Principles of classification and mapping of permafrost in Central Asia

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1 Permafrost, Phillips, Springman & Arenson (eds) 2003 Swets & Zeitlinger, Lisse, ISBN Principles of classification and mapping of permafrost in Central Asia G.F. Gravis & E.S. Melnikov Institute of Earth Cryosphere, Russian Academy of Sciences, Moscow, Russia Guo Dongxin, Li Shuxun, Li Shude, Tong Boliang, Zhao Lin & Nan Zuotong Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, China N. Sharkhuu Institute of Geography, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia A.P. Gorbunov, S.S. Marchenko & E.V. Seversky Permafrost Institute, Russian Academy of Sciences, Kazakhstan Alpine Geocryological Laboratory, Almaty, Kazakhstan ABSTRACT: The agreement to prepare a uniform permafrost map of Central Asia by an international team (China, Mongolia, Russia and Kazakhstan) was reached at the International Symposium in Mongolia in September In this paper we consider some initial results of mapping mountain and plateau permafrost in Central Asia as the first step for geocryologists of the four countries. A brief review of the experiences in small-scale mapping of permafrost in Russia, China, Mongolia and Kazakhstan is provided. We distinguish two types of cryogenetic zones: high-latitudinal (polar) and low-latitudinal (alpine). The altitude of 500 m a.s.l. is suggested as a criterion for division of permafrost area into two types of cryogenesis. We propose two morphological types of alpine cryogenesis within the Central Asian permafrost area: mountain and plateau. General regularities of permafrost distribution, its structure and temperature, ice content and distribution of periglacial phenomena in the Central Asian permafrost area are briefly described. 1 INTRODUCTION The distribution, mapping and modeling of permafrost in Argentina, Canada, China, Kazakhstan, Mongolia, the Nordic and European countries, and Russia were one of the major topics of the International Symposium on Mountain and Arid Land Permafrost which took place in Ulaanbaatar, Mongolia, September 2 4, According to the first recommendation of the Symposium, an international team of experts (China, Kazakhstan, Mongolia and Russia) is required to prepare a uniform map of Central Asian permafrost (Brown, 2001). Mapping of mountain permafrost of Central Asia is complicated by two circumstances. First, nonuniform approaches, and as a whole, lack of studies of permafrost in this vast region. Secondly, lack of distinctions in the principles of permafrost mapping. The poor information about frozen ground in the majority of mountains of Central Asia requires an understanding of the general regularities of permafrost formation. It is important to analyse the experiences of permafrost mapping in the different countries and to employ a common usage of this experience. This collective experience and choice of the most acceptable methods of classifying and mapping are the basis for development of the uniform approach to the compilation a permafrost map of Central Asia. of southern Russia, Mongolia, China, Kazakhstan and adjacent countries (Figure 1). At present, except for the IPA permafrost map (Brown et al., 1997), there is no uniform map of Central Asian permafrost conditions. However, small scale permafrost maps have been compiled for Central Asian territories of these regions. Heginbottom et al. (1993) summarised corresponding major developments in permafrost mapping. The following is a brief review of these mapping approaches. 2.1 China The map of snow, ice and frozen ground in China (1:4,000,000), compiled by Lanzhou Institute of Glaciology and Geocryology, Academia Sinica (1988) shows regional distribution of the three types of frozen ground and the cryogenetic phenomena in these permafrost regions. These are (1) high latitute permafrost in Northeast China, (2) permafrost on Qinghai-Xizang Plateau and (3) alpine permafrost in mountains of 2 SMALL-SCALE MAPPING OF MOUNTAIN PERMAFROST IN CENTRAL ASIA The Central Asian region is the largest area of alpine permafrost in the world. This region includes the territories 297 Figure 1. The Central Asian permafrost region.

