An avalanche is a mass of snow that quickly slides down a mountainside. Snow falling in the mountains during all year round, does not remain motionless: it slowly, imperceptibly to the eye, slides down under the weight of its own weight or collapses in avalanches and ice avalanches. An avalanche can be caused by a variety of reasons: the movement of climbers, the fall of a collapsed cornice, various atmospheric phenomena.

All types of ice collapses are a very serious danger, which is directly dependent on the size of the collapse. The speed of the ice collapse is many times higher than the speed of the avalanche and approaches the speed of the fall of the stone. The climber is exposed to the greater danger, the closer he is both to the place where the collapse occurred and to the center of its further movement. Ice collapses can occur from the movement of the ice itself, from overloading the ice mass, from thawing and softening of ice, etc. During an icefall, due to softening of ice from heat and imbalance during the movement of the glacier, a seraks or a separate block of ice may fall.

Due to the overload of the eaves hanging on the crest, it can break off and fall down. On an icy slope, a piece of ice can break off from faults, and finally, sometimes, although extremely rarely, entire glaciers and icy mountain slopes collapse.

For example, in 1902, the entire northeastern slope of Mount Dzhimarai-Khokh (Kazbegi region) collapsed.

The ice rolled down 12 km. 36 people died, about 1800 head of cattle. The people's resort Karma-don was littered.

The occurrence of avalanches depends on the amount and condition of snow, on the base on which the snow lies, on various atmospheric conditions, on the impact external force on the snow cover (shock from a fallen cornice, rockfall, movement of a group of climbers).

The snow mass is kept on the slope by the adhesion force both between the snow layer and the base on which it lies, and the internal adhesion between individual snowflakes. When this connection is broken, avalanches occur. Avalanches can slide everywhere where the steepness of the slope exceeds 20-25°.

Snow is divided into four main types: powdered, fallen at low temperatures or blown downwind; wet, falling out high temperature or exposed to its action after falling out; packed snow; firn snow. Each type of snow can form an avalanche under the right conditions, but dry, powdery snow is the most dangerous. The speed of movement of avalanches depends on the base soil on which the snow lies, on the steepness of the slope, on the state and size of the snow mass set in motion.

Under equally favorable conditions for avalanches, a powdery, dusty avalanche will move at the highest speed. At the upper end and along its sides, the avalanche moves much more slowly than in the middle.

Avalanches have many varieties, but we will only point out the main ones. The most frequent are avalanches from freshly fallen snow. They are further divided into dry and wet. Due to the insignificant connection of individual snow particles with each other and with their base, the occurrence of dry avalanches is usually sudden, and they can be caused very easily, but especially on a smooth solid base (ice, firn, packed snow). Most often they are in winter.

Wet avalanches form from snow that has fallen at high temperatures, or from snow lying on slopes that are heavily lit by the sun. The subsequent drop in temperature turns the unstable wet snow into a harder snow mass, which reduces or even eliminates the risk of an avalanche.

On the windward side of the slope, powdery, dry snow is covered with a crust under the influence of wind and frost, which has no connection with the snow and only rests on it. Violation of the integrity of this crust causes slumping of the entire snow layer located above the place where the crust breaks, and then a layer avalanche is formed.

Sometimes this crust is quite strong, it can withstand the weight of the body, gives the beginner the impression of a reliable cover, and in this case one may not notice the threat of a formation avalanche. In addition, it is generally difficult to determine the place and moment of occurrence of such an avalanche.

All these types of avalanches are classified as surface avalanches. When snow, usually old, wet snow, slides with its entire mass, exposing the ground on which it lay, such an avalanche is called an unpaved avalanche. Usually this type of avalanches is observed in the spring.

You should not start the route immediately after a snowfall, it is better to wait until avalanches slide down or the snow thickens. In clear weather, it is necessary to wait two days, three in fog and cloudy weather - three to four days, in severe winter frost - up to six days. Snow couloirs, avalanche chutes and slopes covered with deep, powdery or wet snow lying on an icy base should be avoided as much as possible.

With unreliable snow on steep slopes, it is best to climb “head on”, without crossing such slopes and not moving along them in zigzags. It is necessary to cross the avalanche-prone slope as high as possible, keeping away from each other and stepping in the footsteps of the one ahead. If an avalanche has just appeared, you should try to strengthen yourself with an ice ax or run away to the near edge of the avalanche. If the climber is dragged down by the avalanche, he must stay upright. If the speed of movement and the condition of the snow allow you to get out, you need to run away or get out from the middle of the avalanche to its edges, where the speed and strength of the avalanche is less. You have to drop your handbag. If it was not possible to leave the avalanche, then the climber's task is to prevent himself from being sucked into the snow, freeing his arms and legs and doing the swimmer's movements. Keep facing forward.

