Mudflow. Conditions for the formation and development of mudflows

Mudflow source is a section of a mudflow channel or mudflow basin that has a significant amount of loose clastic soil or conditions for its accumulation, where mudflows originate under certain water conditions.

A mudflow (mudflow) is a name given to rapid channel flows consisting of a mixture of water and rock fragments that suddenly appear in the basins of small mountain rivers.

The immediate causes of mudflows are rainfall, intensive melting of snow and ice, breakthrough of reservoirs, earthquakes, and volcanic eruptions. Despite the variety of causes, the mechanisms of debris flow generation have much in common and can be reduced to three main types: erosion, breakthrough and landslide.

With the erosion mechanism of origin, the water flow is first saturated with debris due to the washout and erosion of the mudflow basin, and then the formation of a mudflow wave in the channel.

With a breakthrough mechanism of origin, a water wave, due to intense erosion and involvement of debris masses in the movement, immediately turns into a mudflow wave, but with variable saturation.

With a landslide-landslide initiation mechanism, when a massif of water-saturated rocks (including snow and ice) is washed away, the flow saturation and the mudslide wave are formed simultaneously (the saturation is immediately almost maximum).

Mudflows are: water-rock; water-sand and water-silt; mud; mud-stone; water-snow-stone.

A water-rock mudflow is a flow in which coarse material predominates. It is formed mainly in the zone of dense rocks.

Water-sand is a stream in which sandy and silty material predominates. Occurs mainly in the zone of loess-like and sandy soils during intense rainfalls, washing away huge amount fine earth.

Mud mudflow is close to water-silt mudflow. It is formed in areas where rocks of predominantly clayey composition occur.

A mud-stone mudflow is characterized by a significant content of clay and silt particles in the solid phase, with their clear predominance over the rock component of the flow.

A water-snow-rock mudflow is a transitional stage between the mudflow itself, in which the transport medium is water, and a snow avalanche.

The formation of mudflows is caused by a certain combination of geological, climatic and geomorphological conditions: the presence of mudflow-forming soils, sources of intensive soil watering, as well as geological forms that contribute to the formation of fairly steep slopes and channels.

The sources of solid components for mudflows are glacial moraines with loose filling, loose clastic material of screes, landslides, landslides, washouts, channel blockages and obstructions formed by previous mudflows, and woody plant material. The sources of water supply for mudflows are rains and downpours, glaciers and seasonal snow cover, and the waters of mountain rivers.

The most common mudflows are rain-fed mudflows, the main condition for the formation of which is the amount of precipitation that can cause the washout of rock destruction products and involve them in movement (Table 1.12).

Table 1.13

Conditions for the formation of rain mudflows

Regions of Russia	Daily maximum rainfall in mm at 20% probability	Minimum amounts of mudflow-forming precipitation, mm/day.
North Caucasus
Central Caucasus
Tien Shan
Pamir-Altai
Altai and Sayans
Cisbaikalia and Transbaikalia
Mountains of the northeast
Primorye
Amur region
Kamchatka

The formation of mudflows occurs in mudflow catchments, the most common form of which in plan is pear-shaped with a drainage funnel and a fan of hollow and valley channels that pass into the main channel. The mudflow catchment includes three main zones in which mudflow processes form and occur:

mudflow formation zone (mudflows fed with water and solid components);

transit zone (mudflow movement);

unloading zone (massive deposition of mudflows).

The areas of mudflow catchment areas range from 0.05 to several tens of square kilometers. The length of the channels ranges from 10-15 m (micro mudflows) to several tens of kilometers, and their steepness in the transit zone ranges from 25-30 (in the upper part) to 8-15 (in the lower part). At lower slopes, the process of deposition of mudflow mass begins. The mudflow movement stops completely at a slope of 2-5.

The result of the impact of a debris flow on various objects depends on its main parameters: density, speed, advancement, height, width, flow rate, volume, duration, inclusion size and viscosity.

The density of the mudflow depends on the composition and content of the solid component. Usually it is at least 100 kg. in one cubic meter of water, which with a rock density of 2.4-2.6 g/cm 3 leads to a density mudflows approximately 1.07-1.1 g/cm3. As a rule, the density of a mudflow fluctuates between 1.2-1.9 g/cm 3 .

The speed of movement of a mudflow in transit conditions (depending on the depth of the flow, the slope of the channel and the composition of the mudflow mass) ranges from 2-3 to 7-8 m/s, and sometimes more. The maximum speed can exceed the average by 1.5-2 times.

The height of the mudflow varies widely and can be: for powerful and catastrophic mudflows 3-10 m, for low-power mudflows - 1-2 m.

The width of the mudflow depends on the width of the channel and in most mountain basins in transit areas ranges from 3-5 m (narrow canyons, necks, deeply incised channels of small basins) to 50-100 m.

The maximum mudflow flow ranges from several tens to 1000-1500 m 3 /s.

The volume of mudflow deposits (the volume of loose clastic rock in its natural occurrence, removed from the mudflow source and channel) determines the zone of impact of the mudflow. As a rule, the total volume of debris flow determines the type of debris flow and its destructive effect on the structure. Most mudflow basins in Russia are characterized by mudflows of low and medium thickness.

The duration of mudflows ranges from tens of minutes to several hours. Most of the recorded mudflows lasted 1-3 hours. Sometimes mudflows can occur in waves of 10-30 minutes with non-mudflow intervals between them of up to several tens of minutes.

The maximum sizes of coarse inclusions are characterized by the size of individual blocks and boulders of rock and semi-rock, and can be 3-4 m in diameter. The mass of such blocks can be up to 300 tons.

The viscosity of coherent mudflows ranges from 3-4 poises (unit of dynamic viscosity (P). 1P = 0.1 Ns/m 3 =0.102 kgf) to several tens and sometimes hundreds of poises. With significant viscosity, mudflow resembles a thick concrete solution. The viscosity during the transition from a non-cohesive mudflow to a coherent one is approximately 2.5-4.0 poise.

Thus, the ranges of the main parameters of mudflows should be accepted:

density - (1.2-1.9)10 3 kg/m 3;

viscosity - 4-20 poise;

speed in transit conditions:

For slopes - 10-27 - 2.5-7.5 m/s;

Maximum possible - 14-16 m/s;

maximum slope of stopping movement - 2-5;

mudflow height: catastrophic up to 10 m;

powerful 3-5 m;

average  2.5 m;

low-power  1.5 m;

flow width in transit sections - 5-70 m;

flow rate (range) 30-800 m 3 /s, possible maximum 2000 m 3 /s;

duration 0.5-3 hours;

repeatability 15-20 years;

size of large inclusions 3-4 m;

mass of inclusions 200-300 tons.

Mudflow (mudflow) is a rapid mud or mud-stone flow, consisting of a mixture of water and rock fragments, suddenly appearing in the basins of small mountain rivers.

It is characterized by a sharp rise in water level, wave movement, short duration of action (on average from one to six hours), and a significant erosion-accumulative destructive effect.

Mudflows pose a threat to populated areas, railways, roads and other structures located in their path.

The immediate causes of mudflows are heavy rains, intense snow melting, outbursts of reservoirs, and, less commonly, earthquakes and volcanic eruptions.

