Pressure Ridge Formation Video
This video was taken of the inital rupture of an overlapped, along-shore pressure ridge. Several minutes before the rupture I was taking off my skates about 200 feet out on the lake. I heard a lot of creaking in the ice that seemed to be coming from shore so I headed in and stood near shore and away from the areas where the ice had been deformed in the past couple days (the probable path of a new ridge). As you can hear in the video, the creaking became more frequent close to the time of the rupture. This suggests that least in some cases there is warning that something is about to happen.
The ice was 5-6" thick and was a few days old. The temperature was around 10 deg. The offset in the ice after the rupture was about 20" of overlap. In most places elsewhere the ridge was a simple overlapped ridge.
The ice in the main rupture shown in the video became a loose plate ridge. You can see late in the rupture process that the near side of the tented ice was pushed vertically into the water making room for the rest of the plates to float relatively freely.
Capuring this video involved a great deal more luck than planning