Bubbles Befuddle Bear

Having put his career as a figure skating champion on hold for now.... little bear decided to investigate becoming an ice researcher instead. Peering through the ice, little bear decided that it was at least as thick has he was tall... and maybe more than double his height! He could see rocks and sticks under the ice... and even in the ice, which was kind of neat.

Little bear noticed cracks in the ice, which at first gave him a bit of cause for concern, but then he noticed that they were quite shallow and not really significant. Nothing to be worried about. One of the most perplexing things that he found were air bubbles trapped in the ice! And not just random air bubbles, but columns of air bubbles... What the heck? How did those air bubbles form? What was causing them to form as columns.

Little bear decided that there was only so much he could learn from frozen air bubbles by lying on the ice. He could speculate on what caused them... but he wouldn't be able to prove it, because the ice was way too thick! And he is just a little bear... He did think that maybe there was a clam or something burrowed under the lake bottom, where the water wasn't frozen, and these bubbles were pockets of the clam's exhaled air bubbles... Or maybe it was rotting vegetation releasing bubbles of gas?? Or maybe it was a hot water spring releasing gas??

Little bear actually wasn't too far off the mark. Apparently these columns of air bubbles are caused by rotting vegetation releasing methane gas. The water freezes, gas collects under the surface, more water freezes below that and the air bubble is preserved in ice.