Where and when they sat down. Consequences of mudflows and landslides. Forces acting on a parallelepiped located on a slope

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 resulting dam reached 300 m, maximum depth lakes - 284 m, length - 53 km. Such large-scale disasters happen rarely, but the troubles they bring are incalculable.

Landslides are the movement of rock masses down a slope under the influence of gravity.

Landslides form in various rocks as a result of disruption of their balance and 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.

Based on their scale, landslides are divided into large, medium and small-scale.

Large Landslides are usually caused by natural causes and form 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.

Based on their 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.

The activity is influenced by the slope rocks that form the basis of the landslide, as well as the presence of moisture. Depending on the quantitative indicators of the presence of water, landslides are divided into dry, slightly wet, wet and very wet.

According to the mechanism of the landslide process, landslides are divided into shear landslides, extrusion landslides, viscoplastic landslides, hydrodynamic landslides, and sudden liquefaction landslides. Landslides often show signs of a combined mechanism.

Based on the place of formation, landslides are divided into mountain, underwater, snow and artificial earthen structures (pits, canals, rock dumps).

In terms of 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. Thus, on July 13, 1990, on Lenin Peak in the Pamirs, as a result of an earthquake, a large derailment snow avalanche demolished the climbers' camp, located at an altitude of 5300 m. 48 people died. It was the biggest tragedy in domestic mountaineering.

Mudflows (mudflows). On June 8, 1921, at 24:00, a mass of earth, silt, stones, snow, sand, driven by a mighty stream of water, collapsed on the city of Alma-Ata from the mountains. This stream demolished the dacha buildings located at the foot of the city along with people, animals, and orchards. A terrible flood burst into the city, turning its streets into raging rivers with steep banks of destroyed houses. Houses along with their foundations were torn down and carried away by a stormy stream. The result was great loss of life and enormous material damage. The cause of the mudflow is heavy rainfall in the upper part of the Malaya Almaatinka River basin. The total volume of mud-stone mass of 2 million m 3 cut the city with a 200-meter lifeless strip. It's just Selis a stormy mud or mud-stone flow that suddenly appears in the beds of mountain rivers.

The immediate causes of mudflows are heavy rainfalls, washing out 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 degradation of soil cover on mountain slopes, rock explosions during road construction, stripping operations in quarries, improper organization of dumps and increased air pollution, which has a detrimental effect on soil and vegetation cover.

one example of the disaster that a mudflow can bring.

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.

The length of mudflow channels can range from several tens of meters to several tens of kilometers. The width of the mudflow is determined by the width of the channel and ranges from 3 to 100 m. The depth of the mudflow can be from 1.5 to 15 m.

The volume of mudflow mass can be equal to tens, hundreds of thousands and millions of cubic meters.

The speed of movement of mudflows in individual sections of the channel varies. On average, it ranges from 2 to 10 m/s or more.

The duration of movement of mudflows is most often 1-3 hours, less often - 8 hours or more.

The frequency of mudflows varies depending on different mudflow-prone areas. 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.

Based on the composition of the transferred material, they are distinguished:

mud flows - 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 - a mixture of water with large stones.

Based on the nature of their movement, mudflows are divided into connected and disconnected 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. Disjointed streams consist of water, gravel, pebbles and stones. The flow follows the bend of the channel at high speed, subjecting it to destruction. According to their 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.

Landslides (mountain collapse)- 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, 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 (the volume of falling rock masses) and the scale of manifestation (involvement of the area in the process).

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

Consequences of landslides, mudflows, landslides. Landslides, mudflows, and avalanches cause great damage to the national economy, the natural environment, and lead to 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 and hidden by rock layers. settlements, national economic facilities, forest lands, blocking of river beds and overpasses, death of people and animals, changes in the landscape.

In particular, these dangerous geological phenomena threaten the safety of railway trains and other ground transport in mountainous areas, destroy and damage bridge supports, rails, and coatings highways, power lines, communications, oil pipelines, hydroelectric power stations, mines and other industrial enterprises, mountain villages, vacation sites.

Significant damage is caused to agriculture. Mudflows lead to flooding and littering of agricultural crops with debris over areas of hundreds and thousands of hectares. Arable lands located below landslide areas often become swampy. At the same time, crop losses and an intensive process of land withdrawal from agricultural use occur.

These phenomena can cause significant damage to the cultural and historical heritage of the peoples inhabiting mountainous areas.

The scale of the consequences is determined by:

the size of the population caught in the landslide zone;

the number of dead, wounded and homeless;

the number of settlements affected by the natural disaster;

the number of national economic facilities, health-improving and socio-cultural institutions that were destroyed and damaged;

area of flooding and obstruction of agricultural land;

number of dead farm animals.

The secondary consequences of these natural disasters are emergencies associated with the destruction of technologically hazardous objects, as well as the interruption of economic and vacation activities.

Landslides, mudflows and landslides on the territory of the Russian Federation take place in the mountainous regions of the North Caucasus, the 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, the 1963 landslide in Italy with a volume of 240 million m3 covered 5 cities, killing 3 thousand people.

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.

In 1985 in Colombia, as a result of the eruption of the Ruiz volcano, a gigantic mudflow occurred, which overwhelmed the city of Armero, resulting in the death of 22 thousand people and the destruction of 4.5 thousand residential and administrative buildings.

