Лёд и Снег • 2012 • № 3 (119)
унежныи покров и снежные лавины
УДК 551.578.46+549.01+548
Evolutionary conception of snow metamorphism based on crystal-morphology and the theory of symmetry
© 2012 г. E.G. Kolomyts
Institute of Ecology of the Volga River Basin Russian Academy of Sciences, Togliatti
egk2000@mail.ru
Статья принята к печати 18 февраля 2012 г.
Auto-regulation, classification of snow crystals, crystal-morphology, snow cover, theory of symmetry.
Авторегуляция, классификация форм снежных кристаллов, кристалломорфология, снежный покров, теория симметрии.
The paper presents a novel approach to the study of development of microstructures in snowpack based on the crystal-morphology and on the fundamental laws of natural symmetry. An empirical deterministic model describing the sublimation-metamorphic cycle in seasonal snow cover and the polymorphic variants of this cycle is suggested. Staging in the formation of crystal shapes and self-development of snow microstructure in snow layers is revealed. The crystal shapes are the result of successive process of superposition of ice crystal-chemical symmetry and dissymmetry of the soil - snow cover - atmosphere system, according to the known P. Curie principle. Morphological classification of snow crystals in seasonal snow cover is developed on the base of evolutionary model. Evolution of snow microstructure is conditioned by a marked degree by probabilistic conformity to natural laws, manifesting itself in the processes of auto-regulation of metamorphism. These processes include two types of regulation: the self-regulation of snow layers, on the one hand, and the regulation related to external conditions - under the influence of atmospheric perturbations, on the other hand. The accounting the processes of auto-regulation of snow metamorphism for allows development of new methods in short- and long-term avalanche forecast.
Introduction
Up to now, the studies of the processes within snow-pack are based on considering the snow cover mainly as a continual matter-energy system. The phenomenological approach (according to classic thermodynamic) — to interpret snow on the ground as a three-component porous material exposed to irreversible viscous deformations [18, 23, 25, 42, etc.] and reflecting the winter hydro-meteorological conditions [5, 15, 20, 22, 31, 40, etc.] - is already a traditional one. In this respect, the understanding of the relation of the most important physical-mechanical properties of snow to the external conditions is developed well enough [26, 35]. A number of mathematical models of great theoretical and applied significance have been developed, with one of the main purposes - to be used in snow avalanches forecast [16, 19, 22, 31].
The modern studies consider snow cover it as a heterogeneous environment varying in time in its microstructural and stratigraphic characteristics [6, 9, 19, 32, 34, 39, etc.]. It would be useful to find regularities in these variations and to describe the mechanisms control-
ling evolutionary transformations of snow microstructure. The morphology of snow crystals is mainly studied in laboratory experiments and observations of individual free growth and morphogenesis of the snow crystals [7, 18, 29, 32, 43, etc.]. Such results are used in interpretation of the on-site observations. However, it is very difficult to reproduce in laboratory the full natural diversity of evolutionary metamorphic processes in natural snow cover.
In the beginning of the snow cover studies in the regions of Siberia and Far East the author [4] faced poorness of information, which could be obtained by use of conventional methods of the field analysis of microstructure in seasonal snow. Snow cover is a crystalline body, and hence the processes of snow metamorphism obey the basic laws of crystallography [2, 9, 11]. By some reasons, the methods of contemporary crystal-morphology are not sufficiently employed in modern snow science, to some extent retarding further development of this branch of glaciology. This can be the reason why the glaciological engineering so far has no sufficiently developed scientific and methodical basis for predicting the whole class of snow avalanches in terminology [7],
particularly the avalanches of prolonged development, as defined in [17] - associated mainly with the evolutionary processes of metamorphism in snow cover.
Though the last «International Classification for Seasonal Snow on the Ground» [24] made considerable step forwards in relation to this as compared to the previous ones [21, 36, 41] through orientation on the processes in classifying the crystals shapes in snow layers, still the conventional analysis of snow microstructure mainly employs the quantification of the granulometric parameters of snow [8, 18, 19, 25, 37, etc], with the shapes of crystals considered as the essential but not the main microstructural property in snow cover [24, 26].
