phenom: pingos of the far north

What is a pingo? An ice-cored hill that only exists where permafrost exists, because permafrost is what pushes the ice upwards like a giant pimple. There are about 5,000 of these in the world, and 25% of them – 1350, to be precise – exist in the Mackenzie Delta on the Tuktoyaktuk Peninsula.

I love this beautiful visual from Doug Wilkinson’s 1975 book The Arctic Coast (Natural Science of Canada Ltd., McClelland publishers), probably because it reminds me of childhood hours shading drawings with pencil crayons. The accompanying text:

The most spectacular form of ground ice is the pingo, ice-cored hills found in the Mackenzie Delta that are often a thousand feet high. Pingos are formed as a result of what is called a “closed” system of unfrozen soil developing within an area of permanently frozen ground.

A large lake, beneath which there is no permafrost, fills with sediment or partially drains away (1). Permafrost will form on the bottom and sides so as to trap a huge core of unfrozen, water-saturated doil above it (2). Year by year, the freezing continues (3); hydrostatic pressure forces the water upward toward the surface of the land (4) to form a huge ice “pingo.”

And another diagram demonstrating how pingos can push up even through a “lens” of water:

I was eager to see pingos at last when we were in Tuktoyaktuk, NWT, over New Year’s Eve 2009. However, we didn’t see them at all on the drive into Tuk because a low-lying ice fog kept our view contracted to 500 metres or so.

The next day, on Dec 30, I walked along one of the many spits that dangle into the winter-frozen Beaufort Sea. Pingo views at 12:0 and 1:00 pm – the brightest times of day – were like this:

Those bumps in the distance are two of the most famous pingos in the world: Ibyuk and Split. Ibyuk, on the left, is about 50 metres high and is “the tallest pingo in Canada and the second tallest in the world,” according to Parks Canada. It is the world’s largest growing pingo, though, and it continues to grow at a rate of about 2 centimetres per year. Ibyuk is estimated to be more than 1,000 years old.

That’s old ice. Does the fact that Ibyuk has an estimated age mean there’s a reliable formula to determine the age of a pingo by measuring its dimensions? Simply Science, a research publication by The Aurora Institute in Inuvik, NWT, says otherwise:

Pingos, like plants and animals, grow most rapidly when young. A few grow nearly 1 m (3 feet) in the first year. The growth rate slows with time until, eventually, growth ceases. Contrary to what might be expected, the age of a pingo cannot be estimated by its size. This is because the diameter of a pingo is established at birth by the shape, depth, and permafrost conditions of the residual pond where growth commenced. A pingo then grows higher but only a little wider. Therefore, a small pingo can be much older than a large pingo, or vice versa. Most of the Tuktoyaktuk area pingos are hundreds to thousands of years old so that the birth of a pingo is a rare event.

Pingos eventually collapse under their own pressure, as this Parks Canada photo shows.

The 50 m thick ice core of lbyuk Pingo is protected from melting by about 15 m (48 feet) of frozen peat and sands. Disturbing the surface can cause pingos to melt faster – less insulation on the ice = less stability. I regret not having my camera handy when we were in the grocery store and I saw a poster saying: “You can help save the pingos!” Driving a skidoo or ATV all over a pingo surface can damage the surface dramatically, the poster pointed out, so a bit of winter fun can lead to increased melt rates.

Only a tiny number of humans on the planet get to experience pingos as a backyard phenomenon, as you can see on this map from Canada’s Polar Environments (University of Guelph). But if you’re interested in  Pingo Canadian Landmark Park as a destination, despite it’s weirdly clunky name, check out information on the Parks Canada website.