Background Information
Lake Superior is the world’s largest freshwater lake, located in the Laurentian Great Lakes region of Eastern North America, and is shared by the Canadian provinces of Ontario and Manitoba, and U.S. states of Minnesota, Wisconsin, and Michigan. It covers an area of 82,100 square kilometers. Winter in the Lake Superior region is especially cold and long with temperatures of -30 Celsius and sometimes below. This, coupled with the lake’s shallow waters, offers excellent potential for the lake to freeze over.
Relevant Data
The last time the lake froze over, or ‘iced over’, was in 2014 and before that, in 1994. During the last big freeze in 2014, the lake’s generally open water was entirely covered in ice – a rare and vivid spectacle. Ice cover on Lake Superior is generally considered to be a biannual event and while a complete ice cover can occur, it isn’t every cold winter that Lake Superior completely freezes over.
Expert Perspectives
Ice on the surface of Lake Superior reduces the number of marine organisms in the lake such as krill and plankton, thereby impacting the feeding habits of the fish in the lake. According to Dan Jaecks, a research fishery biologist with the U.S. Geological Survey, there has been an overall decline in fish numbers in the lake, attributed in part to ice formation during winter periods. He believes, however, that the overall health of the lake’s fish populations is still good due to other factors such as water quality, surface habitat and nutrient levels.
Experts at the Great Lakes Environmental Research Laboratory note that while ice cover on the lake may seem to be less frequent, the number of days with ice cover have remained fairly consistent since data collection began in 1973. This, they believe, is because of the incoming cold air in the winters and its impact on water temperature.
Analysis And Insights
Lake Superior’s entire surface freezing over is not necessarily an annual event. The changing weather patterns, however, have made it more likely that in some years the entire lake could potentially freeze over. Its shallow waters and long winters make it the one of the most likely of all the Great Lakes to freeze over.
Recent studies show that winds during ice formation are a major factor in determining whether or not Lake Superior will freeze over completely. Strong winds can cause large areas of broken ice that can prevent the lake from completely freezing over. It is also important to note that the lake typically remains well below freezing temperatures in winter. In fact, the lake resists ice formation until temperatures drop down to -2 degrees Celsius.
Ice Forming Patterns
Lake Superior produces complex patterns of ice formation each winter. On the lake’s eastern side, the ice forms along the northern shore and can quickly spread to the southern shore. On the lake’s western side, temperatures are usually a bit warmer, causing the ice to form more gradually and in a different pattern.
Much of the ice that forms on Lake Superior is second-year ice, meaning the ice forms around the edges of the lake and gradually spreads across the surface from winter to winter. This ice can be up to one meter thick in some areas.
Ice Impact On Heat & Cold
The presence of ice on the lake also affects winter temperature extremes. With the ice acting as a barrier against consistent temperature conditions in the environment, the temperature could vary greatly from one side of the lake to another. For example, southeast Wisconsin, located to the east of the lake, tended to experience warmer temperatures than northwest Wisconsin on the lake’s western side.
Regional Benefits & Costs
The freezing of Lake Superior has both benefits and drawbacks for the region. On the one hand, the lake’s ice can provide recreational opportunities such as snowmobiling, ice fishing, and ice skating. On the other hand, the presence of frozen water can cause significant economic losses for shipping and transportation companies as boats are unable to traverse the lake.
Historical Trends
Historically, the lake typically froze completely over at least every few years with records showing ice over occurring in the winter of 1901 to 1902, 1913 to 1914, 1940 to 1941 and 1945 to 1946. The last time the lake froze over completely was in 1994 with the ice thick enough for visitors to walk from Ashland, Wisconsin to Ontario, Canada.
Frequency Of Ice Cover
It is important to note that while the lake generally freezes over every few years, the frequency is significantly higher in some areas. For example, in the Apostle Islands, located to the east of Lake Superior, the ice cover has been as high as 54 percent in some winters. In other years, however, the ice cover has been as low as 7 percent.
Impact Of Climate Change
Scientists have predicted a decline in the frequency of ice cover in the Great Lakes region due to the effects of global warming. The impacts of climate change are evident with an increase in the annual average temperature recorded in the Great Lakes region. This has led to an overall decrease in the number of ice days on the lake as well as an increase in the rate of snowmelt in the spring months. This can cause a further decline in the frequency of ice cover in Lake Superior.
Overall, Lake Superior’s ice cover is highly unpredictable and varies greatly from winter to winter. Climate change will continue to have an impact on the frequency of ice cover and its long-term effects are yet to be seen.