In 1982, a mudflow 6 km long and up to 200 m wide hit the villages of Shiveya and Arenda in the Chita region. Houses, bridges, 28 estates were destroyed, 500 hectares of cropland were washed away and covered, people died.

Characteristics

The speed of movement of mudflows is on average 2-4 m/s, sometimes 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.

Causes

Mudflows occur as a result of intense and prolonged rainfall, rapid melting of glaciers or seasonal snow cover, as well as due to the collapse of large quantities of loose debris into the riverbed (with terrain slopes of at least 0.08-0.10). The decisive factor in the occurrence may be 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.

According to the mechanism of their origin, they distinguish between erosive, breakthrough and landslide mudflows.

Places of occurrence

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 water 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 in 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.

Classification

Seismic debris flows

As a result of earthquakes, broken fragments of glaciers or rocks can block the path of rivers, forming very unstable dams. When such a dam is destroyed, water is released from it not gradually, but instantly, which contributes to the accumulation of unimaginable kinetic energy by the flow.

Lahars

Lahars are mudflows of volcanic origin. As a result of lava ejection or pyroclastic flows, snow cover and glaciers on the slopes of the volcano rapidly melt, and the resulting water mixes with ash and rocks. During the eruption of Vesuvius in 79, under the ashes of which Pompeii was buried, the city of Herculaneum was covered with a three-meter layer of mud-stone mass brought by the lahar. During excavations, it was discovered that the mudflow shell of Herculaneum is much denser than the ash layer of Pompeii.

Messengers

Connected people include mud-stone streams, in which water is practically not separated from the solid part. They have a large volumetric weight (up to 1.5-2.0 t/m³) and great destructive power. Water-stone flows are classified as incoherent. Water transports debris and, as its velocity decreases, deposits it in the channel or fan area on the foothill plain. Volumetric weight of mudflows

The following zones are distinguished in the mudflow basin:

Origin zone (feeding)
Transit zone
Accumulation zone

According to the degree of saturation with sediment and its fractional composition

Mud mudflows - a mixture of water with fine earth with a small concentration of stones, volumetric weight y = 1.5-2 t/m³
Mud-stone mudflows - a mixture of water, pebbles, gravel, small stones, y=2.1-2.5 t/m³
Water-rock (alluvial) mudflows - a mixture of water with predominantly large stones, y=1.1-1.5 t/m³

Fighting mudflows

Mudflows can cause enormous destruction. The fight against mudflows is carried out mainly by securing soil and vegetation cover and constructing special hydraulic structures.

To combat mudflows, preventive measures and construction of engineering structures are carried out.

The use of certain control methods is determined by the zones of the mudflow basin. Preventive measures are taken to prevent the occurrence of a mudflow or weaken its effect at the very beginning of the process. The most radical remedy is afforestation on mudflow-prone mountain slopes. The forest regulates flow, reduces the mass of water, and cuts streams into separate weakened streams. It is forbidden to cut down forests or disturb the turf cover in the catchment area. Here it is advisable to increase the stability of slopes by terracing, intercept and drain water with upland ditches and earthen ramparts.

In mudflow channels, dams have the greatest effect. These structures made of stone and concrete, installed across the riverbed, delay the mudflow and take away some of the solid material from it. Half-dams push the flow toward the shore, which is less susceptible to rupture. Mud catchers are used in the form of pits and basins laid in the path of flows; they build bank-protecting retaining walls that prevent erosion of the banks of the riverbed and protect buildings from the impact force of mudflows. Guiding dams and mudflow reservoirs are effective. Dams direct the flow in the desired direction and weaken its effect.

In areas of settlements and individual structures located in the zone of proluvium deposition, diversion channels are installed, guide dams are installed, and river beds are taken into high stone banks that limit the spread of the mudflow. To protect road structures, the most efficient are mudflow drains in the form of reinforced concrete and stone chutes that allow mudflows to pass above or below structures.

Notes

Literature

Chernomorets S.S. Mudflows before and after disasters. - M.: Scientific world, 2005. - 184 p.

Links

Chernomorets S.S., Seynova I.B. Mudflows on volcanoes. - Moscow: Publishing House UC DO, 2010. – 72 p. ISBN 978-5-88800-341-1

Natural disasters
Earth	Avalanches Earthquakes Lahar Sel Volcanic eruptions
Water	Floods Limnological eruptions Tsunamis
Weather	Blizzards Cyclonic storms Droughts Hail storms Heat waves Tornadoes
Fire	forest fire
Health and illness	Epidemic Mass famine

Wikimedia Foundation. 2010.

Synonyms:

See what “Sel” is in other dictionaries:

mudflow- sel/… Morphemic-spelling dictionary

I; m. [from Arab. sail stormy stream] A muddy or muddy stone stream (usually of powerful destructive force) that suddenly appears in the bed of a mountain river as a result of rapid snowmelt, rainfall, etc. ◁ Mudflow, oh, oh; Mudflow, oh, oh. S flows. * *… … encyclopedic Dictionary

mudflow- mudflow: According to GOST 19179; Source … Dictionary-reference book of terms of normative and technical documentation

OBZH – 7

Subject: Landslides and their characteristics

The purpose of the lesson: study the phenomenon of mudflow, factors influencing its formation, possible consequences, methods of protection.