2 West and East China. Permafrost conditions of the territory along the Qinghai-Xizang Highway have been studied in detail and mapped (Tong et al., 1983) at the scale of 1:600,000. The distribution map (1:4,000,000) of frozen ground in China was compiled by Xu & Guo (1982). The relation of climate, vegetation, soils and natural landscapes determine the latitudinal zonation from south to north of Northeast China (Guo et al., 1981). A map of permafrost and periglacial phenomena distribution on Qinghai-Xizang Plateau and adjacent mountain regions was compiled at 1:3,000,000 (Li & Cheng, 1996). The map reflects the boundaries of regions such as predominantly continuous permafrost, sporadic permafrost, seasonally frozen ground, shortterm frozen ground, as well as the distribution of periglacial phenomena. A Map of Geocryological Regionalization and Classification in China at a scale of 1:10,000,000 has appeared as an appendix in the book Geocryology in China (Zhou et al., 2000). Permafrost regions of China are divided into three major frozen ground regions: Eastern, Northwestern and Southwestern. Within each region of frozen ground, sub-regions are identified. In the Nortwestern and Southwestern regions sub-regions are selected as consistent with geomorphological units. Generally, the principle of mapping mountain and plateau permafrost in China is based on permafrost zonality index or on degree of permafrost thermal stability depending on mean annual ground temperatures (Cheng, 1983, Cheng & Dramis, 1992). A GIS-based map of permafrost distribution and thickness on Qinghai-Xizang Plateau using simulated data of soil temperature measurements from Chinese weather stations was presented recently (Nan et al., 2001). 2.2 Mongolia Permafrost in Mongolia is concentrated in Altai, Hovsgol, Khangai and Khentei mountainous regions. Distribution, thickness and temperature of permafrost in Mongolia vary with altitudinal zonation of mountains. Based on altitudinal zonation of changes in permafrost distribution geocryological maps of Mongolia have been compiled (Gravis et al., 1990) at a scale of 1:2,500,000. The southern Siberian permafrost is characteristic of Mongolian territory. The southern permafrost boundary in Mongolia has not been studied and determined sufficiently. Permafrost conditions in the Selenge River Basin have been studied and mapped relatively well as compared to other territories of Mongolia (Sharkhuu, 1993). 2.3 Russia In 1956, I.Y. Baranov created the first geocryological map of the USSR (scale 1:10,000,000). The updated map (scale 1:5,000,000) was completed in In 1982 one more variant of this map (scale 1:7,500,000) was published ( Geocryological map of USSR, 1982). The compilation of the Geocryological map of the USSR (scale 1:2,500,000) was started at the Geocryology Department of the Moscow State University under the initiative of V.I. Kudryavtsev (Kudryavtsev et al., 1977). The map was completed in 1991 under the direction of E.D. Ershov and subsequently published (Ershov, 1996). The map is the most complete source of the geocryologic cartographic information for the territory of Russia (see Williams and Warren 1999 for the English language translation). The Map of Morphology and Permafrost Temperature of Northeast and South of Siberia (scale 1:2,500,000), compiled under the direction of I. A. Nekrasov (1976) is an example of a special geocryological map. The relation between temperature and thickness of permafrost was used within the mountain territories. Another example is the special Geocryological Map of USSR (scale 1:4,000,000) compiled under the direction of A. I. Popov (1985). Two types of distribution of cryolithogenesis are shown: syngenetic and epigenetic, and the composition of ground and typical cryogenic textures are shown. The geocryological mapping on the landscape base began to develop in 1960s in Western Siberia (Melnikov, 1981). Here geocryological maps were made only for the plains. The first attempt to use the experience of these operations for mapping of the entire permafrost area of Russia there was Geocryological Map of Russia and Mongolia (scale 1:10,000,000) compiled under the direction of E.S. Melnikov in 1993, which incorporated into the circumarctic map (Brown et al., 1997). The compilation of such a map was possible due to appearance of landscape maps covering all territories of the former USSR (Isachenko, 1985; Gudilin, 1987). The most recent usage of landscape contours for geocryological mapping is demonstrated on the 1:7,500,000 map by Melnikov et al. (1996). The mountains areas are depicted in differing colours for the altitudinal belts: arctic deserts and stony tundra; mountain tundra; mountain sparse growth of trees; mountain taiga; and mountain steppes. Within the altitudinal belts the boundaries of complexes of cryogenic geological processes were delineated depending on relief and composition of ground. 2.4 Kazakhstan The problems in the study of geocryological conditions of the mountain countries were specifically analysed by members of the Kazakhstan Alpine Geocryological Laboratory of Permafrost Institute SB RAS under the direction of A.P. Gorbunov. Geocryological conditions of Pamir, Gissaro-Alai, Tien Shan and 298

