Aokigahara (青木ヶ原), also known as the Sea of Trees (樹海 Jukai) or the Suicide Forest, is a forest on the northwestern flank of Japan's Mount Fuji, thriving on 30 square kilometres (12 sq mi) of hardened lava laid down by the last major eruption of Mount Fuji in 864 CE.[1] The western edge of Aokigahara, where there are several caves that fill with ice in winter, is a popular destination for tourists and school trips. Parts of Aokigahara are very dense, and the porous lava absorbs sound, helping to provide visitors with a sense of solitude.[2]

The forest has an historical reputation as a home to yūrei: ghosts of the dead in Japanese mythology. In recent years, Aokigahara has become internationally known as "the Suicide Forest", one of the world's most prevalent suicide sites, and signs at the head of some trails urge suicidal visitors to think of their families and contact a suicide prevention association.

Geography
The forest floor mostly consists of volcanic rock which can be difficult to penetrate with hand tools. Since the forest is very dense, in recent years, hikers and tourists trekking through Aokigahara have begun to use plastic tape to mark their paths to avoid getting lost.[3] Designated trails lead to several tourist attractions such as the Narusawa Ice Cave, Fugaku Wind Cave and Lake Sai Bat Cave which are three larger lava caves near Mount Fuji, the ice cave being frozen year-round.[4]

Aokigahara has been falsely portrayed as a place where navigational compasses go haywire. Needles of magnetic compasses will move if placed directly on the lava, aligning with the rock's natural magnetism, which varies in iron content and strength by location. However, a compass behaves as expected when held at a normal height.[2] The Japan Ground Self-Defense Force has conducted its ranger courses including navigation training in the forest since 1956.[5]

Flora and fauna
Mammals include the Asian black bear,[6] small Japanese mole,[7] bats,[1] mice,[1] deer, fox, boar, wild rabbit, Japanese mink and Japanese squirrel.[8] Birds include great tit, willow tit, long-tailed tit, magerahigara, higera, great spotted woodpecker, pygmy woodpecker, bush warbler, Eurasian jay, Japanese white-eye, Japanese thrush, brown-headed thrush, Siberian thrush, Hodgson’s hawk-cuckoo, Japanese grosbeak, lesser cuckoo, black-faced bunting, oriental turtle dove, and common cuckoo.[8]

There are ground beetles and other insects,[1] including many species of butterflies, even in the forest interior Argynnis paphia, Chrysozephyrus smaragdinus, Celastrina argiolus, Celastrina sugitanii, Curetis acuta, Favonius jezoensis, Neptis sappho, Parantica sita and Polygonia c-album are found.[9]