Qualla: Narusawa Ice Cave

Narusawa Ice Cave: Introduction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Osumi Akari, CC BY-SA 4.0. Step underground at the base of Mount Fuji and the temperature drops to 3 degrees Celsius in midsummer. The Narusawa Ice Cave is a 156-meter lava tube where enormous ice pillars -- some reaching three meters tall and half a meter thick -- grow upward from the cave floor each winter like frozen stalagmites. The cave formed during one of Mount Fuji's most violent recorded eruptions in 864 AD, when lava poured not from the summit crater but from a new vent called Mount Nagao on the volcano's northeast flank. That eruption lasted ten days, split a lake in two, and created the vast lava plain now buried beneath the Aokigahara forest -- the dense, silent woodland known as the Sea of Trees.

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Image: Osumi Akari | CC BY-SA 4.0

Narusawa Ice Cave: Born in Fire, Dressed in Ice

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Bernat Agullo from Tokyo, Japan, CC BY-SA 2.0. The cave's creation is a story of opposing elements. When the 864 eruption sent rivers of molten rock flowing northwest, the outer layers of lava cooled and hardened first, forming a rigid shell while still-molten rock continued to drain through the interior. The result was a hol...

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Image: Bernat Agullo from Tokyo, Japan | CC BY-SA 2.0

Narusawa Ice Cave: The Shogun's Cold Storage

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit TF1124 (talk), Public domain. Centuries before mechanical refrigeration existed, the people living around Mount Fuji recognized the cave's practical value. During the Edo period (1603-1868), workers carved rectangular blocks from the ice pillars and packed them for transport to the shogun and his court in Edo...

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Image: TF1124 (talk) | Public domain

Narusawa Ice Cave: Into the Aokigahara

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Kounoichi, CC BY-SA 4.0. The cave sits within the Aokigahara forest, a woodland so dense that its canopy blocks most sunlight and muffles sound. The forest grew atop the hardened lava flows from the 864 eruption, its trees rooted in thin soil over volcanic rock. The same eruption that created the Narusaw...

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Image: Kounoichi | CC BY-SA 4.0

Narusawa Ice Cave: A Trio of Underground Monuments

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Osumi Akari, CC BY-SA 4.0. Narusawa Ice Cave is one of three major lava tubes at Mount Fuji's northern base, all designated as Natural Monuments of Japan in 1929. Fugaku Wind Cave, located nearby, is known for its constant cool breezes and was also used for silkworm cocoon storage. Lake Sai Bat Cave, the t...

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Image: Osumi Akari | CC BY-SA 4.0