How to melt an ice cave

Installing a door to keep heat out of an ice cave does just the opposite

ICE PALACE  Frigid winter breezes serve as natural air conditioning for ice caves such as the Ningwu ice cave in China’s Shanxi province, new research finds. Caves sealed by airtight doors block circulation and could melt within decades, the researchers warn.

© Wang Shen/Xinhua Press/Corbis

If you want to keep an ice cave cold, don’t shut the door.

That’s the lesson learned from studying China’s largest year-round ice cave, which thankfully has no doors to close and is just fine. Cold winter breezes act as natural air conditioning and keep this frozen grotto perpetually chilly, researchers report October 22 inThe Cryosphere. And summer heat barely penetrates its depths.

The 3-million-year old Ningwu ice cave in China’s Shanxi province contains a single entrance connected to the top of a bowling-pin-shaped chamber. Geologists Shaohua Yang and Yaolin Shi of the University of Chinese Academy of Sciences in Beijing digitally re-created the 85-meter-deep formation and found that buoyant, warm outside air doesn’t flow very deep into the cave. Winter’s cold air, meantime, flushes heat out of the cave system. This convection process maintains freezing temperatures year-round even as a thousand visitors explore the cave each day.

Well-intentioned caretakers for at least two other ice caves have installed airtight doors, hoping to keep out heat and trespassers. But the doors also block winter’s frigid air and will cause the spectacular ice formations to completely melt within 40 years, the researchers predict.

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