Definition of a snow avalanche: varieties, safety. Avalanche danger in the territories of the Southern and North Caucasus federal districts. Why are avalanches dangerous?

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Luckily our tent had been set up hours earlier by our stronger carrier, Pemba. We rushed into this little tent that looked like it was going to slip through a crack, and we stood there in the icy night, the thermometer dropped below -27 degrees Celsius, and strong gusts of wind made so much noise as they crashed into the tent that we couldn't sleep. We descended to base camp still at a bad time, but are ready to attempt the summit in the next attack to avoid the risks associated with the ice cover and the physical exhaustion of each ascent and descent.

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COURSE WORK

on the topic: “Snow avalanches are a threat to the sustainable development of mountain areas”

Introduction

1. General concept of avalanches

1.1 Example of avalanche disasters

2. The nature of avalanches

3. Cause of avalanches

4. Avalanche classification

4.1 Genetic classification

4.2 Morphological types

4.3.1 Level slopes

4.3.2 Narrow cuts

4.4.1 Avalanche sources

4.4.2 Avalanche pools

5. Avalanches and snow cover

6. Avalanches and terrain

7. Avalanches and vegetation cover

8. Avalanche protection

8.1 Avalanche control measures

Conclusion

Bibliography

Applications

Introduction

Every year the development of mountain areas increases - roads, mines, hydroelectric power stations are built, cities, recreation and sports centers are erected. The development of mountains is associated with numerous natural processes occurring here. These are earthquakes, avalanches, mudflows, landslides, collapses, catastrophic movements of glaciers. Such phenomena are accompanied by rapid displacements of huge masses of snow, rocks, mud-stone mixtures and powerful floods. The study of these catastrophic phenomena, the development of methods for their prediction and the justification of measures to protect against them are becoming relevant and practically significant.

Natural disasters in the mountains arise from exogenous processes. The most widespread natural phenomena, widespread throughout the mountains, include avalanches and mudflows. Familiarity with their main features, distribution and conditions of development shows the complexity of the problem of studying the nature of these phenomena and, in particular, developing forecasts. Many components of the natural environment are involved in the formation of avalanches and mudflows, each of which is in continuous change. The combination of various natural conditions leading to the formation of avalanches and mudflows turns out to be new each time, different from the previous ones.

Within an avalanche or mudflow region, only the main types can be distinguished, for example, meteorological situations that cause avalanches and mudflows. To predict individual avalanches or mudflows, special observations are required in a given avalanche collection area or basin. This is too labor-intensive and, most importantly, does not completely solve the security problem. The main direction in the fight against natural destructive processes during the development of mountainous territories is the organization of reliable protection against them. The most acceptable methods of protection against avalanches and mudflows these days are related to their localization. But a fundamental solution to the problem of protecting and combating avalanches lies in a set of measures that influence the course of avalanche and mudflow formation processes. These measures include the complete construction of avalanche catchment areas with snow retention structures, terracing and planting of plantations in the area of ​​the mudflow basin, and the construction of dams in mudflow channels.

Natural phenomena are closely interconnected. For example, in small catchment areas avalanches form in winter and mudflows in summer; avalanche snowfields, creating dams in the riverbed, cause the emergence of mudflows when these dams break through; landslides and landslides prepare material for mudflows, etc. That is why the need for an integrated approach when developing systems of measures to protect against avalanches and mudflows becomes obvious. These activities should be aimed at such basic natural components as runoff, geological processes, and vegetation cover.

A special role in this regard belongs to the preservation and restoration of vegetation cover, especially forests. Deforestation on mountain slopes leads to soil erosion, avalanches and mudflows. Forest restoration is not only protection from these processes, but also the involvement of lands in economic turnover.

Based on all of the above, I can speak with confidence about the prospects of my work and its significance not only for geographers, but also for the common population.

Among the natural destructive phenomena inherent in mountains, snow avalanches occupy a special place. In terms of breadth of distribution and frequency of occurrence, they are significantly superior to rockfalls, landslides, landslides and mudflows.

General concept of avalanches

Avalanches are one of the most widespread and dangerous natural phenomena in mountainous countries. Many avalanches in the Alps, which occur systematically in the same places, received their own names. Mentions of avalanches are found in the writings of ancient writers who lived more than 2000 years ago. The ancient Greek historian Polybius (201 -120 BC) writes about losses from avalanches when Hannibal's troops crossed the Alps (218 BC). The ancient Roman geographer Strabo (63 BC - 20 AD) wrote about the avalanche danger that awaits a traveler in the Alps and the Caucasus.

An avalanche is a snowfall that occurs on steep mountain slopes. The masses of snow that have come into motion slide along the surface of the slope or fall down, passing part of the way in free fall. Avalanches are accompanied, depending on the state of the snow, by deafening noise and grinding sounds. Unlike rock falls, snow falls usually increase significantly during movement due to the capture of new layers of snow lying lower down the slope. The speed of avalanches can reach 80-100 m/s, the volume of deposited snow masses of one avalanche is 2-6 million m3, and the thickness of snowfields is up to 20-50 m.

1.1 Example of avalanche disasters

Avalanche disasters occur as a result of meteorological situations, as well as during avalanches, when rarely operating avalanche apparatuses “come to life.”

In January 1951, the entire Alpine mountain range, about 700 km long and up to 150 km wide, was in the zone of avalanche disasters. Snowfall, accompanied by blizzards, continued in many areas for seven days and ended with a sharp warming. The amount of snow that fell in some places exceeded the annual precipitation norm by 2-3 times and reached 2-3 m. The slopes were overloaded with snow, and massive avalanches began. The entire transport network of the Alps was disrupted - highways and railways were in some places destroyed or littered and temporarily closed. Avalanches occurred in places where many generations of residents had not known them. Hotel buildings and protected forests were destroyed.

