What Happens When You Enter Fuji's Sea of Trees: How Aokigahara Forest Formed and Why People Get Lost

Aokigahara lies to the northwest of Mount Fuji, a forest stretching across roughly 30 square kilometers. There are several theories about the origin of the name "Jukai" (Sea of Trees), but it is generally thought to come from how the forest looks from above. The lush green trees spread out like a carpet, and when the wind blows, the forest sways so that it looks like the sea rippling with waves. That, it is said, is how it came to be called the Sea of Trees.

The birth of this forest is closely tied to Mount Fuji's eruptions. This area was originally home to a large lake called Senoumi. During the great Jōgan eruption, which began in 864, lava flows poured in and completely covered the lake. Remnants of Senoumi can be seen today in Lake Shōji and Lake Sai.

Even on land buried by lava, life eventually returned. The first to spread were "pioneer plants" that could survive in harsh conditions, and trees are thought to have begun growing after that. However, roots cannot penetrate hard lava. As a result, even now, more than 1,000 years later, the roots of trees such as Japanese cypress and hemlock lie exposed on the surface. In some places, you can reportedly see roots undulating like waves.

While it is a dreamlike place, the narrator says that most people do not have a favorable impression of Aokigahara. That is because people continue to come here to end their own lives. This is said to trace back to Seichō Matsumoto's novel Nami no Tō (Tower of Waves), published around 1960. Its ending, in which the protagonist ultimately takes her own life in the forest, caused a huge stir, and the number of people trying to do the same reportedly increased from then on.

In recent years, to keep more people from following suit, the exact number of people who have gone missing or taken their own lives in Aokigahara is no longer officially announced. Local municipalities also approach and talk with visitors to prevent tragic outcomes. According to the video, 346 people were approached in fiscal 2020, and some of them appear to have been taken into protective care.

So, once you enter the Sea of Trees, can you never come out again? The narrator's answer is "Not at all." Parts of the forest have walking trails maintained for tourists, and you can get close by car or bus. People pass through every day, and there is nothing frightening about it, the narrator says.

From the trails, you can see the ground thick with moss and ferns, and the faint sunlight filtering through the trees overhead. The narrator describes this as a dreamlike space. They also mention that you might encounter plants and animals such as the ghost plant (ginryōsō), sometimes simply called a "ghost."

The forest is also known for its lava caves. Low-viscosity lava from past eruptions cooled and hardened from the surface first as it flowed. Meanwhile, the lava inside kept flowing, and when only the interior lava drained away, a hollow was left behind. This can become a cave. Among the largest of these is said to be Fugaku Wind Cave. It has a total length of 201 meters, stays cool even in summer, and has an average temperature of 3 degrees. It draws many tourists as one of the signature attractions of the Mount Fuji area. The narrator explains that if you are just visiting as a tourist, there is nothing particularly dangerous, and it is a place where you can feel the workings of nature on a grand scale.

But once you leave the trail and start walking where there is no path, the forest shows a different face. The trees grow dense, and only a little light reaches the ground. The ground is covered in moss and ferns, and tree roots writhe across lava so rugged there is barely anywhere to put your feet. On such uneven ground, walking suddenly becomes difficult, and even covering a short distance turns into a struggle.

Just a short distance from the trail, you feel surrounded by forest. The same kind of forest stretches in all 360 degrees as far as you can see, and even if you try to use the sun as a guide, the trees block it so you cannot get an accurate sense of direction. Even if you try to turn back, you no longer know which way you came from. In fact, in 2025, a man who had been gathering mushrooms got lost in the forest after just about 10 minutes and had to be rescued by police.

Why does this happen? The narrator explains that without a landmark to serve as a reference point, humans cannot walk as straight as they think, and introduces a study published in 2009. In this study, participants were made to walk in a German forest and in the Sahara Desert. When the sun or moon was visible, participants were able to walk relatively straight. But on cloudy days or when blindfolded, they began walking in circles around the same area, even though they believed they were going straight.

Their paths reportedly did not even form neat circles. In many cases, participants changed direction irregularly within an area less than 20 meters in diameter. In situations with no external cues at all, they got no farther than 100 meters from their starting point on average. In other words, the conclusion drawn from the study, as presented in the video, is that the human sensorimotor system is not built to walk accurately in a straight line without landmarks.

According to the narrator, Aokigahara is an environment where this weakness is especially likely to show. The dense trees hide the sun's position, distant buildings are hard to see, and in some places even Mount Fuji cannot easily be made out. On top of that, each time you climb over tree roots or uneven lava, your body's balance shifts slightly, and your sense of direction gradually drifts. The farther you get from the trail, the less you know where you came from, the narrator says.

On the other hand, the narrator points out that some of the commonly told stories involve misconceptions. The best known is the claim that "compasses spin around and are useless in the forest." In reality, if you hold a compass correctly, you can determine direction well enough, the narrator says. Because the lava that forms the ground contains magnetic minerals such as magnetite, the needle can be affected if you bring a compass close to the lava. Even so, it is not as though compasses malfunction constantly throughout the entire forest. The idea that "compasses don't work at all" is a superstition, the narrator states.

There is a similarly exaggerated image of cell phone reception and GPS, the narrator says. There appear to have been places in the past where signals had trouble reaching, but in recent years more cell towers have been built, and the problem is not as serious as it once was. The video's explanation is that if you are properly prepared, you will not be completely cut off the moment you enter the forest.

Even so, getting lost is dangerous because people lose their composure, the narrator says. People in a panic can do things they would never normally consider. In cases of people lost in forests, they may pass right by rescue teams without noticing, or in extreme cases even behave as if they are avoiding rescue. However irrational it may seem in theory, people gripped by fear cannot easily maintain sound judgment. The narrator concludes that the essence of what makes the forest frightening lies in this psychological state.

When it comes to other things to fear in the forest, the first thing many people may think of is stumbling upon a body. The narrator says that this possibility is not zero, but that it is not so common that you would encounter one on a single visit. As mentioned earlier, ongoing outreach and searches are conducted, and the forest as a whole is not filled with such places, the narrator says.

Rather, what you realistically need to watch out for is wild animals, the narrator points out. Asian black bears have been sighted in the surrounding area, and deer sometimes dash through the forest at high speed. The narrator frames these not as supernatural phenomena but as realistic risks that humans who venture into nature must face.

The video's conclusion is that Aokigahara is a place where you can enjoy nature as long as you stay on the trails and are properly prepared. But it is also a place where one wrong step makes you realize how easily humans lose their sense of direction and become ruled by fear. The narrator says that what is frightening about the forest is not some unknowable presence, but the way human weakness is laid bare in nature.

The narrator also acknowledges that Aokigahara has, in some respects, been sensationalized as an object of fear. That said, they describe it as a place that could be called a symbol of vitality, where, after lava flows from an eruption covered everything, life slowly took root again over a long period of time. The narrator closes by asking that if you visit this quiet forest that has nurtured life for more than 1,000 years, you stay on the trail and spare a moment's thought for the long history of life layered beneath your feet.