Two hikers recently stumbled upon an amazing phenomenon while exploring the High Tatras Mountains in Slovakia–a frozen lake with a surface as clear as glass. In a viral video shared by Tomas Nunuk, one of the hikers, he and his friend find themselves walking on ice so transparent that the rocks at the bottom of the lake are clearly visible, making for a surreal, dizzying experience.
According to one Reddit user, the formation of such strikingly clear ice has to do with the rate of freezing: “If the water is cooled too quickly it doesn't have enough time to reject any impurities as it crystallizes–those impurities are then held within the crystal lattice and distort the crystal lattice. Thus, if there are impurities such as trapped gases, organic material and other minerals or dissolved salts (an inhomogeneous mixture) the ice will appear optically translucent, or even opaque. However, if the water cools and freezes over a longer duration of time, it has time to reject these impurities as it crystallizes. This eventually gives rise to a more homogenous mixture and less defects in the crystal lattice which creates clear, transparent water ice.”