OF SNOW AVALANCHES

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The hazard of snow avalanches to life and property increases from year to year. It is enhanced by the general rise in population, which places more 1 communities and structures in the hazardous areas; by the growing popu-1 larity of skiing, which attracts ever more thousands to the snowy moun-1 tainslides, and by the expanding networks of communications — high­ways, pipelines, power lines, electronic relay systems—whose mountain crossings must be protected. Concern about the avalanche problem is by | no means new, but in recent years there has been an intensification of efforts to find effective ways of controlling hazard. Several useful tech­niques have been developed, and other interesting ideas are under study.

There are two basically different types of snowslide, one much more dangerous than the other. They are known respectfully as "loose snow" avalanches and "slab" avalanches.

Loose-snow slides occur frequently, but they seldom grow very large or cause much damage. It is the slab type of avalanche, which j sets in motion as one massive body a large area of snow, that presents the principal menace and is the main object of control efforts.

Investigations of the predisposing conditions are focused essential- ] ly on the structure and nature of the snow itself, particularly its cohe­sion. This has two aspects: on the one hand, the strength of bonding between the snow crystals within a layer; on the other, the degree of bonding of one layer to another. Cohesion between the snow particles depends in large part on the age and nature of the snow crystals, which vary considerably in form. Crystals of certain compact, nonstellar types |

tend to become firmly cemented together. Weather conditions also play a part: strong bonding between crystals is encouraged by wind-packing and by riming — the accretion of supercooled water droplets as the snow is deposited.

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The most elementary defense against avalanches is to attempt to fore­cast their occurrence so that people and transient traffic can be warned to stay clear. Although physical studies and experience have armed us with many clues, avalanche forecasting is still an art rather than a sci­ence. The variables that determine when conditions are ripe for the trig­gering of a slide are numerous and complex. It is difficult to measure the mechanical properties of snow samples with any precision even in the laboratory, because the characteristics of a sample can change rapidly while it is being handled. There are, however, significant factors that can be measured in the field: the density and thickness of the snow slab, the size of the load compared with the shear strength of the substratum, certain patterns of the snow structure. With information thus obtained it is possible to predict quite accurately the probability of the occurrence of avalanches within the given area. It is not possible, however, to fore­cast precisely where and when a slide will take place, because of un­known variables such as the existence of creep tensions and the unpre­dictability of the various natural or manmade shocks (earth tremors, construction blasting or the like) that can trigger the fracture of a slab.

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Today there are available a number of engineering techniques for control of avalanches, some providing passive defence (protection against actual slides), others designed to prevent their occurrence. Fun-

damentally there are two different ways to prevent or control avalanch-I es: (1) modification of the terrain and (2) modification of the snow. Which includes the deliberate release of slides when and where they will do little or no harm. The first general method is expensive and requires continued maintenance, but it is reasonably permanent and offers maximum protection. The second is comparatively cheap but must be applied repeatedly, perhaps many times each winter. Modifi-1 cation of the terrain is usually chosen when the problem is to protect a] large area or fixed installations; modification of the snow is employed most commonly for protecting highways and ski slopes.

■ Give the Russian for:

to be enhanced by, the expanding networks of communications, concern about the problem, to be concerned about the problem, by no means new, in recent years, intensification of efforts, effective ways of controlling, to develop useful techniques, to be under study, basically different types, to be known as, to be referred to as, fre-1 quently, seldom, principle menace, to focus investigations, particu­larly, on the one hand, on the other hand, to tend to become, to encourage, to be encouraged by, to attempt, to forecast, to predict, to arm somebody with clues, to be an art rather than a science, to measure with any precision, with information thus obtained..., the probability, within given area

■ Give the English for:

Предсказывать, скорее искусство, чем наука, измерять с ка-1 кой-либо точностью, информация, полученная таким обра-1

зом, в пределах данного района, разрабатывать полезные ме­тодики, ощущать беспокойство по поводу проблемы, никоим образом, находиться в процессе изучения, за последние годы, основная угроза, сконцентрировать исследования, в особен­ности, с одной стороны..., с другой стороны, поддерживать, рассматривать как, эффективные способы контроля, увели­чиваться

Answer the questions

— What areas can be considered as potentially hazardous?

— What can enhance the hazard of snow avalanches?

— Is the avalanche problem new?

— What is the difference between "loose snow" avalanches and "slab" avalanches?

— What characteristic of snow is considered as the most important while studying the avalanche problem?

— What are the principle ways of controlling the avalanches? What are their advantages and disadvantages?

Render the text in English

Лавины тоже относятся к оползням. Крупные снежные лави­ны являются катастрофами, уносящими десятки жизней.

С точки зрения механики лавина возникает так же, как и дру­гие оползневые смещения. Силы сцепления снега переходят оп­ределенную границу, и гравитация вызывает смещение снежных масс по склону.

Снежная лавина представляет собой смесь кристалликов снега и воздуха. Снег быстро меняет свойства после своего выпада-1 ния, то есть подвергается метаморфизму. Кристаллики снега растут, пористость снежной массы уменьшается. На определен­ной глубине под поверхностью перекристаллизация может при­вести к образованию поверхности скольжения, по которой пласт снега сползает. Нарушение пласта снега в верхней части склона обычно приводит к возникновению лавины.

Гладкие травянистые склоны являются лавиноопасными. Ky-i старники, большие камни и другие препятствия такого рода сдерживают возникновение лавин. В лесу лавины образуются очень редко, однако одиночные деревья на склоне не препят­ствуют возникновению лавин.

По величине лавины делятся на большие, средние и малые. Большие уничтожают на своем пути все жилища и деревья. Сред­ние опасны лишь для людей, малые практически не опасны.

Существует несколько косвенных причин возникновения ла­вин: неустойчивость склона, перекристаллизация снега, обра­зование плоскости скольжения, снежные наносы с большим уг­лом, чем склон. Прямой причиной часто является сотрясение. И камень, упавший на снежное поле, может вызвать лавину.

Как и в случае других оползневых смещений, наиважнейшую роль здесь играют превентивные меры. Важное значение пред­ставляют исследования предшествовавших лавин, т.к. большин­ство из них спускается по одним и тем же трассам.