Purposes and problems

Geocryological conditions and their spatial variability are dictated by the features of the natural environment (such as geological and tectonic structure, hydrogeological and thermal-physical conditions, landscape-climatic surroundings and topography) and by the history of the development of the permafrost in the Cenozoic. Geocryological conditions in the regions of the seasonally and perennially freezing zones are studied following geocryological surveys. The development of principles and methods for such surveys are to a great extent associated with the work of V.A. Kudryavtsev.

The geocryological survey represents by his definition a system of field, laboratory and office work the purpose of which is: to study the principles of formation and development of seasonally and perennially frozen ground and low-temperature geological processes as a function of the natural conditions, their change in the Pleistocene and Holocene, as well as a result of the economic development of the region; to compile geocryological maps and to make geocryological forecasts on this basis as well as to work out the measures to control the permafrost processes and to protect the environment.

For purposes of the geocryological survey we can examine the following matters (15):

1) the principles of the distribution of seasonally and perennially frozen ground over the area depending on the variability of the geological-geographical environment and on the details of heat exchange at the Earth's surface;

2) the cryogenic structures (occurrence and condition of the cryogenic strata and of the layered structure of the permafrost across the section) as they depend on geological structure, neotectonics, the effects of surface and groundwater, and on climate dynamics in the Cenozoic;

3) the composition and properties of frozen, freezing and thawing materials of the geological-genetic complexes and formations in the various landscape-climatic conditions;

4) the cryological features of frozen strata (cryogenic texture, macroinclusions of ice and ice content of Quaternary deposits and Pre-quaternary bedrock) and their dependence on the composition, genesis, age and neotectonic development, type of freezing and dynamics of the permafrost process;

5) the characteristics of the temperature regime at the soil surface, at the base of the seasonal and perennial freezing or thawing ground and at the level of zero annual amplitude, on the basis of analysis of their dependence on the individual natural factors;

6) the dynamics of the depths of seasonal and perennial freezing and thawing and their dependence on the system of natural environmental factors;

7) the spatial change of the thickness of the permafrost over the area and across the section in connection with the existing natural conditions and the history of regional geocryological development;

8) the characteristics of the formation and development of taliks, relating to their genesis, distribution and manifestation;

9) the characteristics of the cryogenic processes and phenomena, their distribution and development;

10) the nature of the interaction between the permafrost and the groundwater;

11) the engineering-geocryological conditions and engineering- geological severity of the terrain in relation to its economic development and geocryological forecast;

12) the experience from construction and other kinds of development with regard to the type of engineering structures, the character of the development and the dynamics of the permafrost process;

13) the history of the permafrost as a function of the dynamics of climate, geological history of the region and nature of human activity.

All the questions listed above or at least some part of them can be resolved depending on the scale of the survey and its aim within the area under investigation. These questions must be considered when making up a program for a geocryological survey.

Methodology

The methodological basis for geocryological surveys representing the scientific background, has been developed and formulated by V.A. Kudryavtsev (see Introduction, ยง5). In V.A. Kudryavtsev's opinion the most important conclusion is that the main object for study is the earth materials themselves. It is impossible to establish the principles of ground temperature regime and all the other permafrost characteristics without studying the materials. It is the seasonally and perennially frozen layers which should be the main object of research when studying geocryological conditions.

With allowance made for this fact the process of geocryological survey is based on the following premises:

1) the main result of a geocryological survey is the establishment of geocryological conditions through the study of the geocryological characteristics in their interaction with the natural surroundings, their change over the territory and the history of development;

2) variations in the geocryological conditions over the territory depend on variations of natural conditions, structure, and type of tectonic structure, geothermal and hydrogeological conditions and topography, landscape-climatic environment and the history of cryogenic development of the territory;

3) a change of one of the cryoformative factors from one region to another causes a change of geocryological conditions;