In a dry, dusty avalanche, cover your mouth so as not to suffocate from snow dust that fills your mouth and airways.

It is not difficult to say how avalanches arise: on steep mountain slopes, individual layers of snow or the entire snow cover lose their adhesion to the ground or the underlying layer. Due to the enormous weight of the snow, stress is generated inside the snow mass, leading to cracks; it spreads over them and slides down.

Of course, in reality, the science of avalanches is much more complicated, because snow is not a dead mass, having fallen to the ground from clouds, it is constantly changing. At first, it forms, depending on temperature and wind strength, a relatively light and loose cover. An avalanche can sometimes be set in motion by minor disturbances in the structure of the snow cover.

Even a slight heating on a solar noon can increase the tension between the upper and lower layers of snow so much that it will lead to the excavation of the snow shelf. This cause of avalanches is considered the most common.

The four most dangerous types of avalanches are:

1. Dry avalanches consisting of loose snow are very dangerous. They break into the valley at high speed and are accompanied by a monstrous shock wave that crushes even massive concrete barriers. They form on the principle of a growing snowball.

2. Of particular danger are glacial avalanches, which occur, in particular, when the tongue of a glacier breaks off. With their incredible weight, they develop a very high speed. Forces operate in them that can grind even ice, hard as a stone, into powder. Such avalanches have caused many devastating disasters.

3. The term "ground", "soil" and "surface" avalanche designate layers of snow cover that come into motion; soil and soil avalanches slide down the slope and cause its powerful erosion; after the snow melts, the blown material settles at the bottom of the valley. In contrast, surface avalanches slide into the valley on deep, very stable layers of snow.

4. Snow shelves break off along one long line and slide into the valley along their entire width directly along the ground or along an unstable snow layer.

FACTORS PROVOTING AVALANCHES

It is not difficult to say how avalanches arise: on steep mountain slopes, individual layers of snow or the entire snow cover lose their adhesion to the ground or the underlying layer. Due to the monstrous weight of snow, stress is created inside the snow mass, leading to cracks; it spreads over them and slides down.

However, these days, avalanches are increasingly being triggered by reckless skiers and snowboarders. Thrill-seekers, despite the prohibitions, leave the safe track on unstable slopes, getting special pleasure from skiing on virgin snow untouched by skis, and this endangers not only own life but also the lives of other people.

FORMATION OF CRYSTALS

During the circadian rhythm with its temperature fluctuations individual snowflakes disintegrate and stick together into crystals.

The surface of the snow cover hardens, forming a crust. Under the weight of snow, the lower layers are compressed more and more. From the rays of the sun and warm air currents, snowflakes melt and stick together into an ice layer.

If fresh snow falls after this, the danger of avalanches increases sharply for several days, since the new layer initially does not adhere well to the snow crust (which is called firn). Only when it settles and bakes more strongly with the base, the snow cover again acquires greater stability.

The situation becomes especially dangerous in cases where a lot of snow falls or when the old layer of snow has not yet had time to harden. Therefore, avalanche surveillance services take drill samples in particular dangerous places- mainly on steep slopes, ridges and slopes, heavily indented by trenches and mounds - and carefully study individual layers. Thus, the uniformity and strength of the entire snow cover are determined. The weaker the individual layers are interconnected, the higher the risk of avalanches. The situation is assessed by three factors: the structure of the snow cover, weather conditions (by the amount of fresh snow, wind strength and direction) and the terrain (steepness, shape, underlying material, and which way the slope is facing).

Avalanche development

1. Loose snow slides over a layer of denser snow.

2. Having accelerated, a mass of snow can rise into the air.

3. The avalanche picks up speed, sometimes reaching up to 350 km/h.

Dry avalanche

Dry avalanches are composed of loose snow and rush especially rapidly.

They begin with small snow landslides, but due to ground shaking and the occurrence of a shock wave, they quickly increase.

STONES THROWING DOWN

Avalanches also include rock masses falling down, that is, rockfall, collapse, mudflow.

During a rockfall, individual stones or stone blocks fall out of a rocky wall; with a more powerful collapse, a large stone mass collapses or rolls down.