Sometimes the destruction of buildings or the destruction of forests is caused by an air wave formed in front of the front of a moving dust avalanche. This is how an observer conveys the picture of the impact of an air wave. “The large barracks, long before the snow core of the avalanche reached it, fell apart like a cardboard house. Beams and boards flew in an arc through the air and fell on the opposite slope, but the snow of the avalanche itself stopped before reaching the bottom of the valley.”

Nature of avalanches

The snow cover lying on the mountain slopes is in a state of unstable equilibrium. The adhesion forces inside the snow mass and at the boundary with the earth's surface counteract the force of gravity, which tends to throw the snow to the foot of the slope. The properties of the snow layer itself are constantly changing both due to changes in meteorological conditions and under the influence of processes occurring inside the snow layer. New snowfalls and blizzards increase the weight of snow masses, sharp changes in air temperature change the stress level of layers of solid snow, thaws give rise to intense melting, rain weakens the bonds between ice particles in the snow. Snow settlement and compaction increase the stability of the snow cover on the slope, while the migration of water vapor leads to the formation of loosening horizons.

In recent years, avalanche researchers have zoned areas by type of activity. This is important for understanding the nature of avalanches, as well as for organizing protection against them. In the scheme for zoning the territory of Russia according to the predominant types of avalanche formation, five groups of regions are identified:

1) Arctic regions with blizzard and inflation avalanches;

2) northern regions with avalanches from blizzard and freshly fallen snow;

3) inland continental regions with avalanches of sublimation diaphthoresis;

4) areas of the southern mountain belt with avalanches from freshly fallen snow, snow boards and advective avalanches;

5) Pacific and coastal areas with avalanches from wet, blowing and complexly stratified snow.

Groups of areas are divided into separate areas, which reflect the specifics of avalanche occurrence in a given mountainous country.

Causes of avalanches

The moment the avalanche occurs, i.e. the removal of snow masses from a slope means that gravity overcomes the adhesion forces inside or at the lower boundary of the snow cover.

Researchers identify four main causes of avalanches.

The first is the overload of the slope with snow during prolonged snowfalls and blizzards (when there is a rapid increase in snow mass). Mass avalanches are usually caused by this very reason.

The second is a decrease in the strength of snow during recrystallization. Snow, as a porous medium, is a good heat insulator. In temperate climates, the temperature in the ground layer of snow cover usually stays around 0°, while on the surface it fluctuates greatly. At significant negative temperatures on the surface of the snow cover, a temperature gradient arises inside the snow column and the migration of water vapor from the lower (warm) horizons to the upper (cold) horizons begins. The removal of part of the substance from the lower horizons leads to their loosening and the formation of a layer of deep frost, the adhesion forces in which are insignificant. Avalanches that occur mainly for this reason are relatively rare, but large in volume and destructiveness. They are sometimes called delayed-action avalanches, since the moment of their release is not related to weather conditions, as happens with avalanches that form when slopes are overloaded during snowfalls and blizzards.

The third is the temperature reduction of the snow layer. It occurs as a result of sharp fluctuations in air temperature. Snow is plastic at a temperature of about 0° and becomes brittle as the temperature decreases. If the snow cover lying on a slope is compacted, it may be in a stressed state, i.e. have compression and tension zones (it should be noted that the formation reacts to changes in external conditions as a whole). In this case, due to sudden cooling, cracks appear in the snow. A rupture in a snow layer can cause an avalanche if the shear pressure exceeds the adhesion forces.

The fourth is the weakening of bonds during snow melting. With the appearance of water under the surface of the snow, the bonds between firn crystals or grains and between layers of snow are weakened or destroyed. Depending on the intensity of snow melting and the depth of wetting of the snow layer, different types of avalanches are formed. When radiation melts snow, covering a thin layer, small surface avalanches are formed on the southern slopes. During thaws (especially with warm wind or rain), wet avalanches of medium power form; in this case, the upper (wet) layer of snow slides over the lower one, which is not affected by water filtration processes. During prolonged thaws and rains, when the entire thickness of the snow is soaked, powerful ground avalanches occur, moving along the ground and capturing a mass of debris.

Avalanche classification

Studying the main causes of avalanches helps to approach the problem of dividing avalanches into main types, i.e. to their classification. There are several classifications of avalanches, which are based on different characteristics: type of snow (loose or dense), water content in the snow, nature of movement, sliding surface, morphology of the path. The division of avalanches into main types is given in table. 1.

However, the general classification of avalanches should reflect their most essential features and serve the practical purposes of organizing avalanche protection. These requirements are best met by two approaches to dividing avalanches into main types. The first is genetic - based on taking into account the causes of avalanches, which were discussed above; its value lies in the possibility of developing a forecast for the onset of avalanche danger. The second approach is based on taking into account the topography of the snow collection basin and the path of the avalanche. This principle of dividing avalanche devices allows one to calculate the volumes and ranges of avalanches, i.e., it is necessary when mapping avalanche-prone areas.

4.1 Genetic classification of avalanches

Genetic classification of avalanches, most fully developed by the Soviet researcher V.N. Akkuratov, includes the following classes and types of avalanches.

I. Class of dry (cold) avalanches. Such avalanches usually consist of dry snow; disappear mainly in winter; The escape routes are not strictly limited - they can descend along a flat slope and partially through the air. They have maximum speed and can form an air wave. The following types of avalanches belong to the dry class:

Avalanches of freshly fallen snow. Such avalanches occur due to overloading of slopes during prolonged snowfalls. For avalanches, 0.3-0.5 m of fresh snow is enough. In snowy areas of temperate climates, this type of avalanche is the main one.

Avalanches of blizzard snow. The reason for their occurrence is the high growth rate of the gravity component on the slope. This is the most typical type of avalanche for areas with a moderately cold climate and stormy wind conditions.

