Lake Learning Column: How lake ice melts
After this unusually cold winter and blizzards the past couple weekends, I think we're all ready for the ice to come off the lakes! The last couple weeks we've been in that in-between time when we can't start boating on the lakes because the ice is still on them, but the ice isn't safe to walk on anymore.
The ice went out in southwest and south central Minnesota this past week. This is the latest the ice has stayed on the lakes in southern Minnesota since 2001. The average date of ice-out for Detroit Lake is April 20, Lake Sallie is April 18, and Ottertail Lake is April 15. It looks like this year we will be later than the average. The MN Climatology Working Group has a fun website that tracks the ice cover daily on numerous Minnesota lakes. You can find it here: http://climate.umn.edu/doc/ice_out/ice_out_status_08.htm.
So how does the lake ice melt? You may have noticed that the ice turned black in some spots and now it looks slushy and opaque. Once the snow melts off the top of the ice, the ice is exposed to the sun. The ice then acts like a greenhouse to the lake water, and as the sun shines on the ice, it heats the water underneath the ice. The ice then starts to melt from the bottom, where it is touching the water. When the ice thickness erodes to between 4 and 12 inches, it transforms into long vertical crystals called "candles." These conduct light well, so the ice starts to look black, because it is not reflecting much sunlight.
As the sun continues to heat the ice, the water below the ice continues to warm. Meltwater fills in between the crystals, which begin breaking apart. The surface appears grayish as the ice reflects a bit more light than before.
Then, all we need is a windy day to break the surface ice apart. The ice candles will often be blown to one side of the lake, making a tinkling sound as they knock against one another, and pile up on the shore. It's amazing how this final process seems to take just a few hours where one day the lake is ice-covered and the next it is not.
Over the next week, the speed of the ice-out process will be dependent on how much sun and wind we get. Only time and the weather will tell how much later than average our ice will go out this year.
I'm already looking forward to sparkling blue water, boat rides and the walleye opener!
Until next week, enjoy the lakes.
The text about lake ice melting was adapted from Ed Swain, MPCA.
(Moriya Rufer is the Lakes Monitoring Program Coordinator for RMB Environmental Laboratories in Detroit Lakes, 218-846-1465, firstname.lastname@example.org.)