Polygonal lake ice cover

During an observation of the surface of a lake in the Valdai hills, the author identified spring ice cover (shuga) displaying a distinct polygonal pattern. This paper presents, for the first time, its structural and material characteristics and proposes a hypothesis regarding the potential behavior of the ice cover under specific conditions: the separation of the cover into two distinct fluid layers. The upper layer consists of water and has a higher density than the lower layer, which is primarily composed of ice grains and maintains fluidity due to the remaining water. It is hypothesized that the polygonal pattern in the ice cover forms in the newly established two-layer fluid system as a result of Rayleigh-Taylor instability.