Problems and results of studies of mountain glaciers in the Soviet Union

Transcription

1 World Glacier Inventory - Inventaire mondial des Glaciers (Proceedings of the Riederalp Workshop, September 1978; Actes de l'atelier de Riederalp, septembre 1978): IAHS-AISH Publ. no. 126,1980. Problems and results of studies of mountain glaciers in the Soviet Union V. M. Kotlyakov Abstract. Results of studies of mountain glaciers undertaken in the USSR for the last 15 years are considered. The data of the glacier inventory of the USSR serve as the primary source of information. Methods of determining the firn line altitude, data for which are contained in the inventory, are discussed. The paper describes a glaciological method of calculating precipitation in the alpine zone, based on the concepts of Ahlmann and developed further by Krenke and Khodakov. Using this method, calculations were carried out at a small scale for the total territory of the USSR and in detail for the Pamirs and Caucasus. It revealed that the amount of precipitation, in particular solid precipitation, is far greater in the mountains than on the abutting plains and piedmonts. In conclusion, the problem of compiling an inventory of surging glaciers is discussed. Problèmes et résultats des recherches sur les glaciers montagnards de l'union Soviétique Résumé. On présente les résultats des recherches sur les glaciers montagnards qui ont été entreprises durant les 15 dernières années. Les données contenues dans l'inventaire des glaciers de l'urss sont la principale source d'informations. Les méthodes employées pour la détermination de l'altitude de la ligne de névé, qui fait partie des données recensées, sont discutées. On décrit une méthode glaciologique, basée sur le concept d'ahlmann et approfondie par Krenke et Khodakov pour la détermination des précipitations en zone alpine. A l'aide de cette méthode, on a effectué des calculs relativement sommaires pour l'ensemble du territoire de l'urss et des calculs détaillés pour le Pamir et le Caucase. 11 en découle que les précipitations, et en particulier les précipitations solides, sont beaucoup plus abondantes dans les montagnes que dans les plaines adjacentes et qu'au pied des montagnes. Enfin, on discute du problème de l'établissement d'un inventaire des glaciers sujets à des crues catastrophiques. INTRODUCTION With regard to the goals of this Workshop, this paper deals with studies of the glacier regime undertaken in the USSR in the last years. These investigations were stimulated by the compilation of the glacier inventory of the USSR, the data of which are already broadly used for glaciological, climatological and hydrological purposes. Present studies of mountain glaciers in the USSR were initiated during the International Geophysical Year, when the glaciers of the polar Urals and Elbrus, the Fedchenko Glacier in the Pamirs, Tsentralniy Tuyuksu Glacier in the Zailiyskiy Alatau, Karabatkak in the Central Tien-Shan, Aktru in Altay and the glaciers of Suntar-Khayata Range in East Siberia were studied. During , observations of heat, ice and water balances for the IHD programme were carried out on seven selected mountain glacier basins. They comprised Bolshaya Khadata basin in the polar Urals; Marukh, Dzhankuat and Gergety basins in the Caucasus; Abramov basin in the Alay Range; Tsentralniy Tuyuksu in Zailiyskiy Alatau and Aktru basin in Altay. On some of them the studies are still in progress under the International Hydrological Programme. In 1963 permanent surveys of glacier variations were started in the Soviet Union and since 1973 they have been developed and made more up-to-date. Comprehensive observations of the glacier regime under this programme are being performed on the Obruchev Glacier in the polar Urals, Shumsky Glacier in Dzhungarskiy Alatau and on the above-mentioned Abramov, Tsentralniy Tuyuksu and Karabatkak glaciers. 129

