Narusawa Ice Cave: Lava tube with 10 feet tall ice pillars buried at the foot of Mt. Fuji

Narusawa’s Ice Cave is a lava tube filled with icicles and ice pillars at the foot of Mt. Fuji in Japan.

Lava tubes are natural tunnels that form under lava flows that solidify after a volcanic eruption. Lava hardens faster in the top layer of lava flow where molten rocks come into contact with cold air, and maintains liquid at high red temperatures in layers colder than the middle layer. As a result, when the volcano stops erupting, the lava flow nuclei drain and hardens the outside, leaving empty conduits and caves.

The Ice Cave in Narusawa is one of several caves that formed when Mount Fuji erupted violently in 864 AD. The eruption took place on the northeastern side of the volcano and spitted out from a new vent called Mount Nagao, not from the entrance to the central summit on Mount Vaji.

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The eruption lasted for 10 days, creating a large lava plain covered in the forest of Aoki Forest, a dense forest also known as the “sea of ​​trees.” The explosion also split the lake in half and cut two out of five Fuji Volcano lakes.

The Ice Cave is one of the three largest caves in the region, along with the Fugaku-style cave and the Rhino Bat Lake Cave (also known as the Psycho Lake Bat Cave). According to Wind Cave & Ice Cave, which manages and offers cave tours, the Narusawa Ice Cave is 490 feet long (150 meters) and 12 feet high (3.6 meters). The average temperature in the cave is slightly above 37 degrees Fahrenheit (3 degrees Celsius) due to a particular geology. This means that moisture can freeze, especially in winter.

The water dripping from the cave ceiling forms stal limestone and stalagus that meet in the middle during the coldest times. The best time to visit the Ice Caves in Narusawa is in winter or early spring, where these ice columns can reach 1.6 feet (0.5 m) thick and 10 feet (3 m) high, according to the Wind Caves and Ice Caves.

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Caves are tourist attractions, but historically they were used to keep seeds and silkworm coco cool. According to Wind Cave & Ice Cave, people carved rectangular blocks from ice pillars.

“They were stored in a refrigerated environment to prevent coco growth, maintain seed quality and promote budding,” the company states on its website.

The cave also holds ancient tree ruins. Ancient trees are photographs from the website, which were toppled by lava flows during the eruption of AD 864.

Narusawa’s Ice Caves are located just 0.5 miles (800 m) east of the Fugaku-style Cave, which stretches deeper underground, boasts impressive lava layers and boasts rare moss colonies, according to the National Tourism Agency of Japan. The wind cave does not have echoes as the walls of pure basalt rock are absorbed. Unlike ice caves, there is no frozen water that lets sound waves bounce back.

Discover more incredible places that highlight the incredible history and science behind some of the most dramatic landscapes on Earth.