Classification of mudflows

All if, according to the mechanism of origin, are divided into three types: erosion, breakthrough and landslide-landslide.

With erosion, the water flow is first saturated with debris due to the washout and erosion of the adjacent soil, and then a mudflow wave is formed.

Breakthrough is characterized by an intensive process of water accumulation, at the same time rocks are eroded, a limit is reached and a breakthrough of a reservoir (lake, intraglacial reservoir, reservoir) occurs. The mudflow mass rushes down the slope or river bed.

During a landslide, a mass of water-saturated rocks (including snow and ice) is torn away. The flow saturation in this case is close to maximum.

Each mountain region has its own causes of mudflows. For example, in the Caucasus they occur mainly as a result of rains and downpours (85%).

In recent years, the natural causes of mudflows have been supplemented by technogenic factors, violation of the rules and regulations of mining enterprises, explosions during the construction of roads and the construction of other structures, logging, improper conduct of agricultural work and disturbance of soil and vegetation cover.

When moving, a mudflow is a continuous stream of mud, stones and water. The steep leading front of a mudflow wave with a height of 5 to 15 m forms the “head” of a mudflow. Maximum height The shaft of the water-mud flow sometimes reaches 25 m.

The classification of mudflows based on the causes of occurrence is given in Table. 2.4.

In Russia, up to 20% of the territory is located in mudflow zones. Mudflows are especially active in Kabardino-Balkaria, North Ossetia, Dagestan, in the Novorossiysk region, Sayano-Baikal region, in the area of ​​the Baikal-Amur Mainline, in Kamchatka within the Stanovoy and Verkhoyansk ranges. They also occur in some areas of Primorye, the Kola Peninsula and the Urals. Back in 1966, more than 5 thousand mudflow basins were registered on the territory of the USSR. Currently, their number has increased.

Table 3. Classification of mudflows based on the root causes

	Root Causes	Distribution and origin
1. Rain	Showers, prolonged rains	The most widespread type of mudflows on Earth is formed as a result of erosion of slopes and the appearance of landslides
2. Snow	Intense snowmelt	Occurs in the mountains of the Subarctic. Associated with the breakdown and waterlogging of snow masses
3. Glacial	Intensive melting of snow and ice	In high mountain areas. The origin is associated with the breakthrough of melted glacial waters
4. Volcanogenic	Volcanic eruptions	In areas of active volcanoes. The largest. Due to rapid snowmelt and outburst of crater lakes
5. Seismogenic	Strong earthquakes	In areas of high seismicity. Rupture of soil masses from slopes
b. Limnogenic	Formation of lake dams	In high mountain areas. Dam destruction
7. Anthropogenic direct impact	Accumulation of technogenic rocks. Poor quality earthen dams	At dump storage areas. Erosion and sliding of technogenic rocks. Dam destruction
8. Anthropogenic indirect impact	Disturbance of soil and vegetation cover	In areas where forests and meadows are cleared. Erosion of slopes and channels

Based on the main factors of occurrence, mudflows are classified as follows: zonal manifestation - the main factor of formation is climatic conditions (precipitation). They are zonal in nature. The convergence occurs systematically. The paths of movement are relatively constant; regional manifestation ( main factor formations - geological processes). The descent occurs sporadically, and the paths of movement are not constant; anthropogenic - this is the result of human economic activity. Occur where there is the greatest load on the mountain landscape. New mudflow basins are formed. The gathering is episodic.

Classification by power (based on transferred solid mass):

Powerful (strong power), with the removal of more than 100 thousand m3 of materials. Happens once every 5-10 years.

Medium capacity, with removal from 10 to 100 thousand m3 of materials. Happens once every 2-3 years.

Low power (low power), with removal of less than 10 thousand m3 of materials. They happen every year, sometimes several times a year.

The classification of mudflow basins by the frequency of mudflows characterizes the intensity of development or its mudflow activity. Based on the frequency of mudflows, three groups of mudflow basins can be distinguished:

high mudflow activity (with recurrence once every 3-5 years or more);

average mudflow activity (with recurrence once every 6-15 years);

low mudflow activity (with a frequency of once every 16 years or less).

Mudflows are also classified according to their impact on structures:

Low-power - small erosion, partial blocking of openings in culverts.

Medium power - severe erosion, complete blocking of holes, damage and demolition of foundationless buildings.

Powerful - great destructive force, demolition of bridge trusses, destruction of bridge supports, stone buildings, roads.

Catastrophic - complete destruction of buildings, sections of roads along with the road surface and structures, burial of structures under sediments.

Sometimes a classification of basins is used based on the height of the sources of mudflows:

alpine. The sources lie above 2500 m, the volume of discharge from 1 km2 is 15-25 thousand m3 per mudflow;

mid-mountain. The sources lie within the range of 1000-2500 m, the volume of removal from 1 km2 is 5-15 thousand m3 per mudflow;

low mountain. The sources lie below 1000 m, the volume of discharge from 1 km2 is less than 5 thousand m3 per mudflow.

Landslides (mountain landslides) are the separation and catastrophic fall of large masses of rocks, their overturning, crushing and rolling down on steep and steep slopes.

Landslides of natural origin are 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 processes, erosion, dissolution and the action of gravity. The formation of landslides is facilitated by: the geological structure of the area, the presence of cracks and zones of crushing rocks on the slopes. Most often (up to 80%) modern collapses are associated with the anthropogenic factor. They are formed mainly during improper work, during construction and mining.

Landslides are characterized by the power of the landslide process (volume of falling rock masses) and the scale of manifestation (involvement of area in the process).

According to the power of the landslide process, landslides are divided into large (rock detachment of 10 million m3), medium (up to 10 million m3) and small (rock detachment of less than 10 million m3).

According to the scale of manifestation, landslides are divided into huge (100-200 ha), medium (50-100 ha), small (5-50 ha) and small (less than 5 ha).

In addition, landslides can be characterized by the type of collapse, which is determined by the steepness of the slope of the rockfall masses.

Landslides, mudflows, landslides cause great damage national economy, the natural environment, lead to human casualties.

Main damaging factors landslides, mudflows and collapses are impacts of moving masses of rocks, as well as the collapse and flooding of previously free space with these masses. As a result, buildings and other structures are destroyed, settlements, economic facilities, agricultural and forest lands are hidden by rock layers, river beds and overpasses are blocked, people and animals die, and the landscape changes.

Landslides, mudflows and landslides on the territory of the Russian Federation occur in mountainous regions North Caucasus, Urals, Eastern Siberia, Primorye, Sakhalin Island, Kuril Islands, Kola Peninsula, as well as along the banks of large rivers.

Landslides often lead to large-scale catastrophic consequences. Thus, a landslide in Italy in 1963 with a volume of 240 million m3 covered 5 cities, killing 3 thousand people.

In 1982, a mudflow 6 km long and up to 200 m wide hit the villages of Shiveya and Arenda in the Chita region. As a result, houses, road bridges, 28 estates were destroyed, 500 hectares of cropland were washed away and covered, and people and farm animals also died. The economic damage from this mudflow amounted to about 250 thousand rubles.

