Abstract: Natural emergencies. Landslides, mudflows and landslides
Sel- a rapid, stormy mud or mud-stone flow consisting of a mixture of water, sand, clay and debris rocks, suddenly appearing in the basins of small mountain rivers. The reason for its occurrence is intense and prolonged downpours, rapid melting of snow or glaciers, breakthrough of reservoirs, less often - earthquakes, volcanic eruptions.
Having a large mass and high speed of movement (up to 40 km/h), mudflows destroy buildings, roads, power lines, and lead to the death of people and animals. The steep leading front of a mudflow wave with a height of 5 to 15 m forms the “head” of a mudflow (the maximum height of the water-mud flow shaft can reach 25 m), the length of mudflow channels ranges from several tens of meters to several tens of kilometers.
Particularly active mudflows are formed in the North Caucasus. Due to the negative role of the anthropogenic factor (destruction of vegetation, quarrying, etc.), mudflows began to develop and Black Sea coast North Caucasus (Novorossiysk region, Dzhubga - Tuapse - Sochi section).
Protective measures:
Strengthening mountain slopes (planting forests);
Anti-mudflow dams, dikes, ditches;
Periodic release of water from mountain reservoirs;
Construction of protective walls along river beds;
Reducing the rate of snow melting in the mountains by creating smoke screens.
Catching mudflows in special pits located in river beds.
Effective warning and warning system.
Collapse- this is a rapid separation (separation) and fall of a mass of rocks (earth, sand, clay stones) on a steep slope due to loss of slope stability, weakening of cohesion, and integrity of rocks.
A collapse occurs under the influence of weathering processes, movement of ground and surface water, erosion or dissolution of rock, and soil vibrations. Most often, collapses occur during rainy periods, snow melting, and during blasting and construction work.
The damaging factors of a collapse are the fall of heavy masses of rocks that can damage or crush even strong structures or cover them with soil, blocking access to them. Another danger of landslides is the possible damming of rivers and collapse of the banks of lakes, the waters of which, in the event of a breakthrough, can cause floods or mudflows.
Signs of a possible collapse are numerous cracks in steep rocks, overhanging blocks, the appearance of individual rock fragments, blocks separating from the main rock.
Landslide- sliding displacement of rock masses down the slope under the influence of gravity; occurs, as a rule, as a result of erosion of the slope, waterlogging, seismic tremors and other factors.
The following factors can be the causes of landslides.
1. Natural:
Earthquakes;
Overmoistening of slopes with precipitation;
Increase in slope steepness as a result of erosion by water;
Weakening of the strength of hard rocks due to weathering, washing out or leaching
The presence of softened clays, quicksand, and fossil ice in the soil:
2. Anthropogenic:
Deforestation and bushes on slopes. Moreover, deforestation can occur much higher than the site of a future landslide, but water will not be retained by the plants above, as a result of which the soils become waterlogged far below;
Blasting, which is essentially a local earthquake and contributes to the development of cracks in rocks;
Plowing slopes, excessive watering of gardens and vegetable gardens on slopes;
Destruction of slopes by pits, trenches, road cuts,
Clogging, clogging, blocking of groundwater outlets;
Construction of housing and industrial facilities on slopes, which leads to destruction of the slopes and an increase in the force of gravity directed down the slope.
The damaging factor of landslides is heavy masses of soil that fall asleep or destroy everything in its path. Therefore, the main indicator of a landslide is its volume, measured in cubic meters.
Unlike landslides, landslides develop much more slowly, and there are many signs that allow timely detection of an incipient landslide.
Signs of an incipient landslide:
· gaps and cracks in the ground, on roads;
· disruption and destruction of underground and surface communications;
· displacement, deviation from the vertical of trees, poles, supports, uneven tension or breakage of wires;
· curvature of the walls of buildings and structures, the appearance of cracks on them;
· change in water level in wells, boreholes, and any reservoirs.
Landslide prevention measures include: monitoring the condition of slopes; analysis and forecasting of the possibility of landslides; carrying out complex engineering protective works; training of persons living, working and resting in a hazardous area on life safety rules.
Snow avalanches arise as a result of the accumulation of snow on mountain peaks during heavy snowfalls, strong snowstorms and a sharp drop in air temperature. Avalanches can also occur when deep frost forms, when a loose layer (quicksand snow) appears in the thickness of the snow.
Gathering snow avalanches observed annually in the mountainous regions of the North Caucasus, Sakhalin, Kamchatka, Magadan region, in the Khibiny Mountains, and the Urals.
Most avalanches descend along certain chutes - narrow hollows on steep mountain slopes. 200–300, and sometimes up to 500 thousand tons of snow can fall down these hollows at the same time.
In addition to flume avalanches, there are basic and jumping avalanches. Major avalanches slide down the mountain slopes in unspecified places; as a rule, they are small and do not pose any particular danger. Jumping avalanches are flume avalanches that meet “springboards” on their way and with great strength“jump” over them, acquiring an increasing speed of movement, and as a result, the force of destruction increases.
Avalanches often occur suddenly and begin their initial movement silently. When avalanches move in narrow mountain gorges, an air wave of increasing strength moves ahead of them, causing even greater destruction in comparison with the falling mass of snow. Repeated avalanches leave deep traces in the mountain landscape. Avalanches often fall into river beds and block them, forming long time dams.
Avalanche danger is caused by sudden changes in weather, heavy snowfalls, heavy snowstorms, and rain. To prevent avalanche danger, there is a special mountain avalanche service.
Catastrophic avalanches in the world occur on average at least once every two years, and in some mountainous areas - at least once every 10–12 years.
When people fall under avalanches, it should be remembered that a person, being covered with avalanche snow, can remain alive for only a few hours, and the chance of survival is higher, the thinner the layer of snow above him. Among people who were in an avalanche for no more than 1 hour, up to 50% can survive; after 3 hours, the probability of remaining alive does not exceed 10%. Therefore, work to rescue people caught in an avalanche must begin even before the rescue team arrives.
If you find someone covered, first of all, free your head, clear your mouth, nose, and ears of snow; then carefully (taking into account the possibility of fractures) they remove him from under the snow, transfer him to a place protected from the wind, wrap him in dry clothes, give him a hot drink, and if there are no signs of life, begin artificial ventilation and other resuscitation measures.
D actions of the population in case of threat of landslides, landslides, mudflows
The population living in landslide, mudflow and landslide-hazardous zones should know the sources, possible directions of movement and the main characteristics of these hazardous phenomena. The population of mountainous areas is obliged to strengthen their houses and the territories on which they are built, as well as to participate in the construction of protective hydraulic and other protective engineering structures.
Warning of the population about natural disasters is carried out through sirens, radio, television broadcasting, as well as through local warning systems that directly connect the hydrometeorological service unit with populated areas in hazardous areas.
Before leaving a house or apartment during evacuation, it is necessary to remove the property from the yard or balcony into the house; the most valuable property that cannot be taken with you should be protected from moisture and dirt; doors, windows, ventilation and other openings should be tightly closed, and the electricity should be turned off. , gas and water.
Highly flammable and toxic substances should be taken out of the house and, if possible, buried in a hole or hidden in a cellar.
In all other respects, citizens must act in accordance with the procedure established for organized evacuation.
If there was no warning about the danger or it was made immediately before the natural disaster, then residents, without caring about their property, should quickly go to a safe place. Natural places for escape from a mudflow or landslide are mountain slopes and hills that are not prone to landslides, landslides or flooding by mudflows. When climbing to safe slopes, do not use valleys, gorges and recesses, since side channels of the main mudflow can form in them. In the case when people, buildings and structures find themselves on the surface of a moving landslide area, they should, after leaving the premises, move upward if possible, when braking a landslide, beware of stones, fragments of structures, earthen ramparts, and screes rolling off its back part. When a fast-moving landslide stops, a strong shock is possible. This poses a great danger to people in the landslide.
Landslides, mudflows and collapses are dangerous geological phenomena.
In 1911 In the Pamirs, an earthquake caused a giant landslide. About 2.5 billion m 3 of soil slid. The village of Usoy and its inhabitants were overwhelmed. The landslide blocked the valley of the Murgab River, and the resulting dam lake flooded the village of Saraz. The height of this formed dam reached 300 m, the maximum depth of the lake was 284 m, and the length was 53 km. Such large-scale disasters happen rarely, but the troubles they bring are incalculable.
Landslides - This is the displacement of rock masses down a slope under the influence of gravity.
Landslides form in various breeds as a result of disruption of their balance, weakening of strength. They are caused by both natural and artificial (anthropogenic) reasons. Natural causes include an increase in the steepness of slopes, eroding their bases with sea and river waters, seismic tremors, etc. Artificial causes include destruction of slopes by road excavations, excessive removal of soil, deforestation, improper agricultural practices of agricultural land on slopes, etc. According to international statistics up to 80% of modern landslides are associated with anthropogenic factors. They can also arise from earthquakes. Landslides occur when the slope is steeper than 10°. On clay soils with excessive moisture, they can also occur at a steepness of 5-7°.
Landslides are classified according to the scale of the phenomenon, activity, mechanism and power of the landslide process, and place of formation.
By scale Landslides are divided into large, medium and small scale.
Large Landslides are usually caused by natural causes and occur along slopes for hundreds of meters. Their thickness reaches 10-20 m or more. The landslide body often retains its solidity.
Medium and small scale landslides are smaller in size and are characteristic of anthropogenic processes.
The scale of landslides is characterized by the area involved in the process. In this case, they are divided into grandiose - 400 hectares or more, very large - 200-400 hectares, large - 100-200 hectares, medium - 50-100 hectares, small - 5-50 hectares and very small - up to 5 hectares.