A mudflow is an avalanche consisting of a mixture of stones and liquid mud. Such liquid rock avalanches can be triggered by precipitation or rapid changes in the ice sheet, with often catastrophic consequences. So, in 1938, 200 people died in Los Angeles when a mudflow hit the city.

The first victims of the avalanche were the military.

The first victims of the avalanche, which are mentioned in history, were warriors. When Hannibal and his army marched north across the Alps in 218 BC, the White Death claimed about 18,000 men, 2,000 horses, and several elephants.

The largest snow disaster of modern times is also related to the military. In December 1916, in the First world war on the Austrian-Italian front, in just two days, about 10,000 soldiers found death under avalanches. After a week of continuous snowfall, both belligerents began to fire from artillery pieces slopes located above enemy positions. The shots caused a powerful avalanche, which buried entire sections of the front along with the troops.

During the First World War, avalanches in the Tyrolean Alps claimed 60,000 lives. Italian and Austrian troops fought for three years in the highlands, suffering from lack of supplies, cold and snow. One of the soldiers recalled: “Nature was our most terrible enemy ... Entire platoons were knocked down, blown into the abyss, filled up without a trace.” The heaviest was December 1916, when 4 m of snow fell in 48 hours, which led to avalanches that killed about 10,000 who fought on both sides of the front.

In Peru, the May 31, 1979 earthquake and the resulting avalanche killed 66,000 people. The force of the shocks reached 7.7 on the Richter scale, the epicenter was located near the large port and industrial city of Chimbote, and the consequences were the most disastrous in the 20th century. A massive layer of soil and ice broke from Mount Huascaran, which demolished the village of Ranrairca, destroyed 5,000 inhabitants and filled up the mountain resort of Yungay. Nearly all of its 20,000 inhabitants perished here.

DECEIVELY IDYLL

After many days of heavy snowfalls, the sun finally came out and warmed the western and southern slopes of the mountains. Fresh snow, not yet compacted, began to slide down faster and faster; soon many small and large avalanches were rushing into the valley. According to experts, on steep slopes, their speed reached 400 km / h, which gave enormous energy to the snow masses. Even massive defensive structures and large houses were demolished like toys.

A 300-meter avalanche with a roar broke off in 1999 from the top of Griskopf, bringing death with it.

In the Austrian Galtür on February 23, 1999, 31 people died in a few minutes, and thousands of guests and inhabitants of this skiing paradise were locked up for many days in the Paznau valley.

On the ruins of Galtür

Rescue and assistance to the victims at first had to be dealt with only local residents and their sports guests, as the valley was completely cut off from outside world: the road was covered with a ten-meter layer of snow. Mountain safety authorities have banned rescuers from making their way along the roads to the affected valley due to the high likelihood of new avalanches. Help to the disaster area arrived only the next day by helicopters of the Austrian Air Force.

Victims suffocate or get crushed

An avalanche can carry up to a million tons of snow from a slope and drive an air shock wave in front of it, which, like a bomb explosion, destroys everything in its path. Whoever meets her on the road will be crushed.

Most avalanche victims die very soon, as a snow wall rushing at a speed of 100 km / h and above creates a shock wave; it instantly clogs the lungs and airways of the victim with snow, and the person dies of suffocation. The survivors of this first onslaught are killed when they find themselves inside an avalanche that hurls them against rocks, trees, and other obstacles at great speed.

How deeper man is buried under an avalanche, the less likely it is to get him out of there alive. After all, if a cubic meter of freshly fallen snow weighs only 60-70 kg, then the packed snow mass of an avalanche presses on the body with a weight of more than a ton, does not allow breathing and simply flattens a person.

Many avalanche victims suffocate already under a meter layer of snow, as fresh air does not reach them.

Therefore, rescuers advise in case of an accident, if possible, press your palms to your face in order to create at least a small space for air, and then the victim, if he is lucky, can hold out until the rescuers arrive. And also, the use of a special one will help the victim hold out for some time until rescuers arrive under a layer of snow.

People covered by an avalanche are searched for by probes. This must be done quickly, because after 20 minutes half of the victims die. The chance of rescue is increased if rescuers and victims carry “ ” with them, which send and receive signals.

STUDYING AVALANCHES

On February 25, 1999, the Sion Valley in the Swiss Alps shook with a terrible roar. In a few seconds the ground shook and the valley was filled with deafening thunder. 600,000 tons of snow fell down the mountainside at a speed of 300 km/h.

