Walking on the snow

Another good walk today - not so very far but the snow-mobile tracks were hard and we didn't need snowshoes.
You see Jan and Jude in the picture, and behind them these strange snow features, reminding me of karst limestone features (see extra too).  They appeared after a period of very cold weather, followed by several days of + degrees and some thawing.  Obviously drainage features but the drainage is beneath the surface. I can't find any online explanations of how they form.
Once back from our walk we made a fire and sat outside with soup, crackers, and then mulled wine (glögg) and biscuits.
Another good and fun day.