By activity landslides can be active or inactive. Their activity is determined by the degree of capture of bedrock of slopes and the speed of movement, which can range from 0.06 m/year to 3 m/s.
According to the mechanism of the landslide process landslides are divided into shear, extrusion, viscoplastic, hydrodynamic carryover, and sudden liquefaction landslides. Landslides often show signs of a combined mechanism.
By place of education landslides are divided into mountain, underwater, snow and artificial earthen structures (pits, canals, rock dumps).
By power Landslides can be small, medium, large and very large. They are characterized by the volume of displaced rocks, which can range from hundreds to 1 million m3. A type of landslides are snow avalanches. They are a mixture of snow crystals and air. Large avalanches occur on slopes of 25-60°. They cause great damage and cause loss of life.
Mudflows (mudflows) is a stormy mud or mud-stone flow that suddenly appears in the beds of mountain rivers.
Immediate reasons The origin of mudflows are heavy rainfalls, washing of reservoirs, intensive melting of snow and ice, as well as earthquakes and volcanic eruptions. Anthropogenic factors also contribute to the occurrence of mudflows, which include deforestation and soil degradation on mountain slopes, rock explosions during road construction, stripping operations in quarries, incorrect organization dumps and increased air pollution, which has a detrimental effect on the soil and vegetation cover.
When moving, a mudflow is a continuous stream of mud, stones and water. Mudflows can transport individual rock fragments weighing 100-200 tons or more. The leading front of the mudflow wave forms the “head” of the mudflow, the height of which can reach 25 m.
Debris flows are characterized by linear dimensions, volume, speed of movement, structural composition, density, duration and recurrence. In areas fed by rain and snow, mudflows can occur several times during the year, but more often once every 2-4 years. Powerful mudflows are observed once every 10-12 years or more.
Mudflows are classified according to the composition of the transported material, the nature of the movement and power.
According to the composition of the transferred material distinguish:
Mud flows are a mixture of water, fine earth and small stones;
Mud-stone flows - a mixture of water, fine earth, gravel, pebbles and small stones;
Water-stone streams are a mixture of water and large stones.
By nature of movement Mudflows are divided into connected and incoherent flows. Cohesive flows consist of a mixture of water, clay, sand and represent a single plastic substance. Such a mudflow, as a rule, does not follow the bends of the channel, but straightens them. The loose streams are composed of water, gravel, pebbles and rocks. The flow follows the bend of the channel at high speed, subjecting it to destruction.
By power Mudflows are divided into catastrophic, powerful, medium and low power.
Catastrophic mudflows are characterized by the removal of more than 1 million m3 of material. They happen on the globe once every 30-50 years. Powerful mudflows are characterized by the removal of material in a volume of 100 thousand m3. Such mudflows rarely occur. In mudflows of weak power, the removal of material is insignificant and amounts to less than 10 thousand m 3. They occur every year.
Consequences of landslides, mudflows, landslides. Landslides, mudflows, landslides cause great damage to the national economy, natural environment, lead to human casualties.
The main damaging factors of landslides, mudflows and landslides are impacts from moving masses of rocks, as well as the flooding and obstruction of previously free space by these masses. As a result, buildings and other structures are destroyed, settlements and objects are hidden by rock layers national economy, forest lands, blocking of river beds and overpasses, death of people and animals, changes in the landscape.
Landslides, mudflows and landslides on the territory of the Russian Federation occur in the mountainous regions of the North Caucasus, the Urals, Eastern Siberia, Primorye, Sakhalin Islands, Kuril Islands, Kola Peninsula, as well as along the banks of large rivers.
Topic No. 4 Emergencies natural and man-made
Earthquakes
Volcanic eruptions
Strong winds
Floods
Atmospheric precipitation
Earthquakes
Earthquakes are tremors and wave vibrations. earth's surface, which occur as a result of a sudden rupture of the earth's crust or upper mantle.
Several million very weak earthquakes are recorded annually on Earth, 150 thousand weak, 19 thousand moderate, almost 7 thousand strong, about 150 destructive. The consequences of earthquakes are associated with numerous casualties and huge economic losses. Over the past 4,000 years, earthquakes have killed more than 13 million people. Half of the world's population lives in earthquake-prone areas, where earthquakes of magnitude 7 or more are possible, and about 70% of cities are located.
Almost 20% of Russia's territory is seismically dangerous, of which 5% is subject to extremely dangerous earthquakes.
1/10 of the population of our country lives in earthquake-prone areas; more than 100 cities are located. The most dangerous seismic areas are: North Caucasus, Kamchatka, Lake Baikal region, Sakhalin.
Due to their origin, earthquakes can be natural or man-made.
Natural arise as a result of the activity of natural forces: tectonic processes in earth's crust, volcanic eruptions, strong landslides, landslides, collapses of karst voids, large meteorites falling to the Earth, collisions of the Earth with large space objects.
Anthropogenic arise as a result of human activity: high-power explosions, collapse of underground engineering structures, pushing through the upper layer of the earth's surface during the construction of artificial reservoirs with large volumes of water, construction of cities with a high density of multi-story buildings, intensive mining.
The area where an underground shock occurs is called the earthquake source . Most often it is located at a depth of 10–100 kilometers. The size of the earthquake source can range from tens to hundreds of kilometers.
The center of the earthquake is called hypocenter. Its projection on the earth's surface is epicenter. The epicenter and the surrounding area are called pleistoseismic zone. This zone is characterized by the greatest impact of earthquake forces and the greatest destruction. An earthquake produces seismic waves , which diverge in different directions from the source at a speed of 2–8 km/s. Seismic waves are the main damaging factor of an earthquake. They are recorded by special devices - seismographs. .
Earthquake energy has been measured on the Richter scale since 1935.
The consequences of earthquakes largely depend on the strength, location, population density in the affected area, time of day, seismic resistance of objects, the level of preparation of the population for actions in emergency situations, and the efficiency of search and rescue operations by special units.
Several aftershocks are observed during an earthquake different strengths. The time of the first tremors is several seconds. Subsequent tremors are observed behind him – aftershocks. The time between shocks can range from several seconds to several days.
Earthquakes are accompanied by roar and rumble from the bowels of the earth. Cracks run along the surface of the earth; their width reaches several meters. The earth shakes, chasms form and disappear, swallowing everything that is on the surface. Earthquakes are accompanied by fires and lead to landslides, rockfalls, landslides, and mudflows. During tremors, residential buildings, industrial buildings, hydraulic and transport structures are damaged. Earthquakes destroy cities and villages in a matter of minutes, undermine the economies of states, and injure and kill people. If the source of an earthquake is under water, this leads to the formation of high waves - tsunamis, which reach the shore and bring a lot of trouble to coastal areas.
Signs of an approaching earthquake : swaying of the building, swaying of lamps, clinking of glass and dishes, the sound of breaking glass, growing rumble.
Consequences of earthquakes:
Injury and death of people as a result of the collapse of buildings, people falling into rubble, electric shock, gas, smoke, fire, water;
Fires resulting from damage to electrical networks, fuel, gas, and flammable materials storage facilities;
Release of radioactive, chemically hazardous and other hazardous substances as a result of the destruction of storage facilities, communications, and technological equipment at nuclear energy facilities, chemical industry, utilities;
Transport accidents and disasters;
Violation of life support systems, including electrical networks, water supply, sewerage.
Actions in case of earthquake:
You should remain calm, composure, act quickly and confidently.
A safe place during an earthquake is a street (square) away from buildings. If an earthquake catches you in a car, you should stop away from buildings and tall trees and wait for the aftershocks to end without leaving the car.
It is necessary to leave the building after the end of the first shock quickly and in the most shortcut. Anyone who cannot move independently needs assistance.
You can’t waste time getting ready; you should take only the necessary things, documents, and money with you.
You cannot use the elevator during an earthquake.
Jumping to the ground from the upper floors of a building is extremely dangerous.
Climb to the roof of a building, accumulate on stairwells and on stairs during an earthquake you are not allowed.
When leaving an apartment or house, you should turn off electricity, water and gas.
The safest place in the apartment , house are: corners of main walls, openings in these walls, space under load-bearing structures.
Safe positions when staying indoors are:
Squatting, the body is tilted forward, the head and face are covered with the hands;
Standing facing a load-bearing wall;
Lying on your stomach along the supporting structure.
In the house you must have:
Backup source light (flashlight, matches, candle, lamp);
A supply of non-perishable food products and a reserve supply of drinking water;
First aid kit;
Self-powered radio for listening to emergency radio messages;
In partially destroyed buildings, in the absence of the ability to evacuate on your own, you must wait for help. To facilitate the search, you need to give signals with your voice, wave a cloth, or use a flashlight in the dark.
Volcanic eruptions
Geological formations that arise above channels or cracks in the earth's crust, through which hot lava, ash, hot gases, steam, water, and rock fragments erupt onto the surface of the earth and into the atmosphere, are called volcanoes.
Most often, volcanoes form at the junction of the Earth's tectonic plates. They can occur not only on land, but also on the seabed. In this case, islands are often formed. There are thousands of islands in the World Ocean that were formed as a result of volcanic eruptions: the Azores, Hawaiian, Canary Islands, Galapagos and many others.
Volcanoes are extinct , asleep , valid . In total, there are almost 1,000 extinct and dormant volcanoes on land, and 522 active volcanoes. The largest number of volcanoes are located in Indonesia, Japan, Central America, New Guinea, Chile, the Greater and Lesser Sunda Islands of the Malay Archipelago. On the territory of Russia volcanic danger Residents of Kamchatka, the Kuril Islands, and Sakhalin are susceptible; there are more than 70 active volcanoes.
