Colours Produced by Cavities in Ice
Air trapped in ice fissures and bubbles can produce a stunning display of interference colours. Most often the colours can be seen as a brownish or bluish hue around bright reflections. The colours occur at the critical angle of partial to total reflection, which is roughly 82°. In our case it seemed at first sight that the colours belonged to a snow blanket or hoarfrost halo. But the colours originated in the ice itself, or rather in enclosed cavities. The frost had come very suddenly. The water level had decreased very quickly and the thin ice layer was under tension and cracking loudly from time to time.
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