You never know what you might see when venturing out to the shore of a Great Lake in the dead of winter. On Lake Michigan Sunday, it was ice volcanoes.

An employee of the National Weather Service office in Grand Rapids, Michigan, shared the photo above of a pair of ice volcanoes erupting at Oval Beach, Michigan, some 40 miles southwest of Grand Rapids on the eastern shore of Lake Michigan.

"These are some of the best photos of ice volcanoes I have seen," Tom Niziol, a contributor for Weather Underground's Category 6 blog, said in a Facebook post Sunday night.

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(MORE: Three Great Lakes Set High-Water Records in January)

Despite the name, ice volcanoes are not really volcanoes. They do not erupt hot, molten lava like Mount St. Helens in Washington state, for example.

Rather, Niziol explained on Facebook that ice volcanoes form as building waves beneath the lake's surface ice sheet force the water upward. That causes an increase in pressure on the ice sheet, and eventually, the water punctures a hole in the ice and sprays out through it.

"If it's very cold, then that spray freezes up, eventually building a cone like the ones we see here," Niziol added. "They can be very dangerous to climb on, however, because they are hollow and built over that hole in the ice. Don't ever go venturing out onto them."

NWS-Grand Rapids also shared the photo below that shows a close-up view of one of the ice volcanoes at Oval Beach.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.