The Great Lakes, along with thousands of smaller, inland lakes, are wintertime havens for outdoor recreation. Ice fishing, hockey, snowmobiling and hiking are great ways to enjoy the winter, but they come with risks. Knowing those risks and understanding how to mitigate their dangers make these activities more fun and much safer as well.

Thinning and displaced ice have resulted in multiple fatalities and rescues in the past two weeks.

The obvious but sometimes overlooked danger of going out on the ice is the risk of falling through. Ice has to be at least four inches thick to be safe to walk on. For those who take a snowmobile out on the ice, eight inches is a minimum to be safe, and if you are going to drive a car, at least 10 to 12 inches of ice is considered safe.

Some recent incidents include:

Another, lesser-known danger when venturing onto the ice is becoming stranded when the ice drifts away from shore. If the wind is offshore or blowing from land to lake, it can actually cause ice sheets to break away from the shoreline under certain conditions, becoming an “ice floe.” It can happen even when temperatures are freezing and the ice is thick.

People have become stranded on ice floes twice in the past week on the Great Lakes. On Sunday, seven adults and three children became stranded on a sheet of ice that broke away from the shoreline at Edgewater Park in Cleveland. The ice floe they were on had drifted almost a mile from shore before they were rescued.

In the satellite animation below, you can actually see a very faint, hairline crack that developed in the ice sheet just offshore from Cleveland on that Sunday morning, exactly where the people were stranded.

On that same afternoon, farther north, off Lake Huron’s Georgian Bay in Ontario, two hikers were stranded as a piece of ice broke away from the shore and drifted about two miles into the bay. They were rescued by a helicopter deployed by the Ontario Provincial Police. There were no reported injuries in either of the events.

So why did these two events occur Sunday afternoon? It was a combination of factors, but the overwhelming reason for the ice floes to break from the shore was an offshore wind.

In Cleveland that morning, the wind direction was out of the southeast at 10 to 15 mph. That direction results in a perfectly oriented offshore wind. Several hours of offshore winds put enough pressure or force on the ice field to lead to several large cracks along the Lake Erie shoreline near Cleveland. The same scenario played out on Georgian Bay, where offshore winds also broke the ice sheet and set it adrift toward open water.

Wind speed also plays an important role in breaking up the ice cover. The stronger the wind, the more force it produces on the ice pack and the more water it sends under the ice pack to break it up.

Last week, as Lake Erie began its rapid freeze-up, the winds came out of the northeast for a couple of days, driving the ice pack toward the western end of the lake. This past weekend and into this week, strong winds reversed direction to the southwest and west, gusting over 20 mph for the past five days, and over 40 mph on two of the last three days. As a result, the ice pack is almost unrecognizable right now, being broken up for the most part on the entire open portion of the lake, with only the far downwind end of the lake near Buffalo having a dense, immovable ice pack.

There’s possibly another factor that has contributed to such a rapid ice breakup on Lake Erie over the past few days, and why it might be more dangerous for those who venture out onto the ice on the Great Lakes right now.

It was a very mild start to the ice season on the Great Lakes. In fact, in January, Lake Erie only had about 3 percent ice cover, one of the lowest values since records started being kept in 1973.

That all changed in the past couple of weeks as the weather pattern flip-flopped and produced an exceptionally cold Arctic outbreak across the region at precisely the time that Lake Erie usually has its greatest seasonal increase in ice cover. It was the perfect timing for the lake to almost freeze over completely (ice extent reached 86 percent) in a matter of days.

That flash freeze didn’t produce a thick ice cover, but rather a relatively thin layer of ice. It doesn’t take that much force from the wind to crack that ice cover, and that’s exactly what has happened over the past few days. I equate it to putting a tray of water into a really cold freezer: It doesn’t take much to develop a pretty thin skin of ice on the tray, nor a lot to crack it, and that’s probably what has happened on Lake Erie.

Therefore, those who want to venture out onto the ice must know the conditions before they go. One of the best ways to keep updated is to monitor the local National Weather Service forecasts and additional information on ice conditions.

In recent days, the National Weather Service office in Cleveland has issued statements warning people to be careful about venturing out onto the ice.

Tom Niziol recently retired as winter weather expert at the Weather Channel after a 32-year career at the National Weather Service office in Buffalo.

Jason Samenow contributed to this report.