3 Table 1. Characteristics of comparing principle and terminology for permafrost zonation used in each country of Central Asia. Country (author), land Principle of permafrost Terminology of form and region zonation permafrost distribution Permafrost extent CHINA 1.1. Middle height mountain Latitudinal zones Islands 30% region in the North-East Predominantly continuous 30 75% China (Xu & Guo, 1982) Quinghai-Xizang Index or degree of Down belt 0 to 0.5 C High Plateau (Cheng, 1983). permafrost thermal Middle belt 0.5 to 3 C stability Up belt 3 C 1.3. Alpine mountains in West and Altitudinal belts Islands East China (Zhang et al., 1985). Predominantly continuous KAZAKHSTAN (Gorbunov et al., 1996) High Altitudinal subbelts Sporadic 40% Alpine Tien Shan and Pamir Discontinuous 40 80% mountains. Continuous 80% MONGOLIA (Gravis et al., 1990) Middle height Latitudinal zones Sporadic 1% (Altai, Hovsgol, Khangai and Scattered islands 1 5% Khentei) mountain and surrounding Islands 5 40% arid land regions Discontinuous 40 80% Continuous 80% SOUTHERN RUSSIA (Ershov, 1996) Mountainous regions Latitudinal zones Southern discontinuous 0.5 to 2 C with depressions and separate plateaus and plains Northern continuous 0.5 to 2 C Dzungarskyi Alatau, located within the territories of Tajikistan, Kyrgyzstan, Uzbekistan and Kazakhstan were investigated (Gorbunov, 1978, 1988, Gorbunov et al., 1996) in areas between N and E. The regional altitudinal zonality of permafrost distribution for different mountain areas were elaborated (Gorbunov, 1978, 1988). The structures of altitudinal geocryological zonality, regularity of permafrost and cryogenic features distribution and climatic factors were the basis for regionalization of mountain permafrost. Based on altitudinal zonality of permafrost distribution maps of permafrost distribution have been compiled at 1:2,500,000; 1:1,000,000; 1:500,000 and larger scales. Mapping of mountain permafrost in Kazakhstan uses an approach based on the division of mountain ranges into sub-belts of different types of permafrost distribution (Table 1). The altitudinal boundaries of these sub-belts displace upwards from Dzhungar Alatau towards the southern part of Eastern Pamir about 140 m with a decrease of latitude by 1. 3 GENERAL REGULARITIES OF PERMAFROST IN CENTRAL ASIA 3.1 Distribution General regularities of permafrost distribution are determined by latitudinal and altitudinal zonality of changes in climatic and topographic factors. Altitudinal zonality of permafrost distribution has been studied in different regions of high mountains (Cheng, 1983, Qiu, 1993, Jin et al., 2000, Zhou et al., 2000, Gorbunov, 1978, 1988) and middle heights of the arid mountains of Mongolia (Gravis et al., 1990, Sharkhuu, 1993). According to the general patterns, extent and thickness of permafrost increase in geographic latitudinal zonality from south to north and in a rise of mountain altitudinal belts. The low limit of discontinuous permafrost in Altai, Khangai and Khentei mountains, all located at the same latitude, 2100, 1700 and 1300 m a.s.l., respectively. (Sharkhuu, 2000) Regional patterns of permafrost distribution depend on features and effects of winter air temperature inversion, vegetation and snow covers, ground composition and water content, slope orientation and steepness, surface and groundwaters, climatic and geothermal conditions, and so on. Therefore, distribution and development of the permafrost varies from place to place within a given permafrost region. Coarse debris, forest and mossy covers provide a considerable cooling effect and therefore favour permafrost formation or preservation. However, where the snow cover is thick (over cm), cooling or warming effects on permafrost can be small. Small islands, patches and lenses of permafrost in arid steppe lands of Mongolia, China and Kazakhstan can be developed only in damp and silty sediments of depression and valleys. There are always taliks under large lakes, river channels and along active hydrothermal and neotectonic fractures in regions with continuous permafrost. Generally the difference in altitudes of permafrost distribution on south-facing and north-facing slopes is about m (Qui et al., 1983). The difference in elevations of the snowline on glaciers of northern and 299

4 southern slopes essentially increases in accordance with increase of aridity and continentality of climate. For Dzhungar Alatau this difference is usually about 100 m, in Tien Shan m, for Pamir m. The difference of altitudes of permafrost boundaries is much more: in Dzhungar Alatau as it reaches m, in Tien Shan and in Pamir m. It is necessary to note that the above comparison is only relevant for slopes with an approximately identical steepness, soil-vegetative cover and geologic structure. For Transili Alatau Range (Northern Tien Shan) there is a difference of about 350 m for the lower boundary of discontinuous permafrost between sunny and shaded slopes. But for the lower limit of sporadic permafrost this value is greater and reaches 500 m. 3.2 Temperature Permafrost temperature and heat flux are the main parameters of thermal characteristics of permafrost. These parameters are very important to estimate not only distribution and thickness of permafrost, but also stability or sensitivity of permafrost to climate changes and human activities. They are obtained by means of temperature