About 7% of the world's population lives dangerously close to active volcanoes. According to some estimates, more than 40 thousand people died as a result of volcanic eruptions in the 20th century.
In places where magma and gases escape to the surface of the earth, one or more holes are formed - craters . Most often, the crater is located at the top of a volcano and has a funnel or cauldron shape.
The main damaging factors of the volcano are : hot lava, gases, smoke, steam, hot water, ash, rock fragments, blast wave, mud-stone flows.
Lava- This is magma that has escaped to the surface of the earth.
The lava temperature can reach 10,000 °C or more. Lava forms lava flows with high fluidity. The lava flow speed is 100 km/h. Lava can spread tens of kilometers from a volcano, affecting an area of hundreds of square kilometers.
During an eruption, volcanic ash and gases are released into the atmosphere to a height of 15–20 kilometers. The thickness of the ash layer can reach 10 meters within a radius of up to 200 kilometers from the volcano.
If the gas pressure in the magma is very high and it experiences resistance from the Earth, the eruption has the character of an explosion.
Characteristic feature volcanoes are their repeated eruptions.
Reducing the number of human casualties and material damage from volcanic eruptions is achieved through constant monitoring of them and forecasting upcoming eruptions.
The main ways to combat volcanic eruptions:
Cooling lava with water;
Construction of artificial channels for drainage of lava and mud-stone flows;
Construction of protective dams;
Timely evacuation of the population from dangerous areas.
Despite the real danger and threat, people continue to settle and live near volcanoes.
Avalanches, landslides, landslides
Avalanche- this is a sudden movement of a mass of snow, ice, rocks down the slopes of mountains, posing a threat to human life and health.
Avalanches account for approximately 50% of accidents in the mountains. The conditions for the formation of avalanches are a snow-covered mountain slope with a steepness of 15–30 degrees, heavy snowfall with an increase rate of 3–5 centimeters per hour. The most avalanche-dangerous periods of the year are winter-spring; up to 95% of avalanches are recorded at this time. An avalanche can occur at any time of the day, most often it occurs during the daytime - 68%, at night - 22% or in the evening - 10%.
The movement of an avalanche begins in conditions when the component of gravity of the snow cover in the direction of the slope exceeds the adhesion force of snow crystals to each other. Before the movement begins, the snow masses are in a state of unstable equilibrium. They come into motion for the following reasons:
Heavy snowfall or accumulation of large amounts of snow on the slopes when it is carried by the wind;
Low adhesion force between the underlying surface and freshly fallen snow;
Thaw and rain, followed by the formation of a slippery layer of water between the underlying surface and freshly fallen snow;
Sudden change in air temperature;
Mechanical, acoustic, wind effects on snow cover.
The speed of avalanches is 20–100 m/s. The pressure (impact force) of an avalanche can amount to tens of tons per square meter.
The dangerous factor of avalanches is their enormous destructive power. Avalanches sweep away everything in their path, they are the cause of many emergencies in the mountains: they damage and destroy buildings, communications, power lines, roads, equipment, injure and kill people.
The main reason death in avalanches is asphyxiation ( asphyxia ). While an avalanche is moving, it is almost impossible to breathe in it; the snow clogs the airways, and snow dust penetrates the lungs.
A person dies in an avalanche not only from suffocation, he can freeze, receive mechanical injuries to the head and internal organs, fractures of the limbs or spine. This occurs as a result of impacts on the ground, rocks, trees, stones.
Avalanche protection includes the following preventive measures: study, observation, forecasting, informing the population about a possible emergency threat, training people to act safely in avalanche-prone areas, artificially causing avalanches, using avalanche plantings, creating engineering structures in avalanche-prone areas, including canopies, tunnels, corridors. If there is a threat of avalanches, ski slopes, mountain roads and railways are closed, people are prohibited from going to the mountains, and the work of rescue teams is intensified.
Collapse- this is the separation and fall of large masses of rocks on steep and steep slopes of mountains, river valleys, and sea coasts due to the loss of adhesion of the detached mass to the parent base.
Landslides can injure people, destroy transport routes, block equipment, create natural dams with the subsequent formation of lakes, and cause the overflow of huge amounts of water from reservoirs.
Landfalls happen:
Large - mass 10 million cubic meters or more;
Medium - weight from several hundred to 10 million cubic meters;
Small - several tens of cubic meters.
The formation of landslides is facilitated by the geological structure of the area, the presence of cracks on the slopes, crushing of rocks, and a large amount of moisture.
The collapse does not begin suddenly. First, cracks appear on the mountain slopes. It is important to notice the first signs in time and take rescue measures. In 80% of cases, collapses are associated with human activity. They occur when construction work or mining is carried out incorrectly.
Landslide is the displacement of rock masses along a slope under the influence of its own gravity.
The main reasons for the formation of landslides:
Increase in slope steepness as a result of erosion of the base by water;
Weakening the strength of rocks when they are weathered or waterlogged;
Seismic tremors;
Violation of mining technology;
Deforestation and destruction of other vegetation on slopes;
Incorrect agricultural technology for using slopes for farmland.
The power of a landslide is characterized by the volume of displaced rocks, which can be up to millions of cubic meters.
Landslide classification
Sel ( mudflow ) is a sudden flow of water that appears in mountain rivers with high level content (up to 75%) of stones, dirt, sand, soil.
The most mudslide-prone region in Russia is the North Caucasus; there are more than 186 mudflow-prone basins. Mudflows are also observed in Kabardino-Balkaria, North Ossetia-Alania, Dagestan, the Urals, the Kola Peninsula, Kamchatka.
The main causes of mudflows:
Heavy rains in the mountains;
Intensive melting of snow and ice;
Dam failure mountain lakes;
Deforestation and destruction of vegetation on mountain slopes;
Blasting in quarries;
Violation of rock development technology.
A prerequisite for the formation of mudflows is the presence on the slopes of a large number of rock destruction products, a large volume of water for the sliding of these rocks, and the presence of a steep drainage. A mudflow is capable of transporting large rock fragments.
Classification of mudflows
The length of the mudflow is up to tens of kilometers. The width is determined by the width of the channel. The depth of the flow can reach 15 meters. The movement speed ranges from 2 to 10 m/s.
Strong winds
Wind is the movement of air masses relative to the earth's surface.
The earth is shrouded in a thick layer of atmosphere (air). A characteristic feature of air is its constant movement. This movement is primarily due to different temperatures air masses, which is associated with uneven heating of the Earth's surface by the Sun, as well as with different atmospheric pressure.
The main characteristics of the wind are: speed , direction of movement , strength . Wind speed is measured in meters per second (m/s) or kilometers per hour (km/h) using a special device - an anemometer. A weather vane is used to determine the direction of the wind. Wind strength is determined in points on the Beaufort scale (English hydrograph F. Beaufort, 1806). Depending on the speed of air movement, direction, temperature, location, duration, the following strong winds of the planet are observed.
Relationship between Beaufort scores and wind speed
| Beaufort points | Wind speed, m/s | Wind characteristics | Wind action |
| 0 – 0,5 | Calm | Smoke rises vertically | |
| 0,60 – 1,7 | Quiet | Smoke rises obliquely | |
| 2–6 | 1,80 – 12,4 | Light, weak, moderate, fresh | From the rustling of leaves to the swaying of branches |
| 7–8 | 12,50 – 18,2 | Strong, very strong | Tree branches break |
| 18,30 – 21,5 | Storm | Pipes and tiles are torn off | |
| 21,60 – 25,1 | Storm, strong storm | Trees are uprooted | |
| 25,20 – 29 | Fierce Storm | Great destruction | |
| 12–17 | More than 29 | Hurricane | Devastating actions |
Hurricane (typhoon). This is a huge wind destructive force speed of 117 km/h or more, lasting several days. Hurricanes are accompanied by large amounts of precipitation and a drop in air temperature. The width of the hurricane ranges from 20 to 200 kilometers. Most often, hurricanes sweep over the USA, Bangladesh, Cuba, Japan, the Antilles, Sakhalin, and the Far East. Forecasters assign each hurricane a name or four-digit number. Hurricanes carry enormous energy.
Hurricane winds injure and kill people, tear off roofs from houses, collapse buildings, overturn vehicles, wash ashore and sink ships, break wires and damage power line supports, destroy crops and crops, contribute to the rapid spread of fire, carry huge amounts of sand, snow, earth.
Squall . A short-term, sharp increase in wind with a change in the direction of its movement. The duration of the squall ranges from several seconds to tens of minutes. Wind speed is 72–108 km/h. A squall is formed during the warm period of the year as a result of the active penetration of cold air into the warm layers of the atmosphere. The danger lies in the sudden occurrence of enormous wind force and a sharp drop in air temperature.
Tornado (tornado). This atmospheric vortex in the form of a dark sleeve with a vertical curved axis and a funnel-shaped expansion in the upper and lower parts. The air rotates at a speed of 300 km/h counterclockwise and rises upward in a spiral, drawing in various objects. The air pressure in the tornado is reduced. The height of the sleeve can reach 1000–1500 meters, the diameter can range from several tens above water to hundreds of meters above land. The length of a tornado's path ranges from several hundred meters to tens of kilometers. The speed of the tornado is 50–60 km/h.
A tornado originates in a thundercloud and falls to the ground (water). Most often this occurs in the warm sector of the cyclone before the cold front. The tornado moves in the same direction as the cyclone. It is accompanied by thunderstorms, rain, hail, and a sharp increase in wind. Along the path of a tornado, destruction is inevitable as a result of the impact of rapidly rushing air and a large pressure difference in the internal and peripheral parts of the tornado. Tornadoes pose an extreme danger to ships on the high seas. A tornado can lift a building, a car, or a person high into the air. Getting caught in a tornado always results in injury or death.
