After a slow start, this winter had some colder than usual cold snaps, so the ice built up to over a foot thick. Ice responds to thermal stresses, and so you end up with some pretty amazing formations. I didn't get pictures at its highest, but we had ice that came almost up to the top of the wall, over three feet high. This photo shows the "breaking wave" after several days of melting.
The waves are caused by thermal expansion during the day, which is often 30 degrees warmer than the night. It is exaggerated by having cracks a few inches wide form in other parts of the lake, then the cracks fill in with water, which freeze the next night to start the process all over again, giving more height to already existing waves.
I was down looking at the ice, and decided to take a walk along the top of the wall. I was surprised that one of the stones did not seem to be as flat as its neighbors. So, I climbed down to lake level to take a closer look. I sure was surprised to see this:
The ice waves had gotten purchase on the stone as perhaps it was jutting out above its lower neighbor, pushed the stone up several inches, then shifted the smaller rock so that it lay below, and then when receding, lowered the stone back onto the smaller rock. And there it now is. We need to figure out what to do about this. If we just put a strap around the smaller rock and yank, the large stone will drop and because it did not rotate around the lower rear corner, but the upper rear corner, it will end up sticking out several more inches. There's also the danger that if it falls hard it could actually rock itself forward and over and fall into the lake. Not likely, but really quite horrible if it happens. But, getting some kind of a jack to bear on it seems difficult. And, getting it to rotate back into place rather than sticking out even further (to encourage this to happen yet again the next year we have incredible ice) seems really tricky too. Maybe we will call our original contractor and see if they have any ideas!
It got really cold again after those pictures, and now we have even more fascinating waves of ice:
These waves were pushed up in the space of one day. I looked out yesterday and all that ice was flat. I spent about 15 minutes around noon just listening to the ice. It makes amazing ptoing! noises when it cracks with thermal stresses, and it was doing that all over the lake. Closer by, there were no violent noises, but there were occasional hisses and crackles. I couldn't really see it rising in real-time, but as the ice was lifting itself it displaced some surface water, and so I could see water welling up through the cracks after some noises. I want timelapse photography!