I will cheat on my explanation...
From Wikipedia:
"A pressure ridge is an ice formation typically found on large frozen lakes during the winter. In the most basic sense, a pressure ridge is a long crack in the ice that occurs because of repeated heating and cooling on the surface of the lake.
In cases of extreme cold, ice will shrink in volume like any other solid, opening up cracks in the surface of lakes that are completely frozen over. The cracks quickly fill with water and freeze again, but when the temperature rises later, the ice expands and forces itself upward along the lines of the crack, in much the same fashion that plate tectonics creates mountain ranges, albeit on a much smaller scale. Pressure ridges can sometimes extend for miles, making an ice road impassable for truckers hauling freight to far northern locations."
Usually a pressure ridge is very easy to spot from a distance unless there is a lot of snow cover on the lake. You must be very cautious when crossing one, and when traveling in the vicinity of where one may have been that settled back down. The ice can be quite thin/unstable and often times pockets of open water can be left. As far as open water you must watch ahead of you for apparent wet spots as well as differences in the coloration of the ice. Depending on where you are leaving land from there are some usual spots in the Rattlesnake area that have ridges and/or wet spots so I am sure some of the residents in the area can point out where to avoid.
I usually tell newbies to winter lake travel to watch the ice fisherman, they are usually "in the know" of where to go. When you start to see trucks on the ice it is a good sign that you should be safe on a sled (beyond a normal doubt). Sounds silly, but just because sleds are out there, it does not mean things are safe. A few times this spring when I was out in the airboat I witnessed sleds that had no right being out there and were lucky to make it home without getting wet.
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