In 1989, landslides in Checheno-Ingushetia caused damage to 2,518 houses, 44 schools, 4 kindergartens, 60 healthcare, cultural and public service facilities in 82 settlements.

Mudflows consist of large masses of destroyed rocks in a loose state, which accumulate over years at the bottom of gorges and steep slopes. During intense downpours or during the outburst of glacial lakes located above, mud-stone mudflows are formed and flow down, destroying everything in its path.
In mountainous areas, heavy rainfall or rapid snowmelt causes the formation of temporary torrential streams. A powerful stream flowing down steep slopes has enormous force and, like mountain rivers, carries along small rock fragments, large blocks and boulders. Acting like a battering ram with captured debris, such a stream destroys the ledges and unevenness of the mountains encountered along the way, carries them along with it and becomes more and more saturated with stone material.

Next, the flow captures the upper layers of fine-clastic material and soils and gradually turns from water into mud-stone. Such a flow is called mudflow or silt. Temporary mud-stone flows are widespread in the Caucasus and Central Asia. The content of transported material in debris flows is very high and sometimes exceeds the water content. Erupting from a mountain gorge onto the plain, the mudflow quickly loses speed and spreads out over a relatively large area in the form of an alluvial cone. Water from a mudflow flow is filtered to its base, and the transported rock material is deposited to form a fan or dry delta.

Mudflows are a mixture of soil, stones and water with a fairly high density of 1.2-1.9 t/m³, which flows down the beds of various mountain rivers and dry valleys after rainstorms at a speed of up to 6 m/s. When leaving the ravine, in places where the slope decreases, the velocity of the mudflow also decreases and an alluvial cone is formed.

The detrital mass brought by such a flow consists of almost unrounded fragments and is completely unsorted: among large blocks and boulders there are gravel-sand-clay particles. Deposits of debris flow cones are called proluvial or proluvium. Debris flows pose a great danger to populated areas located in their zone of action. The famous mudflow of 1921, which burst out of a mountain gorge near Almaty, demolished all the buildings located at the foot of the mountain. Then he burst into the city, turning the streets into raging mud-stone rivers.

Houses were torn off their foundations and carried away along with people. A mass of stone material of about 1.5 million tons was carried into the city.

Figure-1. Destruction of populated areas caused by mud-stone flows

Mudflows arise suddenly and last a relatively short time, lasting a few hours, but are capable of forming significant volumes of mud-stone materials that are washed away in one mudflow. A mudflow is capable of washing away and carrying stones with a diameter of up to 1.5 meters. Considering the high speed of the mudflow and the volume of transferred stones, the protection of cities and villages, as well as various structures located in the action area, is a big problem.

To solve such problems, it is necessary to erect expensive and complex structures such as retaining walls or dams. Depending on how much water the mud-stone flows contain, the mudflow can move as a homogeneous viscous mass or as a turbulent flow of water, stones and mud. The stream carries along a huge number of stones of various diameters and washes away huge volumes of soil from the surface. In a mudflow, small stones move in suspension, while larger ones move by rolling along the bottom of the thalweg.

Methods for protecting buildings from mudflows

Mountain rivers and mudflows are capable of carrying stones of enormous size and in large quantities, which can pose a threat not only to various structures and communications such as bridges, roads, but also to nearby cities. If construction is inevitable in the area where mudflows form, various measures are taken to protect structures from mudflows.

For example, bridges are built with spans that do not restrict the flow of mudflows, and single-column supports are used. The openings of bridges are significantly increased, since it is difficult to predict the volume of mudflows, which vary depending on the amount of precipitation. The openings of small bridges quickly become clogged with sediment and in this case the mudflow flows over the bridge and embankment.

In order to protect cities and large structures of great importance, sediment-retention dams are installed on the upper side of mountain slopes. Such dams slow down the speed of mudflows and cause sediment deposition. There are two types of dams: continuous and intermittent. Continuous dams are built when the width of the river bed exceeds 100 meters.

In this case, the required length of the dam depends on the width of the channel and also on the size of the particles that mudflows deposit. The length of the dam in this case is determined by the formula:

L=b*B, where b is the coefficient of restriction of the channel by the dam, B is the width of the channel.

Intermittent type dams are built when the channel width is up to one hundred meters. In this case, the length of the dam is determined by the formula and the dam opening is determined depending on the passage required quantity mudflows with a given frequency. In the transverse profile, such dams are built with a trapezoidal cross-section. The width of the dam at the top ranges from 0.5 to 2.0 meters, depending on the size of the transferred stones and the intensity of the mudflow.

Figure-2. Construction of partition walls to combat mudflows

A measure to combat mudflows is, first of all, the restoration of vegetation cover with a powerful root system, as well as the installation of partition walls (Figure 2). The construction of terraces can be used as an anti-mudflow measure (Figure 3).

Figure-3. Terracing scheme to combat mudflows

Along the terraced slope, the mudflow will flow from step to step, ending up in the ditches prepared for it. IN lately To combat mudflows, dams constructed using the directed explosion method are used. For example, such a dam was created in 1966 in the Medeo tract in the mountains near Alma-Ata. With the help of an explosion, almost 2 million tons of rock were placed into the dam. Along with mudflows, there are channelless flows from slopes. A complex of loose formations that accumulate at the foot of mountains as a result of temporary mountain flows washing away the clastic material that appears during the weathering of the bedrock composing these mountains is called proluvium.

Table-1. Comparison of properties of water-continental sediments

Proluvium is characterized by poorly sorted and weakly rounded fragments. It forms alluvial cones that can merge into one strip bordering the base of the mountains. The difference in power, duration of action and direction of water flows determines the difference in the properties of the rocks they deposit.

This difference is most clearly visible from the comparison shown in Table 1. From Table 1 it is clear that with a fairly close mineralogical and granulometric composition various types fluid deposits surface waters have different properties. This should be taken into account when designing and constructing structures.

Classification of mudflows

The study of the formation and action of mudflows made it possible to classify them according to a number of characteristics. According to the research of E.K. Rabkova, it is possible to distinguish between coherent or structural mudflows, turbulent-flowing water-stone and turbulent-flowing mud-stone. Structural or cohesive mudflows form in mountainous areas. IN geological structure The presence of clay rocks and clays is mandatory in the drainage basin. In addition, there are rocks that can produce screes and difficult-to-crush fragments: limestones, shales, crystalline rocks.

The volumetric mass of the flow is very high and amounts to 1.9-1.6 t/m³. Clay fractions make up no more than 25-30% of the solid part of the flow. The rest consists of sand, crushed stone, gravel and boulders. Water is included in the mudflow mass as one of the components. To maintain the movement of the flow, a rectilinear direction is necessary, without bends. Such a flow moves as one structural whole and, when stopped, freezes without breaking up into its component parts. Structural flows destroy all structures and other obstacles encountered along the entire width of the movement. With slopes of 0.05-0.06 degrees on the alluvial cone, the bottom of the channel is covered with a layer of frozen mudflow.