2 130 V. M. Kotlyakov Studies of the surface regime of mountain glaciers and conditions in which they exist are based mainly on the results of the investigations mentioned, but the glacier inventory of the USSR still serves as the main source of information. USSR GLACIER INVENTORY It was decided to compile the glacier inventory in our country in 1962, and its publication was started in About 20 different establishments of the Academy of Sciences, the Hydrometeorological Service and universities are participating in this work. The inventory is based on large-scale maps with obligatory airphoto interpretation. However, we often need additional field studies, and from 1968 to 1973 a special expedition from the Institute of Geography of the USSR Academy of Sciences worked in the Pamirs and gathered information needed for the compilation of the inventory of this highland. Besides airphoto interpretation, helicopter observations of all the glaciers were undertaken and on about ten of them ground studies were carried out (Bazhevefa/., 1975). The glacier inventory of the USSR is compiled according to special guidelines (Anonymous, 1966). It contains mainly data on locations of glaciers, their dimensions (length, width, thickness), altitudes of their different parts and, in particular, the firn line which is the main index providing the base for hydroclimatological calculations. The glacier inventory is a series consisting of 110 issues. Initiated at the beginning of the sixties, the inventory is published in the form of tables and photos. The work of including the data of the inventory in the water inventory (Cadastre) of the USSR and arranging the data on computer files is in progress (see the paper of V. F. Suslov in these proceedings). In the course of compiling the inventory, the total number of its parts reached 10. This can be accounted for by the inevitable clarification of the data and the development of quite new glacierized areas. For example at the end of the 1960s the area of Kuznetskiy Alatau, South Siberia, was first studied in detail and dozens of glaciers with remarkably high (for this continental area) mass and heat exchange were found. Thus, another part of the inventory was published. By now about 70 per cent of the inventory has been published and the rest of its issues are completed. As the compilation of the Soviet glacier inventory is practically finished three important problems now face us. The data of the inventory should be converted into the form of the World Glacier Inventory proposed by the Temporary Technical Secretariat. Secondly, we have to work out some methods of using the inventory data for studies of the glacier regime and general climatology in glacierized areas. Third, the large amount of quantitative data given in the inventory will serve as the basis for compilation of some maps of the World Atlas of Snow and Ice Resources. This is the next step in our job of studying glaciers by cartographic methods. Problems of the third kind are discussed in another paper by Dreyer and myself, whilst in this paper we draw attention to the second point ; the use of inventory data for studies of the glacier regime and climatological problems. According to the USSR glacier inventory data, the picture of present glaciers of the USSR is quite clear by now. Glaciers in the country occupy about km 2, about km 2 of this total are covered by mountain glaciers. The total number of mountain glaciers, each with an area of more than 0.1 km 2, is about Proceeding from the approximate thickness of glaciers, on average varying from 60 to 150 m in different mountain glacier basins, and their total area known from the inventory, ice storages in glaciers have been calculated. To transform the calculated ice volume into amounts of accumulated water, we used the coefficient of 0.86, i.e. the mean ice density in mountain glaciers. As a result, we obtained the values of perennial ice storages in the mountains of the Soviet Union (Table 1 ). At present,

3 Mountain glaciers in the Soviet Union 131 TABLE 1. Storage of perennial ice in the mountains of the Soviet Union Glacierized area Area of glaciers [km 2 ] Ice storage [km 3 ] Amount of accumulated water [km 3 ] Caucasus Pamirs and Alai Tien-Shan Dzhungarskiy Alatau Altay and Sayans Mountains of Siberia Kamchatka and Koryak mountains mountain glaciers of the USSR contain about 2600 km 3 of ice, in which nearly 2250 km 3 of water are accumulated. This is ten times more than the annual discharge of rivers, flowing from glacierized areas of our country. Compilation of the glacier inventory raised the problem of classifying morphological types of glaciers. The following scheme has been adopted in the guidelines (Anonymous, 1966) of our inventory (Fig. 1): Expanded-feot Piedmont Conic summit gâaciei Fuit sommet FIGURE 1. Types of glaciers adopted in the glacier inventory of the USSR. (1) hanging glacier: situated on small areas of mountain slopes with no pronounced depressions on the slope; (2) spill-over glacier: lies in a shallow depression on the slope from which a short tongue expands; (3) slope glacier: extends along a slope in the shade of the wind or sun; (4) cirque-glacier, situated in well pronounced depressions on the slope (cirques) having distal slope in its lower part and may occupy the whole cirque or only part of it; (5) cirque-valley glacier: has a tongue expanding over the cirque for one or twothirds of its total length;

