| OCR Text |
Show tion. According to Erie's Law the maximum weight of a particle transportable by stream flow varies as the sixth power of the increase in stream velocity. This is why the volume of particles transported by an 8 m/ sec. wind varying at least 2 m/ sec. either way will be nearly 21 times greater at the maximum than at the minimum velocity. The difference in volume is even greater in the gusty winds so frequently observed in Chibin. The heterogeneity of the component particles is a factor in snow density. The more the particles differ in size, the greater the layer density. Density can vary from place to place in the same snowcover by as much as 20- 30%. It is difficult to observe this difference in density once sintering ( fusion) has taken place, even when the snow is broken. Only snow deposited during slight blows is more or less homogeneous. Recrystallization of Dry Snow Freshly fallen snow does not preserve its properties for long. Recrystallization, wind and warmth progressively change the structure, density, physical and mechanical properties, and even the color of snow. To study the changes that take place in snow, we scheduled a series of definite observations. Starting in the winter of 1935- 36, we made observations on the structure and condition of the surface layer of snowcover, and of the changes occurring in it, for 24- hour periods. Every 3- 5 days we did the same for the entire thickness of the snowcover by cutting test holes through to the surface of the ground and taking observations of the individual layers separately. When observations were completed at one test hole, another was dug 0.5 m away in order to avoid weathering effects on the snow tested. The site chosen for the investigation had an even snowcover. This insured observations successive in time for the same layers. Layer structure was usually defined with the aid of a magnifying glass; snow density was measured separately for each layer. Like observations were made on the snowcover as a whole in order to compare snow condition and changes dependent on type of deposition. These same observations on the total snow thickness were made from time to time in level plots and forests, and on slopes and mountain peaks. Due to the ice crusts which at times are wedged into snow at layer boundaries and extend long distances, serving as horizontal markers, it was often possible to trace the same layer through different snow plots. Two or three days, sometimes several hours, after a snowfall, the snow crystals start to become transparent, losing their former white color and taking on a grayish cast. The crystals become thinner, fine details of pattern disappear, the design is simplified, and the basic framework becomes more" clearly defined. Following this, the separate parts fall away and the crystal breaks up into small fragments in such a way that the outlines of the primary star can still be distinguished. These grains or pellets sometimes measure less than 0.5 mm across. Regardless of the crystal type, whether flake, branched star, platelets, skeletal forms, or even simple grains, the snow crystal breaks up into fine pellets. We will refer to snow in this stage as " loose, fine granular snow." Its density is 0.08- 0.15, and in the case of windblown snow, as much as 0.30. - 8- |
