In one of the magazines with yesterdays Sunday Times, there were some photos of ‘hunters’ retrieving mammoth ivory from the melting tundra. One photo caught my eye, which was a couple of men scrambling from a crater. The photos was eye catching because the crater looked like a large subsidence. Does anybody know anything about this land feature or anything similar?

Not much but I would imagine that permanently frozen water takes up quite a lot of space in the ground and when it melts and runs away, the ground sinks.

Interestingly a couple of winters ago on my drive to work an entire ribbon of tarmac about 18″ wide and several hundred feet long lifted by about 2″ out of the road surface – I guess because the utility who dug the trench refilled it during wet weather and the fill was very saturated with water, which increased in volume when it froze.

er…

i’m DEFINITELY no expert, but i’ve got family in norfolk, and everynow and then, we’ll hear news of a tractor falling into a pingo? / pongo? / pingu?

(internet says ‘pingo’ – linky)

maybe my uncle is pulling my leg, but he says they’re a left-over from the ice age.

(the ice has gone, leaving a void in the ground, – which can collapse under the weight of a tractor)

now i talk about it, i suspect i’ve been had…

pingo – periglacial feature. Core of ice forms under ground forcing soil upwards at the margins like ramparts. When the water melts the volume decreases so the ground in the middle sinks and generally fills with water. Got lots of them over here in southwest Wales