Avalanches associated with the recrystallization of snow and the formation of layers of deep frost (the adhesion forces in which are weakened). Usually rare but powerful avalanches.

Avalanches of temperature reduction of snow cover. These avalanches occur as a result of a sharp drop in air temperature. Also a rare type of avalanche.

II. Class of wet (warm) avalanches. Such avalanches are formed from wet or wet snow; they disappear mainly in the spring; the escape paths are usually constant; movement is carried out along the lower horizons of snow or on the ground; the movement speed is lower than that of dry avalanches; the impact is mainly due to the pressure of heavy (water-saturated) snow masses.

Avalanches resulting from radiation thaws. These are low-power avalanches of southern (sunny) slopes.

Avalanches associated with thaws and spring snowmelt usually consist of moist, less often wet snow. The sliding surface is usually the interface between snow layers, i.e. avalanches belong to the category of reservoir avalanches (Fig. 3 a, b, c).

Ground avalanches are formed in the spring from wet snow completely saturated with water, as a result of prolonged thaws and rains or during rapid snow melting during hair dryers. They always go along certain paths, therefore, as a rule, they have names. They transport significant amounts of debris. The inhabitants of the Alps call the roar of these avalanches “avalanche thunder.” The most destructive in the class of wet avalanches.

4.2 Morphological types of avalanches

The morphology of avalanche collection and the movement of avalanches is given great importance in the complex classification of avalanches developed by the Soviet glaciologist Professor G.K. Tushinsky. Taking into account morphology is necessary to study the movement of avalanches and analyze the regime of avalanche activity. Under natural conditions, the morphology of avalanche apparatuses is quite diverse; Its change is associated with differences in the volumes of removal and the avalanche regime. Small avalanches form in small erosion cuts on mountain slopes, or in tectonic cracks. Filling of cracks with snow occurs quickly due to snowstorm transport of snow by winds blowing along the valley. Avalanches of this morphological type are quite frequent - they occur several times a year.

Avalanches that form in large avalanche catchments, which are denudation craters or destroyed pits, occur less frequently. However, they are very large and reach catastrophic proportions. It is precisely for avalanches of this morphological type (from dry snow) that a destructive air wave is characteristic. Under similar relief conditions, the most powerful ground avalanches are formed. Taking into account the morphology of the avalanche apparatus allows us to get an idea of ​​the volume of avalanches and the regime of avalanche activity.

We can distinguish three most characteristic categories of relief forms on which significantly different morphological types of avalanches are formed.

4.3.1 Level slopes

On them, snow slides off in a wide front; The boundaries of an avalanche are not clearly defined and can vary greatly from year to year. These are wasps that resemble surface landslides in soils. The volumes and range of wasp removal are, as a rule, small, but they are dangerous due to the disorder of their manifestation and the absence of clearly identifiable traces of avalanches.

4.3.2 Narrow denudation-tectonic and erosional incisions, usually developing on low slopes

The main feature of these forms is the small area of ​​avalanche collection, which means limited volumes of avalanches. In narrow incisions, sometimes ending in small drainage funnels, typical medium-power flume avalanches are formed. They are characterized by constant descent paths and the formation of an alluvial cone, which is clearly expressed in the relief.

4.3.3 Wide denudation logs

Wide denudation ravines ending in the upper zone of the slope with extensive drainage craters, dilapidated or active ravines with modern glaciers. These forms usually occupy the entire slope - from the watershed ridge to the valley bottom. The path of an avalanche and its deposition zone change from year to year. Specific avalanches change their descent paths and areas of accumulation due to the fact that the location of the avalanche and the volume of snow masses captured along the way varies from year to year. Avalanches that form under these terrain conditions are the most powerful and destructive.

These are the main genetic and morphological types of avalanches. However, in nature, a clear division of avalanches according to their genesis and morphology often turns out to be difficult. This is explained by the continuity of processes occurring in the snow layer and in the atmosphere, the altitudinal zonation of climate and landscapes in the mountains, and the gradual nature of the transition from one relief form to another. So, for example, an avalanche, which began as a dry avalanche from dense snow near a glacier, involves into movement masses of wet snow lying in an erosional ravine within the Alpine zone. A slight overload of the slope during snowfall or blizzards can cause a powerful avalanche if a horizon of deep frost has formed in the thickness of the snow by this time. Smooth, flat slopes in the mountains are rare; more often they have ledges, ridges, and hollows. In such hollows, small but dangerous avalanches form for winter tourists; they occupy an intermediate position between flat slope avalanches (osovs) and denudation incision avalanches (trough avalanches). Thus, there are many types of avalanches that are complex in genesis or transitional in morphology.

4.4 Relief as a factor in avalanche formation

Relief is one of the main components that determine avalanche danger. The presence and degree of avalanche danger when there is sufficient snow is largely determined by the characteristics of the terrain. The absolute and relative height, steepness and orientation of the slopes, the shape of the transverse profile of the valleys, the width of the bottoms and watersheds affect the shape, size and spatial distribution of avalanche foci, frequency, types, impact force and range of avalanches, i.e. on almost all aspects of avalanche activity.

Avalanche activity is influenced by the absolute height, steepness and orientation of the slopes, the depth and density of the relief, the shapes and sizes of relief elements, and surface roughness. The parameters of the avalanche source determine the destructive power of individual avalanches. The avalanche danger of a mountain area is determined by the morphological and morphometric spectra of avalanche foci and the nature of their location in space. When assessing avalanche danger, it is necessary to distinguish and differentiate between avalanche foci, avalanche basins and avalanche-prone areas.

4.4.1 Avalanche sources

An avalanche source is the smallest structural subdivision of an avalanche-prone area that must be considered as a whole.

