Glacial ice has a different colour than regular ice. The strong and deep blue is explained by the glacier’s ice density, which is so high that it absorbs every other colour of the spectrum except blue — so blue is what we see. The ice on a glacier has been there for a really long time and has been compacted down so that its structure is quite different than the ice we see more frequently. Besides, in Iceland glacial ice is not just frozen compacted snow, mainly because it gathers volcanic ash form past eruptions, rock and soil as they carved their way down a mountain’s slope.