What is Aokigahara? How is it related to the volcanic activity of Mount Fuji?

Hello! I'm really happy to chat with you about "Aokigahara Forest". Many people might find this name a bit mysterious or even eerie, but from a natural and geological perspective, it's actually a fascinating and unique place.

Let me break it down for you.

First, what exactly is Aokigahara Forest like?

Picture a vast, primeval forest so dense you can barely see the sky. It stretches out on the northwestern foot of Mount Fuji, spanning two villages in Yamanashi Prefecture.

Its characteristics are striking:

A sea of green: Viewed from above, the entire forest resembles a rolling green ocean – hence the name "sea of trees" (Jukai).
Unique ground: Walking inside, you'll find the footing very uneven. The ground isn't soft soil, but large, moss-covered black rocks. These rocks are strangely shaped and riddled with holes.
Tenacious trees: The trees here grow with incredible effort. Since the ground beneath is hard rock with only a thin layer of soil, roots can't delve deep. Instead, they spread across the rock surface like claws, tangling and gripping the ground to survive. The sight is truly spectacular.
Eerie quietness: The forest interior is remarkably quiet. Legend says the porous volcanic rock absorbs sound effectively, and combined with the dense foliage, this creates an isolated, profound silence.

So, how is this forest related to Mount Fuji's volcanic activity?

This is the core of the story and the coolest part!

Simply put, Aokigahara Forest grows directly on top of an ancient lava flow from Mount Fuji. Its unique nature is entirely thanks to one massive volcanic outburst from the mountain.

Here's what happened:

An epic eruption: Rewind to the year 864 AD, during Japan's Heian period over a thousand years ago. Mount Fuji experienced a colossal lateral eruption (not from the main crater but from its side) known historically as the Jōgan Eruption.
River of lava: Massive amounts of lava poured down the mountainside like a giant, scorching river of magma, carving its way northward and obliterating everything in its path. It buried a large lake that existed there at the time (known as "Seno-umi"), splitting it in two to form the present-day Lake Sai (Saiko) and Lake Shōji (Shōjiko).
Birth of new land: After this enormous lava flow cooled and solidified, it formed a vast, rugged plateau at Mount Fuji's base. This new "landmass" became the "foundation" of Aokigahara Forest.
Miracle of life: Over the next thousand-plus years, wind carried seeds onto this seemingly barren lava. Hardy plants like mosses and shrubs were the pioneers, taking root. Slowly, over time, these plants decomposed, creating a thin layer of soil. Larger trees, like Japanese hemlock and cypress, then began to grow. With the soil layer so thin, they had to spread their roots across the lava surface, creating the intricate, sprawling root systems we marvel at today.

So, you could say: Without that volcanic eruption, there would be no lava field. Without that lava field, there would be no Aokigahara Forest as we know it today. The forest itself is relatively "young" geologically and ecologically, only about 1,200 years old.

Adding a few more interesting points

The Compass Legend: It's often said compasses malfunction in the forest. This isn't supernatural. The volcanic rock forming the land is rich in magnetite, which disturbs the local magnetic field, causing compass needles to deflect. However, this effect usually isn't strong enough to render a compass useless; it's more of a local interference.
Lava Caves: As the lava flow cooled long ago, its surface solidified first while still-molten magma flowed underneath, creating hollow tubes known as "lava tunnels" or "lava caves." Several famous caves are within the Aokigahara area, like the year-round frozen Narusawa Ice Cave and the cool Fugaku Wind Cave. These are now major tourist attractions and direct products of that volcanic activity.

To summarize

Aokigahara Forest is far from an ordinary forest. It's a living testament to the volcanic power of Mount Fuji. Every moss-covered rock, every tree with its twisted roots, tells the story of that cataclysmic eruption over a millennium ago.

So, the next time you hear about Aokigahara Forest, beyond its more widely known associations, you can also consider it a natural wonder shaped by the Earth's forces – a natural laboratory for studying how ecosystems establish themselves in extreme environments.