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| GRAIN SIZE: Observations of grain size and shape should be made in each distinct layer. Grain size is measured as the maximum dimension of a single grain or crystal. In a layer formed by a fall of compound snowflakes, only the separate crystals which make up the flakes should be considered. At least 20 grains should be examined and an estimate made of their average size. For this purpose use the snow card and hand lens. The card is divided by a 1 mm grid pattern. Estimates to the nearest 0.5 mm are sufficiently accurate. When the grains are bonded together the aggregate must be broken apart before the measurements can be made, but grain fragments must not be mistaken for individual grains. In the case of extreme bonding (e.g. ice layer) or in very wet snow, grain size and shape lose their meaning and need not be recorded as individuals, but the 'cluster' size should be measured and noted.
GRAIN SHAPE: Grain shape should be determined using the hand lens |
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FRESH SNOW |
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| TYPE * refers to freshly deposited snow (or snow soon after deposition) composed mainly of whole crystals or parts of broken ones. Ice pellets and hail do not belong in this class and should be identified seperately. TYPE * snow is usually very soft. | ||||||
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GRANULAR |
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| When snow is transformed by metamorphism, it completely looses all crystalline features and its grains become irregular or more or less rounded. It has no sparkle effect even in bright sunlight and can readily recognized by its dull appearance. It is usually fairly soft when wet, but can be very hard when frozen. Type 'O' snow grains may be any size from very fine to very coarse. | ||||||
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FACETS |
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| At temperatures well below freezing and without any apparent melting, snow is transformed into Type '[]' by deposition of water vapor removed from crystals deeper in the profile by the process of sublimation. Deposition of this vapor higher in the profile produces irregular grains with flat facets. These layered facets are visible with a lens and give the snow a distinct sparkle effect in the bright sunlight. Type '[]' snow is usually fairly hard. | ||||||
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| Depth hoar is characterized by its hollow cup-shaped crystals. These crystals are produced by a deposition of sublimed vapor during a long uninterrupted cold period. Depth hoar is most frequently found directly below a more or less impermeable crust in the lower part of the snow cover. The tensile strength of a layer of depth hoar is very low and the structure of the layer collapses at the slightest touch. |
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