Goals and objectives of the lesson: 1. Introduce and consolidate the concept of mudflow.

2. Introduce students to general activities,

Conducted in the world for protection

Populations from the mudflow

3. To develop in students the ability to apply

Theoretical knowledge in practice.

4. Develop the ability to quickly find the answer in

Non-standard situation, develop attention,

Imagination.

To consolidate knowledge on the topic of villages and their characteristics.

Lesson type: learning new material

Visual aids: - - - -

Lesson Plan

Organizational moment 5 min.
Learning new material 30 min.
Control of absorption 5 min.
Defining and explaining homework 5 min.

Questions studied:

1. Possible reasons occurrence of mudflows, their classification.

2. The process of flow formation, methods for forecasting it.

Equipment: - - - -

During the classes

Sat down- a formidable natural phenomenon that usually occurs suddenly and is catastrophic in nature. They cause colossal damage to residents of intermountain valleys and foothills. To combat mudflows, cascades of concrete dams are erected in gorges, drainage canals and dams are built.

Sel - a mud or mud-stone flow that suddenly forms in the beds of mountain rivers as a result of rainfall, rapid melting of glaciers or seasonal snow cover. Moving at high speed, mudflows often cause major destruction in their path.. All movements rocks and clay masses are preceded by various signals: the formation of new cracks and crevices in the soil; unexpected cracks in internal and external walls, water pipes, asphalt; falling stones; the occurrence of a strong roar in the upper reaches of mudflow-prone watercourses, which drowns out other noises; a sharp drop in water levels in rivers; manifestation of a cloud of mud dust accompanying the “head” of the mudflow.

Sat down- floods with a very high concentration of mineral particles, stones and rock fragments (from 10-15 to 75% of the flow volume), occurring in the basins of small mountain rivers and dry ravines and caused, as a rule, by rainfall, less often by intense snow melting, and also the breakthrough of moraine and dam lakes, landslides, landslides, earthquakes. The danger of mudflows lies not only in their destructive power, but also in the suddenness of their appearance. Approximately 10% of the territory of our country is subject to mudflows. In total, about 6,000 mudflow streams have been registered, more than half of which are in Central Asia and Kazakhstan.

According to the composition of the transported solid material, mudflows can be mud (a mixture of water with fine earth with a small concentration of stones, volumetric weight y = 1.5-2 t/m3), mud-stone (a mixture of water, pebbles, gravel, small stones, y = 2 ,1-2.5 t/m3) and water-stone (a mixture of water with predominantly large stones, y==1.1-1.5 t/m3).

Many mountainous regions are characterized by the predominance of one or another type of mudflow in terms of the composition of the solid mass it transports. Thus, in the Carpathians, water-stone mudflows of relatively small thickness are most often found, in the North Caucasus - mainly mud-stone mudflows, in Central Asia- mud flows. The flow speed of a mudflow is usually 2.5-4.0 m/s, but when the jams break through, it can reach 8-10 m/s or more. The consequences of mudflows can be catastrophic. So, on July 8, 1921, at 21:00, a mass of earth, silt, stones, snow, sand, driven by a mighty stream of water, collapsed on the city of Alma-Ata from the mountains. This stream demolished the dacha buildings located at the foot of the city along with people, animals and orchards. A terrible flood burst into the city, turning its streets into raging rivers with steep banks of destroyed houses. The horror of the disaster was aggravated by the darkness of the night. There were cries for help that were almost impossible to say. Houses were torn off their foundations and, along with people, were carried away by a stormy stream.

By the morning of the next day the elements had calmed down. Material damage and loss of life were significant. The mudflow was caused by heavy rainfall in the upper part of the river basin. Malaya Almatinka. The total volume of mud-stone mass was about 2 million m3. The flow cut the city with a 200-meter strip.

Ways to combat mudflows very diverse. This is the construction of various dams to retain solid runoff and pass a mixture of water and small fractions of rocks, a cascade of dams to destroy a mudflow and free it from solid material, retaining walls to strengthen slopes, upland runoff interception and drainage ditches to divert runoff to nearby watercourses, etc. There are currently no methods for predicting mudflows. At the same time, for some mudflow areas, certain criteria have been established to assess the likelihood of mudflows occurring. Thus, for areas with a high probability of mudflows of storm origin, the critical amount of precipitation is determined for 1-3 days, mudflows of glacial origin (i.e., formed during outbursts of glacial lakes and intraglacial reservoirs) - the critical average air temperature for 10-15 days or a combination of these two criteria

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 entire area of origin and impact of a mudflow is called a mudflow basin.

Type of mudflow determined by the composition of the mudflow-forming rocks. Main types of mudflows:

water-stone (a mixture of water with predominantly large stones, y==1.1-1.5 t/m3)

mud (a mixture of water with fine earth with a small concentration of stones, volumetric weight = 1.5-2 t/m3)

mud-stone (mixture of water, pebbles, gravel, small stones, y==2.1-2.5 t/m3)

For a mudflow to occur, three mandatory conditions must simultaneously coincide:

the presence on the slopes of the mudflow basin of a sufficient amount of easily transportable rock destruction products (sand, gravel, pebbles, small stones);

the presence of a significant volume of water to wash away stones and soil from the slopes and move them along the riverbed;

sufficient slope steepness (at least 10-15°) of the mudflow basin and water flow (mudflow bed).