Tornadoes observed in all areas globe. Most often they occur in the USA, Australia, and Northeast Africa.
Storm. Continuous, strong winds of 103–120 km/h, causing heavy disturbances at sea and destruction on land. The storm is the cause of the annual death of dozens of sea vessels and great destruction along the coast.
Storm. Wind speed 62–100 km/h. Such a wind can blow top layer soil over tens and hundreds of km2, transport millions of tons of fine-grained soil particles, snow, and, in the desert, sand over long distances by air. Storms can cover large areas with dust, sand, soil and snow. In this case, the thickness of the applied layer is tens of centimeters. Crops are destroyed, roads are filled up, water bodies and the atmosphere are polluted, and visibility deteriorates. There are known cases of people dying during a storm.
During a winter storm, a huge amount of snow rises into the air, which leads to heavy snowfalls, blizzards, and snow drifts. Snow storms paralyze traffic, disrupt energy supplies, and lead to tragic consequences. The wind helps to cool the body and cause frostbite.
To protect yourself in strong winds, you must:
Stay in the house, shelter;
Be located in the “wind shadow” zone;
Stay away from buildings, trees, tall objects, beware of falling heavy objects, trees, various buildings; the wind can break electrical wires, which pose a risk of electric shock;
Do not sit near a window during strong winds; the glass may break and injure you.
Floods
Flood is the temporary inundation of land areas with water as a result of rising water levels in rivers, lakes, and seas.
Floods are among the most frequently and regularly recurring natural disasters and occupy a leading position in terms of area covered, total economic damage, and human casualties. Floods account for 32% of total number natural disasters that occur annually in the world. They account for up to 30% of material losses from all natural disasters on Earth.
According to the UN, over the past 10 years, more than 250 million people around the world have been affected by floods and almost 9 million have died. Floods may affect 70% of the territory of our planet, with the number of victims amounting to several billion people.
In Russia, hundreds of large cities, tens of thousands of settlements and economic facilities are subject to the threat of floods. 400 km2 of our country’s territory is located in a flood zone, where several tens of millions of people live. In the event of the destruction of the dam of the Khimki reservoir, several administrative districts of the city of Moscow fall into the flood zone.
Water– a formidable element, a potential source of emergency situations. This is due to the fact that 2/3 of the Earth's surface is covered with water. The world's oceans cover an area of 361 million km2. The total volume of water on our planet is 1380 million km3.
Main causes of floods :
Prolonged rainfall;
Intensive melting of snow and glaciers;
Wind surge of water into river mouths and sea coast;
Formation of jams and jams in river beds;
Breakthrough of hydraulic structures;
The release of a large amount of groundwater to the surface;
For any flood, the main characteristics are: level of rise, flow and volume of water, area and duration of flooding, speed of flow and rise of water level, composition of the water flow and others.
High water– a gradual rise in water level caused by the spring melting of snow.
Flood– rapid rise of water due to rain or winter thaws.
Surge floods- occur as a result of wind surge of water into the mouth of the river and on the coast.
Tsunami floods– occur on the coasts of seas and oceans as a result of underwater earthquakes.
Floods as a result of accidents at hydraulic structures– occur as a result of a breach of hydraulic protective structures or the overflow of a large amount of water through them.
Damaging factors floods : rapid flow of a huge mass of water, high waves, whirlpools, low water temperature, objects floating in the water, electric current when power lines are broken, infectious diseases.
Consequences of floods.
Floods lead to the rapid inundation of vast areas, causing injury and death to people and animals, and destruction or damage to buildings and structures, public utilities, roads, power and communication lines. Chemical and fire hazardous substances (petroleum products, fertilizers, pesticides) get into the water. The fertile layer of soil is washed away, the harvest of agricultural products perishes, the terrain changes, reserves of raw materials, fuel, food, feed, fertilizers are destroyed or damaged. building materials. The structure of the soil changes, the soil subsides. Floods cause landslides, landslides, and mudflows. Floods can cause epidemics. The scale and consequences of floods depend on their duration, terrain, time of year, weather, the nature of the soil layer, the speed and height of water rise, the composition of the water flow, the degree of building density and population density, the condition of hydraulic structures, forecast accuracy and efficiency carrying out search and rescue operations in the flood zone.
Landslides, landslides and mudflows are dangerous geological phenomena and, although the reasons for their occurrence are different, they all have a similar impact on nature, humans, and their objects. economic activity. The measures to prevent them, eliminate their consequences, and the basic actions of the population in the event of emergencies caused by them are also similar. The general condition for the occurrence of these dangerous natural phenomena is the beginning of soil or rock displacement. On the territory Russian Federation There are areas where landslides, mudflows and landslides often occur. These are the North Caucasus, the Urals, the Sayan Mountains, Primorye, Kamchatka, Sakhalin.
A landslide is the separation and catastrophic fall of large masses of rocks, their overturning, crushing and rolling down on steep and steep slopes.
Causes of landslides
Collapses natural origin observed in the mountains, on sea shores and cliffs of river valleys. They occur as a result of a weakening of the cohesion of rocks under the influence of weathering, erosion, dissolution, as well as gravity and tectonic phenomena. Any ingress of water or snow into the weaker bonding layers leads to their gradual weakening. This is why landslides most often occur during periods of rain and melting snow. IN winter time frozen water plays the role of fastening cement, preventing separated blocks of rock from coming apart. When the ice in the cracks melts, individual blocks in some rock mass can barely hold on, and even the slightest impact on them is enough for them to fall down the slope or cliff.
Last time greatest number landslides (80%) are associated with human activity. Mainly due to improper work during construction and mining, as well as during blasting and plowing of slopes. Large landslides are also caused by earthquakes. Grandiose landslides occur in the mountains, where they often dam rivers.
Landslide classification
Landslides are characterized by the power of the landslide process, which is determined by the volume of collapsed rocks and the scale of manifestation - the area of the landslide. (See Appendix 1)
- - according to the power of the landslide process, landslides are divided into very small, small, medium, large and gigantic;
- - according to the scale of manifestation - small, small, medium and huge.
Some of the types of landslides are rockfalls, ground collapses and glacier collapses. Another type of landslide is a collapse - the collapse of individual blocks and stones from the soil on steep slopes. Rockfalls are especially widespread. Their movement occurs in the form of a fall along a significant part of the path. The sizes of falling stones are usually not large, and the total volume of rockfall does not exceed tens of cubic meters. The stones move in the form of repeated jumps at speeds of up to approximately 40-60 m/s. The largest rockfalls occur as a result of heavy rainfall. Rockfalls are most dangerous on highways, laid in steep gorges (for example, in Altai, the Caucasus).
Measures to protect against collapses
Mountain collapses are common occurrences in all countries of the world. Their scale can be grandiose and the consequences tragic. They can cause large blockages or collapses of roads and railways, destruction of populated areas and forests, and contribute to the formation of catastrophic flooding and loss of life.
In landslide-prone areas, measures can be taken to move individual sections of roads, power lines and objects to a safe place, as well as active measures to install engineering structures - guide walls designed to change the direction of movement of collapsed rocks.
Protection against landslides involves the use of the following special structures and measures:
- - vertical planning of territories to regulate surface water flows and install drainage systems;
- - changing slope topography to increase their stability;
- - soil fixation.
To protect against landslides and collapses, tunnels and dams are built. The main condition for preventing these dangerous natural phenomena today remains the preservation of the natural equilibrium conditions that have developed in landslide- and landslide-prone areas beyond for many years. Observation and forecasting systems play an important role in warning about these natural disasters.
Actions of the population in the event of a collapse
If you are caught in a landslide:
- - try to hide under a rock or behind the trunk of a large tree;
- - lie face down on the ground, clasp your head in your hands, breathe through your clothes;
- - do not make sudden movements so as not to cause a new collapse.
The consequences of landslides and landslides are the destruction of buildings and structures, the hiding of populated areas, agricultural and forest lands by masses of rocks, the blocking of overpasses and rivers, changes in the landscape, and the death of people and animals.
Characteristics, causes, countermeasures, security measures"
Introduction1. Landslides
2. Sat down
3. Landfalls
5. Rules of behavior for people in the event of mudflows, landslides and collapses
Introduction
Natural disasters have threatened the inhabitants of our planet since the beginning of civilization. Somewhere more, somewhere less. One hundred percent security does not exist anywhere. Natural disasters can cause colossal damage, the amount of which depends not only on the intensity of the disasters themselves, but also on the level of development of society and its political structure.
Natural disasters typically include earthquakes, floods, mudslides, landslides, snow drifts, volcanic eruptions, landslides, droughts, hurricanes and storms. In some cases, such disasters can also include fires, especially massive forest and peat fires.
Are we really so defenseless against earthquakes, tropical cyclones, and volcanic eruptions? Why can’t advanced technology prevent these disasters, or if not prevent them, then at least predict and warn about them? After all, this would significantly limit the number of victims and the extent of damage! We are not nearly so helpless. We can predict some disasters, and we can successfully resist some. However, any actions against natural processes require good knowledge of them. It is necessary to know how they arise, the mechanism, conditions of propagation and all other phenomena associated with these disasters. It is necessary to know how displacements of the earth's surface occur, why rapid rotational movement air in a cyclone, how quickly masses of rock can collapse down a slope. Many phenomena still remain a mystery, but, it seems, only over the next few years or decades.
