Glacial Cave – Hikers under the Mendenhall Glacier near Juneau, Alaska. When conditions are right, streams melt holes into the glacier. At times they are large and stable enough for exploration. The ice filters out most colors of light except for the blue wavelengths leaving a stunning blue glowing from the ice above – Photo and caption by Mark Meyer/National Geographic Photo Contest

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Glacial Cave – Hikers under the Mendenhall Glacier near Juneau, Alaska. When conditions are right, streams melt holes into the glacier. At times they are large and stable enough for exploration. The ice filters out most colors of light except for the blue wavelengths leaving a stunning blue glowing from the ice above – Photo and caption by Mark Meyer/National Geographic Photo Contest

Source: National Geographic, Wikipedia