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Periglacial areas in the mountains are characterized by the highest denudation rates, which is due to active physical weathering, significant gradients and low projective vegetation coverage of the slopes of these areas. The accelerated expansion of periglacial areas that has taken place in recent decades is explained by climate changes that contribute to the melting of mountain glaciers. The improved methodology of studying the relief transformation processes, the rates of various exogenous processes, and the features of material redistribution along the pathways of sediment transportation from the slopes to the river valley bottoms contributed to a dramatic increase in quantitative assessment of spatio-temporal changes in the relief of the mountain periglacial zone. The article discusses various traditional and contemporary methods and approaches to studying the periglacial zone relief and its changes. They are divided into two groups: methods of stationary and semi-stationary observations of exogenous processes and methods for studying sediment redistribution in catchments. Various directions are highlighted within each group of methods, special attention is paid to the latest techniques. The results of observations of the rates of various exogenous processes occurring in the periglacial zone are generalized. It is shown that the intensity of rockfall-talus processes depends on lithology and frequency of daily air temperature fluctuation through zero °C and varies from 0.02 to 1.6 mm/year. Avalanche abrasion in avalanche trays reaches 40–70 mm/year. The rate depends on the area of the slope catchment, within which avalanches descend, and corresponds to the rate of denudation for the slope catchment equal to 0.01–0.05 mm/year. Maximum soil erosion rates are typical for young moraine slopes, where it reaches 100 mm/year in the first years after the glacier melts, and after 50 years slows down to 7–10 mm/year. The main flux of sediments is delivered from the slopes to the river bottoms by occasionally formed mudflows.

The characteristic features of the river network, the structure and functioning of the valleys affected by effusive and explosive volcanism, volcano-tectonic phenomena, gas hydrothermal activity and mud volcanism are revealed. It has been established that within flows and covers of effusives, the formation of new streams channels can occur not only due to backward erosion, but also as a result of the collapse of the roof of the near-surface lava tubes, which are actively used by underground runoff. A high erosion rate, a large volume of solid runoff, and a significant role of deflation in the transformation of the fluvial relief are characteristic for regions of domination of explosive activity. There valleys become zones of accumulation of volcanic material, which is gradually processed by mudflow, alluvial, aeolian and other processes. Volcanic-tectonic activity changes the rivers position, direction of streams and morphology of the valleys, leading to numerous reorganizations of the river network, as a result of which the valleys of modern watercourses often consist of uneven-age fragments. Valleys of hydrothermal zones are characterized by the active development of slope processes, which leads to the formation in them not only of sinter terraces, but also numerous landslide ones. Mud volcanic processes periodically lead to the filling and blocking of the valleys with mud breccia flows, which affects both the composition of the alluvium of watercourses and the morphology of the valleys.

The article presents the results of diatom analysis of bottom sediment cores of Lake Shchuchye located in the northern part of the Khibiny Mountains. Data of radiocarbon dating of lacustrine sediments and comparison with previously published sections of lake sediments in the Kola Peninsula suggest that the accumulation of sediments in Shchuchye Lake began during the final stages of deglaciation in the early Holocene and continued uninterruptedly until the present time. Changes in the composition of diatom associations in sediments reflect alterations in the hydrodynamic regime of the lake associated with the isolation from the Goltsovoye Lake, influence of Kunyok River runoff, evolution of vegetation and weathering processes in the catchment area. We used concentration, variety and composition of species and distinguished 8 separate zones of diatoms. Climate changes in the Holocene are reflected directly in the change of the percentage of indicator species, and indirectly through changes in pH, etc. The early Holocene rise of temperature began in this region later than in the sea coastal area. It may reflect the pecularities of deglaciation, namely — late melting of alpine glaciers. Along with the evolutionary environmental changes some catastrophic events are reflected in the sediments of the Shchuchye Lake. For example, in early stages, there the yield of big quantity of terrigenous deposits into the lake was revealed produced by mud flows and erosion from slopes covered by scarce vegetation at that time. Mudflow processes probably led to the formation of a clear interlayer of terrigenous material in the biogenic sediments in the upper part of the section.