In the broad sense of the word, an emergency situation (ES) is understood as a situation in a certain territory that has arisen as a result of an accident, a dangerous natural phenomenon, catastrophe, natural or other disaster that may result or have resulted in human casualties, caused damage to human health or the environment, significant material losses and disruption of people’s living conditions. Each emergency situation has its own physical essence, causes of occurrence and nature of development, as well as its own characteristics of impact on humans and their environment.
1. Landslides
Mudflow, flow, collapse, landslide
Landslides- This is the displacement of rock masses down a slope under the influence of gravity. They are formed in various rocks as a result of disruption of their balance and weakening of their strength and are caused by both natural and artificial causes. Natural causes include an increase in the steepness of slopes, erosion of their bases by sea and river waters, seismic tremors, etc. Artificial, or anthropogenic, i.e. caused by human activity, the causes of landslides are the destruction of slopes by road excavations, excessive removal of soil, deforestation, etc.
Landslides can be classified according to the type and condition of the material. Some are composed entirely of rock material, others are composed only of soil layer material, and others are a mixture of ice, rock and clay. Snow landslides are called avalanches. For example, a landslide mass consists of rock material; stone material is granite, sandstone; it can be strong or fractured, fresh or weathered, etc. On the other hand, if the landslide mass is formed by fragments of rocks and minerals, that is, as they say, the material of the soil layer, then we can call it a landslide of the soil layer. It may consist of a very fine granular mass, that is, clay, or a coarser material: sand, gravel, etc.; this entire mass can be dry or water-saturated, homogeneous or layered. Landslides can be classified according to other criteria: the speed of movement of the landslide mass, the scale of the phenomenon, activity, power of the landslide process, place of formation, etc.
From the point of view of the impact on people and on construction work, the speed of development and movement of a landslide is its only important feature. It is difficult to find ways to protect against the rapid and usually unexpected movement of large masses of rock, and this often causes harm to people and their property. If a landslide moves very slowly over months or years, it rarely causes accidents and preventive measures can be taken. In addition, the speed of development of a phenomenon usually determines the ability to predict this development; for example, harbingers of a future landslide can be detected in the form of cracks that appear and expand over time. But on particularly unstable slopes, these first cracks can form so quickly or in such inaccessible places that they are not noticed, and a sharp displacement of a large mass of rock occurs suddenly. In the case of slowly developing movements of the earth's surface, it is possible to notice a change in the features of the relief and the distortion of buildings and engineering structures even before a major movement. In this case, it is possible to evacuate the population without waiting for destruction. However, even when the speed of the landslide does not increase, this phenomenon on a large scale can create a difficult and sometimes insoluble problem
Another process that sometimes causes rapid movement of surface rocks is the erosion of the base of the slope sea waves or a river. It is convenient to classify landslides according to the speed of movement. In its most general form, rapid landslides or collapses occur within seconds or minutes; landslides from average speed develop over a period of time measured in minutes or hours; Slow landslides form and move over a period of days to years.
By scale Landslides are divided into large, medium and small scale. Large landslides are usually caused by natural causes. Large landslides are usually caused by natural causes and occur along slopes for hundreds of meters. Their thickness reaches 10-20 m or more. The landslide body often retains its solidity. Medium and small-scale landslides are characteristic of anthropogenic processes.
Landslides may occur active and inactive, which is determined by the degree of capture of bedrock slopes and the speed of movement.
The activity of landslides is influenced by the rocks of the slopes, as well as the presence of moisture in them. Depending on the quantitative indicators of the presence of water, landslides are divided into dry, slightly wet, wet and very wet.
By place of education landslides are divided into mountain, underwater, snow and landslides that occur in connection with the construction of artificial earthen structures (pits, canals, rock dumps, etc.).
By power landslides can be small, medium, large and very large and are characterized by the volume of displaced rocks, which can range from several hundred cubic meters to 1 million m3 or more.
Landslides can destroy populated areas, destroy agricultural land, create danger during the operation of quarries and mining, damage communications, tunnels, pipelines, telephone and electrical networks, and water management structures, mainly dams. In addition, they can block the valley, form a dam lake and contribute to flooding. Thus, the economic damage they cause can be significant.
2. Sat down
In hydrology, a mudflow is understood as a flood with a very high concentration of mineral particles, stones and rock fragments, occurring in the basins of small mountain rivers and dry ravines and usually caused by rainfall or rapid snow melting. Sel is something between a liquid and a solid mass. This phenomenon is short-term (usually it lasts 1-3 hours), characteristic of small watercourses up to 25-30 km long and with a catchment area of up to 50-100 km2.
The mudflow is a formidable force. The stream, consisting of a mixture of water, mud and stones, rapidly rushes down the river, uprooting trees, tearing down bridges, destroying dams, stripping the slopes of the valley, and destroying crops. Being close to a mudflow, you can feel the shaking of the earth under the impact of stones and blocks, the smell of sulfur dioxide from the friction of stones against each other, and hear a strong noise similar to the roar of a rock crusher.
The danger of mudflows lies not only in their destructive power, but also in the suddenness of their appearance. After all, rainfall in the mountains often does not cover the foothills, and mudflows appear unexpectedly in inhabited areas. Because of high speed flow, the time from the moment a mudflow occurs in the mountains to the moment it emerges in the foothills is sometimes calculated in 20-30 minutes.
The main reason for the destruction of rocks is sharp intraday fluctuations in air temperature. This leads to the formation of numerous cracks in the rock and its fragmentation. The described process is facilitated by periodic freezing and thawing of water filling the cracks. Frozen water, expanding in volume, presses on the walls of the crack with enormous force. In addition, rocks are destroyed due to chemical weathering (dissolution and oxidation of mineral particles by intrasoil and groundwater), as well as due to organic weathering under the influence of micro- and macroorganisms. In most cases, the cause of mudflows is rainfall, less often intensive snow melting, as well as outbursts of moraine and dam lakes, landslides, landslides, and earthquakes.
IN general outline The process of formation of a mudflow of storm origin proceeds as follows. Initially, water fills the pores and cracks, simultaneously rushing down the slope. In this case, the adhesion forces between particles sharply weaken, and the loose rock comes into a state of unstable equilibrium. Then the water begins to flow over the surface. The first to move are small particles of soil, then pebbles and crushed stone, and finally stones and boulders. The process is growing like an avalanche. All this mass enters the ravine or channel and draws new masses of loose rock into movement. If the water flow is insufficient, then the mudflow seems to fizzle out. Small particles and small stones are carried down by the water, large stones create a blind area in the riverbed. The stopping of a mudflow can also occur as a result of attenuation of the flow velocity as the river slope decreases. There is no specific recurrence of mudflows observed. It has been noted that the formation of mud and mud-stone flows is facilitated by the previous long-dry weather. At the same time, masses of fine clay and sand particles accumulate on mountain slopes. They are washed away by the rain. On the contrary, the formation of water-stone flows is favored by previous rainy weather. After all, the solid material for these flows is mainly found at the base of steep slopes and in the beds of rivers and streams. In the case of good previous moisture, the bond of stones with each other and with the bedrock weakens.
Shower mudflows are sporadic. Over the course of a number of years, dozens of significant floods may occur, and only then very rainy year there will be a mudflow. It happens that mudflows are observed quite often on the river. After all, in any relatively large mudflow basin there are many mudflow centers, and downpours cover first one or another center.
Many mountainous regions are characterized by the predominance of one or another type of mudflow in terms of the composition of the transported solid mass. Thus, in the Carpathians, water-rock mudflows of relatively small thickness are most often encountered. In the North Caucasus there are mainly mud-stone streams. From the mountain ranges surrounding the Fergana Valley in Central Asia, as a rule, mud flows descend.
It is significant that the mudflow, unlike a water flow, does not move continuously, but in separate shafts, sometimes almost stopping, then again accelerating its movement. This occurs due to the delay of the mudflow mass in the narrowing of the channel, at sharp turns, and in places where the slope sharply decreases. The tendency of a mudflow to move in successive shafts is associated not only with congestion, but also with the non-simultaneous supply of water and loose material from various sources, with the collapse of rock from slopes and, finally, with the jamming of large boulders and rock fragments in constrictions. It is when jams break through that the most significant deformations of the riverbed occur. Sometimes the main channel becomes unrecognizable or is completely submerged, and a new channel is developed.
3. Landfalls
Collapse- rapid movement of masses of rocks, forming predominantly steep slopes of valleys. When falling, the mass of rocks detached from the slope is broken into separate blocks, which, in turn, breaking up into smaller parts, cover the bottom of the valley. If a river flowed through the valley, then the collapsed masses, forming a dam, give rise to a valley lake. Collapses of the slopes of river valleys are caused by river erosion, especially during floods. In high-mountain areas, the cause of landslides is usually the appearance of cracks, which, saturated with water (and especially when water freezes), increase in width and depth until the mass separated by the crack from some shock (earthquake) or after heavy rain or some other - for any other reason, sometimes artificial (for example, a railway excavation or a quarry at the foot of a slope), will not overcome the resistance of the rocks holding it and will not collapse into the valley. The magnitude of the collapse varies within the widest range, ranging from the collapse of small rock fragments from the slopes, which, accumulating on flatter sections of the slopes, form the so-called. scree, and until the collapse of huge masses, measured in millions of m3, representing enormous disasters in cultural countries. At the foot of all steep mountain slopes one can always see stones that have fallen from above, and in areas especially favorable for their accumulation, these stones sometimes completely cover large areas.
When designing a railway route in the mountains, it is necessary to especially carefully identify areas that are vulnerable to landslides, and, if possible, bypass them. When laying quarries in the slopes and carrying out excavations, you should always inspect the entire slope, studying the nature and bedding of rocks, the direction of cracks, and sections, so that quarry development does not violate the stability of the overlying rocks. When constructing roads, especially steep slopes are laid with pieced stones dry or on cement.
