What’s a Pingo?

Pingo (n.): a hill formed largely of ice. See also: hydrolaccolith.

A helicopter flying over Siberia’s Yamal peninsula last summer spotted a 260-foot-wide hole in the ground. Its origins intrigued scientists, who immediately ruled out a meteor; past photographs suggested the crater had formed within the past two years, and we likely would have detected an impact that large. The chasm also doesn’t have the right features or surroundings for a sinkhole.

Two theories eventually came to the fore. The area is rich in natural gas, so the cavity could have been formed in an explosion. The other possibility is that it’s a pingo. You rarely read the word pingo. In fact, my spellchecker thinks I’ve made it up, which is why my draft is covered in red underlines. Oh, well. I press on.

A pingo is a hill that forms when a mass of ice grows beneath an earthen cover, pushing the ground upward. In warmer regions—warmer than Siberia, that is—pingos are typically fed by streams or other water that seep through pores in the soil before freezing. In truly frigid climates, ice can envelop a small lake. As the water freezes, it expands upward.

Pingos come in many shapes and sizes: domed, cone-shaped, elliptical, totally irregular. They can grow more than 150 feet high and 1,500 feet across. The coolest-looking ones are those that have stretched their coverings beyond the breaking point, exposing the ice that forms the core. It looks like a tiny ice volcano.

You sometimes hear pingo used interchangeably with the equally fun-to-say hydrolaccolith (another spellcheck reject). Some geomorphologists, however, use the former to refer to perennial ice formations, while hydrolaccoliths can melt and reform seasonally.

That brings us back to the Siberian hole. Over long periods of time, even large pingos can melt and collapse, leaving craters in the ground. These “pingo voids” (in quotation marks because I really did make that one up) help scientists identify areas once covered in ice. Anthropogenic global warming is accelerating that process, and the hole discovered in Siberia this summer might be evidence of that.

So, the next time someone tells you there’s no evidence of climate change, just stand up and shout: PINGO!