Unusual lake ice conditions
This warm Minnesota winter has caused some unusual lake ice conditions. If you’ve walked along the Detroit Lakes city beach this winter, you’ll see enormous ice pushes. In some places they’re 3-4 feet tall. All winter the ice has thickened and thinned with the weather.
The two main factors affecting this winter’s lake ice conditions are the lack of snow cover and the warm sunny days. For lake ice to get thick, there needs to be many days and nights of below freezing air temperatures. This winter, after the lake froze over, we had sunny days in the 40s. Without the snow cover, the sun shines right through the clear ice and melts it from underneath. These conditions cause the ice to become thinner and bumpy underneath. You can see this bumpy shape if you look under the ice sheets that have pushed up at the city beach. These bumps conduct light well, so the ice starts to look black because it is not reflecting much sunlight. The ice actually started getting black a few weeks ago after a couple sunny days near 50.
The ice pushes and pressure ridges are enormous this year as well. These are due to the wide swings in temperature and sun continuously heating and cooling the ice. When it’s cold, the ice shrinks and opens cracks in the lakes surface. These cracks quickly fill with water and freeze again. When we have warm sunny days, the ice expands. It forces itself up onto the shore causing ice pushes, and the ice plates force up on each other at cracks, causing pressure ridges.
If you have large ice pushes on your shoreline this year, consider leaving them there. They are nature’s way of protecting lake water quality and providing wildlife habitat. They act as a berm to stop runoff from draining directly into the lake. They also provide habitat for birds, frogs, turtles and aquatic insects.
Make sure to check local ice conditions before driving out on the lake. It’s amazing what a couple of sunny days can do to ice without snow cover.
Moriya Rufer, RMB Environmental Laboratories, moriyar@rmbel.info