В долинах рек вулканических регионов помимо экзогенных причин катализатором катастрофических процессов являются эндогенные факторы - в первую очередь, извержения, которые часто вызывают сходы вулканических селей - лахаров, обусловленных таянием покрывающих вулканы ледников, снега или выпадением ливневых осадков непосредственно после извержения. Эта последовательность катастрофических событий “извержение - сход вулканического селя” достаточно распространена и хорошо изучена, но при детальном рассмотрении очевидно, что образование грязекаменных потоков в долинах вулканически активных регионов обусловлено весьма разнообразными причинами и в этой цепочке может быть задействовано еще много факторов и агентов. Часто извержение провоцирует серию из 2-3 взаимосвязанных и последовательно развивающихся катастроф, т.е. формируется каскад катастрофических процессов. Опираясь на конкретные примеры, выделены и рассмотрены 15 цепочек катастрофических процессов в долинах вулканических регионов, обусловленных разноплановой вулканической деятельностью и сопутствующими событиями - сейсмическими толчками, изменением топографии местности, гидротермальной активностью, эрозией. Завершающими звеньями цепочек, как правило, являются сходы селей, причем иногда неоднократные. Их формирование обусловлено размывом водотоками поступившего в долины рыхлого материала или же прорывами плотин возникших подпрудных озер. Время реализации всех событий подобной цепочки может превышать несколько десятилетий и даже столетий.

In the flat western part of the region and near the Caucasus Mineralnye Vody Region, considerable activation of these processes occurs mainly at the expense of climatic conditions and engineering activity. The set of landslide activation factors and extent of their influence on landslide activity differ from year to year. In the last 10 years, the highest landslide activity occurred in 2005 and 2006, the lowest – in 2013. In the period 1992–2015, the largest amount of emergency situations related to landslides occurred in the Kochubeevsky and Andropov Districts (both were 23% of the total number), cities of Stavropol (19%) and Pyatigorsk (15%). Landslide events are most frequent in the spring – summer period (80% of the total number), especially May (30%).

The article contains an idea that extreme geomorphologic processes (hereinafter – EGP) associated with accumulation and transportation of debris – landslides, rockslides and mudflows – forms a cycle. Cycle scheme: after the huge mudflows descend in the mountainous landscape the debris begins to accumulate as a result of landslide-rockslide, fluvial processes and the avalanche overthrow. After reaching a critical mass, even under low effect of any factors (precipitation, temperature, seismicity, frost weathering and snow accumulation) the next mudflows descend is occur. For the first time all these factors are considered in the complex in present article. An integrated analysis of air temperature, precipitation, seismicity and frost weathering diagrams was carried out for the Balkar Cherek River basin. According to preliminary data EGP cycle comes to 4–6 years within research territory.

A detailed analysis of the relief structure and development of gravitational and fluvio-gravitational processes in a valley of the Mzymta river basin (Western Caucasus) was fulfilled using digital elevation models created on the basis of materials of laser scanning. We discovered and mapped a giant complex landslide with syndynamical block-and-ground flow. The genetic and age relationship of processes of various types and resulting landforms and sediments were determined. The landslide has a volume of about 32 million m3 , thickness up to 70 m; its body was displaced at a distance of 150–500 m to the WNW direction over the slip surface with inclination about 12–15°. The formation of the landslide we can presumably associate with the seismic impulse with an azimuth of 280–290°, which occurred about 830–950 A. D. Judging by the orientation of the landslide, the earthquake trigger can be a slip along the Main Caucasian fault. Simultaneously with the landslide the outburst of stone-ground mass down the valley of brook Pslushonok occurred (11–12 million m3 ). Mudflow material from the slopes of the left (southern) side of the valley constitutes a significant part of the volume of the terrace formed. The mudflow also filled the bottom of the Pslushonok valley and the part of the Psluh river valley below the mouth of the brook (the total length being 7.2–7.4 km) and created a dam across the Psluh valley, which was partly eroded after this event.

The distribution of the contemporary mudflows and ancient proluvium-mudflow deposits in the Far East was examined. Mudflows have restricted occurrence in the region with the exception of volcanic and formerly glaciated areas. While climate and relief are homogeneous, the conditions and character of geologic substratum play the main role in mudflows activation. In the volcanic areas of the Kuril-Kamchatka zone with high relief, abundance of unconsolidated sediments on poorly vegetated surfaces, and overmoistening the lahars and mudflows are widespread. The epochs of mudflows activation on the continent happened also during the Middle and Late Pleistocene, especially at the periods of strong climatic changes.

The specific type of gravitational-fluvial screes is revealed by means of multiannual stationary measurements and phototheodolite survey. The tail is situated under the high bench and is forming of the wash of the hollow, which drains the mountain slope. In the tail's deposits, the breakstone is predominant. When the tail reaches the floodplain of the river, low floods do not change solid runoff regime, but the high floods may generate the mudflow. Dynamics of the scree reveals strong correlation with the cycles of solar activity: the latter controls the accumulation of uncon-solidated sediments in the scree.