Avalanche foci are the “atoms” that make up the whole variety of specific avalanche situations. The first definition of the concept of an avalanche source was made by S.M. Myagkov: “An avalanche source is a section of a slope and its foot within which avalanches arise, move and stop.” The literature used suggests the following formulation: “Avalanche source is a section of the earth’s surface within which an avalanche moves.” In the class of flume avalanche sources, chutes, funnels, valleys and cirques are distinguished based on the shape of the initiation zone. Nucleation zones of various types can be approximated by the simplest geometric figures: a trench can be described as a part of a cylinder cut off by a plane parallel to its axis; The funnel is part of a cone, the valley is a prism, and the square is a sphere. These types differ in the pattern of contour lines on topographic maps (Fig. 1).

Fig.1. Schemes of avalanche sources of flume avalanches of different types: b - funnel, c - valley, d - kar

4.4.2 Avalanche pools

Avalanche centers within an avalanche-prone area can be located separately or combined into avalanche basins. An avalanche basin is a collection of avalanche sources that have a common transit or accumulation zone. The difference between an avalanche basin and a complex avalanche source is that in it avalanches do not form a single avalanche flow, but only a single avalanche flow
snowfield in the stopping area.

An avalanche basin consists of avalanche centers connected to each other by overlapping transit or stopping zones. Depending on the complexity of the basin, there are areas in it that simultaneously belong to two or more avalanche centers.

4.4.3 Avalanche-prone areas

Territories within which avalanche centers occur are called avalanche dangerous. Territories located in the same high-altitude landscape belt, with the same type of distribution of avalanche-prone areas and the same depth of relief dissection, are characterized by stable values ​​of avalanche danger indicators. According to the nature of the spatial distribution of avalanche-prone areas, the following territories are distinguished:

with leveled terrain, avalanche-safe;

with a predominant distribution of leveled relief and a local distribution of small avalanche sources that cannot be reflected on the map scale;

with a predominant distribution of steep avalanche-prone areas.

5. Avalanches and snow cover

Avalanches as a natural phenomenon are determined by the corresponding geographical situation. But, existing as a phenomenon, they themselves have a certain influence on this situation, in particular, acting as a factor in the development of the nature of the mountains. Let us dwell on the relationships between avalanches and snow cover, snowfields, and glaciers. Avalanches, like snowfields and glaciers, are one of the derivatives of snow cover.

Indeed, for an avalanche to form, first of all, stable snow cover is necessary. The more stable the snow cover, the longer the period of potential avalanche danger.

The second important indicator of snow cover is its depth; when it reaches 30 cm; the formation of an avalanche becomes possible.

The greater the depth of the snow cover and the faster it changes, the more favorable the conditions for the formation of avalanches. Avalanches can be thought of as a form of solid water runoff. Just as heavy rains cause river floods, heavy snowfalls lead to massive avalanches over large areas or to the formation of avalanches of catastrophic proportions.

Originating in places where snow accumulates in the upper belt of mountains, avalanches create similar accumulations in the lower zone at the foot of the slopes and at the bottom of gorges; such accumulations are called avalanche snowfields. Avalanche snowfields lying in erosional depressions, at the ends of avalanche vents, or at the bottom of gorges are a direct indicator of avalanche danger. The structure of the snow in avalanche snowfields (breccia-like or conglomerate-like) makes it possible to determine the type of snow from which the avalanche was formed.

Avalanches play a significant role in feeding glaciers. The share of avalanche feeding in valley glaciers averages 10% (up to 20%) of the total precipitation. On small glaciers (groups of embryonic and cirque glaciers) it increases to 40%, in some cases exceeding the amount of precipitation. Small glaciers are known that lie well below the snow line and are formed by the merger of several avalanche cones; the existence of such glaciers directly depends on avalanche activity. There is also a special type of large valley glaciers, the so-called Turkestan type, which do not have the usual feeding for glaciers in the firn region - it is provided mainly by avalanches.

6. Avalanches and terrain

Avalanches can occur on short and not very steep slopes, starting from a slope of 15°, with a slope length of 50-100 m. However, most avalanches are formed on slopes with a steepness of 25-60°; On steeper slopes the snow hardly lingers. The depth of the relief or the relative height of the mountains affects the length of the avalanche path and its power. In the case of great ruggedness, characteristic of eroded mountains, the area of ​​avalanche collections, and therefore the volumes of avalanche removal, are limited. Under conditions of glacial relief, the volume of avalanches increases significantly.

6.1 Landforms on slopes and valley floors

Systematically falling avalanches form specific forms of relief on the slopes and bottoms of valleys.

In the alluvial deposits of the valley floor, at the foot of the slopes, knockout pits sometimes form, which are usually filled with water. The rocks captured by the avalanche are deposited in the neighboring area, forming avalanche mounds up to 2-3 m high.

Wet avalanches leave parallel ridges of debris on slopes. The most characteristic element of avalanche relief is the alluvial cone, the surface of which is usually composed of rock fragments with the remains of woody vegetation and turf. Rock fragments, as a rule, are unrolled, angular, and some have completely fresh chips. Another feature of avalanche deposits is the unstable position of the debris. It occurs as a result of their melting from the snowfield.

All these features of avalanche relief when assessing the territory serve as a sign of avalanche danger.

Avalanches are one of the complex processes of mountain destruction. They capture the fragmentary material of the avalanche collection, prepared by weathering processes, tear off the soil and vegetation cover in the drainage channels and cover it all on the bottom of the valleys.

The size and composition of the demolished material varies depending on the altitude position of the avalanche device. In the upper belt of high mountains - the zone of eternal snow and ice - avalanches are practically “clean”. Below, in the glacial zone, where the relief and cover deposits are most actively transformed, avalanches capture and carry out the largest amount of rock fragments. In the belt of alpine meadows and forest belt, the relief is more stable; avalanches are “enriched” here mainly with plant remains, pieces of turf, and soil.