4 132 V. M. Kotlyakov (6) hollow glacier: occupies the bottoms of several coalescing cirques and has a relatively small tongue, its total area is rather large; (7) simple valley glacier: partially or completely fills a mountain valley and has a well pronounced tongue; (8) compound valley glacier: formed by two or more nearly equal ice streams, each having its own accumulation area; (9) dendritic glacier: has numerous tributaries of different area and form; (10) expanded-foot glacier: spreads from the valley to the piedmont plain, where it has an expanded lobe; (11) piedmont glacier: formed by several merging valley glaciers, when they reach a plain; (12) glacier on conic summit: covers totally the slopes of a separately protruding summit; (13) glacier on flat summit: lies on flat inclined surfaces of separate summit or crest and has a dome-like form. Mountain glaciers may form glacier complexes. Transection glaciers and plateau glaciers are most frequent. Despite the relatively detailed classification, in the course of the inventory compilation we had to single out one more type of mountain glaciers. These glaciers were first discovered in the Pamirs and named 'slope glaciers'. They cover vast areas of slightly rough mountain slopes, their lobes expanding down to the mountain foot. Enumerated morphological types of glaciers were used in the glacier inventory of the USSR. Compilation of the World Atlas of Snow and Ice Resources required simplification of this classification. In the Atlas we distinguish 10 types of glaciers, four for polar glaciation and six types for mountain glaciers. Among mountain glaciers we single out hanging, cirque, valley, dendritic and compound valley glaciers, complexes of plateau glaciers, glaciers of flat summits and slopes, glacier complexes of mountain knots and summits. The remaining types are reduced to the six enumerated types, according to some very definite features (Kotlyakov, 1977). The glacier inventory of the USSR contains data on the height of the firn line for the majority of glaciers. This level, or to put it more precisely the equilibrium line, represents the most significant glacioclimatological level in the mountains. Unfortunately, existing methods of compiling the inventory provide no data on the equilibrium Une, but for the majority of glaciers the difference between the position of the equilibrium line and the firn line can be precisely calculated. Therefore, we can use the firn line, identifying it with the equilibrium line. In the guidelines for the compilation of the glacier inventory, several direct and indirect methods of determining the height of the firn line are recommended. They comprise methods by Kurowski, Hôfer, Bruckner, Hess, Reid and Tscheglova. Comparison of these methods, made in different glacierized areas, showed their different precision. In the present phase of glacier retreat the Kurowski method proves to be the best of all the indirect methods. The Hess method evidently fits for stationary glaciers. GLACIER REGIME STUDY In the Soviet glaciological literature the glacier coefficient, i.e. the relation of accumulation area to the ablation area, serves as one of the basic morphological indices. The sense of this coefficient is the same as AAR (Kotlyakov, 1968, p. 334). In conditions of considerable and various snowdrift and avalanche feeding of glaciers it has quite different values. In classical alpine literature of the last century, a glacier coefficient of 3 was broadly used. In particular, the Bruckner method of determining the firn line