4) environmental change and short-term climatic change (3,11,33-years) appear first of all in the change of seasonal freezing and thawing depths, mean annual ground temperatures and cryogenic structure of the layer of annual temperature fluctuation, in taliks and areas of formation of new permafrost as well as in the change of cryogenic processes and character of the phenomena;

5) a change of climatic and geological-structural surroundings in different periods of geological development causes change of all the components of the geocryological conditions on the surface and in the layer of temperature fluctuation as well as across the whole layer of permafrost;

6) the study of the present geocryological conditions involves the study of two groups of geocryological characteristics: heat exchange at the ground surface and in the layer of annual temperature fluctu ation for the upper boundary conditions; and heat exchange at the permafrost base and in the permafrost itself for the lower boundary conditions;

7) reconstruction of the history of geocryological development explaining the present cryological structure and the possible changes in the upper 20 m of the ground-cryogenic layer is possible only when analyzing the history of the whole complex of development of the natural environment;

8) the study of geocryological conditions in the course of the survey is carried out during preliminary, field and office work periods with application of a complex of special permafrost, geological-geophysical, geomorphological, climatic, laboratory and other methods of investigation as well as aerial and satellite photography in various spectral bands;

9) the study of multi-factor dependence of every geocryological characteristic on the cryoforming factors of the natural environment. Informativeness and reliability of a geocryological survey results when it is conducted in combination with engineering-geological and hydrogeological surveys, using scientifically the same methods of integrated research.

The key landscape method

The main methodological provisions of the survey can be realized with the help of the key landscape method. The principle of this method consists of the following. In the first stage the typologic landscape (geological-geographical) of the region is subdivided in accordance with factors and conditions dictating the formation and existence of the particular types and variations of the seasonally and perennially frozen ground. Then the key areas, typical of the separated types of regions (microregions), are selected on the basis of the general map and the factual data collected in the process of earlier research. Integrated investigations on a wide range of problems are solved with the help of different methods centred on these key areas during the field period and individual, general and regional geocryological characteristics are studied. Similarities and differences between the different microregions are established through traverses planned on the landscape regionalization map and with the help of aerial and satellite photographs. In conclusion the geocryological map is compiled by extension of the previously obtained geocryological characteristics to the identical types of regions similar to those studied in the key areas and along survey routes. In this case the landscape method of partitioning of the territory becomes the land scape-indicative method of mapping when mapping the ground temperature regime, seasonal freezing and thawing and cryogenic structure of the layer of annual temperature fluctuation.

Landscape regionalization

This is carried out to reveal the similarities and distinctions between areas under investigation with respect to the complex of natural features and associated permafrost conditions. It is commonly accepted that such combinations of natural complex elements as topography and the rocks, soils, vegetation, microtopography and microclimatic features comprising it form persistent genetic homogeneous areas on the Earth's surface. The topographic elements - microregions or types of terrain - represent such areas. The separation into microregions should be based on the geological structure and geomorphological topographic elements, characterized by uniform origin of rocks, relief (height, steepness and orientation of slopes) and conditions of heat exchange at the ground surface. Within the particular topographic elements the subsequent division of the area is carried out on the basis of more detailed uniformity - of cryoformative conditions (composition and moisture content, type of vegetation cover, swampiness, peati-ness, ground surface microtopography, etc.).

Selection of the features of landscape regionalization under the particular zonal-regional conditions should be made taking into consideration the clearness of boundaries of the natural complexes, while the gradations should be justified by the degree of effect of each cryoforming factor on the geocryological environment of the area.