Dry and wet avalanches differ significantly in their destructive effects. Dry avalanches, which mostly fall on the surface of old snow, are much cleaner than wet ones. In the wet class, ground avalanches are especially abundantly saturated with fragmentary material, which are often colored dirty yellow and gray by the soil and torn soil. Differences in the degree of contamination of different types of avalanches are clearly visible from the analysis of samples taken from the Terskey-Alatau ridge; the weight of the material as a percentage of the weight of the avalanche was 0.01 for dry avalanches, 0.05 for wet avalanches and 0.61 for wet avalanches.

7. Avalanches and vegetation cover

Dense forest provides natural protection against avalanches. It prevents the redistribution of snow by the wind and divides the snow cover into separate areas.

Although the forest resists only local avalanches and cannot protect against large transit avalanches that originate near glaciers, mountain residents have long realized its role. In Switzerland, a law prohibiting logging on mountain slopes has existed since the 14th century. Destruction of forests on mountain slopes always stimulates avalanche activity.

The impact of avalanches on forest vegetation is manifested, first of all, in the formation of so-called combs - strips of deciduous forest among coniferous or mixed forests. Coniferous species do not produce regrowth after damage to the main trunk and are not capable of restoration in areas systematically exposed to avalanches. These areas are usually overgrown with deciduous trees - birch, aspen, alder, poplar. Avalanche sweeps tear the forest belt into separate tracts and make the line of the upper forest boundary uneven.

The outer boundary of the impact of an avalanche or its air wave is marked by characteristic forms of oppression of woody vegetation: tree trunks are inclined or bent, the crown is developed primarily in the direction of the avalanche movement, the bark and tissue of the tree on the side of the avalanche movement are stripped. The combs and alluvial cones of systematically descending avalanches are overgrown with sparse young deciduous forest or shrubs and lush herbs; Moreover, the trunks of the bushes are often stripped, and the crown is developed one-sidedly. The typical shape of the trunks is saber-shaped.

Traces of the impact of avalanches on forest vegetation serve as a good sign for delineating areas exposed to systematic avalanches (very rare catastrophic avalanches destroy even mature protected forests). The age of undeformed deciduous trees makes it possible to determine the years of the last large avalanches.

8. Avalanche protection

The problem of protection against avalanches is especially acute, since they cause enormous damage to the economy of areas subject to the destructive effects of avalanches; people die under them. Avalanches are extremely widespread.

Avalanches pose a threat to human life, destroy or temporarily disable various structures, railways and highways, and destroy forests. The impact of avalanches is associated with the movement of large masses of snow at high speed. The speed of movement of wet avalanches reaches 10-20 m/s, dry - 80-100 m/s. In addition to the great impact force of a mass of snow falling from a slope, an avalanche sometimes forms an air wave in front of it. An air wave arises in front of the front of large dry (dust) avalanches, part of the path of which passes in free fall; it expands the danger zone to a distance of up to 1 km.

Protection against avalanches has been provided, apparently, since the founding of settlements in the mountains. At first, it boiled down to the use of natural protection (rock ledges, etc.) and the preservation of forests on mountain slopes; Later, buildings began to be placed with their end facing the slope, building this end into the slope and strengthening it.

Nowadays, many countries have accumulated significant experience in avalanche protection.

8.1 Complex of anti-avalanche measures

consists of two main categories - preventive and engineering.

Preventive measures come down to warning about avalanche danger and its elimination by artificial dumping. To prevent avalanche danger, maps of avalanche zones and avalanche time forecasts are compiled.

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Introduction

2. Causes of avalanches

3. Main types of snow avalanches

4. Classification of snow avalanches

5. Geographical distribution of avalanche indicators

5.1 Avalanche danger areas Sakhalin region

5.2 Avalanche danger in the territories of the South and North Caucasus federal districts

5.3 Avalanche danger in the Ural District

5.4 Avalanche danger in mountain areas Western Europe

Conclusion

Bibliography

INconducting

One of the most picturesque and attractive landscapes on Earth are mountains. They beckon with their grandeur and desire for the sky, but their pristine, harsh beauty does not tolerate falsehood. Therefore, when going into the skies, be prepared for difficulties in all respects, including encountering avalanche danger. First of all, this applies to extreme sports enthusiasts.

Very old mountains have long since turned into small hills on the plains. Conversion process earth's surface billions of years does not stop for a minute. Therefore, in the mountains you must always be extremely careful, regardless of the weather, the complexity of the route, etc.

Rock and soil collapses, landslides, and also avalanches are the main integral part of the processes that change mountainous terrain. Among the participants in these transformations, a special place is occupied by various gatherings of snow, snow-ice and unstable ice accumulations, which, under certain conditions, also move stones and soil to the foot of the mountains. It should be noted that snow avalanches recur much more often than others, due to the fact that snow is a very active participant in the process of the water cycle in nature. Repeatedly falling winter snow accumulates on mountain slopes and constantly creates avalanche situations, which often end in avalanches.

The sad statistics of avalanche tragedies show that every year in the mountains around the world, dozens and even hundreds of athletes die due to dangerous encounters with snow and other avalanches. Therefore, avalanche safety is a very serious topic that every extreme sports enthusiast needs to thoroughly study.

1. LAvina

Avalanches- snow masses falling from mountain slopes under the influence of gravity. Snow accumulating on mountain slopes, under the influence of gravity and weakening of structural bonds within the snow column, slides or crumbles down the slope. Having started its movement, it quickly picks up speed, capturing more and more snow masses, stones and other objects along the way. The movement continues to flatter areas or the bottom of the valley, where it slows down and stops. Such avalanches very often threaten populated areas, sports and sanatorium-resort complexes, iron and highways, power lines, mining facilities and other utility structures.

Avalanches form within the avalanche source.

Avalanche source- this is the section of the slope and its foot within which the avalanche moves. Each source consists of 3 zones: origin (avalanche collection), transit (trough), and stopping of the avalanche (alluvial cone).