5 Mountain glaciers in the Soviet Union 133 is based upon this ratio dividing the glacier in the proportion of 3:1. It is inferred from new data that in the middle of this century, as a rule, the value of the glacier coefficient in the Alps is less than 2. At present, for the majority of Caucasian glaciers the glacier coefficient varies from 1 to 2. The mass balance of the small Marukh Glacier is near zero with K=l. It is noteworthy, that the mean values of the glacier coefficient on the southern slopes of the Central Caucasus are twice as high as the values of this index on the northern slopes: 2.4 and 1.2 respectively. This might be connected with the greater amount of precipitation on the southern slopes and, consequently, the smaller contribution by the concentration of snow to the accumulation of the glaciers. By now, it has been proved quite conclusively that on the majority of glaciers, excluding some glaciers of flat and conic summits, concentration of solid precipitation occurs due to snowdrift and avalanche transport. Amounts of snow blow to valley glaciers exceed by far the total falling precipitation (in the ratio of 1.5 or 2), while on cirque glaciers this difference reaches 3-4 times and more. To describe this process, a concentration coefficient is introduced, i.e. the relation of the mean snow storage on a glacier to the total annual precipitation at the height of the equilibrium line. The glacier inventory has stimulated the development of a glaciological method of calculating precipitation in alpine areas. This method, based on the Ahlmann concept, was developed by Krenke and Khodakov (1966). It was then used by Krenke (1975) in order to obtain fields of the values in question, and to plot their maps for mountain areas. Such maps have now been prepared for the World Atlas of Snow and Ice Resources. This method presupposes that on the equilibrium line glacier accumulation equals ablation and, therefore, one can calculate the value of ablation to learn the accumulation: A = (t + 9.5f where A is the total melting for the ablation period in mm of water and t is the mean temperature for the same period. We do not know, as a rule, the mean temperature during the summer months on the equilibrium line, but we may calculate it by extrapolating the values of temperature at lower lying weather stations to this level which is known from the glacier inventory. The cooling of 1-2 C on the glacier as compared to rocks must be taken into account. To make calculations more precise Khodakov has deduced a formula relating the difference in temperature (At) to the glacier length (L): log At = 0.28 log L ~ 0.07 Having calculated the total value of melting, which equals accumulation, we may proceed to precipitation, dividing the value obtained by the concentration coefficient of snow. To make the calculated precipitation and accumulation fields more smooth, we used data averaged for groups of 5-15 glaciers. As a result the picture of precipitation in the alpine zone can be obtained which is quite comprehensive as it uses data from thousands of glaciers, and averaged for long term periods due to the conservative nature of glacial processes. Calculations, based on this method, were first performed on a small scale for the whole territory of the USSR and adjacent countries and then in detail for some glacierized areas. We proceeded from the following assumptions. The term 'glacier basin' denotes a basin on whose surface glaciers and permanent snow patches exist down to the outlet. A geographically continuous and similar, with respect to regime, group of glacier basins forms a glacier area, while a group of these areas is united into a glacier region (Avsiuk et al., 1973). Glacier regions of the Caucasus, Alps and Alaska may serve as examples. Snow-ice objects, situated there, form specific glacier systems actively interacting with the environment. The data of the glacier inventory suggest that permanent snow and ice exist under

6 134 V. M. Kotlyakov a certain range of conditions determined by relief and climate. Mountain glaciers usually occur in the belt of maximum precipitation, as a rule presenting narrow (about 10 km wide) bands on the slopes of mountain ranges exposed to the prevailing flow of atmospheric moisture. The amounts of precipitation, especially solid precipitation, occurring in the mountains greatly exceed, often by an order of magnitude, precipitation in adjacent valleys and piedmont. Calculations undertaken in the USSR have shown that the maximum precipitation of Eurasia, over 3000 mm, occurs in Scandinavia and Kamchatka near the Islandic-Kara and Aleutian baric depressions. Precipitation gradually decreases eastward of the Atlantic and quickly westward of the Pacific. It is worth mentioning that the water content in the northwestern margins of all mountain systems of the temperate belt, such as the Pamirs, Caucasus, Tien-Shan and Altay, is nearly the same as that of Scandinavia and Kamchatka. Detailed maps of the height of the equilibrium line, summer temperature of the air and precipitation at this height have been prepared for a number of mountain glacier areas, according to the above-mentioned method and under the guidance of Krenke. These maps permitted us to determine the direction of the main moisture flows in the mountains, to discover the stream-like nature of flows caused by compound networks of big and small ranges, to reveal the occurrence of atmospheric waves in front of and behind orographic obstacles and other regularities of the meso-scale which engender complicated precipitation fields and are reflected in glacier location and morphology. All these climatic peculiarities cannot be revealed by the data from weather stations which are very sparse jn the mountains. Detailed results may be shown with special reference to the Pamirs where over glaciers with a total area of 9170 km 2 are situated. For the relationship between the two main agents of glacierization orographic and climatic - see Table 2. The TABLE 2. Relationship of Pamirian glaciers to relief and climate Area 1. Garmo-Fedchenko Southern slope of Zaalayskiy Range Western areas of the Obikhingou River basin Zulumart Range Lake Karakul 5060 Height of Height Positive the accumulation of difference of line Ranges glaciation [m] [m] [m] Climate Topography height of crests, varying from 4000 m up to 7000 m within the Pamirs, and the positive difference of glacierization, i.e. the difference between the height of the upper boundary of a glacier and its equilibrium line, serves as an index of the former factor. The height of the equilibrium line, characterizes the climatic factor: the lower it lies the greater is the influence of climate. It is seen in the table, that even within one mountain system all four combinations of the two factors are possible, consequently the maximum spreading of glacierization may not coincide with areas of maximum accumulation. A ten-fold decrease of precipitation has been revealed in the Pamirs, from 3500 mm at the western periphery to mm in the East Pamirs, where some places adjacent to desert areas receive only mm of precipitation per year. The altitudinal