In high mountain areas, above the snow line, snow avalanches often have to be reckoned with. They occur on steep slopes, from where accumulated and often compacted snow periodically rolls down. In areas of snow landslides, settlements should not be built, roads should be protected with covered galleries, and forest plantations should be planted on the slopes, which best keep the snow from sliding. Landslides are characterized by the power of the landslide and the scale of manifestation. According to the power of the landslide process, landslides are divided into large and small. According to the scale of manifestation, landslides are divided into huge, medium, small and small.
A completely different type of collapse occurs in areas of rocks that are easily leached by water (limestones, dolomites, gypsum, rock salt). Water seeping from the surface very often leaches large voids (caves) in these rocks, and if such a cave is formed near the earth's surface, then upon reaching a large volume, the ceiling of the cave collapses, and a depression (funnel, failure) is formed on the surface of the earth; sometimes these depressions are filled with water, and the so-called. "failed lakes" Similar phenomena are typical for many areas where the corresponding breeds are common. In these areas, when constructing capital structures (buildings and railways), it is necessary to conduct a soil study at the site of each building in order to avoid destruction of the constructed buildings. Ignoring such phenomena subsequently causes the need for constant repair of the track, which entails high costs. In these areas, it is more difficult to resolve issues of water supply, search and calculation of water reserves, as well as the production of hydraulic structures. The direction of underground water flows is extremely whimsical; the construction of dams and the excavation of ditches in such places can cause the occurrence of leaching processes in rocks previously protected by artificially removed rocks. Sinkholes are also observed within quarries and mines, due to the collapse of the roof of rocks above mined-out spaces. To prevent the destruction of buildings, it is necessary to fill the mined-out space under them, or leave the pillars of the mined rocks untouched.
4. Ways to combat landslides, mudflows and landslides
Active measures to prevent landslides, mudflows, and landslides include the construction of engineering and hydraulic structures. To prevent landslide processes, retaining walls, counter-banquets, pile rows and other structures are constructed. The most effective anti-landslide structures are counter-banquets. They are located at the base of a potential landslide and, by creating a stop, prevent the soil from moving.
Active measures also include fairly simple ones that do not require significant resources or consumption of building materials for their implementation, namely:
- to reduce the stressed state of slopes, land masses are often cut off in the upper part and laid at the foot;
-groundwater above a possible landslide is drained by installing a drainage system;
-protection of river and sea banks is achieved by importing sand and pebbles, and slopes by sowing grass, planting trees and shrubs.
Hydraulic structures are also used to protect against mudflows. Based on the nature of their impact on mudflows, these structures are divided into mudflow control, mudflow dividing, mudflow retention and mudflow transforming structures. The mudflow control hydraulic structures include mudflow passages (chutes, mudflow diversions, mudflow diversions), mudflow control devices (dams, retaining walls, rims), mudflow release devices (dams, thresholds, drops) and mudflow control devices (half-dams, spurs, booms) constructed in front of dams, rims and retaining structures. walls.
Cable mudflow cutters, mudflow barriers and mudflow dams are used as mudflow dividers. They are installed to retain large fragments of material and allow small parts of the debris flow to pass through. Mudflow-retaining hydraulic structures include dams and pits. Dams can be blind or with holes. Blind-type structures are used to retain all types of mountain runoff, and with holes - to retain the solid mass of mudflows and allow water to pass through. Seletransforming hydraulic structures(reservoirs) are used to transform a mudflow into a flood by replenishing it with water from reservoirs. It is more effective not to delay mudflows, but to direct them past populated areas and structures using mudflow diversion channels, mudflow diversion bridges and mudflow drains. In landslide-prone areas, measures can be taken to move individual sections of roads, power lines and objects to a safe place, as well as active measures to install engineering structures - guide walls designed to change the direction of movement of collapsed rocks. Along with preventive and protective measures, an important role in preventing the occurrence of these natural disasters and in reducing damage from them is played by monitoring landslide, mudflow and landslide-prone areas, harbingers of these phenomena and predicting the occurrence of landslides, mudflows and landslides. Observation and forecasting systems are organized on the basis of hydrometeorological service institutions and are based on thorough engineering-geological and engineering-hydrological studies. Observations are carried out by specialized landslide and mudflow stations, mudflow batches and posts. The objects of observation are soil movements and landslide movements, changes in water levels in wells, drainage structures, boreholes, rivers and reservoirs, groundwater regimes. The obtained data characterizing the preconditions for landslide movements, mudflows and landslide phenomena are processed and presented in the form of long-term (years), short-term (months, weeks) and emergency (hours, minutes) forecasts.
5. Rules of behavior for people in the event of mudflows, landslides and collapses
The population living in hazardous areas must know the sources, possible directions and characteristics of these dangerous phenomena. Based on forecasts, residents are informed in advance about the danger of landslides, mudflows, landslides and possible zones of their action, as well as the procedure for submitting danger signals. This reduces the stress and panic that can occur when communicating emergency information about an immediate threat.
The population of dangerous mountainous areas is obliged to take care of strengthening houses and the territory on which they are built, and to participate in the construction of protective hydraulic and other engineering structures.
Primary information about the threat of landslides, mudflows and avalanches comes from landslide and mudflow stations, parties and hydrometeorological service posts. It is important that this information is communicated to its destination in a timely manner. Warning of the population about natural disasters is carried out in the established order by means of sirens, radio, television, as well as local warning systems that directly connect the units of the hydrometeorological service, the Ministry of Emergency Situations with settlements located in dangerous zones. If there is a threat of a landslide, mudflow or landslide, early evacuation of the population, farm animals and property to safe places is organized. Houses or apartments abandoned by residents are brought into a state that helps reduce the consequences natural disaster"and the possible impact of secondary factors, which subsequently facilitates their excavation and restoration. Therefore, the transferred property from the yard or balcony must be removed into the house, the most valuable that cannot be taken with you, protected from moisture and dirt. Doors, windows, ventilation and other openings close electricity, gas, and water supply. Remove flammable and toxic substances from the house and place them in remote pits or separate cellars. Otherwise, proceed in accordance with the procedure established for organized evacuation.
If there was no advance warning of the danger and residents were warned about the threat immediately before the onset of a natural disaster or noticed its approach themselves, everyone, without worrying about property, makes an emergency exit to a safe place on their own. At the same time, relatives, neighbors, and all people encountered along the way should be warned about the danger.
For an emergency exit, you need to know the routes to the nearest safe places. These paths are determined and communicated to the population based on the forecast of the most likely directions of arrival of a landslide (mudflow) to a given settlement (object). Natural safe routes for emergency exit from the danger zone are the slopes of mountains and hills, which are not prone to landslides.
When climbing to safe slopes, valleys, gorges and recesses should not be used, as side channels of the main mudflow may form in them. On the way, assistance should be provided to the sick, elderly, disabled, children and the weak. For transportation, whenever possible, personal transport, mobile agricultural machinery, riding and pack animals are used.
In the event that people and structures find themselves on the surface of a moving landslide area, they should move upward if possible and beware of rolling blocks, stones, debris, structures, earthen ramparts, and screes. At high speed When a landslide occurs, a strong shock is possible when it stops, and this poses a great danger to people in the landslide. After the end of a landslide, mudflow or landslide, people who had previously hastily left the disaster zone and waited out the danger in the nearest safe place, making sure that there is no repeated threat, should return to this area to search for and provide assistance to the victims.
NATURE OF APPEARANCE AND CLASSIFICATION
Landslides, landslides, mudflows, snow avalanches
The most typical natural disasters for some geographical regions of the Russian Federation include landslides, landslides, mudflows and avalanches. They can destroy buildings and structures, cause death, destroy material resources, disrupt production processes.
COLLAPSE.
A landslide is the rapid separation of a mass of rock on a steep slope with an angle greater than the angle of repose, which occurs as a result of loss of stability of the slope surface under the influence of various factors (weathering, erosion and abrasion at the base of the slope, etc.).
Landslides refer to the gravitational movement of rocks without the participation of water, although water contributes to their occurrence, since landslides more often appear during periods of rain, melting snow, and spring thaws. Landslides can be caused by blasting operations, filling mountain river valleys with water during the creation of reservoirs and other human activities.
Landslides often occur on slopes disturbed by tectonic processes and weathering. As a rule, landslides occur when layers on the slope of a massif with a layered structure fall in the same direction as the surface of the slope, or when the high slopes of mountain gorges and canyons are broken into separate blocks by vertical and horizontal cracks.
One of the types of landslides is avalanches - the collapse of individual blocks and stones from rocky soils that make up steep slopes and slopes of excavations.
Tectonic fragmentation of rocks contributes to the formation of separate blocks, which are separated from the root mass under the influence of weathering and roll down the slope, breaking into smaller blocks. The size of the detached blocks is related to the strength of the rocks. The largest blocks (up to 15 m in diameter) are formed in basalts. In granites, gneisses, and strong sandstones, smaller blocks are formed, up to a maximum of 3-5 m, in siltstones - up to 1-1.5 m. In shale rocks, collapses are observed much less frequently and the size of blocks in them does not exceed 0.5-1 m .
The main characteristic of a landslide is the volume of collapsed rocks; Based on volume, landslides are conventionally divided into very small (volume less than 5 m3), small (5-50 m3), medium (50-1000 m3) and large (more than 1000 m3).
In the whole country, very small collapses account for 65-70%, small - 15-20%, medium - 10-15%, large - less than 5% total number landslides. In natural conditions, gigantic catastrophic collapses are also observed, as a result of which millions and billions of cubic meters of rock collapse; the probability of such collapses occurring is approximately 0.05%.