In the middle of an avalanche-prone slope, a group of people is sitting in a massive bunker. All of them pinch their ears that hurt from the roar. The bunker is covered with a three-meter layer of hard, like concrete, snow. However, nothing happened to people - they are employees of a Swiss institute that studies snow and avalanches. They have just caused an explosion to cause a dry avalanche, the largest in the world. Thus, they are watching the most terrible danger that can only lie in wait in the mountains - for avalanches, which, despite the huge costs of protective and rescue measures, claim the lives of 150-200 people year after year in the mountains of Europe alone.

To prevent such catastrophes, Switzerland alone has spent over the past 50 years 1.5 billion francs on the construction of barriers against avalanches and another billion on the cultivation of forests that block the path of avalanches. And not without success: if in 1951 98 people died under snow masses, then at the end of the millennium “only” 17. And despite the fact that now mountainous areas more densely populated than before, and besides, many skiers come here.

This success is by no means accidental. For more than 70 years, the Alpine Republic has been systematically studying the dangers that snow brings with it. The Central Research Institute was founded near Davos on Mount Weisflujoch (altitude 2662 m). Scientists from various scientific fields are developing topics such as “Formation of snow cover”, “Snow mechanics and avalanche formation”.

The purpose of the research, among other things, is to more accurately and timely predict avalanches and to develop effective protective structures that reduce the damage that avalanches cause to nature and buildings. In its forecasts, the institute works closely with meteorologists, because the danger increases significantly when a lot of fresh snow falls on the old snow layers.

The avalanche watch service operating in the countries of the Alpine region is installing more and more automatic weather stations, but accurate forecast avalanches are still not possible. As before, skiers should remember to take reasonable care in the mountains and avoid dangerous places.

NO ABSOLUTE PROTECTION

Despite all the successes of scientists, avalanches, as before, can suddenly come off the slope. They are born from time to time even in the most seemingly safe places. Sometimes even expensive defensive structures are not able to keep them. Until now, far from all the factors that lead to the fact that snow masses come into motion, crush everything that comes in their way, and drag what they have captured down, have not been studied.

PHOTOS OF AVALANCHES IN DIFFERENT REGIONS OF THE WORLD or DEADLY BEAUTY:

Bezengi wall. Avalanche from Dzhangi-Tau. Photo-Baskakov Andrey

Avalanche between Western and Main Victory

An avalanche from the Bezengi wall that descended between the peaks of Dzhangi-Tau and Katyn. View from the hut Dzhangi-Kosh. Photo by Alexey Dremin

Bezengi, Dykh-Tau, 2009 (4x zoom) Photo: Tatyana Senchenko

Avalanche from Western Shkhara, Bezengi.Photo by Vladimir Chistikov

An avalanche from the Belukha massif flying to the Mensu glacier. January 2003. Photo by Pavel Filatov

Avalanche from the northern wall of the Mizhirgi massif - Dykh-Tau. Photo by Vladimir Kopylov

Avalanche from the northern slopes of Pobeda Peak. Photo by Vladimir Kopylov

An avalanche covering the right edge of the l. Small Tanymas. Photo by Georgy Salnikov

Avalanches from Pobeda Peak

Avalanches from the North Face of Dykh-Tau. Photo by Mikhail Golubev

Elbrus. Winter avalanche from the Northern Face of Donguz-Orun. Photo: Innokenty Maskileison

Antarctica

Krasnaya Polyana. Caucasus

An avalanche descended from one of the five-thousanders of the Caucasus Dzhangitau. Bezengi wall. Photo: Mikhail Baevsky

Avalanche on railway in 1935 Canada

A tiger in a lamb's skin called innocent, at first glance, white snow Matthias Zdarsky, an Austrian researcher who studied the question of what an avalanche is. Softly falling snow fascinates even those who dislike winter - too much Nice picture, similar to fairy tale. Yes, and the crystal stars smoothly flying to the ground create a deceptive impression of fragility, defenseless tenderness. However, excessively active snowfalls are fraught with danger, and serious. After all, not only snowdrifts, but also avalanches can grow from small snowflakes. So what is an avalanche? The definition of this concept is given below. And now a little history.

