I'm not familiar with earth science, in particular ice formation in glaciers and I hope you can bear my rather stupid question: Is the change of a "normal" ice layer into glacial ice with frozen air bubbles a continous transition or a spontaneous reaction? Someone told me that the air bubbles inside the snow flake in an ice layer start to freeze. How can air, this mixture of nitrogen, oxygen, carbon dioxide, ... actually freeze? It was a professor of meteorology, who told me that on a winterschool and I tend to believe him but I fail in understanding him. Are there any other changes in the ice solid structure (due to the high pressure), besides that effect of frozen air? Something like a phase transition into a solid-crystal structure? I mean the ice appears to be blue and that might be an indicator of a different absorption effect or a change into a crystal structure.