Morpholithogenic processes which formed relief of Ust'-Kanskaya and Yaboganskaya basins during late Neopleistocene are described. The existence of paleolake formed by the ice dam in the early Wurm near Ust'-Kan village was proved. Glacial dislocations accompany the moraine deposits. There are geologic evidence of mudflows and massive floods on the slope down the lake. During the middle and late Wurm eolian processes and paedogenesis were active. Tectonic movements took place in the second half of the Neopleistocene.

Catastrophic mud-flows on the Black sea coast may be caused by water twisters. The mudflow on the 9 th of August 2002 was one of the most disruptive from the beginning of land development in the region. The precipitation of the twister reached 42 mm/m 2 that gave the main impulse to the mud-flow formation. Its total solid and liquid runoff consist 268305 m 3 and 73222 m 3 respectively. The total water volume carried by twister was more than 600000 m 3 . The mud-flow parameters were obtained by special method based on the mud-flow velocity formula. Initial data were obtained during the field studies. Calculations were fulfilled for the alignment with known morphometric parameters near the river mouth.

There are two stages in the investigation of the mudflows on the Black Sea shores of the Krasnodar Territory the descriptive stage (1903-1963) and special purposed investigations (1963 - present days). The long showers and abundant precipitations originating from the tornado collapsed over the land are the sources of the fluid component of the mudflows. In the four regions of the seashore the sources of solid material of the mudflows are different. Within the Novorossiysk region the mining of the cement primary products - marl plays an important role. In the Gelengic region landslides and earth falls are the main sources of solid material. In the Tuapse region the erosion in the small erosional forms makes the main contribution to mudflows. In the Large Sochi region the mudflows appear in the result of different processes due to diversity of natural conditions and ever-increasing human impact. On the whole the mudflows intensity in the Black Sea shores is much less then in the other mountain regions of the Great Caucasus due to more forestation and less relief amplitudes.

The results of radiocarbon dating of catastrophic gravitational processes in Khibiny Mts (Kola peninsular) and Timansky Ridge are represented. Huge seismogenic collapse in the Khibiny Mts caused mudflow, which changed the configuration of the channel in the valley. It happened 3940-3630 B.C. In the Chut River valley (Timansky Ridge) two layers of turf overlaid by colluvium were dated about 1500 and 1600 A.D. These overlays supposed to be the tracers of seismic events in 1474 and in 1596. Absolute dating of catastrophic events requires correct geomorphologic analysis and calibration of dates.

Anthropogenic mudflow landscape in the Teberda river valley and avalanche-mudflow landscape of the Gonachkhira river valley are described. Mudflow activity at both sites depends mainly on summer cyclones, carrying warmth and precipitation. This influence is especially strong in Gonachkhira valley, where precipitation is heavier. Rapid and different changes are characteristic to landscape of this site. Large mudflow took place in 2004, several micro-mudflows in 2008, and avalanches in 2009-2010. These events each time changed young small forest composition and cover sediment layer. Mudflows in the Lower Teberda site occur on the surface dump of old coalpit. This highly erodible ground undergone heavy washout by melt, rain, and mine water. Rapid alternation of erosion and accumulation lead to high changeability of micro- and mesorelief.

The typology and spatial mapping of ecological-geomorphologic systems of the North-Eastern Caucasus are firstly presented. They are characterized by the unity of the geological-geomorphological and anthropogenic conditions and arising geo-ecological situations. A comparison the types of ecological-geomorphologic systems on the degree of anthropogenic load and indicators of intensity of ecological-economic conditions of the territories allowed to reveal differences geo-ecological situations in the most developed and industrialized regions of North-East Caucasus. Calculated indexes geo-ecological sustainability for each type of ecological-geomorphologic system are compared. The highest index in the highland and lowland types - the territories of forest and meadow lands. The lowest indexes of stability are obtained for the lowland type, almost devoid of greenery. The method of scoring in midland and mountainous types of ecological-geomorphologic systems it is demonstrated the prevalence exogeodynamic processes, which are related not only with natural, but anthropogenic factors, including avalanches, landslides, mudflows, seismicity and other. Not so much these processes are expressed in areas that are attributable to the low mountain and lowland. But as a result of considerable anthropogenic pressure (mainly on land resources) there are high levels of absolute and relative tension ecological-economic conditions of the territory.