A brief excursion into history

In all likelihood, an avalanche is a phenomenon that has existed as long as the steep slopes of mountains, and Polybius also mentions the first large-scale snowfalls that caused the death of hundreds of people in the context of the history of the campaign of the Carthaginian army through the Alps. And in general, this mountain range, chosen by tourists and climbers, “behind” the longest chronicle of disasters. It is not for nothing that even in the 20th century, masses were celebrated in some areas in memory of those who died under snowy debris, because in this case an avalanche is pain and grief for the relatives and friends of those who suffered from its descent. It is also noteworthy that in one of the last winters of the First World War, more soldiers on the Austro-Italian front died from this than directly during hostilities. And December 16, 1916 went down in history as "Black Thursday", when six thousand people were missing in one day. Hemingway, who was in the Alps at the same time and described his definition of what an avalanche means, noted that winter avalanches are terrible, sudden and bring instant death.

Suffered from the "white death" and the inhabitants of Norway, Iceland, Bulgaria, the United States, Russian Federation, Canada, as well as Asian countries: Turkey, Nepal, Iran, Afghanistan, and in the latter by and large not conducted. Tens of thousands of lives and on the account snow avalanches that fell off Mount Huascaran in Peru.

What is an avalanche? Etymology of the word

The ancient Romans called this phenomenon "a pile of snow." Each nation had its own definition. What does avalanche mean? This is a beautiful, exciting and dangerous natural phenomenon. The very meaning of the word “avalanche” is also interesting, in the origins of which is the Latin root lab, meaning “instability”, although it got into the Russian language through German, since the definition of Lavine existed in Old German. Xuan Zang poetically called them "white dragons", and in the time of Pushkin, avalanches were called avalanches. In the Alps and the Caucasus, the names of individual mountains, gorges and valleys are already "speaking". For example, the Lan forest or Zeygalan Hoch (“mountain from which avalanches always come down”). Sometimes the ability to read onomastics, although it does not tell everything about snow blockages, can save you from unforeseen circumstances.

What is an avalanche

An avalanche is a type of landslide, a significant mass of snow that moves or even falls from the slopes of mountains under the influence of gravity. It simultaneously creates an air wave, which accounts for a significant part of the destruction and damage that is almost inevitable in this natural disaster.

Having started its movement, the avalanche can no longer stop, sinking lower and lower and capturing accompanying stones, ice blocks, branches and uprooted trees on its way, turning from ebullient white snow into a dirty mass, remotely resembling a mudflow. The flow can continue its “fascinating journey” until it stops on gentle sections or at the bottom of the valley.

Factors affecting the convergence of snow masses from the mountains

The reasons causing the convergence of avalanches largely depend on the old snow - its height and density, the state of the surface under it, as well as on the growth of new masses of precipitation. The intensity of snowfalls, subsidence and compaction of the cover and air temperature also affect. In addition, a fairly long open slope (100-500 m) is optimally suited for the start of an avalanche path.

The main "architect" of this natural phenomenon is not in vain called the wind, since an increase of 10-15 cm is enough for the snow to melt. Temperature is also one of the most important factors that can provoke a disaster. Moreover, if at zero degrees the instability of snow, although it arises quickly, but also passes no less actively (it either melts or an avalanche descends). And when the low temperature is stable, the avalanche period increases.

Seismic vibrations can also activate the convergence of snow, which is not uncommon for highlands. In some cases, flights of jet aircraft over dangerous zones are also enough.

In general, more frequent snow avalanches are indirectly or directly related to the rapid human economic activity, which is not always reasonable. For example, forests that have been cut down today used to serve as natural protection against snow landslides.

Periodicity

Depending on the frequency, intra-annual convergence (for the winter and spring periods) and the long-term average, which includes, respectively, the total frequency of avalanche formation, are distinguished. There are also systematic avalanches (annually or every 2-3 years) and sporadic ones, occurring a maximum of twice per century, which makes them especially unpredictable.

Movement, the focus of a natural phenomenon

The nature of the movement of snow masses and the structure of the focus determine the following classification: flume snow avalanches, special and jumping. In the case of the first, the snow moves either along the tray or along a certain channel. Special avalanches during movement cover the entire available plot terrain. But with jumpers it’s already more interesting - they are reborn from flume, arising in places of uneven flow. The snow mass has to “jump”, as it were, to overcome certain sections. The latter type is capable of developing the greatest speed, therefore, the danger is very significant.

