The Story of Glaciers
Ribbons of ice, stretched flat in sheets or sculpted by weather and fissured by pressure, glaciers have a raw magnificence that is mind-boggling to behold.
As snow falls on the accumulation area, it compacts to ice. The river of ice is slugged forward by gravity, which deforms its layers as it moves. When the glacier surges downhill, melted ice mixes with rock and soil on the bottom, grinding it into a lubricant that keeps pushing the glacier along. At the same time, debris from the crushed rock is forced to the sides of the glacier, creating features called moraines. Movement also causes cracks and deformities called crevasses.
The ablation area is where the glacier melts. When accumulation outpaces melting at the ablation area, the glacier advances; when there’s more melting or evaporation, the glacier recedes. Since 1980 global warming has contributed greatly to widespread glacial retreat.
Another marvel of glaciers is their hue. What makes some blue? Wavelengths and air bubbles. The more compact the ice, the longer the path that light has to travel and the bluer the ice appears. Air bubbles in uncompacted areas absorb long wavelengths of white light so we see white. When glaciers calve into lakes, they dump a ‘glacial flour’ composed of ground-up rock that gives the water a milky, grayish color. This same sediment remains unsettled in some lakes and diffracts the sun’s light, creating a stunning palette of turquoise, pale mint and azure.