Avalanche-forming factors include: the height of old snow, the condition of the underlying surface, the increase in freshly fallen snow, snow density, snowfall intensity, subsidence of snow cover, snowstorm redistribution of snow cover, air and snow cover temperature.

2. Pcauses of avalanches

Avalanches form when there is sufficient snow accumulation and on treeless slopes with a steepness of 15 to 50°. At a slope of more than 50°, the snow simply falls off, and conditions for the formation of a snow mass do not arise. Optimal situations for avalanches occur on snow-covered slopes with a steepness of 30 to 40°. There, avalanches occur when the layer of freshly fallen snow reaches 30 cm, and old (stay) snow requires a cover of 70 cm thick. It is believed that a smooth grassy slope with a steepness of more than 20° is avalanche dangerous if the snow height on it exceeds 30 cm. With increasing slope steepness the likelihood of avalanches increases. Shrub vegetation is not an obstacle to the gathering. The best condition for the snow mass to begin to move and gain a certain speed is the length of the open slope from 100 to 500 m. Much depends on the intensity of the snowfall. If 0.5 m of snow falls in 2-3 days, then this usually does not cause concern, but if the same amount falls in 10-12 hours, then snowfall is quite possible. In most cases, the snowfall intensity of 2-3 cm/h is close to critical.

Wind also plays a significant role. So, in a strong wind, an increase of 10 - 15 cm is enough, and an avalanche can already occur. The average critical wind speed is approximately 7-8 m/s.

One of the most important factors influencing the formation of avalanches is temperature. In winter, when the weather is relatively warm, when the temperature is close to zero, the instability of the snow cover increases greatly, but quickly passes (either avalanches occur or the snow settles). As temperatures drop, periods of avalanche danger become longer. In spring, with warming, the likelihood of wet avalanches increases. The lethality varies. An avalanche of 10 m3 already poses a danger to humans and light equipment. Large ones are capable of destroying capital engineering structures and forming difficult or insurmountable blockages on transport routes.

Speed ​​is one of the main characteristics of a moving avalanche. In some cases it can reach 100 m/s. The ejection range is important for assessing the possibility of hitting objects located in avalanche zones. A distinction is made between the maximum emission range and the most probable, or long-term average.

The most probable ejection range is determined directly on the ground. It is assessed if it is necessary to place structures in the avalanche zone for a long period. It coincides with the boundary of the avalanche fan. The frequency of avalanches is an important temporal characteristic of avalanche activity. A distinction is made between average long-term and intra-annual recurrence rates. The first is defined as the frequency of avalanches on average over a long-term period. Intra-annual frequency is the frequency of avalanches during the winter and spring periods. In some areas, avalanches can occur 15-20 times a year.

The density of avalanche snow is one of the most important physical parameters, which determines the impact force of the snow mass, the labor costs for clearing it, or the ability to move on it. For dry snow avalanches it is 200 - 400 kg/m 3 for wet snow - 300 - 800 kg/m 3.

An important parameter, especially when organizing and conducting emergency rescue operations, is the height of the avalanche flow, most often reaching 10 - 15 m.

The potential period of avalanche formation is the time interval between the first and last avalanches. This characteristic must be taken into account when planning the mode of human activity in a dangerous area. avalanche snow destructive natural

It is also necessary to know the number and area of ​​avalanche foci, the start and end dates of the avalanche period. These parameters are different in each region. In Russia most often such natural disasters occur on the Kola Peninsula, the Urals, the North Caucasus, in the south of Western and Eastern Siberia, Far East. Avalanches on Sakhalin have their own characteristics. There they cover all altitude zones - from sea level to mountain peaks. Descending from a height of 100 - 800 m, they cause frequent interruptions in train traffic on the Yuzhno-Sakhalinsk Railway. In the vast majority of mountainous regions, avalanches occur annually, and sometimes several times a year. How are they classified?

3. ABOUTMain types of snow avalanches

Currently, this is the most advanced classification, which is widely used in the world and adopted by Khibiny avalanche workers for practical work. Based on the analysis and long-term observation of V.N. Akkuratov identified 9 main types of snow avalanches:

1. Avalanches of dry, freshly fallen snow - during a snowfall, a layer of freshly fallen snow is formed, consisting of snow crystals formed in the atmosphere, with a density of 50-200 kg/m 3, the stability of such snow on a slope depends on the rate of increase in its height and the strength of adhesion to the soil or at the contact of early deposited snow.

2. Blizzard snow avalanches - are formed by redistribution of snow cover as a result of blizzard snow transfer. Wind-blown snow is deposited in negative landforms and on leeward slopes. The rate of formation of a snowstorm layer on a slope depends on the direction and intensity of snow transport and the profile of the earth's surface.

3. Avalanches of sublimation diaphthoresis - are formed as a result of snow recrystallization, which determines the appearance of loosened layers and interlayers in the snow cover.

4. Avalanches of thermal contraction of snow - associated with stresses arising as a result of changes in the linear dimensions of the snow field under the influence of temperature changes.

5. Avalanches from freshly fallen wet snow - are formed as a result of an increase in snow cover due to snowfall at positive temperatures.

6. Insolation avalanches - are formed as a result of absorption of solar energy by snow cover. The volumes and speed of such avalanches are not great.

7. Advection avalanches - are formed in the spring as a result of the advection of warm and humid air masses that bring Kola Peninsula Atlantic cyclones. Melt and rainwater, seeping into the snow cover, are filtered down the slope and concentrated in the narrowing area, where hydrodynamic pressure is created sufficient to destroy the snow cover in the stream bed.

8. Advection-insolation avalanches - occur in May, when the melting of the snow cover is caused by an increase in air temperature due to a hairdryer from the free atmosphere in combination with the penetration of solar energy into the snow cover.