measurements in boreholes at permafrost key or monitoring sites. There are many such sites in Russia, Mongolia, China and Kazakhstan (Burgess et al., 2000). In order to obtain the above parameters, Sharkhuu carried out geotemperature measurements in more than 400 boreholes with depth of m (Sharkhuu, 2001) and located mainly in the Hovsgol, Burenkhaan, Erdenet, Argalant, Nalaikh and Baganuur areas of Mongolia. According to general regularities, the MAGT in the mountain altitudinal belt decreases about C for each 100 m rise above the absolute surface height, and the latitudinal zonation increases by C for each 100 km from north to south. Under the influence of warming ( 20 cm thick snow cover, subsurface flow and infiltration of waters in well drained ground) and cooling (forest and moss covers, high moisture content and silty ground and free air convection in coarsely fragmental deposits) there is a reduction of C for each factor. The differences in ground temperatures between south-facing and north-facing slopes of mountains ranges from 0.5 C to 3.0 C depending on the steepness of slope. There exists winter air temperature inversion in intermountain valleys and depressions located at altitudes of m a.s.l. Values of geothermal gradient range from 0.01 C/m on the watersheds and slopes of mountains to C/m in valleys and depressions. Thermal observations in boreholes in Tien Shan and Pamir demonstrate a significant variability of thermal regime (3 6 C) and thickness of permafrost ( m) within short distances even at the same altitudinal level. This is the result of the influence of topography, lithology, tectonics, hydrology, slope orientation, air temperature inversions etc. In the Inner Tien Shan (Ak-Shiyrak Range, 42 N), at the elevations of m, the lowest ground temperature is 5 C in the bedrock (Paleozoic schist) and 6.7 C in the ice-rich Late Pleistocene moraines. The corresponding thickness of permafrost is and m. In view of these findings it is rather circumspectly to use high-altitude gradients for estimating the thermal characteristics of the ground at the various hypsometric levels. 3.3 Ice content The periglacial features in Mongolia have been studied at different times (Gravis et al., 1990, Sharkhuu, 2001). Mountain permafrost in Mongolia is mainly epigenetic. In the upper ( m) layers of the rock weathering zone, the ice content is 3 10%. High ice content permafrost is characteristic of lacustrine and sometimes alluvial sediments with ice content 10 50%. Drained debris and gravely sands have massive visible cryogenic textures, with ice contents that do not exceed 10 20%. However, ice content of epigenetic freezing water bearing gravely and sandy deposits have an iciness 20 40%. Rock glaciers, moraines, lacustrine deposits have the highest ice content, and rocky massifs the least ice. Ice content often reach 50% and even more. Syngenetic frozen unconsolidated sediments with ice wedges are common in most of the intermountain depressions with continuous and discontinuous permafrost in southern Russia. These sediments possess a very high ice content. However, predominantly epigenetic frozen sediments in areas with sporadic and isolated permafrost are usually characterised by medium and low ice contents. 4 UNIFIED CLASSIFICATION AND TERMINOLOGY Differences in permafrost maps of China, Kazakhstan, Mongolia and southern Russia are the result of (1) various degrees of permafrost research between territories, (2) various techniques of analysis of permafrost information, (3) lack of unified principles and approaches in mapping mountain permafrost and (4) a lack of unified common classification, terminology and legend for mapping mountain permafrost. In order to elaborate principles of mapping mountain permafrost, it is necessary first of all to compile the permafrost classification of the Central Asian territory. We suggest to divide the permafrost are: high latitude and alpine. The circumpolar area of cryogenesis is entirely defined by its high-latitudinal location and intrinsically mainly one of geocryological altitudinal 300

5 zonation zone of perennial frozen ground. The lead processes of cryomorphogenesis are long-term freezing and seasonal thawing-freezing. The area of alpine (low-latitudinal) cryogenesis is typical between 30 N and 30 S. Here all processes of cryogenesis are predetermined hypsometrically. In other words, the longterm, seasonal and short-term freezing thawing is rather limited both in space and in time. These circumstances determine the complex structure of altitudinal geocryological zonality of the alpine cryogenetic zone. It is possible to consider a lack of cryogenetic processes in the territories below 500 m a.s.l. as a diagnostic sign of the alpine area of cryogenesis (Gorbunov, 1988). Hence, it is necessary in mountains of Central Asia to refer to this area as alpine cryogenesis. It is necessary to select two morphological types within the area of alpine cryogenesis: mountain and plateau. To the first type are referred frozen and frosty (dry permafrost) rocks of mountain ranges and valleys. Within this area the alpine type of relief predominates. The second type includes permafrost of accumulative and denudation flatness (plateau). The classical examples of these two morphological types are Western Pamir and