7 Mountain glaciers in the Soviet Union 135 maximum of precipitation was not registered even at 5000 m. In glaciological observations were first undertaken on the Pamirian firn plateau, situated at a height of 6000 m a.s.l. (Diurgerov and Urumbaev, 1977). They showed, that even at such great heights accumulation exceeds 1000 mm per year. Evidently, the zone of maximum precipitation as well as its altitudinal relationship does not exist within the real zone of glacierization. We believe that the regularities of the distribution of precipitation, air temperature, height of the equilibrium line and glaciers themselves, revealed in the Pamirs, are typical of all inland glacierized areas. THE INVENTORY OF SURGING GLACIERS In conclusion, we would like to mention another problem, connected to the compilation of the inventory of surging glaciers of the USSR. This problem faces the Soviet Section of Glaciology at present. The necessity of this catalogue is explained by the great danger of glacier surges and water-ice-stony mudflows, engendered by the outbreaks of glacier-dammed lakes. The development of glaciological studies makes it possible to discover more and more surging glaciers. In the Pamirs alone their number exceeds 100. However, precise criteria for distinguishing surging glaciers from 'normal' glaciers have not yet been worked out. But a number of well pronounced features of glacier surges, which may be recognized by remote sensing, including satellite observations, do exist. A special programme of satellite images and visual observations of surging glaciers has been successfully fulfilled by the cosmonauts on board the Soviet orbital station 'Saljut-6'. The inventory of the surging glaciers of the USSR will be mainly based on air photography and satellite images, which will allow us to determine not only surging glaciers themselves, but their phase (active or passive) and also traces of former surges. When interpreting the images we look for the features typical of surging glaciers: droplike form of the tongue or its spreading as an accumulation cone, marginal faults, zones of fractured ice and numerous crevasses on the glacier surface, thrust of glacier tongues over other glaciers and their slopes, occurrence of glacier-dammed lakes, displacements, bands and typical loops of moraines on the glacier surface, traces of former mudflows, scours of alluvial deposits and cut accumulation cones below the glacier tongue. At present guidelines for the surging glacier inventory are being worked out in our country, and compilation of the inventory itself is planned for the next 3-4 years. REFERENCES Anonymous (1966) Rukovodstvo po Sostavleniyu Kataloga Lednikov SSSR (Guidelines for the Compilation of the Glacier Inventory of the USSR): Gidrometeoizdat, Leningrad. Avsiuk, G. A., Kotlyakov, V. M., Khodakov, V. G. and Golubev, G. N. (1973) Problemy gjdrologii lednikov i lednikovykh raionov (The problems of hydrology of glaciers and glacierized areas). Vodn. Resursy, no. 2, Bazhev, A. B., Kotlyakov, V. M., Rototaeva, O. V. and Varnakova, G. M. (1975) The problems of present-day glaciation of the Pamir-Alai. In Snow and Ice (Proceedings of the Moscow Symposium, August 1971), pp : IAHSPubl.no Diurgerov, M. B. and Urumbaev, N. A. (1977) Gliatsiologicheskie issledovania Pamirskogo firnovo-ledianogo plato (Glaciological studies of the Pamir firn-ice plateau). Mater. Glyatsiol. Issled., Kronika, no. 31, Kotlyakov, V. M. (1968) Snezhny Pokrov Zemli i Ledniki (Snow Cover of the Earth and its Glaciers): Gidrometeoizdat, Leningrad. Kotlyakov, V. M. (editor) (1977) Programma i metodicheskie ukazania po sostavleniyu Atlasa snezhno-ledovykh resursov mira (Programme and guidelines for the compilation of the World Atlas of Snow and Ice Resources). Mater. Glyatsiol. Issled., Kronika, no. 29,