Turbulent-flowing water-stone mudflows also form in mountainous zones. The drainage area of ​​such flows is composed of intrusive rocks, as well as limestones, sandstones and well-cemented conglomerates. The presence of coarse material: gravel, pebbles, coarse sand is also possible. The presence of clayey rocks is not significant. The volumetric mass of the mudflow in such streams it is 1.6-1.3 t/m3. The stream is poorly saturated with fine earth. Individual boulders and boulders reach 1-2 m in circumference. The nature of the movement of individual flow waves is pulsating and jammed. The presence of large fragments and the jammed nature of the movement determines a large destructive force. Some sorting of the carried out material is possible on the alluvial cone.

Turbulent-flowing mud-stone mudflows are formed in both mountain and foothill zones. The drainage area is characterized by a predominance of fine-clastic and clastic material, sandy loam and loam. The presence of a large amount of crushed stone and pebbles is noted. The volumetric mass of the mudflow is relatively small and amounts to 1.4-1.05 tons /m³. The flow is saturated with suspended fine fractions and pebbles drawn along the bottom.

The deposition of large masses on the alluvial cone leads to the flow overflowing the barriers, accompanied by the destruction of roads, bridges and other structures. Unlike structural flows, destruction occurs not by impact, but by erosion. The nature of the flow movement is congestion-free. At the removal cone, some sorting of the drawn material by size occurs.

Table-2. Main types of mudflows and possible causes

Main types of mudflows and possible causes

Classification of mudflows according to the granulometric composition of the solid component:

1. Water-stone - is a mixture of dirty water with stones large sizes(rock fragments, boulders, etc.) with a volumetric weight of 1.1–1.5 t/m³. The water-rock flow is formed mainly in the zone of dense rocks.

2. Mud - is a mixture of dirty water with particles of clay and silty soil in the solid phase with a slight concentration of stones. Volumetric weight ranges from 1.5-2.0 t/m³.

3. Mud-stone flow is a mixture of water with particles of fine earth and stones of predominantly small size. The volumetric weight of such a flow is 2.1–2.5 t/m³.

4.Water-snow-rock consists mainly of water, snow avalanches and stones of different sizes. Such a mudflow is very heavy and the mudflow reaches up to 5–12 t/m².

Classification of mudflows by genesis:

1. Alpine type - this type is characterized by seasonal rapid melting of snow (Canada, USA, Andes, Himalayas, Alps)

2. Desert type - found mainly in semi-arid or arid areas that experience sudden heavy rainfall. Most often observed in areas such as Arizona, Nevada, California.

3. Lahars are mud flows of volcanic origin that appear on the slopes of volcanoes after heavy torrential rains.

The following mudflows are distinguished based on their frequency:

a) high activity (repeated within 3-5 years and maybe more often)

b) average activity (repeated within 6-15 years)

c) low mudflow activity (repeated once every 16 years).

By impact on structures:

1. Low-power - they create small erosions at the base and clog the culverts of structures.

2. Medium-power - they create strong erosion at the base of bridges and culverts, completely clog the openings of culverts. They can also demolish foundationless structures.

3. Powerful and has great destructive power. It can demolish bridge trusses, supports of bridges and overpasses, and also destroy roads.

4. Catastrophic - completely destroys buildings and sections of roads.

By water source:

1. Rain - such mudflows are typical for low-mountain and mid-mountain mudflow basins that do not have glacial feeding. The conditions for the formation of these mudflows are heavy rainfall, washing away destroyed rocks from the slopes.

2. Glacial - they are characterized by low-mountain and mid-mountain mudflow basins without glacial feeding. They are formed due to heavy precipitation that can wash away the products of rock destruction.

3. Volcanogenic - formed mainly during earthquakes. Sometimes in some cases they are formed during a volcanic eruption.

4. Associated mudflows - can consist of water, sandy and clayey soil particles. The mudflow moves as one whole and does not follow the bends of the river bed, but flows over the banks. In some cases, it can destroy and straighten river beds.

5. Unbound flows are capable of moving at high speed, while constant rolling of stones and abrasion occurs due to frequent collisions. The flow usually follows the river bed, destroying it in places and repeating its bends.

By volume of transferred solid mass:

According to the main factors of occurrence

1. Zonal manifestation. They are formed due to heavy precipitation and are of a zonal nature. As a rule, mudflows occur systematically along the same paths.

2. Regional manifestation. They are formed due to geological processes. As a rule, the paths of movement of mudflows are not constant and the flow is episodic.

3. Anthropogenic. Occur as a result of human economic activity.

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Debris flows, or mudflows, are widespread in most mountainous areas of the world. Mudflows are destroying settlements, enterprises, railways and roads, communication and power lines, destroy orchards and vineyards, and cause great damage to other agricultural lands. There are numerous cases of disasters accompanied by human casualties. The fear instilled by mudflows is so great that mountain residents call them the “Black Death.” Annual losses from mudflows in the USSR amount to up to 100 million rubles. per year.

Considering the danger of mudflows and the damage they cause, the Central Committee of the CPSU and the Council of Ministers of the USSR, in the resolution on combating water and wind erosion (1967), paid great attention to the tasks of combating mudflows and ways to solve them.

According to Prof. S. M. Fleishman, in the USSR, mudflow danger threatens more than 50 cities, of which 5 are the capitals of the union republics (Alma-Ata, Yerevan, Frunze, Dushanbe, Tbilisi). On the territory of our country, mudflows occur in almost all mountainous regions from the Arctic to the subtropics: in the Crimea, the Carpathians, the North Caucasus, the Transcaucasus, the Pamirs, Tien Shan, Altai, Sayan Mountains, Sakhalin, Kamchatka, the Kuril Islands, in the mountains of the Kola Peninsula , on the Verkhoyansk Range, Chersky Highlands, Okhotsk-Kolyma Highlands, Franz Josef Land, Novaya Zemlya, etc. The total number of mudflow-prone basins in the USSR, according to engineer. I. I. Kherkheulidze, exceeds 5 thousand.

In the history of disasters caused by mudflows on the territory of the USSR, a powerful mudflow that hit Alma-Ata in the summer of 1921 occupies a special place.

The winter of 1920/21 and the spring and early summer of 1921 in Alma-Ata were heavy with precipitation. In 9 months, they fell 130 mm more than the average for the whole year. In the Trans-Ili Alatau mountains, at the foot of the northern slope of which the city is located, a lot of snow has accumulated. In June the heat reached thirty degrees and the snow began to melt quickly. On June 8, 1921, in the afternoon it began to rain, which soon turned into downpour. Three hours later, the rain stopped, and there was silence and evening coolness.

And suddenly the residents heard a loud noise. It resembled the noise of an approaching train, but was much louder. From the side of the mountains towards Alma-Ata there was a water shaft 4-5 m high, carrying earth, silt, snow and large trees uprooted from the mountains. The first blow of this powerful stream fell on the country houses located at the very foot of the mountains. He demolished them like houses of cards, destroyed the orchards and, picking up logs, boards, people and animals, rushed further towards the city. The stream moved along the old river bed. Malaya Almaatinka, filled up and leveled, along which the street named after Karl Marx was laid. Breaking through the channel anew, the stream invaded the central part of the city, demolishing and destroying houses or moving them from their foundations. In the darkness of the night, the streets turned into raging rivers. The shafts of mud-stone flow followed one after another at intervals of 30 - 60 s. The stream carried huge boulders that continued to destroy buildings, and viscous mud was deposited along the entire path, burying people and animals in these deposits. The width of the stream reached 200 m, and the height of its shafts reached 8 - 10 m.