LANDSLADES.
A landslide is a sliding movement of rock masses down a slope under the influence of gravity.
Natural factors that directly influence the formation of landslides are earthquakes, intense waterlogging of mountain slopes precipitation or groundwater, river erosion, abrasion, etc.
Anthropogenic factors (associated with human activity) are cutting of slopes when laying roads, cutting down forests and shrubs on slopes, blasting and mining operations near landslide areas, uncontrolled plowing and watering of land on slopes, etc.
According to the power of the landslide process, i.e., the involvement of rock masses in the movement, landslides are divided into small - up to 10 thousand m3, medium - 10-100 thousand m3, large - 100-1000 thousand m3, very large - over 1000 thousand m3.
Landslides can occur on all slopes, starting from a steepness of 19°, and on cracked clay soils - at a slope steepness of 5-7°.
SAT down.
A mudflow (mudflow) is a temporary mud-stone flow, saturated with solid material ranging in size from clay particles to large stones (bulk mass, usually from 1.2 to 1.8 t/m3), which pours from the mountains onto the plains.
Mudflows occur in dry valleys, ravines, ravines or along mountain river valleys that have significant slopes in the upper reaches; they are characterized by a sharp rise in level, wave movement of the flow, short duration of action (on average from one to three hours) and, accordingly, a significant destructive effect.
The immediate causes of mudflows are heavy rains, intensive melting of snow and ice, breakthrough of reservoirs, moraine and dam lakes; less often - earthquakes and volcanic eruptions.
The mechanisms of debris flow generation can be reduced to three main types: erosion, breakthrough, landslide.
With the erosion mechanism, the water flow is first saturated with debris due to the washout and erosion of the surface of the mudflow basin, and then the formation of a mudflow wave in the channel; The saturation of the mudflow here is closer to the minimum, and the movement of the flow is controlled by the channel.
With the breakthrough mechanism of mudflow generation, the water wave turns into a mudflow due to intense erosion and the involvement of debris masses in the movement; the saturation of such a flow is high, but variable, turbulence is maximum, and, as a consequence, the processing of the channel is the most significant.
During the landslide initiation of a mudflow, when a massif of water-saturated rocks (including snow and ice) is torn off, the flow saturation and the mudflow wave are formed simultaneously; The flow saturation in this case is close to maximum.
The formation and development of mudflows, as a rule, go through three stages of formation:
1 - gradual accumulation on the slopes and in the beds of mountain basins of material that serves as a source of mudflows;
2 - rapid movement of washed away or disequilibrium material from elevated areas of mountain catchment areas to lower areas along mountain beds;
3 - collection (accumulation) of mudflows in low areas of mountain valleys in the form of channel cones or other forms of sediments.
Each mudflow catchment consists of a mudflow formation zone, where water and solid materials are fed, a transit (movement) zone, and a mudflow deposit zone.
Mudflows occur when three natural conditions (phenomena) occur simultaneously: the presence of a sufficient (critical) amount of rock destruction products on the slopes of the basin; accumulation of a significant volume of water for flushing (carrying down) loose solid material from the slopes and its subsequent movement along the riverbed; steep slope slopes and watercourse.
The main reason for the destruction of rocks is sharp daily fluctuations in air temperature, which leads to the appearance of numerous cracks in the rock and its fragmentation. The process of rock crushing is also facilitated by the periodic freezing and thawing of water filling the cracks. In addition, rocks are destroyed due to chemical weathering (dissolution and oxidation of mineral particles by subsoil and groundwater), as well as due to organic weathering under the influence of microorganisms. In areas of glaciation, the main source of formation of solid material is the terminal moraine - a product of the activity of the glacier during its repeated advance and retreat. Earthquakes, volcanic eruptions, mountain falls and landslides also often serve as sources of accumulation of mudflow material.
Often the cause of the formation of mudflows is rainfall, which results in the formation of an amount of water sufficient to set in motion the products of rock destruction located on the slopes and in the channels. The main condition for the occurrence of such mudflows is the rate of precipitation, which can cause the washout of rock destruction products and their involvement in movement. The norms of such precipitation for the most typical (for mudflows) regions of Russia are given in Table. 1.
Table 1
Conditions for the formation of mudflows of rain origin
There are known cases of the formation of mudflows due to a sharp increase in the influx of groundwater (for example, a mudflow in the North Caucasus in the Bezengi River basin in 1936).
Each mountain region is characterized by certain statistics of the causes of mudflows. For example, for the Caucasus as a whole
The causes of mudflows are distributed as follows: rains and downpours - 85%, melting of eternal snow - 6%, discharge of melt water from moraine lakes - 5%, outbursts of dammed lakes - 4%. In the Trans-Ili Alatau, all observed large mudflows were caused by the outburst of moraine and dam lakes.
When mudflows occur, the steepness of the slopes (relief energy) is of great importance; The minimum slope of the mudflow is 10-15°, the maximum is up to 800-1000°.
IN recent years anthropogenic factors have been added to the natural causes of the formation of mudflows, i.e. those types of human activity in the mountains that cause (provoke) the formation of mudflows or their intensification; such factors, in particular, include unsystematic deforestation on mountain slopes, degradation of ground and soil cover by unregulated livestock grazing, improper placement of waste rock dumps by mining enterprises, rock explosions during the laying of railways and roads and the construction of various structures, neglect of land reclamation rules after stripping operations in quarries, overflow of reservoirs and unregulated discharge of water from irrigation structures on mountain slopes, changes in soil and vegetation cover due to increased air pollution from waste from industrial enterprises.
Based on the volume of one-time removals, mudflows are divided into 6 groups; their classification is given in table. 2.
Table 2
Classification of mudflows by volume of one-time emissions
Based on the available data on the intensity of development of mudflow processes and the frequency of mudflows, 3 groups of mudflow basins are distinguished: high mudflow activity (recurrence
Mudflows once every 3-5 years and more often); average mudflow activity (once every 6-15 years and more often); low mudflow activity (once every 16 years or less).
Based on mudflow activity, the basins are characterized as follows: with frequent mudflows, when mudflows occur once every 10 years; with averages - once every 10-50 years; with rare ones - less than once every 50 years.
A special classification of mudflow basins is used according to the height of the sources of mudflows, which is given in Table. 3.
Table 3
Classification of mudflow basins according to the height of the sources of mudflows
According to the composition of the transferred solid material mudflows are distinguished:
Mud flows are a mixture of water and fine earth with a small concentration of stones (volumetric weight of the flow is 1.5-2.0 t/m3);
- mud-stone flows- a mixture of water, fine earth, gravel pebbles, small stones; there are large stones, but there are not many of them, they either fall out of the flow, then move again with it (volumetric weight of the flow is 2.1-2.5 t/m3);
- water-stone streams- water with predominantly large stones, including boulders and rock fragments (volumetric flow weight 1.1-1.5 t/m3).
The territory of Russia is distinguished by a variety of conditions and forms of manifestation of mudflow activity. All mudflow-prone mountain areas are divided into two zones - warm and cold; Within the zones, regions are identified, which are divided into regions.
The warm zone is formed by temperate and subtropical climatic zones, within which mudflows occur in the form of water-stone and mud-stone flows. The main reason for the formation of mudflows is rainfall. Regions of the warm zone: Caucasus, Ural, South Siberian, Amur-Sakhalin, Kuril-Kamchatka; regions of the warm zone of the North Caucasus, Northern Urals,
Middle and Southern Urals, Altai-Sayan, Yenisei, Baikal, Aldan, Amur, Sikhote-Alin, Sakhalin, Kamchatka, Kuril.
The cold zone covers mudflow-prone areas of the Subarctic and Arctic. Here, under conditions of heat deficiency and permafrost, snow-water mudflows are predominantly common. Regions cold zone: Western, Verkhoyansk-Chersky, Kolyma-Chukchi, Arctic; cold zone regions - Kola, Polar and Subpolar Urals, Putorana, Verkhoyansk-Chersk, Priokhotsk, Kolyma-Chukotka, Koryak, Taimyr, Arctic islands.
In the North Caucasus, mudflows are especially active in Kabardino-Balkaria, North Ossetia and Dagestan. This is, first of all, the river basin. Terek (rivers Baksan, Chegem, Cherek, Urukh, Ardon, Tsey, Sadon, Malka), river basin. Sulak (Avar Koisu, Andean Koisu rivers) and the Caspian Sea basin (Kurakh, Samur, Shinazchay, Akhtychay rivers).
Due to the negative role of the anthropogenic factor (destruction of vegetation, quarrying, etc.), mudflows began to develop on the Black Sea coast of the Caucasus (region of Novorossiysk, Dzhubga-Tuapse-Sochi section).
The most mudslide-prone areas of Siberia and the Far East are the areas of the Sayano-Baikal mountainous region, in particular, the Southern Baikal region near the northern slopes of the Khamar-Daban ridge, the southern slopes of the Tunkinsky loaches (Irkut river basin), the river basin. Selenga, as well as certain sections of the Severo-Muysky, Kodarsky and other ridges in the area of the Baikal-Amur Mainline (north of the Chita region and Buryatia).
High mudflow activity is observed in certain areas of Kamchatka (for example, the Klyuchevskaya group of volcanoes), as well as in some mountain basins of the Verkhoyansk Range. Mudflow phenomena are typical for the mountainous regions of Primorye, Sakhalin Island and the Kuril Islands, the Urals (especially the Northern and Subpolar), the Kola Peninsula, as well as the Far North and northeast of Russia.
