Ice is a crystalline mineral composed of water with attributes of a very special rock. Like magmatic rock it originates from a solidified fluid. Water solidifies below 32°F (0°C) while magma already solidifies at 1800°F (1000°C). Freshwater has its maximum density at a temperature of 39.2°F (4°C) and is therefore highly buoyant and floating. Oceanic salt water freezes at 28.8°F (-1.8°C) whereat the salt freezes out in brine channels leaving behind ice of pure freshwater. Falling snow accumulates as a sedimentary rock and recrystallizes under its own pressure like a metamorphic rock called glacier. The stage of glacier ice metamorphism is a function of decreasing air bubble content trapped in the ice while the ice density increases. Fresh fallen snow contains air up to 90%, annual granular firn snow about 50% and multi-year ice about 20-30%. After decades the glacier ice contains less than 20% air and hence absorbs the entire electromagnetic spectrum of visible light despite the shortest blue fraction, giving it its distinct layered bluish appearance. The bluest and hence oldest ice is located at the glaciers terminus that often exhibits impressive snouts.
Canon 20D, Canon EF-L 24-105mm, f/8, 1/15sec, ISO 400, tripod