you see today is essentially a 10,000-year-old coat of lava draped over a much older, irregular foundation.

The 1707 Hoei Eruption: Fuji's Last Explosion

The Hoei eruption (宝永噴火) of 1707 was triggered shortly after a massive earthquake in the same year, one of the largest in Japanese recorded history. The eruption did not produce lava flows but instead ejected enormous volumes of volcanic ash and pumice.

According to the Tokyo Metropolitan Government's ashfall simulation data, ash from the Hoei eruption reached Edo (present-day Tokyo), roughly 100km away. Significant ash accumulations were recorded across the city. The eruption created the Hoei crater (宝永火口), a prominent scar still visible on Fuji's southeast flank that you can explore on the summit crater Ohachi-meguri trail.

The Hoei eruption's VEI (Volcanic Explosivity Index) rating varies in the literature, with Japanese and international sources placing it between VEI 3 and VEI 5. Regardless of the exact classification, it demonstrated that Fuji is capable of eruptions with significant regional impact.

Is Mount Fuji Still Active? Volcanic Monitoring Today

Yes, Mount Fuji is an active volcano. The JMA maintains it at Volcanic Alert Level 1 (normal conditions) as of 2026, meaning no unusual volcanic activity has been detected. However, Level 1 does not mean "inactive" — it simply means the mountain is behaving normally for an active volcano.

JMA's Five-Level Volcanic Alert System

The JMA uses a five-level alert system (火山警戒レベル) for all monitored volcanoes in Japan:

Level	Status	Action
1	Normal	No restrictions
2	Near-crater warning	Restricted areas near crater
3	Mountain entry restricted	Do not approach the mountain
4	Evacuation preparation	Prepare to evacuate surrounding areas
5	Evacuation	Immediate evacuation required

Fuji is monitored around the clock using seismometers, GPS ground deformation sensors, and cameras installed by both JMA and university research teams. A swarm of deep low-frequency earthquakes was recorded beneath Fuji between 2000 and 2001, drawing attention from volcanologists, though no surface activity followed.

What Happens If Fuji Erupts Again

The Japanese government has developed detailed hazard maps and evacuation plans for areas surrounding Mount Fuji. According to Tokyo Metropolitan Government simulations, a Hoei-scale eruption today could deposit several centimeters of ash across the greater Tokyo area, potentially disrupting transportation, power grids, and water supplies for millions of people. These plans are regularly updated and practiced by local municipalities.

Tectonic Setting: Where Three Plates Collide

Mount Fuji sits at one of the most geologically significant locations on Earth. According to the Geological Survey of Japan, the mountain is positioned near the junction of three tectonic plates: the Eurasian Plate, the North American Plate, and the Philippine Sea Plate.

The Philippine Sea Plate subducts beneath the Eurasian Plate along the Suruga Trough to Fuji's south, while the Pacific Plate dives under the North American Plate along the Japan Trench to the east. This rare triple-junction configuration creates an unusually active zone of magma generation beneath the mountain.

This tectonic setting explains why Fuji exists at all. The subducting plates release water into the mantle, lowering the melting point of rock and generating magma that rises to feed the volcano. It also explains why the surrounding region experiences frequent earthquakes, including the Hoei earthquake that preceded the 1707 eruption.

Frequently Asked Questions