Narusawa Ice Cave: A lava tube filled with 10-foot-tall ice columns at the foot of Mount Fuji.

The average annual temperature in Narusawa Cave is around 37°F, which contributes to the permanent ice cover. (Photo: amana images inc. via Alamy) KEY FACTS

Name: Ice Grotto Narusawa Hyoketsu

Location: Fuji Five Lakes Region, Japan

Coordinates: 35.475766342241734, 138.6658965143265

Uniqueness: Formed by volcanic lava from Mount Fuji, contains large ice formations.

Narusawa is a lava channel decorated with ice columns and crystal formations at the base of Fuji.

Lava tubes are natural cavities that form under cooled magma flows. The upper layers harden faster due to contact with air, while the inner layers remain fluid. After the eruption is complete, the liquid core drains away, leaving empty tunnels.

Narusawa Grotto was formed during the powerful eruption of Mount Fuji in 864 AD. Activity occurred through the side crater of Nagao to the northeast, rather than through the central vent.

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The ten-day eruption formed the lava plateau now occupied by the Aokigahara (“Sea of Trees”) forest. The event also split a lake, creating two of the Five Fuji Lakes.

Narusawa is one of the three largest caves in the region, along with Fugaku Wind Cave and Saiko Bat Cave. The length of the grotto is 150 m with a height of up to 3.6 m. Geological features maintain a temperature of about 3 ° C, contributing to the freezing of moisture, especially in winter.

The dripping water forms stalactites and stalagmites, which reach their peak in the cold season. The best time to visit is winter or early spring, when the ice structures reach 1.6 feet in diameter and 10 feet in height.

Ice columns in the cave can reach 10 feet in height.

Historically, the grotto was used to store silk cocoons and seeds. Ice blocks were cut and stacked into primitive refrigeration chambers.

“Cold storage slowed down cocoon development and improved seed germination,” explains Wind Cave & Ice Cave.

OTHER UNIQUE OBJECTS

– Hang Son Doong: the largest cave on the planet with internal jungle and rock walls.

— Carlsbad Caverns: New Mexico's surreal underground caverns with gypsum formations.

— Marble Caves: Chile's turquoise caves with mineral layers.

Photographic evidence shows the remains of trees buried by lava in 864.

Narusawa is 800 m from Fugaku Wind Cave, which features deep lava structures and moss colonies. Fugaku's basalt walls absorb sound, creating an acoustic vacuum.

Learn more about amazing natural features and their geological history.

TAGS unique places japan

Sasha PareSocial NetworksStaff Correspondent

Sasha is a science journalist at Live Science (UK). She holds a BA in Biology from the University of Southampton and an MA in Science Communication from Imperial College London. Her work has appeared in The Guardian and Zoe. She enjoys tennis, cooking and antiques.

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