Boundarywaters

     The ice on Saganaga Lake went out on April 10th last year but it's a different story out there this year.  Sag is usually one of the last lakes in the Boundary Waters and on the Gunflint Trail to go out.  It's deep, it's large and it's pretty far north.
     Other lakes in the Boundary Waters and on the Gunflint Trail tend to go out a week or so earlier than Saganaga.  We have clues we look for on the Gunflint Trail to determine/guess when the ice will go out.  We keep track of when the Cross River starts flowing, when the ice is gone from the moose pond and when the Seagull River opens up.  We also keep track of other lake ice out dates in Minnesota at this website.    
     For a few days we were making good progress on melting ice.  There was quite a bit of open water in front of the Voyageur Canoe Outfitters lodge.  Then it got cold again and we got a layer of insulating snow on top of the ice and that put a halt to the melt.  
     The forecast for this week calls for warmer temperatures and that should get the ice melting again.  The average ice out date for Saganaga is May 3rd but we've had it as late as May 17th in 1996.  Ever wonder how the ice goes out?  Wonder no more.

How Lake Ice Melts

A wonderful description of how lake ice melts away appeared on the web blog "Air Mass", hosted by the Star Tribune's Bill McAuliffe. Ed Swain, of the Minnesota Pollution Control Agency describes the process of freezing and thawing lakes.

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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!