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Do not adjust your set! 
Photo by Rod Benson
This photo was taken from near the base of Siyeh Glacier in the east-central part of Glacier National Park. The view shows a 1-mile long lake named Cracker Lake, which was formed in a basin carved by the Siyeh Glacier during the last ice age. Such lakes, referred to as “tarns” or “cirque lakes”, are common in Glacier Park.
Got Milk?. . .
The beautiful turquoise color shown in the photo is the true color of the water. Sometimes called “glacial milk”, the unusual color is due to the presence of “rock flour”, which consists of tiny clay particles formed as rocks stuck to the bottom and sides of a glacier grind against bedrock. This abrasion reduces some of the bedrock to a fine powder that looks like the flour used to make bread. As the ice melts this rock flour is exposed and transported away by meltwater, often into a nearby tarn such as Cracker Lake.
They won’t settle down! . . . .
Meltwater also transports pebbles, sand, and silt into the lake, but these larger rock particles quickly settle to the bottom of the lake. In contrast, the much smaller particles of rock flour remain suspended in the water until the fall when the meltwater stops flowing or the lake freezes over. Only then does the water become calm enough to let rock flour settle to the bottom. A core sample from the middle of the lake would probably reveal alternating layers of silt and clay called “varves”. . . . One layer of each (varve) for every year the lake has been in existence.
Why so blue? . . .
Sunlight includes many different wavelengths of light ranging from the longer “reds” to the shorter “violets” (ROYGBIV). A white T-shirt is white because it reflects all of the wavelengths, a black shirt is colorless because it absorbs all of the wavelengths, and a red shirt is red because it absorbs the OYGBIV and reflects the R (red wavelengths). Apparently the tiny particles of rock flour suspended in the lake are just the right size to reflect more of the blues and some of the greens than any of the other wavelengths.
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