Rune Pettersen carefully walks over the frozen lake. He taps his knife on the ice to break the surface. Then he holds a lit match next to the hole. Boom!
What's happening here? I'm not sure, but this 2014 article in Smithsonian describes a similar phenomenon at a frozen lake in Canada:
Methane bubbles form in bodies of water when dead organic matter (leaves and animals) falls into the water and sinks to the bottom, to the delight of bacteria waiting below. The bacteria munches on the matter and poops out methane, which turns to white floating blobs when it comes into contact with frozen water.
My favorite part of the video is when Pettersen uses the gas to brew coffee. This use of natural methane could be a useful survival skill.