University of Wisconsin seen from L. Mendota. Photo by Spencer9.
Lake Mendota "is asleep for the winter, but it is dreaming. Marie feels that she can hear the dreams of the lake running through the ice, like thoughts in a language we don't know. The ice begins to creak. It makes banging noises, and groans, and makes little pings and snippy-snap sounds, and sometimes there are long, drawn-out booms, like cannonfire heard from a distance. The cracks and adjustments in th ice can be heard racing from island to island and across the bays, traveling for miles and moving very fast, giving out stereo sounds. Apart from that, the world seems quiet, without wind, without any clicking or rustling of branches, without any sound of a living thing. Overhead, the misty river of the Milky Way turns slowly with the handle of the Little Dipper around the North Star. The north Star is motionless, and everything else in the sky is moving. A meteor crosses the sky--just a zip in the corner of Marie's eye, and it's gone."
FromThe Wild Trees, by Richard Preston, p.66-7. I substituted Lake Mendota for Lake of the Woods.
As air temperature changes, the ice is constantly expanding or contracting. When the ice contracts, it pulls away from the shore, or forms cracks in the middle. These voids fill with new ice. When the ice expands again, the added ice is too much for the space between the shores, and so the ice pushes against the shore, bulldozing up the soil into ridges. Or the expanding ice pushes against itself to create pressure ridges in the middle of the lake. There is always a big pressure ridge off the tip of picnic point.
When the wind blows, it also pushes on the ice, creating more cracks and pressure ridges.
All of these motions are accompanied by cracking sounds. Sound travels much faster in ice than in air, and ice is an excellent conductor of sound--so cracks anywhere on the lake can be heard loudly and at once. One crack may propagate quickly over a long distance, creating the strange "stereo" effects.
The ice is completely safe, despite all the frightening sounds.
Tips for your trip
Dress warmly, especially on feet. Pick a time with little wind. A hood is warmer than a hat
A pole or walking stick helps.
A flashlight helps getting down to the ice.
Take some hot cocoa and maybe a folding chair. Leave the booze behind, unless you want a Darwin Award.
If you see open water (unlikely), avoid it by at least 10 feet.
The hazzard from pressure ridges (near shore or in middle) is mainly from slipping on the sloping ice.
Wait 2-3 days after a heavy snowfall for slush to freeze.
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