Dust, crystal size, and visible layers
Glacier ice contains so-called cloudy bands that appear whitish when the ice core is polished and the visual stratigraphy is recorded. Especially in the relatively dirty glacial ice, the layers are related to the content of dust and other impurities. Measurements of the size of the ice crystals show that the crystals in the ice are smaller in ice with relatively more impurities. This effect is due to the fact that the impurities prevent the formation of large undisturbed crystals.
The left picture shows the visual layers in a glacial ice sample of approx 8 cm ⋅ 8 cm. The horizontal cloudy bands are formed from compacted layers of snow with relatively high impurity content, e.g. from storms during spring, when the atmospheric dust load is high. The right picture shows the same sample placed between two crossed polarizers. The different orientation of the individual crystals shows up as colour differences, although the ice itself is clear. It can be seen that the crystals are smaller in the cloudy bands (i.e. the layers with high dust content).
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Ice Core Drilling Projects