In the Caucasus, mudflows form mainly in June-August. In the area of the Baikal-Amur Mainline in the lowlands they form in early spring, in the middle mountains - at the beginning of summer, and in the highlands - at the end of summer.
SNOW AVALANCHES.
A snow avalanche or a snowfall is a mass of snow set in motion under the influence of gravity and falling down a mountain slope (sometimes crossing the bottom of a valley and emerging onto the opposite slope).
Snow accumulating on mountain slopes tends to move down the slope under the influence of gravity, but this is opposed by resistance forces at the base of the snow layer and at its boundaries. Due to overloading of slopes with snow, weakening of structural connections within the snow mass, or the combined action of these factors, the snow mass slides or crumbles from the slope. Having begun its movement from a random and insignificant push, it quickly picks up speed, capturing snow, stones, trees and other objects along the way, and falls to flatter areas or the bottom of the valley, where it slows down and stops.
The occurrence of an avalanche depends on a complex set of avalanche-forming factors: climatic, hydrometeorological, geomorphological, geobotanical, physical-mechanical and others.
Avalanches can occur anywhere there is snow cover and sufficiently steep mountain slopes. They reach enormous destructive power in high mountain areas, where climatic conditions favor their occurrence.
The climate of a given area determines its avalanche regime: depending on climatic conditions In some mountainous areas, dry winter avalanches during snowfalls and snowstorms may predominate, while in others, spring wet avalanches during thaws and rains may predominate.
Meteorological factors most actively influence the process of avalanche formation, and avalanche danger is determined by weather conditions not only at the moment, but also over the entire period since the beginning of winter.
The main factors of avalanche formation are:
- amount, type and intensity of precipitation;
- depth of snow cover;
- temperature, air humidity and the nature of their changes;
- temperature distribution inside the snow layer;
- wind speed, direction, nature of their changes and blizzard snow transfer;
- solar radiation and cloudiness.
Hydrological factors influencing avalanche danger are snow melting and infiltration (seepage) of melt water, the nature of the influx and runoff of melt and rain water under the snow, the presence of water basins above the snow collection area and spring swamping on the slopes. Water creates a dangerous lubrication horizon, causing wet avalanches.
High-altitude glacial lakes pose a particular danger, since the sudden displacement of a large amount of water from such a lake when ice, snow or soil masses collapse into it or a dam breaks causes the formation of snow-ice mudflows, similar in nature to wet avalanches.
Of the geomorphological factors, slope steepness is of decisive importance. Most avalanches occur on slopes with a steepness of 25-55°. Flatter slopes can be avalanche-prone under particularly unfavorable conditions; There are known cases of avalanches falling from slopes with an inclination angle of only 7-8°. Slopes steeper than 60° are practically not dangerous for avalanches, since there is snow on them large quantities does not accumulate.
The orientation of the slopes relative to the cardinal points and the directions of snow and wind flows also affects the degree of avalanche danger. As a rule, on the southern slopes within the same valley, other things being equal, snow falls later and melts earlier, its height is much less. But if the southern slopes of the mountain range face moisture-carrying air currents, then the greatest amount of precipitation will fall on these slopes. The structure of slopes affects the size of avalanches and the frequency of their occurrence. Avalanches that originate in small steep erosion grooves are insignificant in volume, but fall most often. Erosion furrows with numerous branches contribute to the formation of larger avalanches.
Avalanches are very large sizes arise in glacial circuses or cirques transformed water erosion: if the crossbar (rocky threshold) of such a pit is completely destroyed, then a large snow funnel is formed with slopes turning into a drainage channel. When a blizzard transports snow, a large amount of precipitation accumulates in the kars and is periodically discharged in the form of avalanches.
The nature of watersheds influences the distribution of snow across landforms: flat plateau-like watersheds facilitate the transfer of snow into snow collection basins, watersheds with sharp ridges are an area for the formation of dangerous snow blows and cornices. Convex areas and upper bends of slopes are usually places where snow masses are released, forming avalanches.
The mechanical stability of snow on slopes depends on the microrelief associated with the geological structure of the area and the petrographic composition of the rocks. If the surface of the slope is smooth and even, then avalanches occur easily. On rocky, uneven surfaces, a thicker snow cover is required so that the gaps between the ledges are filled and a sliding surface can be formed. Large blocks help retain snow on the slope. Fine-clastic screes, on the contrary, facilitate the formation of avalanches, as they contribute to the appearance of mechanically fragile deep frost in the lower layer of snow.
Avalanches form within the avalanche source. Avalanche source- this is the section of the slope and its foot within which the avalanche moves. Each avalanche source consists of zones of origin (avalanche collection), transit (trough), and stopping (alluvial cone) of the avalanche. The main parameters of the avalanche source are the elevation (the difference between the maximum and minimum heights of the slope), the length, width and area of the avalanche catchment, the average angles of the avalanche catchment and transit zones.
The occurrence of avalanches depends on a combination of the following avalanche-forming factors: the height of old snow, the state of the underlying surface, the amount of increase in freshly fallen snow, snow density, the intensity of snowfall and subsidence of snow cover, snowstorm redistribution of snow cover, temperature regime air and snow cover. The most important of them include the increase in freshly fallen snow, snowfall intensity and snowstorm redistribution.
During the period of absence of precipitation, an avalanche can occur as a result of processes of recrystallization of the snow layer (loosening and weakening of the strength of individual layers) and intensive melting under the influence of heat and solar radiation.
Optimal conditions for avalanches occur on slopes with a steepness of 30-40°. On such slopes, avalanches occur when the layer of freshly fallen snow reaches 30 cm. Avalanches form from old (stale) snow when the snow cover is 70 cm thick.
It is believed that a flat grassy slope with a steepness of more than 20° is dangerous for avalanches if the snow height on it exceeds 30 cm. Shrub vegetation is not an obstacle to avalanches. As slope steepness increases, the likelihood of avalanches increases. With a rough underlying surface, it increases minimum height snow, which can cause avalanches. A necessary condition for the avalanche to start moving and gain speed is the presence of an open slope 100-500 m long.
Snowfall intensity is the rate of snow deposition expressed in cm/hour. A thickness of 0.5 m of snow deposited in 2-3 days may not cause concern, but if the same amount of snow falls in 10-12 hours, widespread avalanches are possible. In most cases, the snowfall intensity of 2-3 cm/h is close to the critical value.
If, in calm conditions, avalanches cause a 30-centimeter increase in freshly fallen snow, then in strong winds, an increase of 10-15 cm can already be the cause of their descent.
The influence of temperature on avalanche danger is more multifaceted than the influence of any other factor. In winter at relatively warm weather When the temperature is close to zero, the instability of the snow cover increases greatly - either avalanches occur or the snow settles.
As temperatures drop, periods of avalanche danger become longer; at very low temperatures (below -18 °C) they can last up to several days or even weeks. In spring, the increase in temperature inside the snow layer is important factor, promoting the formation of wet avalanches.
The average annual density of freshly fallen snow, calculated from data over several years, usually ranges from 0.07-0.10 g/cm3, depending on climatic conditions. The greater the deviation from these values, the greater the likelihood of avalanches. High densities (0.25-0.30 g/cm3) lead to the formation of dense snow avalanches (snow boards), and unusually low snow densities (about 0.01 g/cm3) lead to the formation of avalanches of loose snow.
Based on the nature of the movement, depending on the structure of the underlying surface, avalanches are distinguished between wasps, flume and jumping avalanches.
Osov - separation and sliding of snow masses over the entire surface of the slope; he represents snow landslide, does not have a specific drainage channel and slides across the entire width of the area it covers. Clastic material displaced by wasps down to the foot of the slopes forms ridges.
Trough avalanche- this is the flow and rolling of snow masses along a strictly fixed drainage channel, which expands in a funnel-shaped manner towards the upper reaches, turning into a snow collection basin or snow collection (avalanche collection). Adjacent to the avalanche chute below is the alluvial cone - a zone of deposition of debris thrown out by the avalanche.
Bouncing Avalanche- This is the free fall of snow masses. Jumping avalanches arise from flume avalanches in cases where the drainage channel has steep walls or areas of sharply increasing steepness. Having encountered a steep ledge, the avalanche lifts off the ground and continues falling at a high jet speed; this often generates an air shock wave.
Depending on the properties of the snow that forms them, avalanches can be dry, wet or wet; they move through snow (ice crust), air, soil, or have a mixed nature.
Dry avalanches from freshly fallen snow or dry firn during their movement are accompanied by a cloud of snow dust and rapidly roll down the slope; Almost all avalanche snow can move this way. These avalanches start moving from one point, and the area covered by them during the fall has a characteristic pear-shaped shape.
Avalanches of dry compacted snow (snow boards) usually slide across the snow in the form of a monolithic slab, which then breaks into sharp-angled fragments. Often, a snow board that is in a stressed state cracks immediately due to subsidence. When such avalanches move, their frontal part becomes very dusty, as fragments of snow boards are crushed into dust. The separation line of the snow layer in the avalanche initiation zone has a characteristic zigzag shape, and the resulting ledge is perpendicular to the surface of the slope.
Wet avalanches from firnized snow (soil avalanches) slide along the ground, moistened by seeped melt or rainwater; When they descend, various debris materials are carried away, and avalanche snow has a high density and freezes together after the avalanche stops. With an intensive flow of water into the snow, catastrophic avalanches sometimes form from the snow-water and mud mass.
Avalanches also differ in the time of fall relative to the cause that caused the avalanche. There are avalanches that occur immediately (or within the first days) from intense snowfall, blizzards, rain, thaw or other sudden weather changes, and avalanches that arise as a result of the hidden evolution of the snow layer.
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