Ice eggs

They may collect into heaps of balls or 'eggs' on beaches where they pack together in striking patterns.

[1][2][3] The gentle churn of water, blown by a suitably stiff breeze makes concentric layers of ice form on a seed particle that then grows into the floating ball as it rolls through the freezing currents.

[4] Given enough time, the frozen balls can grow to become boulder size.

In 2016, giant snowballs washed up on a beach in Siberia, some measuring a metre (about 3 feet) across.

[5] An ice specialist from the Finnish Meteorological Institute has been quoted as saying ice balls are rare, but not unprecedented, and occur about once a year on the Finnish coastline as conditions allow.