Regional features of the area under study and the scale of the survey introduce new criteria for the selection of features and regionalization gradations. Thus it is necessary to analyze the structural-geological and geographical conditions and to prepare a classification of regional features before the landscape regionalization mapping. Depending on the survey scale, topographic elements and their parts differing from each other by their complexity and area can be separated as microregions. Thus when the small-scale survey (1:100000 - 1:500 000) is conducted, the large topographic forms characterized by uniformity of development and geological structure are mainly separated as microregions. These are, for example, watersheds having particular heights of their ground surface and degree of dissection; watershed slopes to river valleys subdivided into 2-3 gradations according to their steepness; river valley elements with various surface conditions (degree of forest cover and swampiness,etc.). When the medium-scale surveys (1:25 000 - 1:50 000) are conducted the areas are subdivided into a number of smaller ones depending possibly on the soil composition and properties as well as on more detailed consideration of the other natural factors typical of the areas being subdivided. Thus, for instance, within watersheds homogeneous in geological structure, the areas with different combinations of soil beds and composition, microtopographic features, different degree of swampiness, different vegetation cover, etc. can be distinguished.

When the large-scale survey (1:2000 - 1:10000) is conducted and the whole area is situated within one or two topographic elements, for example, in river valleys or on one particular watershed or its slopes, etc., such details of the components of the natural complex components which are considered too small when conducting the small-scale and medium-scale investigations, become more and more important as the regionalization of the landscape is pursued further. Thus, for instance, when a large-scale survey is conducted, areas are distinguished by the prevailing composition of the deposits and their moisture content and also by lithologic features of particular sections as well as by moisture distribution across them. Thus, for example, the areas are separated by degree of forest cover depending on the density of a stand of trees and on degree of surface shading etc.

The key areas

During the field work period it is profitable and economically attractive to carry out geocryological studies not with the same detail over the whole territory but to concentrate them within particular, smaller areas, susceptible to the use of all the methods of investigation. These key areas should include the most typical widespread microregions as well as anomalous areas occurring locally. They are subdivided into general and specialpurpose areas according to the thrust of the investigations. Within the general-purpose key areas the principle conditions of the permafrost, typical of the region, are studied. Within the special-purpose key areas the particular thematic questions of a regional and methodological character are solved, including the problem of determination of geocryological relationships.

When the small- and medium-scale surveys are conducted it is profitable to select key areas, not for every microregion individually but to cover a few microregions simultaneously. This allows not only the establishing of geocryological relationships for each microregion, but also the tracing of their spatial variability.

When a large-scale survey is conducted the special problems associated with the particular economic development of the region are dealt with.

In practice the sizes of the general-purpose key areas vary from 1 to

10 km2 in the small-scale survey and from 0.2 to 1 km2 in the large-scale survey depending on the complexity of the geocryological conditions; the sizes of the special-purpose areas vary from 0.2 to 2 km2 and from 0.1 to 0.3 km2, correspondingly. The number of key areas depends on the complexity of zonal and regional terrain conditions, i.e. on the number of landscape types, each of which should be studied within not less than two key areas. The use of aerial and satellite photographs is of great importance for their selection, with their representation of larger territories and with the possibility of the preliminary integrated interpretation of natural conditions and cryogenic formations. In an effort to use geological surveying and prospecting data more completely and rationally it is profitable that key areas for small- and medium-scale surveys should be located on the site of mineral deposits, that is, where there has been construction and a dense network of bore-holes, shafts, trenches and pits.

The number of key areas (sites) is specified by the stage of the project and by the permafrost and other engineering-geological features considered when the large-scale survey is carried out.

Exploratory traverses

These are carried out when conducting geocryological surveys to study microregions distinguished on the landscape regionalization map and to ensure the proper extrapolation of the factual data on the key areas to the whole territory under investigation. Therefore the main problems for exploratory investigation are the following: 1) to follow geological, geomor-phological, and geobotanic boundaries to investigate the changes in natural conditions 2) to determine the depths of seasonal freezing and thawing and the changes depending on the combination of particular factors of the natural environment of each microregion; 3) to study and to map cryogenic and other geological formations; 4) to sample surface waters and the upper water-bearing horizons (suprapermafrost water and vadose water); 5) to map and to sample groundwater outlets and icings; 6) to study the cryolithologic section of the genetic types of Quaternary deposits in pits, clearings and exposures; 7) to study dislocations and breaks of continuity and jointing in exposures and their expression at the surface; 8) to study the experience being gained from construction and other kinds of economic development of the region.