The immediate impetus for the occurrence of a mudflow can be:

intense and prolonged downpours;

rapid melting of snow and glaciers;

earthquakes and volcanic activity, etc.

Anthropogenic factors often lead to the occurrence of mudflows: deforestation carried out on slopes, blasting operations, quarrying, and mass construction.

Anthropogenic factors

IN last years anthropogenic factors have been added to the natural causes of the formation of mudflows, that is, those types of human activities that cause the formation of mudflows or their intensification. These factors include:

Deforestation on mountain slopes;

Degradation of soil cover by unregulated grazing;

Incorrect placement of waste rock dumps by mining enterprises;

Explosions during the construction of railways, roads and various structures;

Insufficient land reclamation after stripping operations and unregulated water discharge from irrigation structures on slopes;

Deterioration of soil and vegetation cover by waste from industrial enterprises.

Thus, the destruction of vegetation, quarrying, cutting of slopes by roads, and massive construction on slopes led to the development of mudflows on almost the entire Black Sea coast of the Caucasus (from Novorossiysk to Sochi).

How to prepare for a mudflow

Usually the places where mudflows can occur are known. Before going to the mountains, study these places along your route and avoid them, especially after heavy rains. Always remember that it is almost impossible for someone caught in a mudflow to escape. You can only escape from a mudflow by avoiding it. Before leaving home, during early evacuation, turn off electricity, gas and water supply. Close doors, windows and vents tightly.

Early measures to prevent mudflows

In mudflow-prone areas, anti-mudflow dams and dams are built to retain solid runoff and pass a mixture of water and fine rock fractions, a cascade of dams to destroy the mudflow and free it from solid material, retaining walls to strengthen slopes, upland runoff interception ditches and drainage ditches to divert runoff to nearby watercourses, etc., are being constructed bypass channels, the level of mountain lakes is reduced, the soil on the slopes is strengthened by planting trees, observations are carried out, a warning system is organized and evacuation is planned.

How to act in case of a mudflow

Having heard the noise of an approaching mudflow, you should immediately rise from the bottom of the ravine up the drainage, at least 50-100 m. You must remember that heavy stones can be thrown from the roaring flow over long distances, threatening your life.

Actions after a mudflow

Provide assistance to the victims and assistance to the formations and authorities clearing debris and drifts along the path of the mudflow and in places where the bulk of the mudflow was carried out. If you are injured, try to provide yourself with first aid. If possible, the affected areas of your body should be kept in an elevated position, ice (wet cloth) and a pressure bandage should be applied to them. See your doctor.

There are currently no methods for predicting mudflows. At the same time, for some mudflow areas, certain criteria have been established to assess the likelihood of mudflows occurring. Thus, for areas with a high probability of mudflows of storm origin, the critical amount of precipitation is determined for 1-3 days, mudflows of glacial origin (i.e., formed during outbursts of glacial lakes and intraglacial reservoirs) - the critical average air temperature for 10-15 days or a combination of these two criteria

Mudflow stages

After rains and earthquakes, mudflows do not occur immediately, but go through three stages:

1. Accumulation of large water-mud-stone masses in the upper reaches of the mudflow basin.

2. Rapid movement of water-mud-stone masses from top to bottom along mountain river beds or their valleys.

3. Flooding of low-lying areas of mountain valleys by mudflows, formation of various forms of sediments.

Characteristics of debris flows

Mudflows are relatively short-lived, their duration ranges from tens of minutes to several hours. This is explained by the fact that the products of rock destruction are almost simultaneously involved in the movement of mudflows along steep channels.

Debris flow speeds range from 2-3 to 8-10 m/s, and sometimes more. It is significant that the mudflow, unlike a water flow, moves unevenly, in separate shafts - sometimes slowing down, sometimes accelerating its movement. Delays (congestions) of the mudflow mass occur in the narrowing of the channel, at sharp turns, and in places where the slope sharply decreases. If usually the mudflow flow speed is 2.5-4.0 m/s, then after slowing down, when the jams break through, it can reach 8-10 m/s. The steep leading front of a mudflow wave with a height of 5–15 m forms the “head” of the mudflow. The maximum height of the water-mud flow shaft reaches 20-25 m. A mudflow can also be characterized by the average dimensions of its cross-section (width, depth) and the length of the channel.

Types of mudflow formation

The width of the mudflow depends on the width of the channel along which it moves and ranges from 3-100 m. The depth of the flow can be 1.5-2 m (mudflows of significant depth), 10-15 m or more (catastrophic mudflows). The length of mudflow channels reaches several tens of kilometers. These characteristics directly depend on the above-described structure (composition) of the debris flow and on the type of debris flow generation mechanism. Scientists distinguish three types of mudflow formation.

With the erosion mechanism, the water 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, 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, and, as a consequence, the processing of the channel is most significant. During the landslide-landslide mechanism, a massif of water-saturated rocks (including snow and ice) is torn down, the flow saturation and the mudslide wave are formed simultaneously; The flow saturation in this case is close to maximum. The maximum dimensions across the diameter of coarse-grained inclusions (boulders, rock fragments) for non-cohesive rock-water mudflows can be 3-4 m, and for coherent dense mud-stone mudflows - 8-10 m. Calculate how much such fragments weigh!

Fastening:

What combination of conditions is necessary for a mudflow to occur?

