This Impossible Ice Cave Stays Frozen Through Summer
On a pleasantly warm summer's day in the mountains of Shanxi Province in
China, the walls and floor of Ningwu cave are covered with layers of frozen
water. Ice stalactites stretch down from the ceiling, and ice stalagmites reach
up from the floor, even when temperatures outside soar to the high teens. The
cave is 85m deep and set into the side of a mountain more than 2,000m above sea
level. Undoubtedly, the sight is dazzling, but is it unique?
Naturally occurring ice caves are dotted across Europe (Iceland is home to the
beautiful ice cave of Vatnajokull) and a number of spectacular ice caves are
found in Russia, Central Asia and North America. This incredible phenomena draws
in gobs of tourists, with many wondering what keeps these natural freezers so
Ice caves have been an object of study for more than 150 years, but how they
remain so cold has sparked controversy. Explanations have included a local
reversal of geothermal heat, whereby the warm currents from Earth's hot mantle
might sometimes miss a particular patch of ground, causing icy deposits if a
cave of the right shape happens to be in that area.
While this may be a plausible explanation for some ice caves, scientists
studying the Ningwu cave at the Chinese Academy of Geological Sciences beg to
differ. Yaolin Shi points out that while geothermal heat does vary in places,
these often influence surface temperatures too. Meaning that if it is colder
underground because of a lack of geothermal heat, it will be colder at the
Ningwu cave, however, acts differently. In this particular location, summer
temperatures at the surface can reach 62°F even when the cave temperature hovers
at around 32°F. Clearly, there is quite a discrepancy between the two.