The snow is treacherous and may well creep up unnoticed and inaudibly, falling in an unexpected shock wave, destroying everything in its path. Features of the movement of these natural masses underlie another division into types. A formation avalanche stands out in it - this is when the movement occurs relative to the snow surface located below, as well as a ground avalanche - it slides directly on the ground.

scale

Depending on the damage caused, it is customary to divide avalanches into especially dangerous (they are also spontaneous) - the volume of material losses amaze the imagination with their scale, and simply dangerous - they impede the activities of various organizations and endanger peaceful measured life settlements.

snow properties

It is also important to note the classification associated with the properties of the snow itself, which is the basis of the avalanche. Allocate dry, wet and wet. The former are characterized by a high convergence rate and a powerful destructive air wave, and the masses themselves are formed at sufficiently low temperatures after significant snowfalls. A wet avalanche is snow that has chosen to leave the cozy slopes at above freezing temperatures. The speed of movement here is less than in the previous ones, however, the density of the cover is also greater. In addition, the base can freeze, turning into a hard and dangerous layer. For wet avalanches, the raw material is viscous, wet snow, and the mass of each cubic meter is about 400-600 kg, and the speed of movement is 10-20 m / s.

Volumes

Well, the simplest division is small and almost harmless, medium and dangerous to humans, as well as large ones, which on their way wipe buildings and trees from the face of the earth, turn vehicles into a pile of scrap metal.

Can avalanches be predicted?

It is extremely difficult to predict the convergence of avalanches with a high degree of probability, since snow is an element of nature, which, by and large, is practically unpredictable. Of course, there are maps of dangerous areas and both passive and active methods preventing this phenomenon. However, the causes and consequences of avalanches can be different and very noticeable. TO passive methods include special shield barriers, forest areas, observation points for dangerous areas. Active actions consist in shelling areas of possible collapses from artillery and mortar installations in order to provoke the convergence of snow masses in small batches.

Snow avalanches sliding down from the mountains in any of the options are No matter how small or large they are. It is extremely important to take into account all the factors influencing the emergence of snow masses and their movement along an indefinite route to unknown targets, so as not to sacrifice too expensive gifts to the elements.

All about avalanches: interesting facts

  1. The speed of an avalanche can reach 100-300 km/h. A powerful air wave instantly turns houses into ruins, crushes rocks, demolishes cable cars, uproots trees and destroys all life around.
  2. Avalanches can come from any mountains. The main thing is that they are covered with snow cover. If there have been no avalanches in a certain area for 100 years, then there is always the possibility that they can occur at any time.
  3. Approximately from 40 thousand to 80 thousand people lost their lives during the First World War, they remained buried under avalanches in the Alps. The data is approximate.
  4. In America (California), people surrounded Mount St. Gabriel with deep ditches. Their sizes are equal to football fields. Avalanches descending from the mountain linger in these ditches and do not roll into settlements.
  5. This destructive natural phenomenon is called differently by different peoples. The Austrians use the word "schneelaanen", which means "snow stream", the Italians say "valanga", the French - "avalanche". We call this phenomenon an avalanche.

According to the nature of the movement and depending on the structure of the avalanche focus, the following three types are distinguished:

  • - tray,
  • - wasp,
  • - jumping.

The trough moves along a specific drain channel or avalanche chute.

Osovaya is a snow landslide that does not have a specific runoff channel and slides across the entire width of the site.

The jumping one arises from the flumes where there are sheer walls or sections with a sharply increasing steepness in the drain channel. Having met a steep ledge, the avalanche breaks off the ground and continues to move through the air in the form of a huge jet. Their speed is especially great.

Depending on the properties of snow, avalanches can be:

  • - dry,
  • - wet
  • - wet.

Dry avalanches are usually caused by a low cohesive force between the recently fallen (or transferred) 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 damage. The pressure of the shock wave can reach values ​​of 800 kg / m². The most likely conditions for the occurrence of this type of avalanches are when the temperature is low.

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

Wet avalanches usually occur against the background of unstable weather conditions, the immediate cause of their descent 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 a quick "grasping" of the snow mass after a stop, which makes it difficult to carry out rescue operations.

According to the nature of the sliding surface, the following types are distinguished:

  • - reservoir, when the movement is carried out on the surface of the underlying layer of snow;
  • - unpaved - the movement occurs directly on the surface of the soil.

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

  • - spontaneous (especially dangerous), when their descent causes significant material damage to settlements, sports and sanatorium complexes, railways and roads, power lines, pipelines, industrial and residential buildings,
  • - dangerous phenomena- avalanches that impede the activities of enterprises and organizations, sports facilities, as well as threatening the population and tourist groups.