9. Hydropressure avalanches - arise as a result of the pressure of subsnow flows of water.

4. TOclassification of snow avalanches

Based on the nature of the movement and depending on the structure of the avalanche source, the following three types are distinguished:

Tray,

Jumping.

The flume moves along a specific drainage channel or avalanche flume.

Osovaya is a snow landslide, does not have a specific drainage channel and slides across the entire width of the area.

Jumping occurs from flumes where there are steep walls or areas of sharply increasing steepness in the drainage channel. Having encountered a steep ledge, the avalanche lifts off the ground and continues to move through the air in the form of a huge jet. Their speed is especially high.

Depending on the properties of the snow, avalanches can be:

Wet

Wet.

Dry avalanches, as a rule, occur due to the low adhesion force between the recently fallen (or transported) mass of snow and the underlying ice crust. The speed of dry avalanches is usually 20-70 m/s (up to 125 m/s, which is 450 km/h; some sources limit the speed of such avalanches to 200 km/h with a snow density of 0.02 to 0.3 g/ cm. At such speeds, an avalanche from dry snow can be accompanied by the formation of a snow-air wave, producing significant destruction. The pressure of the shock wave can reach values ​​of 800 kg/m². The most likely conditions for the occurrence of this type of avalanche are when the temperature is low.

Wet avalanches occur in the spring as a result of an increase in the weight of the snow mass during warm winds (fen) in high mountain zone, during drizzling rains in the upper reaches of snowy valleys, as well as during snowfall at zero ambient temperature. Wet avalanches are common mainly in the high mountain zone.

Wet avalanches usually occur against a background of unstable weather conditions, the immediate cause of their disappearance is the appearance of a water layer between layers of snow of different densities. Wet avalanches move much slower than dry ones, at a speed of 10--20 m/s (up to 40 m/s), but have a higher density of 0.3--0.4 g/cm³, sometimes up to 0.8 g/cm³] . A higher density causes the snow mass to quickly “set” after stopping, which complicates rescue operations.

Based on the nature of the sliding surface, the following types are distinguished:

Layered, when movement is carried out on the surface of the underlying layer of snow;

Ground - movement occurs directly on the surface of the ground.

According to the degree of impact on economic activity and the natural environment, avalanches are divided into:

Natural (especially dangerous), when their collapse causes significant material damage to populated areas, sports and sanatorium-resort complexes, railways and highways, power lines, pipelines, industrial and residential buildings,

Dangerous phenomena - avalanches, which impede the activities of enterprises and organizations, sports facilities, and also threaten the population and tourist groups.

According to the degree of repeatability, they are divided into two classes

Systematic

Sporadic.

Systematic ones go every year or once every 2-3 years. Sporadic - 1-2 times per 100 years. It is quite difficult to determine their location in advance. There are many known cases where, for example, in the Caucasus, villages that had existed for 200 and 300 years suddenly found themselves buried under a thick layer of snow.

5. Ggeographical distribution of avalanche indicators

5.1 Avalanche danger in the Sakhalin region

From the point of view of a potential threat to the population and economy, Sakhalin and the Kuril Islands should be classified as the most avalanche-prone territories in Russia . If, for example, in the Caucasus, avalanche activity begins to manifest itself mainly at altitudes of more than 1000-1500 m above sea level, where human activity gradually decreases, then in the Sakhalin region avalanches cover the entire production and cultural zone from mountain peaks to sea level.

Over 41 years of regular snow avalanche observations, the service staff registered 27,190 avalanches, the total volume of these avalanches was 50.6 million m 3, and the maximum volume of one avalanche was 800 thousand cubic meters. According to archival data and survey information, the largest avalanche disaster in terms of the number of human casualties was noted on Sakhalin on February 9, 1945 at the Oktyabrsky mine in the Aleksandrovsky district. According to official data, about 250 people were trapped in the avalanche, of which 131 died. This avalanche is apparently the largest avalanche disaster in the former Soviet Union. On Kuril Islands in the regional center of Severo-Kurilsk on December 25, 1959, a giant avalanche destroyed several buildings of the Tanfuin base. More than 120 people were trapped in the snow, of which, according to official data, 36 people died. In total, during the period under review, the number of people caught in avalanches was more than 500 (of which 296 people died).

Currently, objects in 43 settlements in the region are in avalanche-hazardous zones. Specialists of the Snow Avalanche Service have prepared avalanche danger maps for the following settlements: Nevelsk, Kholmsk, Tomari, Sinegorsk, Bykov, Uglegorsk, Severo-Kurilsk. According to estimates, more than 7,000 people and 750 objects for various purposes are at risk of avalanche danger on Sakhalin and the Kuril Islands. Possible damage from avalanches could amount to about 150 million rubles. The region's railways and roads are threatened by about 1,000 avalanches; damage from avalanches can amount to 5.5 million rubles.

5.2 Avalanche danger in the territories of the Southern and North Caucasus federal districts

In federal districts, avalanche danger is typical for 6 regions located within the mountainous territories of the northern slope of the Greater Caucasus. On its southern slope, avalanches pose a danger in the Greater Sochi region in the Krasnodar Territory.

In the zone of dangerous influence of avalanches there may be settlements, transport communications, communication and power lines, oil and gas pipelines, tourist hotels, various camps, etc. More often than others, roads and railways suffer from avalanche activity, the destruction and debris of which lead to long interruptions in traffic.

For the period from 2005 to the present time in the territories of the constituent entities Russian Federation Southern and North Caucasian federal districts registered 8 emergency situations caused by avalanches, which killed 31 people, injured 80 people, and saved 49 people.

In total, over the past 5 years, 2220 avalanches occurred on the territory of the constituent entities of the Russian Federation and federal districts, of which 1732 were spontaneous, 488 avalanches were forced by avalanche control services.

