Crop circles formations in ice
Normal" ice circle in Russia, (likely) Winter 2007/08
Some believe that the natural explanation for this phenomenon are underwater vortices cause by through-running streams that follow natural outlines of bays and coves just as visible also in the above shown images, as well as differences in the water's temperature that might impact also the forming of the above ice-structure in such a way.
However, some rare examples of geometrically more complex patterns put the above described theory to the test - at least if presented as a simple single vortex-system or as the sole explanation for all patters in ice.
This seems also to be the case with another discovery from Russia, published by "englishrussia.com" mid July 2008. Here a central circular ice disc - likely discovered the previous winter or early spring - is surrounded by dozens of smaller different sized ice discs, that are even able to carry a grown up person's weight (see: following image).
Back to the above described natural explanation a close-up view shows smaller ice-circles seemingly in the making, at the edge of the normal ice sheet (red arrows). The hydrological structure of this pond might provide a reasonable explanation but has to be quite complex and (to my knowledge) previously undescribed.