One of the many glaciers we observed on our day cruise in Prince William Sound. In the old days, the boats would blast their horns and the glaciers would 'calf' (i.e. a chunk would fall off into the Sound) but with global warming, the glaciers are receeding too quickly already and the authorities put a stop to the honking. The glacier looks blue because blue is lowest visible wavelength to the human eye and all other colours are absorbed by the ice (same reason the sky is blue- Physics 101). Blue is refracted and that is the colour we see. When the boat sped away from the glacier, the roar of the engine did cause the glacier to calf (I suspect the captain pulled full throttle for that very purpose- since major pieces of ice then fell and splashed. The splashes eventually rocked the boat.