Minnesota DNR: 'Extreme caution' on rapidly deteriorating lake ice

Minnesota's lake ice is particularly sketchy this time of year

A car through the ice on Lake Minnetonka in 2017
Courtesy of Hennepin County Sheriff's Office 2017

Some Minnesotans are used to being out on the ice in early March.

But this winter has been about 3 degrees warmer than average overall. And temperatures in the past week have been running between 5 and more than 10 degrees warmer than average across much of the region.

Temperature departure from average over the last week
Temperature departure from average over the last week
Midwest Regional Climate Center

Thursday the Minnesota DNR sent out this update on rapidly deteriorating ice conditions in Minnesota’s lakes.

Minnesota Department of Natural Resources conservation officers urge people to exercise extreme caution on and around lake ice, as conditions in some parts of the state have deteriorated rapidly. Several people and vehicles have fallen through the ice in recent days, continuing a trend that has played out for much of this winter.

While thick ice remains in some areas, especially to the north, conservation officers in areas south of the Twin Cities already are warning people to stay off the ice. In some instances, the ice is deteriorating around the edges of lakes, while in others conservation officers report large holes in ice away from the shore. All across Minnesota, ice conditions become highly variable when the weather is warm and the sun gains strength.

The release points out that early March is still a time of year when ice is historically thick enough on many Minnesota Lakes. But this year is different in many spots. And late-season is a historically dangerous time on lake ice.

“Just because you were on the ice at this time last year – or the year before that – doesn’t mean the ice is safe this year,” said Lisa Dugan, recreation safety outreach coordinator for the DNR Enforcement Division. “The calendar isn’t a useful tool in determining the quality of the ice. The only thing that matters is the current ice conditions.”

Minnesota has had only one ice-related fatality during the 2019-2020 ice season. But nearly every year, fatal incidents happen when people engage in late season ice-top recreation.

Temperatures will continue to run above average overall in the next week. Use some common sense out there Minnesota.

A car through ice on Lake Minnetonka in 2016.
Courtesy of Hennepin County Sheriff 2016

Here’s a great description of how lake ice melts from the Minnesota Department of Natural Resources.

  • In the late fall, the lake loses heat to the atmosphere, and then on a day or night when the wind is not blowing, ice forms. The ice gets thicker as long as the lake can continue to lose heat.

  • In most Januaries and Februaries, snow both reflects sunlight and insulates the lake. With a thick snow layer, the lake neither gains nor loses heat. The bottom sediment is actually heating the lake water slightly over the winter, from stored summer heat.

  • Around March, as the air warms and the sun gets more intense, the snow melts, allowing light to penetrate the ice. Because the ice acts like the glass in a greenhouse, the water beneath it begins to warm, and the ice begins to melt FROM THE BOTTOM.

  • When the ice thickness erodes to between 4 and 12 inches, it transforms into long vertical crystals called "candles." These conduct light even better, so the ice starts to look black, because it is not reflecting much sunlight.

  • Warming continues because the light energy is being transferred to the water below the ice. Meltwater fills in between the crystals, which begin breaking apart. The surface appears grayish as the ice reflects a bit more light than before.

  • The wind comes up, and breaks the surface apart. The candles will often be blown to one side of the lake, making a tinkling sound as they knock against one another, and piling up on the shore. In hours, a sparkling blue lake, once again!

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