The mudflow caused enormous damage to the city. About 500 houses were damaged, and 20 were completely destroyed. The flow brought about 5 million tons of mud-stone material to Alma-Ata and its suburbs. The fields, gardens and vegetable gardens were covered with a layer of mud, similar to concrete when frozen and up to 1.5 - 2 m thick.

Catastrophic mudflows are repeated at certain intervals. Before the described incident, similar mudflows struck Alma-Ata twice - in 1841 and 1887.

A catastrophic mudflow went down the river. Malaya Almaatinka also in August 1951. The Malaya Almaatinka River originates from the Tuyuk-Su glacier (Trans-Ili Alatau), which has a length of 5.5 km and an area of ​​4.4 km 2. Just like other glaciers, a moraine lies at the tongue of the Tuyuk-Su glacier - a large accumulation of rock fragments transported by the glacier and deposited at the melting site. In the summer of 1951, part of the moraine settled, creating a hollow in which rainwater began to accumulate, forming a lake. Water from the lake penetrated into the moraine and began to saturate it. A strip of moraine, saturated with water, having a length of 600 - 700 m, a width of 50 - 60 m and a height of 15 - 20 m, began to slide, broke off and collapsed into the river. Malaya Almaatinka. A powerful mudflow formed, which carried out about 200 thousand m 3 of mud-stone material, including blocks weighing up to 2 tons. Having gone down the riverbed to the Medeo rest house, the mudflow carried away and broke all the bridges for 10 km.

Another mudflow disaster is widely known, which also occurred in Kazakhstan in the Trans-Ili Alatau mountains, 50 km from Almaty. Here, at an altitude of 1788 m above sea level, there was one of the most beautiful lakes in the world - Issyk. The slopes of the mountains overgrown with vegetation descended to the emerald water, and the peaks, white from snow, rose in a surprisingly blue sky. The beauty of the lake attracted many tourists every year. Lake Issyk arose several thousand years ago as a result of a gigantic landslide, which blocked the river bed and formed a dam. On July 7, 1963, another disaster destroyed the lake. E. M. Kalmykina and A. P. Gorbunov talk about it this way.

The disaster was caused by a mudflow that descended along the river. Zharsai - tributary of the river. Issyk (Fig. 44). Zharsai originates from two large glaciers, which have accumulated a huge moraine in the upper reaches of the river with a volume of several tens of millions of cubic meters. In the summer of 1963, a collapse that occurred on one of the glaciers created a dam, which then accumulated a lake of melt water. On July 7, water from the lake broke through the dam and rushed down the riverbed, capturing moraine material.

River valley Zharsai has a large slope in the upper reaches (325 m per 1 km). Therefore, the mudflow developed a significant speed (up to 10 km/h). He rushed along a winding riverbed, paused at obstacles, rolled over them and rushed on. Having reached the lake. Issyk, a mudflow crashed into him. Fountains of water shot up, and waves up to 12 m high ran across the surface of the lake. Under the impact of the waves, the dam that once caused the formation of the lake broke. The waters rushed into the breakthrough and rushed further along the river bed. Issyk. After 5 hours the lake ceased to exist. More than 18 million m3 of water flowed out of it, taking with it 2 million m3 of stone material. The mudflow not only destroyed the lake, but also changed the entire appearance of the Issyk gorge, destroyed boat piers, boats, boats, and destroyed the road. Fortunately, the hotel where people were at that time, the dining room, shops, and service buildings were not damaged.

There are also other cases of disasters that are very similar in cause and nature to the catastrophe that destroyed the lake. Issyk. Such, for example, is the catastrophe that caused the death of the lake. Yashilkul, located at an altitude of 2600 m above sea level in the mountains of the Kichikalai ridge bordering the Fergana Valley (Uzbekistan). This lake was formed several centuries ago by a grandiose landslide, which created a rocky dam-dam, which then accumulated about 15 million m3 of water. In June 1966, due to the abundant melting of snow in the mountains, the water in the lake began to quickly rise, overflowed it, began to erode, and then broke through the dam. A powerful mudflow broke out through a breakthrough and passed along the river. Isfayramsay, located below the lake, flooded a significant part of the Fergana Valley and deposited the mud there. The lake was destroyed.

The Georgian Military Road is periodically subject to the destructive effects of mudflows. In the 50s and 60s this happened three times - in 1953, 1958 and 1967. The summer of 1967 was very rainy. In the area of ​​the Daryal Gorge, the annual norm of precipitation fell in June and July. On the night of August 5-6, p.m. A powerful mudflow occurred along the Terek River, eroding the river bed and destroying bank protection structures. It caused great damage to the Georgian Military Road and nearby structures. The roadbed was washed away, bridges and pipes were washed away, the roadway was littered with rock debris and boulders with a diameter of 2.5 - 3 m. The mudflow tore steel pipe the gas pipeline laid here destroyed residential buildings and outbuildings in the village. Upper Lare, damaged the headworks of the Ezminskaya hydroelectric power station. For three hours, while the mudflow continued, the water flow in the river. Tereke increased 30 times, amounting to 1500 m 3 /s. For 20 km from the place where the mudflow came down from the mountains, in the riverbed. The Terek River deposited several million cubic meters of stone materials and mud brought by the mudflow.

Mudflows are common not only in the USSR. For example, in the USA, mudflows are observed in the states of California, Utah, Nevada, Wyoming, Colorado, Virginia, Washington, Idaho, Oregon and Alaska. The Los Angeles area is especially famous for its mudflow disasters. This is a city with a population of more than 3 million people. covers an area of ​​50X80 km and is located on a plain near the coast Pacific Ocean near the San Gabriel mountain range (spurs of the Cordillera), the height of the peaks of which reaches 3 thousand m. The area is rich in sediments. Showers over the coastal plain and in the mountains are more intense. For example, a rainstorm that began on December 29, 1933 lasted 53 hours and produced 292 mm of precipitation, and in 1943 650 mm of precipitation fell per day. Water falling in the mountains rushes into Los Angeles and its suburbs in powerful mudslides, causing destruction, loss of life and damage. The catastrophes that occurred in 1934 and 1938 were especially large.

The mudslide that struck Los Angeles on January 1, 1934 was preceded by a heavy and prolonged rainstorm. In two days the amount of precipitation exceeded the annual norm. Streams of water rushed from the mountain slopes, carrying earth, stones and large trees uprooted. The flows came in shafts up to 6 m high, demolishing buildings or breaking through walls. Roads were destroyed and littered with stones, more than 400 houses and about 500 bridges were damaged, and 200 houses were completely destroyed. The number of casualties was 84. In March 1938, a catastrophic mudflow, also caused by a rainstorm, interrupted Los Angeles's communications with the outside world for several days. Railways and roads were destroyed, telegraph and telephone lines were destroyed, and many bridges and buildings were demolished. The mudflow brought about 11.5 million m 3 of mud-stone material to the city. Losses caused by the mudflow amounted to $50 million. 200 people died, and 10 thousand were left homeless.

