A few common denominators Francois. Although I photographed these in December, and already cold enough to skim ice on the beaver ponds, the flows through the ponds of steady brook kept useable warmer waters in the margins, so that although the hard night freezes were doing their work the "wicking" materials were kept flowing with those warmer temps...as they egressed that protective wicking, the frigid air temps did their "liquid nitrogen-like freezing" as the water left the protective materials. I had never seen the form Thierry posted but now have identified boggy areas along streams where I will be looking in the future. The rotted tree falls contain the cellular decomposing material within that obviously are able to do the same work on a larger scale. Anywhere with ground water tempered by flows and where decomposing (interior) organics can behave as wicks would likely hold promise...and of course before sun or rising temperatures in the morning releases them back to flow. Any ground where you would not want to cross in canvas shoes in spite of surrounding cold conditions....(think fresh wick in kerosene lamp...as long as the kerosene is available in flowing form the wick will draw...in the case of the freezing we have just added another interesting element instead of flame. I'm so glad Thierry brought the high form to our attention!
Thank you for taking the time to point me in the right direction. I know a place about 45 km from home, where I might find the right conditions for thread ice. Unfortunately, this winter has been way too warm to get freezing at lower elevations (so far, December has been 11°c [20F] above average temperature) and yesterday we got snow.