Why is glacier ice blue?

Snow white didn’t get her name out of the blue. So why is snow sometimes blue and not white?Snow white didn’t get her name out of the blue. So why is snow sometimes blue and not white?
Blue ice occurs when ice is compressed, air bubbles are squeezed out and ice crystals enlarge, making the ice appear blue.

Snow is white because light is scattered and reflected at the boundary between ice and air similar to the bubbles at the top of a dark beer. Small pockets of air reflect and scatter the visible light. Ice only appears blue when it is compressed enough that bubbles do not interfere with the passage of light.

Therefore, glacial ice started out as white snow. As more and more snow fell, the layers built up and the pressure caused the compression of the snow. Pressure squeezed out the air bubbles and formed compact ice with a blue hue. The top layer of a glacier usually appears white from snowfall or from weathering of the ice.