8 136 V. M. Kotlyakov Krenke, A.N. (1975) Climatic conditions of present-day glaciation in Soviet Central Asia. In Snow and Ice (Proceedings of the Moscow Symposium, August 1971), pp : IAHSPubl.no Krenke, A. N. and Khodakov, V. G. (1966) O svyasi poverkhnostnogo tayania lednikov s temperaturoi vozdukha (Connection of the glacier surface melting and air temperature). Mater. Glyatsiol. Issled., Kronika, no. 12, DISCUSSION Miiller: You mentioned that you are computerizing your fine set of data which is so far presented in tabular form. What system do you use to locate your glaciers in the computer data bank? Geographical coordinates or a UTM system? Kotlyakov: For computerizing glacier inventory data in our country we use the system worked out for all kinds of water resources. In principle it is a hydrological system. We use water basins of different orders: the first digit for big basins, covering large parts of the country, the second digit for second order and the third digit for third and fourth orders followed by the glacier number. For this system we need nine spaces on the computer card. As for geographical coordinates, I do not find them very convenient for use for large glaciers which are rather common in mountains and, in particular, in polar regions. Ommanney: Your guidelines for cataloguing surging glaciers sounds most useful. Have they been published or will they be available? Kotlyakov: Two years ago we had a very useful discussion in our country on the subject and set up a special working group to work out guidelines for compilation of an inventory of surging glaciers. The guidelines should be finished within a year and will be available in Williams: During your lecture you showed a slide entitled 'morphological classification of mountain glaciers adopted in the Catalogue of Glaciers in the USSR'. Is this classification scheme the same one that will appear in the forthcoming World Atlas of Snow and Ice Resources? Kotlyakov: No. The slide is an English version of the classification scheme published in the Catalogue: the scheme used in the Atlas is simplified. It also includes ice caps, outlet glaciers etc. and accounts for ten types of glacier altogether. It will be shown in the Workshop paper by Dreyer and me. Kasser: You showed a map of the Pamirs with isotherms of long-term summer temperatures at the elevation of the firn Une. What is the definition of this temperature and of the related time interval? Kotlyakov: In accordance with the formula used in our calculations we use the mean summer

9 Mountain glaciers in the Soviet Union 137 temperature, i.e. the average temperature for June, July and August. We find this temperature very useful for calculations and it could also be received in a very simple way. Miiller: In the table of empirical formulae that you showed, I was very interested in the form of your nonlinear equation for calculating ablation from the mean summer temperature. Is this equation valid for all USSR glaciers outside of the Arctic? Braithwaite suggested a linear equation where the parameters must be determined for each region in his PhD thesis. Kotlyakov: The formula that you mention is based upon all available data including the polar regions. It was developed and tested by Krenke and Khodakov. We now have a more precise empirical formula which includes the short-wave radiation balance as well as temperature but the first formula is more convenient for calculations because of its simplicity. This equation gives us good results for the large regions where we make a lot of calculations and take a group of glaciers rather than single ones. Braithwaite: I would like to comment that I entirely agree with Kotlyakov's nonlinear equation relating to summer mean air temperature. My linear model was in fact a linearization of such a relationship. This is one reason why the parameters in such a model are different for different regions: they contain information about mean temperatures, lengths of summer etc. Actually the original nonlinear version of my equation, developed for arctic situations, is in remarkable agreement with the equation of Krenke and Khodakov.

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