List the main components of a debris flow?

Lesson summary:

- What new did you learn in the lesson?

When and where can this knowledge be useful to you?

Homework: paragraph 4.4.

MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

FEDERAL AGENCY FOR EDUCATION

State educational institution

higher professional education

"ROSTOV STATE CIVIL UNIVERSITY"

Department of Engineering Geology, Foundations and Foundations

Essay

on the topic: "Mudflows"

Completed:

student of group PZ-119

Maliko Elena

Checked:

Prof. Peredelsky L.V.

Rostov-on-Don 2013

Chapter 1. General information

1.1 The concept of mudflow

1.2 Genetic classification of mudflow phenomena

Chapter 3. Mudflow disasters

4.1 Preventive measures

4.2 Engineering protection

Bibliography

Chapter 1. General information

1.1 The concept of mudflow

Mudflows (from Arabic, "sayl" - a stormy stream) are sudden short-term mountain streams consisting of a mixture of solid material and water. Mudflows occur as a result of heavy and prolonged rainfall, during periods of rapid melting of snow and glaciers, as well as when dams, dams, etc. break.

Mudflows are a formidable natural phenomenon, often of a catastrophic nature. A huge mass of water rushes down the gorges, washing away and capturing eluvium and colluvium along the way. As a result water flow enriched with solid material and turns into a mud-stone flow.

In the area of mudflows, there is a constant threat of destruction of bridges, dams, pipelines, buildings and structures in populated areas, blockage of perennial plantings, crops, etc. with mud-stone masses. Areas prone to mudflows are called mudflow-dangerous.

The huge mudflow on July 8, 1921, which suddenly burst out of a mountain gorge on the river, is well known. Malaya Almaatinka near Almaty and collapsed on the city. More than 200 buildings were ripped off their foundations and destroyed, killing about 400 people. The mudflow carried 1.5 million tons of mud-stone material onto the city area.

Mudflows are common in all mountainous regions of the world, except Antarctica. In Russia, 25% of its entire territory belongs to mudflow-prone areas ( North Caucasus- Kabardino-Balkaria, Dagestan, North Ossetia; Kola Peninsula, Sayan Mountains, Baikal region, Kamchatka, etc.). The classic areas where mudflows occur in the CIS are the mountainous regions of Central Asia, Transcaucasia and Kazakhstan.

The characteristic features of mudflows, in addition to suddenness and short duration of action, are the pulsating nature of the movement (due to the resulting congestion), very high speed of movement (up to 10 m/s), high erosive and impact-destructive ability due to the presence of solid material. The volume of individual blocks entrained by a mudflow can reach more than 60 m3, the mass is about 150 tons, and the energy of mudflow pressure on an obstacle is from 5 to 12 tons per 1 m2.

The great destructive impact of mudflows is due to high movement speeds and the presence of rock fragments in them. Along their path, mudflows often create deep channels that are usually dry or contain small streams. Mudflow material is deposited in the foothill plains. Useful areas are buried under a layer of mud, sand and stones.

If we take these properties as guiding ones, mudflows or mudflow-like phenomena, in addition to mudflows themselves, should include flows in which the solid component is represented by snow and ice, as well as specific flows formed in the subaqueous environment. Based on the systematization of the main types of mudflows and mudflows, taking into account the manifestation environment, material composition and parameters. Four groups of flows are identified.

Actually mudflows - mud and water-stone flows, mudflows.

Paracelaceae, including snow-water and ice-water flows. The solid component in them is represented almost exclusively by snow and ice. They differ from the actual mudflows in their significantly lower density and weak erosion-accumulation activity.

. Ultra mudflows: gigantic in scale (they are in the nature of geological disasters), unique in terms of formation conditions.

. Quasi-debris flows -mudflow-like phenomena on the bottom of seas and oceans, known as turbidity currents. Their scale exceeds the scale of ultra-mud flows on land, and the movement continues on the almost flat surface of the abyssal plains. Includes two types of flows - high and low density.

Figure 1. Rain mudflow.

.2 Genetic classification of mudflow events

Classes Main factor of formation Main features of distribution and regime Type Cause and mechanism of origin I. Mudflows of zonal manifestation; climatic (variability of hydrometeorological elements) distribution is widespread and has a zonal character; mudflows are systematic; the descent paths are relatively constant 1) rain showers and prolonged rains, causing erosion of slopes and riverbeds, landslides 2) snow intensive snow melting, causing a shift of waterlogged snow or soil masses, breakthrough of snow dams 3) glacial intensive melting of snow and ice, causing a breakthrough of accumulations of melted glacial waters, collapse of moraines and ice P.Mudflows of regional manifestation geological (active endogenous processes) distribution is limited to areas of greatest tectonic activity; mudflows are episodic; the descent paths are not constant 4) volcanogenic explosive volcanic eruptions, accompanied by the descent of crater lakes, rapid snow melting, etc. 5) seismogenic - earthquakes with a force of 8 points and above, causing the failure of soil masses from the slopes 6) limnogenic - destruction of natural lake dams, accompanied by erosion of the riverbed by a breakthrough wave Sh.Anthropogenic mudflows Economic activity (violation of the stability of mountain landscapes) They develop in areas of the greatest economic pressure on the mountain landscape; the frequency of disappearance is increased compared to the natural background, less often it is episodic in nature; characteristic of the emergence of new mudflow basins7) anthropogenic (technogenic) storage of mine dumps on steep slopes and their subsequent erosion; construction of low-quality earthen dams and their destruction, etc. 8) natural-anthropogenic deforestation and degradation of meadow vegetation due to irrational exploitation of the territory, unleashing erosion and mudflow processes