The destructive power of mudflows is explained by the fact that they move at high speed and carry a huge amount of varied material, and sometimes very large objects. The speed of movement of mudflows, depending on the depth of the flow, the slope of the channel and the consistency of the mudflow mass, ranges from 2 - 3 to 7 - 8 m/s.

The high speed of mudflows is determined by the steep slopes of the ravines along which they move and the considerable length of the acceleration sections. For example, in high mountainous areas mudflows rarely form at an altitude of up to 2500 - 3000 m above sea level and descend from there into valleys where the terrain has an altitude of only 500 - 700 m above sea level. Running this path, the flow acquires enormous kinetic energy. The pressure of mudflows when hitting an obstacle reaches 15-30 tf/m2, or 150,000-300,000 Pa.

The channel along which a mudflow moves is usually winding and has a variable width. At sharp turns or in narrow places, trees get stuck, stones pile up, and silt and soil accumulate. The flow lingers briefly at the jam, then breaks through or passes through it and rushes forward with renewed vigor. This intermittent nature of the movement causes the formation of shafts (waves) often of great height. Thus, the height of the mudflow shafts that occurred on the night of August 17-18, 1891 in Tyrol at the foot of the Austrian Alps reached 18 m.

Mudflows vary in composition. If a stream consists mainly of water and stones with only a small admixture of earth particles, it is called water-rock. If, along with stones, it carries a lot of earth and silt, such a stream is called mud-stone. Streams without stones, only liquid mud, are called mud streams. The composition of a mudflow depends on the nature of the material that the water picks up and carries with it as it flows from the mountains. So, I sat down on the river. Issyk in 1963 consisted of two streams. Along the river Zharsayu in the lake. A typical mud-stone flow descended from Issyk, saturated with moraine material picked up from the glaciers. From the lake, a stream of water and stones rushed further, carrying material from the dam, which it destroyed.

Mudflows can transport huge stone blocks (Fig. 45). For example, a mudflow in Almaty in 1921 carried away rock fragments weighing up to 14 tons.

A powerful mudflow that passed along the river valley on August 13, 1953. Chkheri (Caucasus), carried a block of stone measuring 71 m 3 weighing about 190 tons.

Rivers and streams always carry some amount of silt, clay particles, sand, and pebbles. Lighter particles are transported in water in suspension, while heavier ones roll along the bottom. The nature of the movement of particles in water is similar to the movement of snowflakes in air flow. Saturation of a water stream with suspended particles changes its properties. The density of a liquid saturated with earthy particles is significantly greater than the density of pure water. If the density of water is 1 g/cm3 (at + 4°C), the density of mudflows ranges from 1.2 to 1.8 g/cm3, and according to some scientists even reaches 2.6 g/cm3. Most rocks have a density ranging from 2 to 2.7 g/cm 3 . It is known from hydraulics that a force acts on a body immersed in a fluid, equal to weight displaced liquid and directed vertically upward. This force is called supporting force. High-density mudflows also have a significantly greater supporting force than clean water. In addition, mudflows have high viscosity* (so-called internal resistance liquid when one layer moves over another). Examples of liquids of different viscosities include water, jam syrup, castor oil, glue. If these liquids are spilled on an inclined surface, they will flow along it at different speeds.

*(Examples of liquids of different viscosities include water, jam syrup, castor oil, and glue. If these liquids are spilled on an inclined surface, they will flow along it at different speeds.)

Due to their significant density and high viscosity, mudflows retain large boulders. M.V. Muratov observed in the North Caucasus in the upper reaches of the river. Hasout boulders the size of a football and larger, floating in a mudflow. With a very high viscosity, the mud-stone flow looks like a thick concrete solution with large stones included in it.

For the formation of mudflows, certain conditions are required. First of all, a powerful water flow is needed. This happens during intense downpours, rapid melting of large masses of snow and ice, or when water that has accumulated in large quantities breaks through. In addition, you need a sufficient supply of loose clastic materials that the flow can pick up and carry with it in order to turn from water to mudflow. This accumulation of loose materials occurs during weathering processes or as a result of the transport of rock fragments by glaciers, as well as during landslides, landslides and screes. Finally, the terrain needs to have a steep enough slope to allow the flow to reach high speeds. Such slopes and narrow winding channels, where mudflows can move at high speed, are found in mountainous areas. It is in the mountains that a combination of all the conditions described above is observed.

Therefore, mudflows are a common occurrence in most mountainous areas.

The formation of mudflows is facilitated by deforestation on mountain slopes. The forest protects the mountain slopes from wind and strong heat sun rays. The root system of trees and shrubs and thick grass secure the soil cover and prevent it from being washed away. On bare mountain slopes, weathering processes occur much faster than on slopes covered with dense forest. Therefore, one of the important measures to combat mudflows is to prohibit deforestation in mudflow-prone areas.

A system of special engineering measures to protect against mudflows has also been developed. First of all, they strive to weaken the energy of the flow or stop its movement before it approaches the protected object (for example, a road). Terraces are arranged across steep mountain slopes parallel to one another at a distance of 15 - 20 m.

The slope turns into a gentle staircase, which slows down the flow of water and traps stones.

A system of dams (barrages) is also installed in the channel along which the mudflow usually flows (Fig. 46). To do this, stone or concrete walls with a height of 2 to 5 m are erected across the channel at a certain distance from each other. This creates a kind of “staircase” that slows down the flow and reduces its speed. As a result, transported stones and particles of earth are deposited near the walls blocking the channel. Thus, dams, on the one hand, weaken the energy of the flow, on the other, free it from sediment.

To free the stream from sediment, which is especially important in cases where the mudflow carries large boulders, large pits called sediment traps are dug. Passing through such a nano-trap, the flow deposits the stones it carries and moves on, deprived of the most formidable means of destruction.

The mudflow can also be diverted away from the protected object if there is a suitable channel nearby. For this purpose, a diversion canal is laid or a drainage dam is built (Fig. 47). Hitting such a dam, the mudflow changes direction and goes into a new channel.

After repeated disasters caused by mudflows in the Los Angeles area, major work was launched to protect the city and region from mudflows and floods. The following were built: 20 flood control dams, 105 mudflow reservoirs, 28 settling tanks, a storm drainage system stretching 2.6 thousand km and 32 pumping stations. In addition, breakwaters were built and canals and watercourses were strengthened. The work was completed in 1968, and on January 18, 1969, a rainstorm began that lasted 9 days. More than 330 mm of precipitation fell in Los Angeles. Mudflows rushed from the mountains, but the system of mudflow protection measures worked reliably and the city was protected.

But particularly ambitious works to protect against mudflows were carried out in the Almaty region.

In October 1966, a giant protective dam blocked the Medeo tract, located in the Trans-Ili Alatau mountains, 18 km from Almaty. It was created by an explosion to “dump” rocks from nearby slopes to protect the capital of Kazakhstan from mudflows. A huge charge - 5,268 tons of explosives - made it possible to bring down more than 2.5 million m 3 of stone materials. The resulting dam was 61 m high at its lowest point and approximately 500 m wide at its base.

