One of the features of the Arctic is rather, well, featureless. At least in terms of features we can easily see, but permafrost is an essential characteristic of the Arctic. It is a feature that allows plants to survive in the desert that is the High Arctic, and a force which shapes our terrain, and holds our houses up.
Permafrost is that layer of ground that is exactly that, permanently frozen. Come our summer, only the top layer, known as the active layer, thaws. The depth of the active layers varies, but around here it is probably about 20 cms. Below that the ground never thaws, and this layer of permafrost again varies in depth, but up here is probably in the neighbourhood of 500 metres thick. That's a half a kilometre folks, but below that the heat from the earth kicks in and the ground remains unfrozen.
Plant roots only occupy the active layer, and although it is hard to imagine how plants can survive, never mind thrive in the cold dry desert here, part of the answer lies in the permafrost. Whereas in more temperate climates much of the precipitation that falls or is freed up in the summer melt, soaks into the ground, eventually down to aquifers, here all of the moisture remains in the active layer. Permafrost prevents the moisture from going deep into the earth and thus plants have all the water at their disposal.
That characteristic of permafrost also contributed to a crisis in Pangnirtung this week, and the results also illustrate what happens when the permafrost gets exposed. In Pang, warm temperatures and a modest amount of rain caused a rapid melt of some of the snow from the surrounding mountains. Because of the permafrost all of the rain, and the meltwater released ended up as runoff, causing rivers to swell and become raging torrents of water.
In Pang the community is divided by one such river and the torrent began both eroding the banks that support the bridges linking the community (there are two as I understand it, an older bridge due to come out of service and a new one beside it, just completed and about to be opened), and exposing the permafrost that give the banks the structure and strength to hold up a bridge. First the older bridge collapsed forcing authorities to use the new bridge. Then it became clear that the eroded bank and melted ground would not support the new bridge and it was shut down. This bisecting of the community, if I understand correctly, resulted in half the community cut off from the stores and food supplies, and the other half cut off from water and sewage services.
If you really want the lowdown on the situation in Pang, and many photos of the affair, I heartily recommend visiting Baffin Bloggers and Kluglanoch Corner, two excellent bloggers from Pangnirtung. And as a bonus Kluglanoch Corner has an incredible photo of the storm clouds above the fjord in his post and really cool photos using a technique called HDR on a post farther down.
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Whoa! Thanks for the heads-up, very interesting indeed. My paycheques originate from the other side of that bridge and I am due one this pay period… hmmm…
I had heard last year that they built the new bridge on the wrong side of the old bridge. I’ll bet that’s part of the problem as the new bridge is downstream from the old one, so of course it would be even more vulnerable.
Hi Nancy, judging by the photos I’d say it didn’t matter where they built the second bridge. The water undercut the permafrost and when it melted after being exposed there was nothing left to support. That appeared to be the case on both sides of the old bridge.