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

  • - systematic
  • - sporadic.

Systematic descend every year or once every 2-3 years. Sporadic - 1-2 times in 100 years. It is rather difficult to determine their place in advance. Many cases are known when, for example, in the Caucasus, villages that existed for 200 and 300 years suddenly found themselves buried under a thick layer of snow.

In France, there is such an organization ANENA - the National Association for the Study of Snow and Avalanches. The most the main task this association to reduce the number of avalanche victims among the population. And its very first tool in this matter is informing the broad masses of people, i.e. holding lectures, seminars, courses, etc. for everyone.
Summer is ending new season skiing is not far off. To brush up on some aspects of avalanche safety, here are some translated articles from ANENA's Snow and Safety.
As they say, prepare the sleigh in the summer ...

Author of articles François Sivardière is a teacher at the Technical School of Lausanne, for 13 years he headed ANENA (French National Association for the Study of Snow and Lavigne). Since 2007, he has been an avalanche victim prevention teacher and consultant.

So the first article

Misconceptions about Avalanches.

Snow boards are easy to recognize - WRONG!

If there has not been snowfall for a long time, then there is no danger - WRONG!

When there is little snow, there are no avalanches - WRONG!

A small slope is safe - WRONG!

There are no avalanches in the forest - WRONG!

There are no avalanches in late spring and summer - WRONG!

No, snow boards are not easy to recognize!
Snow boards underlie about 80% of avalanches. Such avalanches are easy to recognize: the avalanche breaks off along a line. If you look at such an avalanche from the side, it seems that a whole piece of the slope is separated and begins to slide down.
The snow boards themselves, on the contrary, can be difficult to recognize. Contrary to some common assumptions, the snow board does not differ in any particular density, or matte color, or some dull sound.
You've probably heard of soft and hard snowboards by now. The fact is that boards can be formed from snow of very different qualities, from soft (the most dangerous because of its attractiveness for skiing) to very hard. Since boards can consist of snow of very different qualities, it becomes obvious that they cannot be of the same density, not of the same color, much less produce the same sounds. In addition, the board can be hidden under a thin or thick layer of fresh snow. Therefore, when trying to identify a snowboard, do not rely on the appearance of snow on the surface.
A more reliable way to identify a snowboard is to evaluate meteorological and topographic features. But this requires a lot of experience and excellent knowledge of the terrain of the area.

It is also worth remembering that snow boards are not only "wind" (that is, formed by the wind), but can also be formed when total absence wind.
And finally, "wind" boards do not necessarily appear on the lee slopes, since the winds in the mountains tend to swirl in a completely unthinkable way. As a result, snow boards can easily form on slopes exposed to dominant winds.

The danger exists even if there has been no snowfall for a long time!
It is a known fact that usually the days following a snowfall are marked by increased avalanche activity. Can we conclude from this that if there has been no snowfall for a long time, then the risk of avalanches becomes low? Unfortunately no.

Freshly fallen snow takes time to pack, stabilize and bond with the underlying layer. And the colder it is, the slower these processes go. Thus, the instability of freshly fallen snow can last for several days, a week or more. This is especially true for slopes on which the sun rarely shines: the slopes of northern exposures. Thus, the rule of three days (it is usually said that "one must wait three days after a snowfall") is not to be taken literally. The formation of bonds in the snow cover is strongly slowed down by cold. Therefore, if there are low temperatures, then you should wait more than three days. At the same time, it is extremely difficult to say with accuracy how many days after the snowfall the cover stabilizes.
In addition, let us recall again about the wind boards, which are the basis for deadly dangerous avalanches and formed under the influence of wind. For the formation of such boards, snowfall is not needed at all: even a moderate breeze is enough to create an avalanche situation on the slopes. Finally, snow boards (wind or not) can remain unstable for a long time after formation. Therefore, be careful and careful, even if there has not been a snowfall for a long time!

