The frozen bubbles you see in a frozen lake are created from rising methane gas. This is what happens when you release the methane gas bubbles and then light them on fire.
The bubbles you see under the surface on a frozen lake are methane gas being released from the organic matter at the bottom of the lake or pond. As the gas rises to the top it freezes as it comes in contact with the frozen water.
This is what happens when a bunch of pyromaniacs get together to light this rising gas on fire.
WARNING: There is explicit language in this video.
Watching these pyros light fireballs on a frozen lake is pretty fun. Better them than us, with all the hazards and whatnot.
You can look at this as a science experiment, but if you guys try this make sure nothing is flammable around the cracks in the ice...you may singe some hair on your arms like these guys.