With the help of excavators and bulldozers, the dam was then given the required shape.

The explosions in Medeo were not only an important practical measure to protect Almaty from mudflows. At the same time, they were also a major scientific experiment by Soviet scientists. Formation of dams using directed explosions - new method in hydraulic engineering. Before the gigantic experiments at Medeo, this method raised many doubts. It was unclear how resistant such a dam would be against water seepage. It was feared that due to the lack of a dense waterproof clay core inside the dam, water would filter through the dam and gradually erode it.

The theory of such explosions has not been developed, which would make it possible to determine how the exploded mass of rock will be located, to calculate the size of the charge, the depth of its placement and to determine other data necessary to create a dam of the required size in the required location.

The possibility of the formation of a strong seismic wave, which, as was assumed, could reach Almaty and cause destruction there, also raised concerns. The experience went well. The dam was formed in a place determined by calculation; and had the required dimensions. The vibrations of the soil in Almaty were felt only by instruments.

On April 14, 1967, a second explosion was carried out in the same place. With the help of 3941 tons of explosives, more than 1 million m 3 of rocks were dropped and placed into the body of the dam. The height of the dam increased by another 30 m.

In July 1973, the giant Almaty dam underwent a very serious test. Hot weather in the first half of 1973 caused intense melting of the glaciers feeding the river. Malaya Almaatinka. Due to the increased influx of water, the moraine bridge between two neighboring glacial lakes was broken. The water rushed down, taking with it loose moraine material. The resulting mudflow was initially small (with a flow rate of about 30 m 3 /s), but, having descended 2 km along the riverbed, it encountered a gabion dam about 8 m high on its way to the Mynzhilki tract. Water accumulated at the dam and then broke through it; in 3 - 4 minutes, about 40 thousand m 3 of water came down through the breakthrough. The stream raised sand, pebbles, and large stones; the water even rolled large blocks up to 4 m in size. The resulting secondary mudflow with a flow rate of more than 1000 m 3 /s was already catastrophic. The mudflow destroyed the metal dam near the Gorelnik camp site and washed out the river bed. Malaya Almaatinka to bedrock for 8 km, tore off the vegetation cover, formed canyons with a depth of 10 to 30 m and, finally, was delayed by a high-rise dam. At the same time, the mudflow reservoir was filled to 85% of its volume. Although the mudflow was stopped by the dam, it turned out that there was a threat of the dam being washed out and the mudflow breaking through to Almaty.

If this had happened, the city would have been destroyed, since the volume of accumulated water reached 8 million m3.

The water was pumped out, and then it was decided to continue filling the dam and raising it further. For this purpose, by 1974 - 1975. Soil was filled from quarries and a mudflow reservoir, as a result of which the height of the dam reached 145 m, and the width at the base was 600 m. The capacity of the mudflow reservoir also increased to 12.5 million m3. The capital of Kazakhstan is now reliably protected from mudflows.

When laying roads, instead of protective structures or in addition to them, a bridge can be built that crosses the mudflow bed at the narrowest point. Then the mudflow passes under the road through the bridge opening.

You can also pass a mudflow over the road by building a herring for this (Fig. 48). A stone or reinforced concrete tray is laid along an arch made of stone or concrete, having a sufficient width and slope, due to which the mud-stone flow sweeps through it without stopping. At the entrance to the herring tray, two oblique guide walls are installed - entrance wings, which collect the flow and prevent it from spreading to the sides.

Anti-mudflow protective structures have a significant cost. Therefore, when surveying roads, it is important to determine in advance the place where mudflows are possible and to assess the degree of mudflow danger. For this purpose, possible sources of mudflows are identified, places where there are accumulations of loose material, the slopes of the terrain in mudflow-hazardous areas of the relief are determined, and traces of old mudflows are looked for. The collected data allows us to make a forecast of mudflow hazard and decide what is more expedient: to change the road route and bypass mudflow-prone areas or to build mudflow protection structures on them.

On roads where there are mudflow-hazardous areas, special monitoring is carried out and measures are taken to prevent the formation of mudflows or weaken their intensity. These measures include, for example: preventive drainage of water from glacial lakes that threaten to burst; clearing accumulations of loose materials that can be captured by mudflows; acceleration of snow melting by dusting the slopes with dark substances from airplanes, etc. In addition, they monitor economic activity people in mudflow-prone areas, prohibiting erroneous actions that could intensify mudflow phenomena (for example, cutting down forest and shrub vegetation, grazing livestock on slopes, etc.).

Typically, various measures to combat mudflows are applied simultaneously and form a single complex. This comprehensive method of combating mudflows is the most successful.

Actions of the population during landslides

Preparing for a landslide:

· study of information about possible locations and boundaries of landslides;

· study of warning signals about the threat of a landslide and the procedure for action when a signal is given;

· if signs of a landslide appear (jamming of doors and windows, cracks in buildings, seepage of water on slopes), report to the landslide station post.

Actions in case of a landslide:

· after a signal about the threat of a landslide, turn off electrical appliances, gas appliances and water;

· preparation for evacuation;

· if the landslide rate is low (meters per month), move buildings to a non-hazardous location, remove furniture and valuables;

· at a speed of more than 1 m per day, evacuation with documents, valuables, food;

· when hitting a blockage - movement to the edge of the landslide masses;

· if liberation is impossible, give a signal to people outside the rubble;

· digging out victims.

Actions after landslide displacement:

· in surviving buildings, checking power supply lines, water supply, and gas supply;

· if there is no damage, assist rescuers in extracting victims;

· self-help and first aid to the victims;

· follow the instructions of the rescuers.

Sel, sil (from Arabic sayl - stormy stream), a temporary stream that suddenly forms in the beds of mountain rivers, characterized by a sharp rise in level and a high (from 10-15 to 75%) content of solid material (products of rock destruction).

Selel is something between a liquid and a solid mass. This phenomenon is short-term (usually it lasts 1-3 hours), typical for small watercourses up to 25-30 km long and with a catchment area of ​​up to 50-100 km².

Average speed the movement of mudflows is 2-4 m/s, reaching 4-6 m/s, which causes their great destructive effect. Along their path, streams carve deep channels that are usually dry or contain small streams. Mudflow material is deposited in the foothill plains.

Mudflows are characterized by the advancement of its frontal part in the form of a shaft of water and sediment, or more often by the presence of a series of successively shifting shafts. The passage of a mudflow is accompanied by significant reformations of the riverbed.

Mudflow occurs as a result of intense and prolonged rainfall, rapid melting of glaciers or seasonal snow cover, as well as due to collapse into the riverbed large quantities loose clastic material (with terrain slopes of at least 0.08-0.10). Decisive factor the occurrence can be caused by deforestation in mountainous areas - tree roots hold the top of the soil, which prevents the occurrence of a mudflow.

Sometimes mudflows occur in the basins of small mountain rivers and dry ravines with significant (at least 0.10) thalweg slopes and in the presence of large accumulations of weathering products.

For the formation of mudflows, the presence of:

· sufficient quantity products of rock destruction on the slopes of the basin;

sufficient volume of water to wash away or remove loose soil from the slopes hard material and its subsequent movement along the riverbeds;

· steep slopes and watercourses.