Since the beginning of the current avalanche period, 273 avalanches have occurred, of which 218 were spontaneous, 55 avalanches were forced.

In the regions there are complexes of the ski tourism industry in the Karachay-Cherkess Republic (Dombay region), in the Republic North Ossetia- Alania (Tsey), in the Kabardino-Balkarian Republic (Elbrus region) and in Krasnodar region(Krasnaya Polyana) with a total number of tourists more than 50,000 people per season.

Avalanche-prone areas are also located in the republics of Dagestan and Adygea.

In total, on the territory of the Southern Federal District and North Caucasus Federal District there are 19 avalanche-prone areas - 200 avalanche-prone areas (449 sources), in 6 regions.

For reference: on the territory of the Southern Federal District there are 2 avalanche-prone areas, 5 avalanche-prone areas (6 hotspots) in 2 constituent entities.

Republic of Adygea - mountainous part of the Maykop region - 1 avalanche-hazardous area;

Krasnodar region - Adler region (Krasnaya Polyana area (Esto-Sadok village (3 hot spots), Adler - Krasnaya Polyana highway (3 hot spots)) - 4 avalanche-prone areas.

On the territory of the North Caucasian Federal District there are 17 avalanche-prone areas, 195 avalanche-prone areas (443 sources) in 4 regions.

Republic of Dagestan - 9 mountain regions of the republic - Tsuntinsky, Tsumadinsky, Tlyaratinsky, Rutulsky, Bezhtinsky, Akhtynsky, Dokuzparinsky, Gumbetovsky, Charodinsky section - a total of 55 avalanche-prone areas

Kabardino-Balkarian Republic - Elbrus, Cherek, Chegem and Zolsky districts - 132 avalanche-prone areas, 21 km from Azau to the Baksan netrin observatory. The most avalanche-prone region of the Kabardino-Balkarian Republic is the Elbrus region, which has 62 avalanche-prone areas, while 12 avalanche-prone areas are outside the firing zone due to the difficult terrain;

Karachay-Cherkess Republic - Karachay and Zelenchuk districts - 5 avalanche areas (21 sources);

Republic of North Ossetia - Alania - Alagirsky (Transkam and Tseysky complex of tourist centers) and Irafsky district - 3 avalanche areas (234 sources).

To actively influence and monitor snow avalanches in the Southern Federal District and North Caucasian Federal District, the North Caucasian paramilitary service for active influence on meteorological and other geophysical processes of Roshydromet has been created and is functioning.

5.3 Avalanche danger in the Ural District

During the period of aerovisual surveys on April 24-30, 1982, in the territory of the Urals from the river basin. Kara to the sources of Shchugor, 572 avalanches with a total volume of more than 33 thousand m 3 were recorded on the western and I46 avalanches with a volume of about 11 thousand m 3 on the eastern slopes of the main watershed. After April 19, avalanches were observed throughout the Urals radiation melting, caused by the establishment of clear sunny weather after a series of light snowfalls from April 15 to April 19. IN winter period avalanche activity was weak. No traces of sufficiently powerful avalanches were found on the alluvial cones. Small old avalanches were noted, the deposits of which were covered with a thin layer of snow.

5.4 Avalanche danger in the mountains of Western Europe

The leading factor in avalanche formation in most of the mountains of Western Europe is intense snowfall. The number of days with avalanche snowfall varies from 1 in the Cantabrian Mountains, Apennines and Greece to 30 in the Alps and even more in Scandinavia. Above the upper forest line in the Pyrenees, Alps, Carpathians, as well as in the ridge parts of the mountains of Iceland, Scandinavia and Spitsbergen, snowstorms become the leading factor in avalanche formation. In the low coastal belt of Scandinavia and Iceland and in areas below the stable snow belt in other mountains, snowmelt plays a significant role in avalanche formation.

The largest avalanche-prone areas outside Russia are the chain of the Hindu Kush, Karakoram and the Tibetan-Himalayan system, as well as the Tien Shan, Altai (in the Mongolian Altai), Bol. Khingan, Elbrus ridge and mountains of Japan.

Zconclusion

Almost all sectors of the national economy associated with the development natural resources mountains, to one degree or another, need information about snow cover and avalanche danger. This information is necessary for the design, construction and operation of engineering structures, recreational development of mountain areas, for accounting and regulation water resources, improving methods of hydrological forecasts, solving environmental problems.

Thus, the identification of spatio-temporal patterns of snow cover in the mountains and territorial and temporal changes in the activity of avalanche formation, as well as the development of methods for calculating the quantitative characteristics of snow cover and avalanche danger are a necessary condition for the successful solution of issues related to the development of mountainous areas, and in general represent a problem of national economic importance.

Bibliography

1. Akifeva K.V., Kravtsova V.I. Score Cards natural conditions avalanche formation as a source for determining the degree of avalanche danger. In the book: Assessment maps of nature, population and economy. M., 1973, p. 62 - 69.

2. Zalikhanov M.Ch. Snow-avalanche regime and prospects for development of the Greater Caucasus Mountains. Rostov-on-Don, 1981. 376 p.

3. Avalanche-prone areas of the Soviet Union. M., 1970. 199 p.

4. Troshkina E.S. Avalanche regime in the mountainous territories of the USSR. M.: Publishing house VINITI, 1992. -196 p.

5. Moskalev Yu.D. "The occurrence and movement of avalanches", Leningrad, Gidrometeoizdat, 1966.-152 p.

6. Perov V.F. "Naturally destructive processes in the mountains"

7. Nefedeva E.A. "The influence of snow cover on landscape connections"

8. Richter G.D. Dictionary of basic terms and concepts in snow science. - In the book: Materials of glaciological research, chronicle, discussions. Vol.

9. Dyunin A.K. In the kingdom of snow Publishing house "Nauka" Siberian branch

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