научная статья по теме PECULIARITY OF GLACIATION IN THE HIGH MOUNTAINS OF SIBERIA Геофизика

Текст научной статьи на тему «PECULIARITY OF GLACIATION IN THE HIGH MOUNTAINS OF SIBERIA»

Материалы гляциологических исследований, вып. 102

Peculiarity of glaciation in the high mountains of Siberia

V. Sheinkman

Хакасский государственный университет, Абакан

Статья поступила в редакцию 10 декабря 2005 г. Представлена членом редколлегии А.Ф. Глазовским

Оледенение Сибири рассматривается как эволюция криогляциальных систем, и на этой основе характеризуются разные части горного пояса, охватывающего Сибирь с юга и востока.

Introduction

The high mountain belt surrounding Siberia on the south and east (here referred to as the 'Siberian Mountains') represents a wide range of environments (Fig. 1). It was the region, where at the end of the 19th century, Peter Kropotkin [18], a famous Russian researcher, first collected material for establishing his Glacial Theory. However, for a long time glaciological and palaeoglaciological phenomena from many mountain regions of Siberia were not studied in any detail. Reliable reconstructions of the Pleistocene glaciation were based on the only superficial geological survey, which had been completed in the 1960—1970-s and eliminated the last blank areas from the geological maps.

However, lack of knowledge did not allow the proper identification of the relics of former glaciations formed under continental climatic conditions dominated by low precipitation, which prevailed in the heart of the Eurasian continent. Until today the discussion revolves around the long-standing debate between adherents and opponents of A.I. Voeikov [6]: this famous 19th century Russian clima-tologist claimed that it was impossible for great glaciers to form in the heart of Siberia because of its dry climate. From the very beginning of the debate many famous scientists took sides, with such celebrities as J.D. Cherski

60' 90' 120' 150' 180'

Fig. 1. Location map. Distribution of the repeatedly ice wedges is shown as generalized after [4] with the added of the present author Рис. 1. Карта района исследований. Распространение повторно-жильных льдов показано по [4] с уточнениями автора

[38] and L.S. Berg [3], supporting Voeikov's point of view, whereas V.A. Obruchev [22], a renowned researcher of Siberia, did not agree. The debate continues, and the discussion in respect to the ancient glaciation in the inland regions of Central and North-east Asia is as topical now as ever; a large body of data shows this today, e.g. the recent sweeping generalizations [23, 24, 49, 54—56, 61].

The first palaeoglaciological reconstructions were largely influenced by the classical European model and did not always take into account the specific environmental conditions of the Siberian Mountains. One reason for this is that the study of Quaternary phenomena largely focused on North-western Siberia, where the environment resembles that of northern Europe [2, 29]. In addition, glacio-logical investigation of modern glaciers in Siberia began in the Western Altai, i.e. in the most humid Siberian region, with its relatively mild climate and accessibility for people. As a result, Alpine palaeoglaciological concepts from Europe were widely transferred to the mountainous regions of Siberia, and for a long time, the similarity of the European and Siberian palaeoglaciological schemes was thought to form a firm basis for subsequent investigations.

Because of their lesser accessibility the East and North-east Siberian Mountains were studied much later and less intensively than those of the West. New information only appeared in the 1970—80s with the next stage of development in Siberia. Then, together with detailed evaluation of geological material, numerous data were collected during geocryological mapping and a general survey of glaciers, icings and ground ice at the area of the former USSR [9, 15, 16, 27]. Eventually, towards the beginning of the 1990s this research included all the formerly neglected regions [17, 21, 30, 31, 39].

All these data demonstrated that the old palaeoglaciological schemes had to be corrected, as the new data obtained at the present-day glacial and cryogenic objects should be taken into the consideration. Evidently, the Quaternary events in the Siberian Mountains did not coincide with their European equivalents, and some of the landforms and sediments previously considered to be of glacial origin were found to have been formed by non-glacial processes. Overall, the development of glaciation in Western Eurasia (the Alpine scheme) was found to be differ fundamentally from that of the mountainous regions of Central and North-Eastern Siberia [14, 41-43, 58-60].

