Ice lifting up due to the pressure crack.
In the 12 winters we've lived on the lake we have never had a pressure crack so large dominate the ice surface in front of our place. This one started off as fairly large, so we thought, last weekend, but since the early week cold snap it really expanded. It cracked about 400 feet off shore, and it zigzags along for about 2 km. In places it's 10 feet across and the ice is piled up 3 to 4 feet high in spots. Both Sunny and I refused to cross over it - as we approached it we could hear the ice cracking again. This is a relatively small crack in comparison to ones on Lake Nipissing at this time of the year, but for Trout Lake in our area, it's huge.