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Japan's iconic 'juhyo' under threat
Mount Zao's famed winter spectacle-towering fir trees encased in ghostly rime ice-is shrinking due to climate change and tree disease, sparking urgent conservation efforts.
The science behind the spectacle
The juhyo, or "snow monsters," form only under precise conditions: sustained westerly winds reaching 26 meters per second (85 feet per second), temperatures between -6.3°C and -0.1°C (21-31°F), and high cloud moisture. These elements create overlapping rime ice ridges, dubbed "shrimp tails," that transform evergreen Aomori todomatsu trees into eerie, towering figures.
"Such conditions align in very few places, making Zao's snow monsters nearly unique to northern Japan," said Fumitaka Yanagisawa, a geochemistry professor emeritus at Yamagata University.
A shrinking wonder
Research unveiled in August 2025 reveals a stark decline. Yanagisawa's team analyzed summit photographs dating to 1933, measuring the formations on a six-point scale. In the 1930s, juhyo spanned 5-6 meters (16-20 feet) across. By the postwar era, they halved to 2-3 meters (7-10 feet). Since 2019, many barely exceed half a meter (1.6 feet).
The culprits: rising temperatures and a dying forest. A 2013 moth outbreak stripped needles from host trees, followed by bark beetles in 2015. Yamagata officials report 23,000 dead firs-roughly a fifth of the prefecture's stands. Fewer branches mean less surface for ice to cling to.
A 2019 study found winter temperatures in nearby Yamagata City have risen 2°C (3.6°F) over 120 years. The lower altitude limit for juhyo formation has climbed, and the formations now persist for fewer days annually.
Climate change accelerates losses
"Unique landscapes are already disappearing due to climate change," said Akihiko Ito, a University of Tokyo ecologist. Japan's alpine zones have warmed faster than the global average since the 1980s. Extreme weather and shifting seasons stress high-mountain forests, reducing growth and density.
"If warming continues unchecked, juhyo may vanish entirely in unusually warm winters by century's end," Ito warned.
Local action to revive the monsters
Yamagata Prefecture launched the Juhyo Revival Conference in March 2023, uniting researchers, officials, businesses, and residents. "Revival is our citizens' strongest wish," said Yoko Honma, a conservation specialist with the prefecture's nature division.
Since 2019, the local forest office has transplanted over 190 saplings from lower slopes to the summit near the ropeway station. "These firs take 50-70 years to mature, so conservation must span generations," Honma noted.
Students join the fight
At Murayama Technical High School, 20 kilometers northwest of Zao, students in a forestry and environmental science course have been propagating Aomori todomatsu since 2022. They collect saplings from Mount Zao, cultivate cuttings, and experiment with artificial propagation.
"When seeds we planted in heavy rain finally sprouted, I felt relief and excitement. But it was heartbreaking to find field mice had eaten the young shoots,"
Rin Oizumi, second-year student
Classmate Kanon Taniai recalled seeing dead and fallen trees near the summit in July 2024. "It made me sad. Growing seedlings is hard, but we want to help bring Mount Zao back to life."
Economic and cultural stakes
The juhyo draw tens of thousands of visitors annually, sustaining hotels, restaurants, and shops. "Their disappearance would devastate the local economy," said Genji Akiba, deputy director of the Zao Onsen Tourism Association.
For Taniai, the mission is about legacy. "They're called snow monsters because nothing else looks like them. I want the world to see them and feel how special Japan's nature is."