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An important point is that the glaciological and geocryological investigations throughout Siberia [9, 15, 16, 27] have demonstrated that high moisture availability, and in turn, high snow accumulation volumes, which are usually associated with the development of glaciers, are not required for the formation of cryogenic ice. On the contrary, a continental climate promotes the freezing of rocks and prevents the development of glaciers. Both processes have occurred in the Siberian Mountains, against a background where the atmospheric circulation throughout the entire Quaternary acted according to the same principle [33, 37, 60].

Unfortunately, the original lack of exchange between glacier and permafrost research resulted in some major disagreement [19, 20]. Some investigators, who promoted the view that cryogenic ice prevailed in Siberia during the Quaternary, underestimated the role of glaciers (e.g. [11, 12, 35]). Whereas others (e.g. [10, 49, 52]), did not considered thoroughly the permafrost and postulated giant ice sheets covering most of Siberia. After having studied both modern and ancient glaciation, as well as permafrost, along the entirely mountain belt surrounding Siberia for many years, the present author would not agree with such extreme points of view. Glaciation must be seen as a development of different glacial and cryogenic ice agents, which can shape the valley morphology either individually, or in combination [41, 42, 59]. In order to reconstruct and assess the events across the region during the Quaternary, the study of former glaciation must include the interaction of both the geocryologi-cal and glacial processes through time.

Methods

Standard methods of reconstructing the extent of former glaciation from landforms and deposits are not always applicable in the Siberian mountain areas. The reason is the interdependency of permafrost processes and formation of glaciers that intimately interacted in Siberia throughout the Quaternary. To unravel the situation the present author has successfully applied a system approach by studying the complete CGS.

Glaciers in the Siberian Mountains are important, but they are not the only members of the CGS. The latter can include different forms of ice that may be regarded as 'glacial phenomena' in a broad sense [8, 46]. Some non-glacier agents of the permafrost genesis can become very active. Icings, for example, are not so infrequently comparable with glaciers both in volume of ice and in the volume of geological work they can achieve, although the processes involved are different [1, 28, 39, 59]. The original glacial landforms and deposits can be significantly modified by these processes [40—42].

Thus the ice bodies consisting of the CGS should be considered as with respect to the water-equivalent mass, also with regard to the cold storage concentrated in those bodies. In order to use a system approach [45], the main units of the CGS and their modes of geological work have to be first defined. Environmental diversity in the Siberian Mountains ranges from rather humid to extremely conti-

nental, and from relatively warm to extremely cold conditions (the coldest point in the Northern Hemisphere is situated in North-eastern Siberia). Most types of the CGS may thus theoretically occur in the Siberian Mountains.

The principal characteristic of the CGS (see below) in this case becomes their cold storage capacity. Five main types of the CGS can be distinguished, based on differences in their temperature regime. The main indicators of glacial environments used herein are as follows: (i) the temperature regime of glaciers and the surrounding rocks, and (ii) the appearance or disappearance of icings and ground-ice phenomena in the non-glaciated areas.

Glaciers, icings and ground ice control the geological work of the CGS. These phenomena also clearly show, by their appearance or disappearance, the conditions of their development. Therefore each of them, and especially their peculiar combination, can serve as good indicators of glacial environments.

Background characteristics conditioning

the development of glaciation

The high mountainous belt surrounding Siberia in the south and east consists of numerous ranges characterized by many similar features. The ranges reach from the Altai through Transbaikalia to the Chukchi Peninsula (see Fig. 1). The highest mountains are found in the southwestern part of the belt, in the Altai, where many ranges exceed 3000 m above sea level, and a few peaks even above 4000 m (the highest point, Mount Belukha in the Katunskiy range, reaches 4506 m). In the Sayan Ranges many mountains reach 3000—3300 m, and the highest peaks of Transbaikalia are close to 3000 m. In North-east Siberia the highest point (Mount Pobeda, Cherskiy Range) reaches a height of 3147 m. On the Chukchi Peninsula the mountains are lower; they are close to the 2000 m level (lower boundary of 'high mountains'), though do not exceed it.

All in all, the Siberian Mountains are characterized by a certain morphological uniformity. Being situated in a relatively homogeneous climate and environment, most of them underwent a single complex of exogenous processes.

At present, most of the mountain belt is under the influence of the Siberian Anticyclone, and the main feature of this area is a continental environment with low temperatures. Due to the westerly winds, precipitation ca

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