The results of long-term West-European and Russian snow studies confirm that under various winter conditions snow cover is transformed from a disordered pile of snow crystals deposited from the atmosphere into something integral, ordered, organized, i.e., creates itself as a certain glacio-system [4, 7, 20, 26, 34, 35 , 37, 41, etc.]. Thus, it may be a priori admitted that the theory of evolution is fully applicable to the metamorphic transformations of seasonal snow cover. Despite the term «evolution of snowpack» is used quite often [5, 20, 28, 31, 35, etc], it is still unclear to what extent the metamorphism of packed snow is a process of its self-development, i.e., the evolutionary process in scientific meaning of this term [6, 33]. For us, the evolution corresponds to directional structural changes in a given natural system, firstly, from simple to complex and, secondly, based on primarily internal interactions in the system, against the background of its adaptation to variable environment.
The centuries-old experience of establishment of the evolution theory in biology has shown that only discrete objects (individuals, species) and their system-forming combinations (populations, communities) as discrete qualitatively definite formations can evolve, while continual characteristics of individuals, populations and communities cannot. In snow cover, such qualitative definiteness is typical only for forms of crystals and for kinds of crystals communities, and not for grain sizes, parameters of grain contacts, surface energy, etc. Grains cannot evolve (in accepted here definition of this term).
We believe that if the form of growing or evaporating crystals as the most important microstructural quality of snow is excluded from consideration, then it makes no sense to consider snow cover evolution as a directional process of its metamorphism. It is necessary to elaborate an evolutionary basis of the theory of sublimation metamorphism of seasonal snow cover for improvement of the scientific and methodical basis of snow avalanche prediction and development of the methods of indication of the winter regime of landscapes by snow microstructures. Solution of this problem is envisioned by way of constructing discrete models of system organization and development of snow cover based on its crystal-morphology and fundamental laws of natural symmetry, as well as developing on the basis of these models
the methods for investigation of the processes of sublimation snow metamorphism from positions of the theory of evolution. This theory, developed within biological sciences [9], has been effectively applied to crystallography and genetic mineralogy [9, 11, 12, 44] (snow cover is a monomineral rock). It can be proved that the transformation of evolutionary units of snow cover (forms of crystals and kinds of crystals communities) is based on their self-development (self-organization and auto-regulation), which has both invariant and stochastic regularities, as well as the properties of adaptation to the varying meteorological regime. All these characteristics of snow cover sublimation metamorphism correspond to the propositions of the general theory of evolution of natural systems. In future, the results of 3D-investigations of snow microstructure such as [28, 38] can be related to the proposed approach.
Starting positions for evolutionary snow studies
The evolutionary snow studies should be based on the probabilistic-statistical approach considering snow cover as a hierarchically organized system of discrete crystal spaces as interpreted by V.I. Vernadsky [2]. This system is based on the key microstructural property of snow: the shapes of growing crystals that reflect the whole complex of internal transformations of deposited snow. We postulate that snow cover is the system of natural assemblages of crystals of certain forms, what in sometimes sense are analogous to the communities of individuals with different quality in living nature, as defined in [9]. New snow crystals grow in a close mutual interaction and simultaneously experience the external regulation, mainly by the atmosphere. With such approach, the analysis of snow microstructure and snow crystal-morphology should be based on the methods of crystal-morphology and fundamental laws of natural symmetry.
The basic law of crystallography states that the form of crystal represents the processes of heat and moisture transfer in the medium surrounding them, and all conformity to natural laws of the growth of real crystals in essence characterizes their divergence from the equilibrium state conforming to the internal (crystal-chemical) structure of the given material. This concerns the staged adaptation of a growing symmetrical single crystal to a dissymmetric medium - according to the principle of superposition of symmetries of P. Curie [9, 11]. This is regarded to the symmetric interpretation of the second law of thermodynamics. In accordance with this principle, the development of snow microstructure
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