OCR Text |
Show polished. This is seen first on steep southern slopes, later on level areas, on the surface of both dense and loose snow. At first, this shiny snow surface consisting of fused crystals is thin and cannot be separated from the underlying snow with which it forms a unit. This skins gradually thickens; the snow beneath it begins to settle because the ice crust acts like hothouse glass-. Later, with thawing, openings begin to appear in the crust overlying snow protuberances. The crust now becomes ragged and covers the snow like lace. During clear weather, with marked warming by the sun ( the temperature may be below 0° C), the ice crust disintegrates into formations resembling broken mirror fragments that are characteristic of the first spring days. These ice fragments are preserved longer in areas pitched to the horizon and facing the sun. In the literature such ice fragments are called " neve glass." In the spring, when thaws and freezes follow one another, one can observe snow grains fused in clumps and platelets, in the greatest profusion on north slopes, covering the snow like scales rather than continuous crusts. Subsurface Crystals The special ice crystals sometimes found in the sub- snow should be mentioned here. In the snow in caverns and pockets, under the branches of creeping trees, in the spaces between snowcovered rocks, crystals of various shapes appear. Sometimes these are goblets, hollow pyramids with one side split lengthwise and the edges turned inward; sometimes they are slim, elongated platelets enlarged at one end, either transparent or showing a pine tree design, sometimes with one end rounded, giving the appearance of a flower petal; often they are simply bundles of needles with facets. By their appearance these formations remind one of coarse, granular snow crystals; they are larger, however, measuring up to 5 cm. One often observes such coarse crystals growing on the inner surface of snow- covered vent holes, or what is left of them, connecting subsurface spaces with the outside air. One also observes these crystals in the spaces formed in snowcover by the sinking of a loose snow layer underneath a dense one. Even in this case, such crystals are not recrystallized snow grains, but special formations like hydrometeors of atmospheric ice. Although these hydrometeors differ considerably as to shape, size, position, position and conditions of formation, the cause of their appearance is the same for all ( hydrometeors: rime, frost flowers, Siberian hoarfrost, " hard bloom," cavern crystals, snow smoke, snow petals, etc. See Anisimov, M. I.: " On the Description of Certain Atmospheric Phenomena," Meterology and Hydrology, 1953, No. 5). The temperature of growing crystals is always lower than the frost point, which means lower than the temperature necessary for the water vapor pressure to be such that the vapor is capable of saturation " over ice" and thus for the excess of water vapor to sublimate into crystals. Since the dew point is below the frost point ( freezing), approximately 0.1° C for every degree below zero, these crystals are able to grow at temperatures below and above the temperature of the surrounding air. These formations are all caused by sublimation and therefore an excess of over- saturated air aids their growth. This explains the free space always found near them. These crystals do not need the presence of other crystals to be able to grow. Subsurface - 17- |