2.1 Rain mudflow is one of the genetic types of mudflows, formed as a result of heavy rains and prolonged rains. The mechanism of generation of d.s. in most cases it is of the erosion type:

washout and erosion of slopes, deep and lateral erosion of the channel lead to an increase in the saturation of the flow with debris and the formation of a mudflow wave. Mass gathering d.s. observed during abnormally high daily precipitation amounts or during a long rainy period ending in downpour.D. With. - the most widespread type of mudflow events on Earth, present in almost all climate types. Accordingly, it is characterized by the widest range of values for the volume of debris flows and the frequency of debris flows.

2.2 Snow mudflow is one of the genetic types of mudflows, the occurrence of which is caused by the processes of accumulation and melting of snow cover and snowfields.

There are two types of s. With. - snow flowsand snowfalls. The first serves as the main type of mudflow phenomena in the middle mountains of the subarctic zone. Snow mudflows are common both in the Subarctic and in the alpine and subnival zones of the highlands of the temperate zone. Most common the mechanism of their generation -breakthrough of temporary dams formed by channel and avalanche snowfields in narrowing valleys. Such breakthroughs usually form water-stone streamsor mudflows; most typical for the Subarctic. The second, more rare mechanism for the origin of snow mudflows is associated with the accumulation (mainly through avalanche demolition and weathering) on the benches of the longitudinal profile of denudation incisions and channels of loose clastic mass, which, when waterlogged, is capable of self-flowing; thus forming mud-stone streams. This type of mudflow occurs in the highlands of the temperate zone. The main impulse ensuring the descent from. pp., is served by intense snowmelt, sometimes with the participation of rain. The period of descent from. With. in the subarctic zone it occurs in spring, in the highlands of the temperate zone - in summer. By volume mudflowsWith. s belong to the medium group.

2.3 Glacial mudflow is one of the genetic types of mudflows, the formation of which is associated with a violation of the stability of glacial-moraine complexes, and the liquid component is formed mainly due to melted glacial waters.

The emergence of l. With. is caused by the breakthrough of glacier-dammed lakes and intraglacial reservoirs, as well as the sliding or disruption of moraine and ice masses.

By composition mudflow massl. With. can be water-stone, mud-stone, water-ice.

L.S. the most powerful mudflows in the highlands; their distribution zones border the areas of modern mountain glaciation. Activation l. With. characteristic of the stage of degradation of glaciation, especially for its initial stages.

Syn: glacial debris flow.

2.4 Volcanogenic mudflow - one of the genetic types mudflow events, the formation of which is caused by a volcanic eruption of a predominantly explosive type. Mechanism of nucleationV. With. associated with the descent of crater lakes, with intense melting of snow and ice, etc.

V. s. - the most powerful among all types of land mudflows (see. Ultra mudflows). The length of their path reaches 300 km, the volume of displaced debris masses is 500 million/m ³, sediment thickness 20 m. With. differ in the inconsistency of the descent path; participate in the formation of volcanogenic-proluvial volcanoes.V. With. - one of the main sources of danger during volcanic eruptions.

2.5 Seismogenic mudflow is one of the genetic types of mudflows, which is caused by an earthquake of magnitude 8 or higher. The origin of the village With. associated with the removal of soil masses from slopes, sometimes with the release of water from mountain lakes. Slides caused by an earthquake can be transformed into a mudflow directly; landslides and landslides create temporary dams, the breach of which serves as an impetus for the occurrence of mudflows.S. With. - rare type mudflow events, characteristic of areas with high seismic activity.

2.6 Limnogenic mudflow is one of the genetic types of mudflows, the occurrence of which is associated with the erosion of natural lake dams and the release of part or all of the water volume mountain lake. Outburst-dangerous lakes are of the dammed (dammed) type; they are formed as a result of damming the river by landslides, landslides, lava flows, ancient glacial moraines, and alluvial cones of lateral tributaries. Similar types of lakes exist for hundreds to first thousand years, and their breakthrough is prepared by long processes of evolution of the lake dam, including suffusion, etc.

L.S. - a rare type of mudflows, characteristic of seismically active highlands.

K l. With. It also does not include some of the rain and snow types of mudflows, the formation of which involves breakthroughs of small ephemeral dammed lakes in river beds; their existence is limited to hours, less often - days.

2.7 Anthropogenic mudflow is one of the genetic types of mudflows, the formation of which is directly related to the consequences economic activity, radically changing environmental conditions.

The centers of origin of a. With. most often serve dumpsand reservoirs; the former provide the solid component of mudflows, the latter - the liquid component during a breakthrough. RepeatabilityA. With. increased compared to the frequency of mudflows of natural origin, less often of an episodic nature; The distribution is local and includes lowland areas.

