Rock Flour

Rock flour, or glacial flour, consists of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock by glacial erosion or by artificial grinding to a similar size. Because the material is very small, it becomes suspended in river water making the water appear cloudy, which is sometimes known as glacial milk.

When the sediments enter a river, it turns the river's color gray, light brown, iridescent blue-green, or milky white. If the river flows into a glacial lake, the lake may appear turquoise in color as a result. When flows of the flour are extensive, a distinct layer of a different color flows into the lake and begins to dissipate and settle as the flow extends from the increase in water flow from the glacier during snow melts and heavy rain periods. Examples of this phenomenon may be seen at Lake Louise and Peyto Lake in Canada and Gjende lake in Norway.