How ice creates mini-mountains

In frozen regions, ice can force the ground into mounds called pingos - conspicuous landmarks in flat landscapes

On a cold day, bare earth crunches underfoot. This is because ice needles have formed, pushing the soil upwards, and the pressure of a footstep crushes them down again. In frozen regions, a similar effect on a grand scale produces unusual hillocks known as pingos.

Pingos can be as much as 50 metres high. They typically start in old lake beds. Freezing water forms into a lens shape and expands as it becomes ice. As more water is added and the ice mass becomes larger, the ground above is gradually forced upwards into a mound. This can grow at the rate of a few centimetres a year.