2.8 Natural-anthropogenic mudflow is one of the genetic types of mudflows, the conditions for the formation of which are associated with a situation in which the consequences of economic activity serve as an impetus for changing the course natural processes and subsequent development mudflow phenomena.As a rule, the reason for the formation of p. - a. With. deforestation, degradation of meadow vegetation in the mountains due to overgrazing, plowing of steep slopes; this leads to increased erosion, increased sediment runoff, and then the development mudflow processes. P-a. With. characterized by high repeatability. and low density (often dominated mudflows), abundance slope mudflow basins. Distribution of p. - a. With. is regional in nature, covering both territories that survived the industrial revolution and areas of ancient civilizations.

Chapter 2. Conditions for the formation and development of mudflows

The main conditions for the development of mudflows are:

) big square drainage basin of a mountain river;

) accumulation of a sufficient amount of loose weathering products in the drainage area and in the beds of watercourses;

) prolonged heavy rains after a dry period or rapid snowmelt; less often - a breakthrough of water from natural or artificial reservoirs (moraine lakes, reservoirs, etc.).

Human engineering and economic activity, and primarily the denudation of mountain slopes through predatory deforestation and destruction of bushes, can have a significant impact on the formation of mudflows.

During engineering-geological surveys for construction in mudflow-prone areas, it is customary to distinguish (Fig. 26.6):

mudflow formation (feeding) zone - the upper part of the mudflow basin, within which loose material accumulates;

transit (transfer) zone - the middle part of the basin, where the movement of the mudflow occurs and its replenishment with solid material;

deposition zone - the lower part of the basin, in which the speed of movement of the mudflow sharply decreases, the transported material is deposited in the form of alluvial cones.

At the initial stages of engineering-geological research, it is necessary to establish the degree of danger of the territory planned for construction development. It is estimated by the volume of material removed after the passage of one mudflow (G.I. Klio-rina, V.A. Osin et al., 1984). The first degree of danger includes territories where the volumes of removal exceed 1 million m3, the second - with volumes of removal from 0.5 to 1 million m3, and the third - less than 0.5 million m3.

Engineering-geological surveys in mudflow-prone areas are carried out in conjunction with engineering-hydrometeorological surveys in agreement with the territorial service of the Ministry of Natural Resources of Russia, which monitors (observes) mudflows in this area.

A mudflow, like any flood, is associated primarily with the intense runoff of surface (rain and melt) waters, which erode, wash away and transport loose material accumulating in the drainage basin of a mountain river, temporary watercourse or some part of them. There are known examples of mixed feeding of mudflows by rain and melt water. Finally, mudflows also occur during outbursts of glacial (for example, on the Malaya Almaatinka River in 1973) and non-glacial lakes and artificial reservoirs.

As is known, the water balance of rivers

Q =x- (z + u).

Since mudflow phenomena are short-term and develop in mountains, i.e. rough terrain, evaporation Gand infiltration Andwithin drainage basins compared to the amount of incoming rain and melt water Xnegligible. Consequently, the flow rate Q should be determined by the amount of rain and melt water entering the drainage basin, the speed and simultaneity of their reaching the main watercourse on which the mudflow is formed.

The speed and simultaneity of water reaching the main watercourse are determined by the size and shape of the drainage basin and the slopes of the surface of its relief. The amount of expenditure, other things being equal, will depend on the size of the basin and the intensity of precipitation.

In conditions of an asymmetrical pool (Fig. IV-3, b) surface runoff will be regulated at the site Pthe flood will increase gradually, it may be longer, but its magnitude (other things being equal) is less than in a symmetrical basin.

Consequently, climatic and often microclimatic conditions of water supply of mountain rivers, which determine the intensity of surface water runoff and hydrological conditions, are the first and most important factor in the formation of mudflows.

The great living destructive force of mudflows occurs under the influence of gravitational forces, which cause the movement of huge water-stone and mud-stone masses at high speeds. The action of these forces characterizes the energy of the relief and is proportional to the excess of the drainage basin over the erosion base and the magnitude of the surface slopes of its relief.

Consequently, geomorphological conditions are the second indispensable factor in the formation of mudflows.

Observations show that the valley of the most mudslide-prone rivers can be divided into three parts.

The upper part (upper reaches of the river), where the valley is expanded and is shaped like a semicircle with steep (from 30-40 to 50-60°), steep slopes in sections, covered with screes, stone placers, with traces of landslides, various landslide movements. The slopes are often dissected by deep gullies, ravines and ravines, along which rain and melt water flow from all sides, forming the main stream. This is the main part of the river’s drainage basin, where mudflows mainly form. The area of this part of the catchment area can vary from several square kilometers to many tens of square kilometers.

The middle (transit) part of the valley, which is a canyon, gorge or a narrow part of the valley with steep and high slopes. The slope of the river bed remains high - up to 25-30°. Even during low-water periods, the river here often occupies the entire bottom of the valley, flowing in one stream or several among piles of blocks, boulders and smaller debris. During a flood, the stream is partially saturated with debris due to the erosion of the river bed, valley slopes, and accumulations at their base.

The lower (mouth) part of the valley, gradually turning into a foothill plain or intermontane depression. This part of the valley is mainly an area of removal and accumulation of proluvial material. Here the slopes of the longitudinal profile of the valley sharply level out and the living force of the flow weakens.

This structure of valleys is not typical for all mudflow-prone mountain rivers and temporary streams, although it is often observed.

There are examples when the middle (transit) part has a small extent or is almost absent. In such cases, the entire valley participates in the formation of a mudflow flood.

The main drainage area of a mountain river valley can be located at different absolute and relative altitudes.