Successful solution of the problems outlined above with high efficiency and on short notice depends first of all on the correct selection of field traverses. When selecting the traverse route it is necessary to follow these rules: 1) the routes should cross all the types of main areas being distin guished in the course of landscape regionalization; 2) the routes should be planned transversely to river valleys with examination of watersheds as well as along them, to study the elements of the valley complex; 3) the density of the route network and distance between observation stations depend on complexity of the area (region). At the same time the greatest number of observation stations per square kilometre should be located on the key areas and sites of detailed work; 4) in the course of surveying the necessary corrections should be introduced into the plan for exploratory investigations.

It is advisable to use topographic maps of 1:100000 scale and geological maps of the same or larger scale for small-scale exploratory surveys. When medium- and large-scale surveys are conducted it is profitable to use maps of the surveying or larger scales. In any case the explorations should be carried out with the map of landscape regionalization and aerial photographs interpreted beforehand. Along with black and white and spectral band aerial photographs it is desirable to use satellite photographs.

Scales for geocryological surveys

By analogy with engineering geological surveys the geocryological surveys are divided into the small scale (1:500000 - 1:100000), the medium-scale (1:50000 - 1:25000), the large-scale (1:10000 - 1:5000) and the detailed (1:2000 and larger).

Geocryological field surveys are not carried out at smaller than 1:500 000 scale while the geocryological maps are compiled in the course of office work by gathering and generalizing the published and field data of geocryological, engineering-geological and other investigations coordinated with the zonal-regional geocryological background. The latter can be obtained from the geocryological maps of smaller than surveying scale and using the geocryological maps of 1:2 500 000 scale for small-scale and general maps.

The small-scale geocryological survey is usually made for large areas with the goal of geocryological, hydrogeological and engineering-geocryological assessment of the region for its potential economic development. Such surveys should be conducted by the regional geological boards of the country, first of all on mineral-rich areas and by other organizations and departments for the purposes of industrial and agricultural development of the individual regions. The selection of the particular survey scale (from 1:500 000 to 1:100000) depends on the complexity of natural conditions, the level of knowledge of the region, the specific thrust of the investigations and the stage of development of the region.

The medium-scale geocryological survey is the target one and is conducted on comparatively small areas that are to be economically developed in a particular way. Such surveys are conducted at the stage of pre-design documentation - technical and economic substantiation and technical-economic estimation - of a project and in some cases depend on the stage of substantiation of a project according to the type of construction and complexity of natural conditions. The medium-scale survey results are optimal when these surveys are conducted on the background of small-scale ones, i.e. when the predetermined geocryological elements are improved and worked out in detail.

The large-scale surveys (1:2000 - 1:10000) are, to a still greater extent than the medium-scale surveys, specialized for a particular type of construction. These surveys are usually conducted at the stage of technical development of a project and elaboration of designs and are supplemented with investigations for each specific structure with its particular technological and construction characteristics.

When conducting the surveys at any scale uniform procedures must be followed, consisting of the study of geocryological features based on geocryological mapping, forecasts of changes in the permafrost environment and the control of cryogenic processes, in an elfort to exploit the geological surroundings harmoniously. At the same time it is obvious that the small-scale survey gives an indication of geocryological conditions of large areas in connection with natural macro- and meso-conditions. The medium-scale survey is conducted for the purpose of studying smaller regions while the large-scale surveys are conducted to study small sites and sections. The small-scale geocryological surveys, as well as all the other types of the small-scale geological survey, are the basis for carrying out the larger-scale investigations. Only on the background of knowledge of characteristics of the permafrost formation and development over large regions can any special manifestation of these characteristics on small sites and particular areas be understood correctly. Thus the detailed geocryological investigations on small areas without wide general study of the permafrost conditions will always be less elfective than a combination of surveys at dilferent scales. The great role of regional investigations including the small-scale (and in some cases the medium-scale) survey follows from this.

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