A Russian beach looked like a set for an epic Siberian Yeti snowball fight after getting suddenly littered with hundreds of gigantic snowballs — ranging in size from baseballs to beach balls — over the weekend.

But these weren’t proof that humanity had suddenly shrunken or that snow had decided to go terrifyingly mutant on us. It’s actually just peculiar weather conditions that get snow to roll themselves into snowballs. “It is a rare natural phenomenon,” says Arctic and Antarctic Research Institute spokesperson Sergey Lisenkov. “As a rule, grease ice forms first, slush. And then a combination of the action of the wind, the outlines of the coastline, and the temperature, may lead to the formation of such balls.”

There are several stages in the formation of sea ice. The first is frazil, which is made of loose crystals of ice that gather and clink together in the wind and waves. Under the right conditions, this stuff congeals into greasy ice, a slushy mix of ice and water that sits on the surface and can resemble an oil slick.

It was this sort of ice that washed over a beach in Nyda, Russia, just off an inlet of the Kara Sea. The grease ice came in with the tide, and when the tide left the slushy mix was left dehydrating on the beach.

The texture of the ice crystals were enough for some of them to get picked up by strong winds and start blowing around on the surface of the beach. Then, like a snowball rolling down a hill, they picked up more and more material as they moved around, until they had picked up nearly all the frosty crystals from the tidal plain.

Residents of Nyda say they’ve never seen anything like this before. “Even old-timers say they see this phenomenon for the first time,” says Valery Akulov with the municipal office.

Freaky snowballs pop up from time to time around the world. In 2013 similar conditions led to the accumulation of snow boulders on the shores of Lake Michigan on Sleeping Bear Dunes National Lakeshore. It’s only the start of the cold season, so who knows? We might have a few more monstrous snowballs in our future.

Photos via Sergey Bychenkov/Arctic and Antarctic Research Institute

Jacqueline Ronson is a science writer based on Vancouver Island, Canada. Before that she lived way up in Whitehorse, where she reported for the Yukon News. These days she likes to talk to smart people about the future of the planet, ride her bicycle, play her banjo, and frolic.