The main condition for the occurrence of mudflows is the amount of rainfall that can cause the washing away of rock destruction products and their involvement in movement.

A potential mudflow source is a section of a mudflow channel or mudflow basin that has a significant amount of loose clastic soil or conditions for its accumulation, where mudflows originate under certain watering conditions. Mudflow centers are divided into mudflow incisions, potholes and centers of dispersed mudflow formation.

Mudflow pothole called a linear morphological formation cutting through rocky, turfed or forested slopes, usually composed of weathering crust of insignificant thickness. Mudflow potholes are characterized by their small length (rarely exceeding 500...600 m) and depth (rarely more than 10 m). The bottom angle of potholes is usually more than 15°.

Mudflow incision is a powerful morphological formation, developed in the thickness of ancient moraine deposits and most often confined to sharp bends of the slope. In addition to ancient moraine formations, mudflow incisions can form on accumulative, volcanogenic, landslide, and landslide terrain. Mudflow incisions are significantly larger in size than mudflow potholes, and their longitudinal profiles are smoother than those of mudflow potholes. The maximum depths of mudflow incisions reach 100 m or more; The catchment areas of mudflow incisions can reach more than 60 km². The volume of soil removed from a mudflow incision during one mudflow can reach 6 million m³.

Under source of dispersed mudflow formation understand an area of ​​steep (35...55°) outcrops, heavily destroyed rocks, having a dense and branched network of grooves in which rock weathering products intensively accumulate and the formation of micro-debris flows occurs, which are then united in a single mudflow channel. They are usually confined to active tectonic faults, and their appearance is caused by large earthquakes. The area of ​​mudflow centers reaches 0.7 km² and rarely more.

The type of mudflow is determined composition of mudflow-forming rocks . Mudflows are: water-stone, water-sand and water-silt; mud, mud-stone or stone-mud; water-snow-stone.

Water-rock mudflow– a flow, which is dominated by coarse material with predominantly large stones, including boulders and rock fragments (volumetric weight of the flow 1.1–1.5 t/m3). It is formed mainly in the zone of dense rocks.

Water-sand and water-silt mudflow– a stream in which sandy and silty material predominates. It occurs mainly in the zone of loess-like and sandy soils during intense rainfalls, washing away huge amounts of fine earth.

Mud mudflow is close in appearance to water-silt, is formed in areas where rocks of a predominantly clayey composition occur and is a mixture of water and fine earth with a low concentration of stone (volumetric weight of the flow 1.5–2.0 t/m3).

Mud-stone mudflow characterized by a significant content of clay and silty particles in the solid phase (pebbles, gravel, small stones), with their clear predominance over the stone component of the flow (volumetric weight of the flow 2.1–2.5 t/m3).

Rock-mud mudflow contains predominantly coarse material compared to the mud component.

Water-snow-rock mudflow– a transitional material between the mudflow itself, in which the transport medium is water, and a snow avalanche.

Mudflows are subdivided by the nature of their movement in the channel on liaisons And incoherent. Connected threads consist of a mixture of water, clay and sand particles. The solution has the properties of a plastic substance. The flow seems to represent a single whole. Unlike a water flow, it does not follow the bends of the channel, but destroys and straightens them or rolls over an obstacle. Incoherent(current)streams moving at high speed. There is constant impact of stones, their rolling and abrasion. The flow follows the bends of the channel, subjecting it to destruction in different places.

Mudflows are classified and by volume of transferred solid mass or, in other words, according to power, and are divided into three groups:

· powerful (strong power) – with the removal of more than 100 thousand m 3 of materials to the foot of the mountains, they happen once every 5–10 years;

· medium power – with removal from 10 to 100 thousand m 3 of materials, occurs once every 2–3 years;

· weak power (low-power) – with the removal of less than 100 thousand m 3 of materials, they occur annually, sometimes several times a year.

Quite often very powerful (exceptionally powerful) mudflows are released, carrying out more than 1 million m 3 of clastic materials; happen once every 30–50 years.

Mudslides can also be classified due to the occurrence (Table 2.5).

Table 2.5

Classification based on the root causes of mudflows

Types	Root causes of formation	Areas of distribution and mechanism of generation
Rain	Showers, prolonged rains	The most widespread type of mudflows on Earth, dominant in the mountains of the equatorial, tropical and temperate climatic zones. The origin of mudflows is associated with erosion of slopes and channels, as well as landslides
Snow	Intensive snowmelt in spring	The dominant type of mudflows in the mountains of the Subarctic; The solid component of mudflows is represented by snow. The origin of mudflows is associated with the failure of waterlogged snow masses and the breakthrough of snow dams
Glacial	Intensive melting of snow and ice	Formed in the zone of modern mountain glaciation; the most powerful are mudflows in the alpine highlands. The origin of mudflows is associated with the breakthrough of accumulations of melted glacial waters, as well as with the collapse of moraines and ice
Volcanogenic (lahar)	Explosive volcanic eruptions	Formed in areas of active volcanoes; reach the largest sizes among all types of mudflows in terms of path length and volume of debris flows. The origin of mudflows is associated with the transformation of pyroclastic flows into mudflows due to rapid snowmelt, with the drainage of crater lakes, etc.
Seismogenic	High-magnitude earthquakes	Formed in areas of high seismicity (8 points or more). The origin of mudflows is associated with the disruption of soil masses from slopes into riverbeds
Limnogenic	Dynamics of development of natural lake dams	They form in areas of the alpine highlands, which are characterized by dam lakes. The origin of mudflows is associated with the destruction of dams and erosion of riverbeds by a breakthrough wave
Anthropogenic direct impact	Creation of accumulations of technogenic rocks in potentially mudflow-prone basins; construction of low-quality earthen dams, etc.	They are formed in dump storage areas of mining enterprises, below reservoirs and in other places. The origin of mudflows is associated with the erosion and sliding of technogenic rock strata, the destruction of dams and erosion of riverbeds, etc.
Anthropogenic indirect impact	Significant disturbances of soil and vegetation cover in potentially mudflow-prone basins	They form in mountains with long-term (historical) or irrational modern exploitation of the territory, in areas of deforestation, degraded meadows (pastures). The origin of mudflows is associated with the erosion of slopes and channels

The danger of mudflows lies not only in their destructive power, but also in the suddenness of their appearance. By the suddenness of the occurrence of a mudflow, one should keep in mind the impossibility of predetermining the date of the mudflow in advance. The frequency of mudflows varies for different mudflow-prone areas. For example, in Transbaikalia, powerful mudflows form within 5–6 years. In basins fed by storm and snow, where there is a constant supply of loose debris material to feed mudflows, mudflows recur frequently (once every 2–4 years, sometimes several times during the year) and are associated with periods of significant precipitation. Powerful mudflows (carrying out 2–4 million m3 of debris) recur relatively rarely – once every 30–50 years.

Damaging effect of a mudflow:

· direct impact of mudflow on humans;

obturation respiratory tract liquid component leading to mechanical asphyxia, debris flow aspiration;

· destruction of buildings, structures and other objects in which people may be located;

· destruction of life support systems.