If you find yourself in the High Tatras mountains of Slovakia, it’s pretty much a no-brainer to take some pictures or capture some video. But while we would have been satisfied with a simple peek at the beautiful, stark landscape, the real show begins when the camera pans down to the icy surface of an alpine lake. Filmed at a high resolution, it appears that the person is standing on glass, the frozen water offering no obstruction to the bottom of the lake below.
What causes this rare occurrence? In order to achieve this kind of transparency, the ice on the lake must form slowly. When temperatures drop rapidly, the ice freezes so fast that impurities such as trapped gasses and organic material will become embedded in the ice, giving it a translucent or opaque whitish colour. When the ice has more time to form, there is time for the water to stabilize and reject these impurities.
Considering the unsettling nature of the clear ice, I don’t blame the person with the video camera for declining to move out into the centre of the lake, as it is hard to judge the thickness. If you’re up at the cottage this winter and champing at the bit to go skating, check out this handy chart, which tells you how safe the different thicknesses of ice are.