Avalanches can come down even when there is little snow!
When it comes to assessing avalanche risk, you can often hear: "little snow means not dangerous." This statement is false! The risk of avalanches does not depend directly on the height of the snow cover.
Avalanche hazard is much more dependent on the quality of the bonds between the snow crystals and the layers that make up the snow cover. If these connections are strong, then the risk is correspondingly lower. But if there is a slack (“weak layer”), then regardless of the height of the snow cover, an avalanche can come down. Don't be fooled by the meager snow cover: statistics confirm that winters with little snow are among the deadliest.
A small thickness of snow cover (mainly in November-February) contributes to the formation of layers without strong bonds. The first layers are usually a poor base for the snow that covers them later. There are no links between these layers. Therefore, the basis, i.e. the lower layers of the snow cover are fragile and unreliable. They break easily and provoke avalanches.
In addition, when there is little snow, skiers look for places where there is more of it, i.e. in wind zones. And snow swept by the wind is prone to melting, usually has poor connections with the substrate, which means it is especially dangerous.
So, beware of avalanches, even when it seems to you that there is little snow!

Even a small slope can be dangerous!
Often when assessing a slope, you can hear: “Everything is in order! The slope is not steep at all.
It often happens that on gentle slopes we lose our vigilance. As if avalanches can only descend on steep slopes. This is not the case, and reports describe numerous cases of avalanches on slopes with a slight slope. Therefore, attention - even a small bias can be dangerous!

Consider, for example, a snowboard 50m long, 10m wide and 20cm thick. Although it seems to us that this is a small board, it nevertheless represents 100m3 or from 10 to 30 tons of snow (depending on the quality of the snow). This is a huge weight and volume, quite sufficient to completely cover and immure a person. In addition, it is possible to die from asphyxia or hypothermia even under a small layer of snow.
And even if the victim is not buried in the thickness of the snow, this mass can drag it a long distance and cause various injuries, often incompatible with life (compression snow blocks, hitting rocks and trees, falling off rocks or into a crack…).
So stay alert even if you are going to ride on a small and not steep slope.

There are also avalanches in the forest!
Let's take a look at the impact forest has on avalanche danger. This sense of security we experience in the forest is often false.

Forests have long and often been used as elements of protection for settlements, roads and structures. But the protection that forests can provide to a skier or snowboarder is not at all as reliable, if not ephemeral. It can even be said that only a forest so dense that it is impossible to drive through it is reliable. What is the matter here? In fact, trees have a dual effect on snowpack stability: with their trunks, but also with their branches.

To begin with, it is necessary to distinguish between forests that retain deciduous cover in winter and forests of other trees. branches coniferous trees, which retain their needles in winter, delay the falling snow. When the mass of snow accumulated on a branch becomes too heavy, the branch bends and the snow falls off. If the temperatures are not too cold, then usually heavy caps of already transformed snow fall from the branches and accumulate under the trees. Such snow is quite stable.
On the contrary, deciduous trees and larches lose their leaves and needles by winter. Their branches hardly retain snow, and the snow cover that forms under them is very similar to the snow cover in open areas.
At the same time, the trunks act as anchors: they seem to pin the snow to the ground. Thus, the snow cushion rests on the trunks, which prevent it from sliding down the slope. However, this delay effect is highly dependent on the frequency of the trunks. That is, it works when the forest is really dense, but in this case it is quite difficult to ride through it.
Therefore, it should be understood that the forest can not always prevent the start of an avalanche, nor stop an avalanche coming from above.
And to be in an avalanche going through the forest is much more dangerous than in an open area! The barrels are nearly impossible to dodge, and are often fatal. Clearings can be especially dangerous, which seem so serene and dull our vigilance, but where the snow is not fixed in any way by trunks, and when detached, such an avalanche inevitably goes down into the forest with all the ensuing consequences.
So, let's remember that an avalanche can happen in the forest, especially if the forest is sparse and bare.

Avalanches descend in late spring and summer too!
When the winter skiing season ends, many of us continue to go backcountry, hiking and mountaineering. Thus, even in summer in the mountains you can meet snow. So, there may be avalanches. Contrary to all stereotypes, they can go regardless of the season. If there is a slope, and there is snow on the slope, then the risk of an avalanche automatically arises.
Naturally, this risk can be greater or less depending on weather conditions and topography.
Two studies (Zuanon, 1995 and Jarry and Sivardière, 2000) show that during the so-called off-season, from 1 May to 15 December, avalanche casualties also occur. In France, for example, statistics say that out of 30 avalanche deaths per year, twenty percent died during the specified non-winter period. It's about not at all about a marginal phenomenon, but a reality that cannot be neglected. In 1997, between July and September, 8 people died in France, which accounted for a third of all avalanche victims that year.
Knowing this, do not neglect your winter habits in summer: follow the forecast and the situation on the ground, have a full set of sensor-shovel-sonde, be vigilant and do not hesitate to turn back or bypass questionable areas.