Where does the mudflow occur? What is a mudflow, and how to escape from this phenomenon? Landslides develop in rocks; blocks slide either along underlying clay layers or along clay weathering products developing in rock cracks.

Sat down– these are channel flows that include a large amount of clastic material (at least 10–15% by volume), having a density 1.5–2 times greater than the density of water, moving in the form of a wave with a front height of up to 20–40 m and at a speed of up to 20–30 m/s (10–100 km/h) and exerting pressure on an obstacle with a force of up to tens of tons per square meter. The height of the front and the speed of movement of the mudflow, depending on the conditions of its occurrence, can take on different values. The mudflows got their name from the Arabic “sayl” - a stormy stream. Mudflows typical for mountain valleys with a channel slope of 6–200; they usually last tens of minutes, less often 4–5 hours, can erode the riverbed to a depth of tens of meters, travel a path of kilometers long, less often - several tens of kilometers, form cones tens of meters wide, hundreds of meters long with a thickness of single deposits usually up to 5 , rarely up to 10 m. Mudflows form in all mountainous regions of the world, except Antarctica.

Mudflows are called rapid channel flows, consisting of a mixture of water and rock fragments, suddenly appearing in the basins of small mountain rivers. They are characterized by a sharp rise in level, wave motion, short duration of action (from 1 to 3 hours), and a significant erosion-accumulative destructive effect. A mudflow is a spontaneous (especially dangerous) hydrological phenomenon if the mudflow threatens populated areas, sports and health resort complexes, railways and roads, irrigation systems and other important economic facilities.

Potential mudflow source– a section of a mudflow channel or mudflow basin that has a significant amount of loose clastic soil or conditions for its accumulation, where under certain water conditions mudflows originate. 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 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, mudflow incisions can form on accumulative, volcanic, landslide, and landslide terrain. They 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 km 2 . The volume of soil removed from a mudflow incision during one mudflow can reach 6 million m3.

Under the source of dispersed mudflow formation understand an area of ​​steep (35–55°) outcrops, heavily destroyed rocks, with 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 km 2 and rarely more.

The type of mudflow is determined by the composition of the 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 in which coarse material predominates 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 are distributed 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 silt 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.

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

Sources of solid supply for mudflows can be: glacial moraines with or without loose filling; channel blockages and obstructions formed by previous mudflows; woody plant material. The sources of water supply for mudflows are: rains and downpours; glaciers and seasonal snow cover (during the melting period); waters of mountain lakes.

The most common mudflows are rain-fed mudflows. They are typical for mid-mountain and low-mountain mudflow basins that do not have glacial feeding. The main condition for the formation of such mudflows is the amount of precipitation that can cause the washout of rock destruction products and involve them in movement.

High-mountain basins with developed modern glaciers and glacial deposits (moraines) are characterized by glacial mudflows. The main source of their solid nutrition is moraines, which are involved in the process of mudflow formation during intensive melting of glaciers, as well as during the outburst of glacial or moraine lakes. The formation of glacial mudflows depends on the ambient temperature.

The immediate causes of mudflows are rainfall, intensive melting of snow and ice, outburst of reservoirs, and, less commonly, earthquakes and volcanic eruptions. Despite the variety of reasons, the mechanisms of mudflow initiation can be reduced to three main types: erosion, breakthrough and landslide (Table 2.16). Thus, during the formation and development of mudflows, three stages of formation can be traced:

more or less long-term preparation on the slopes and in the beds of mountain basins of material that serves as a source for the formation of mudflows (as a result of weathering of rocks and mountain erosion);

rapid movement of rocky, out-of-balance material from elevated areas of mountain catchment areas to lower areas along mountain beds in the form of mudflows;

The number of tools passing through a plot for the same crop determines the degree of simplification of that crop, the final stage of which is direct seeding, which does not require pre-tillage. The amount of organic matter on the surface is maximum. Suitable spins and rotations. . Particular attention should be paid to erosive and risky areas. Such areas should have as much vegetation cover as possible and crops that improve soil structure. Crops at risk of erosion or bare soil can be used interchangeably with such crops to reduce slope length, reduce runoff, and promote water infiltration.

accumulation of mudflows in low areas of mountain valleys in the form of channel cones or other forms of mudflow deposits.

Mudflows form 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 consists of three zones in which mudflow processes form and occur: mudflow zone, where water and solid material are fed; transit zone(mudflow movement); unloading area(massive deposition of debris flows).

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 rainfalls 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 flow 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. Breaking out of a mountain gorge onto the plain, the mudflow quickly loses speed and spreads across a relatively large area in the form of a cone. Water from a mudrock flow filters to its base, and the transported rock material settles 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 fans are called proluvial or proluvium. Debris flows pose a great danger to settlements located within their range of action. The famous mudflow of 1921, which burst out of a mountain gorge near the city of Alma-Ata, 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 about 1.5 million tons.

Picture 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 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 the mudflow 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.

Dams of intermittent type are built when the width of the channel is up to one hundred meters. In this case, the length of the dam is determined by the formula and the opening of the dam is determined depending on the passage of the required amount of 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. Recently, dams constructed using the directed explosion method have been used to combat mudflows. 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 deposits

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 horizon. The difference is in power, duration of action and direction 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 deposits of flowing surface water 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 cohesive 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 straight 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. There is a large amount of crushed stone and pebbles. 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 transported material by size occurs.

Table 2. Main types of mudflows and possible reasons emergence

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 large stones (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 fine earth particles and mostly small stones. 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 - create small erosion at the base, clog culverts 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 non-foundation 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 that do not have 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. Unconnected flows are able to move with high speed in this case, 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 economic activity person.