Qinghai-Xizang (Tibetian) plateau, respectively. As a basis of permafrost classification in Central Asia we can assume the following: landscape and geomorphological characteristics, humidity of mountains using the continental index (CI) of altitudinal permafrost zonality. CI was proposed by A.P. Gorbunov (1978) and is determined as a difference between altitudes of snowline and lower boundary of sporadic permafrost. S. A. Harris (1989) suggested to determine CI as a difference between altitudes of snowline and lower boundary of continuous permafrost. It is necessary to agree with this improvement, as the boundary of continuous permafrost is easier to determine and is more stable. Some definitions such as island, discontinuous and continuous permafrost in connection with the character of alpine permafrost distribution are not absolutely correct. There are a number of difficulties when this approach is used for the mountain permafrost area. On the map continuous permafrost near the upper part of ranges and peaks looks like separate islands, which has no resemblance with continuity. Cheng Guodong (1983) was one of the first to pay attention to this circumstance and proposed an alternative terminology for different types of permafrost distribution in line with its temperature (see Table 1). It is suggested to select three geocryologycal belts subdivided into nine subbelts, where the permafrost belt is subdivided into subbelts: stable, substable and instable permafrost subbelts. On the other hand we should use a terminology and classification for mountain permafrost compatible with circumpolar permafrost areas. As a first step in this direction it is proposed to use the terms island, discontinuous and continuous permafrost, but with the adjective alpine in relation to elevation of lowlatitudinal area of cryogenesis. This allows a comparison of permafrost maps of circumpolar and alpine permafrost areas. For developing the geocryological mapping of Central Asian mountains it is necessary to elaborate on an international landscape base for this territory. It will allow us to realize regionalization of territory in view of the zonal factors, to allocate provinces within neotectonic area distinguished by character and a degree of a relief ruggedness, and also geocryological conditions. It is necessary to select landscapes formed on various geological genetic complexes. Unified classification for a permafrost map of Central Asia can be based on permafrost regionalization of the territory. Each permafrost region and area is characterised by a certain degree of similar permafrost conditions, or of similar patterns of permafrost distribution, thermal state, cryogenic structure and processes. A small-scale uniform permafrost map of Central Asia shows permafrost distribution, temperature (according to borehole data), ice content within the upper layer of permafrost (up to a depth of zero annual amplitude) in accordance with the IPA map classification and also regional distribution of periglacial phenomena. Regional vertical permafrost zonality for different mountain territories is shown as an insert for the map. 5 CONCLUSION This report presents a summary of existing permafrost mapping and classification as well as permafrost conditions in Central Asia. The essential differences in permafrost definition and mapping are discovered. It is notice that not uniform of knowledge of permafrost conditions within the Central Asian region. The first step in compilation of a new regional permafrost map at a scale of 1:2,500,000 must be elaboration of uniform legend adjusted with the authors. The next step is compilation of different parts of the map for Chinese, Mongolian, Russian and Kazakhstan territories. In this operation the landscape maps should widely be used. It should be noted that geocryological characteristics such as permafrost temperatures, depths of seasonal freezing thawing, distribution of cryogenic geological processes are to the largest degree linked with landscape boundaries. Using these links it is possible to extrapolate of permafrost characteristics from of the well investigated territories into poorly investigated regions. The last step in the compilation of Central Asian Permafrost Map consists of joining the separate regional parts into a uniform map. ACKNOWLEDGEMENTS Partial financial support for participation in the Mongolian Symposium and consultations in China 301

6 were provided by grants at the International Arctic Research Center, Fairbanks, Alaska, the National Snow and Ice Date Center, Boulder, Colorado and Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences, Lanzhou, respectively. The authors thank Dr. Jerry Brown for his encouragement and advice for the initiation of this project. We also thank Dr. Stephan Gruber and anonymous reviewer for their valuable comments. REFERENCES Geocryological map of USSR Scale 1:7,500,000. In Baranov, I. Y. (Ed.), Moscow, GUGK. Brown, J International Symposium on Mountain and Arid Land Permafrost and Field Exursions in Mongolia. Frozen Ground, 25: Brown, J., Ferrians, O.J., Jr., Heginbottom, J.A. & Melnikov, E.S. (compiled and edited) Circum-Arctic Map of permafrost and ground-ice conditions. Scale 1:10,000,000. United States Geological Survey. 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