In order, images by Steve Nichol, Youri Loof, and Dominic Barrington
Striped icebergs form as meltwater refreezes in crevasses atop glaciers before air bubbles can become trapped in the ice, or when supercooled seawater freezes inside cracks beneath an ice shelf, which then becomes visible when the iceberg breaks off and flips.
Over time, the weight of accumulated snow contorts and curves these blue bands of ice, as does erosion from waves and wind. dust and volcanic ash falling on the iceberg can darken the ice, while dissolved organic compounds entering from below can shade it towards cyan.
Accumulated snow also compresses air bubbles trapped in the iceberg, thus preventing them from otherwise interfering with the passage of light. Because water absorbs photons from the red end of the visible spectrum much better than the blue end, bubble free ice takes on a blue color.