What you are seeing above are 'Ice circles' which occur in cold climatic areas on the surface of moving water. They have been frequently observed in Scandinavia and North America.
'Ice circles' are extremely rare natural phenomenon which occurs only in slow moving water at a particular speed and at a right temperature. Any variations in the above said variables will distort the formation and will lead to irregular or cracked Ice circles.
Ice circles are thin slabs of Ice which can rotate at slow speed and are formed by eddy currents. Every slab varies in size but they can reach more than 12 ft in diameter.
They usually form at the center of the lake and obtain their shape by grinding the edges to its sides resulting in smooth circle. Some may be irregular in shape just like 'pic 3' and others form in cluster like 'pic 2'. But perfect circles are very very rare and reported only few number of times ( see pic 1 ).
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