For high-mountain basins located above the upper limit of forest distribution, i.e. at elevations approximately above 2500 m, there is a wide distribution of products of physical (frost) weathering, various colluvial accumulations in the form of stone placers, ridges, as well as glacial (mainly moraine) deposits. In such basins, in the formation of mudflows, along with rainwater, a significant role is played by meltwater from glaciers and snowfields, as well as water outbursts from glacial lakes. Mudflows that form in such basins are very dangerous; they are characterized by large volumes, flow rates and enormous destructive power.

In mid-mountain basins, usually located at elevations from 1000-1200 to 2000-2500 m, the filling of floods with solid debris occurs due to the erosion and washing away of various formations - accumulations of landslides, screes, landslides, colluvium, eluvium, alluvium, less often moraine and fluvio-glacial . The formation of mudflows in such basins occurs mainly due to torrential rains. Mudflows here are also quite dangerous.

In low-mountain basins located at elevations below 1000-1200 m, the formation of mudflows also occurs mainly due to rain (storm) water and a wide variety of types of loose formations - colluvial, deluvial, eluvial and alluvial. These sediments contain more clayey rocks and clayey impurities, since chemical weathering processes play a significant role here. Therefore, mud-stone mudflows often form in such basins.

The composition of the mudflow mass is influenced not only by the dominant type of weathering within the basin, but also by the composition of the rocks composing the basin. If in the building mountain ranges A given drainage basin involves clayey, carbonate-clayey, sandy-clayey rocks; the loose material formed during their destruction will also be clayey to one degree or another. Accordingly, the mudflow will be mud-stone or mud.

The volume of debris flows and flow rates within low-mountain basins is usually less than in others.

The most important condition determining the formation of mudflow floods is the accumulation of loose clastic and clayey-clastic material within the drainage basin or in some part of it accessible to washout and erosion by surface river, as well as rain and melt water. This material can be of very diverse origin: colluvial, colluvial, eluvial, alluvial, glacial and fluvio-glacial. In terms of its composition, it can also be very heterogeneous and consist of blocks, fragments, boulders, pebbles, crushed stone, sand, gruss and gravel, sandy loam and loam of different sizes.

The composition of loose material within the drainage basin is also influenced by other geological processes that take part in its formation, such as landslides, screes, landslides, glacial and water-glacial activity, etc. These processes create hotspots in certain areas of the drainage basin loose material washed away during floods.

Important to notethat since a mudflow occurs suddenly and develops at high speed (“avalanche”), the loose material carried away and eroded by it during the transfer process does not have time to undergo any noticeable differentiation and sorting, although it continues to be destroyed, crushed, processed, etc. .d. Therefore, mudflows, both water-stone and mud-stone, are characterized by a large heterogeneity of the composition of solid material, and this should be considered one of their characteristic features. In the zone of removal and accumulation of loose material, where flow rates sharply decrease, the differentiation and sorting of the material brought by it is noticeable and significant.

It was noted above that depending on the altitudinal position of the drainage basin and, consequently, its physical and geographical conditions, the type and composition of loose material changes. In high-mountain basins, conditions are favorable for the accumulation of loose clastic material. Along with this, moraine and fluvio-glacial deposits are common here. Within the mid- and low-mountain basins, along with the accumulation of loose clastic material, the development on the slopes of various clayey deluvial, eluvial, landslide and other formations is characteristic.

Among other geological conditions influencing the formation of mudflows, it is necessary to pay attention to the tectonics of the region; ancient tectonic movements usually cause tectonic disturbance and fragmentation of rocks, zones of disturbance, brecciation, mylonitization, etc. All this further facilitates their erosion and the replenishment of floods with solid material . Therefore, zones and areas of large fragmentation of rocks are also sources of accumulation of loose material for mudflows. The newest and modern tectonic movements, firstly, usually maintain the contrast of the relief, its energy and thereby constantly influence the living force of floods and, secondly, cause earthquakes and, as a consequence, the massive formation of landslides, screes, landslides, avalanches, the role of which in accumulation of loose material within the catchment area has already been noted.

Despite the fact that loose formations accumulating within drainage basins play a large role in the formation of mudflows, their properties, as well as the properties of the mudflow mass, have been studied by almost no one anywhere, although knowledge of these properties is of undoubted interest. There are only fairly numerous data on their granulometric composition. Among the properties characterizing the mudflow mass, there is data on its density, which is determined indirectly - by the method of calculating the possible maximum saturation of mudflows with solid material. The properties of individual facies of proluvial deposits have been studied in detail, but they do not at all characterize the loose formations of catchment areas and mudflow mass.

Thus, the main conditions on which the formation of mudflows depends are the following.

Climatic and microclimatic conditions of the region, which are associated with uneven distribution of precipitation, the formation of showers, accumulation of snow and glaciers and their rapid melting during indefinite summer periods.

Geomorphological conditions that determine the size and shape of drainage basins, their altitude position, slopes of relief surfaces and the structure of mountain river valleys and temporary watercourses.

Geological conditions that determine the accumulation of loose material in drainage basins or in some parts thereof, the development of various geological processes (weathering, gravitational, etc.) involved in the formation of this material, as well as ancient, recent and modern tectonic movements.

Human activities causing disruption of natural balances in watersheds.

The cause of mudflow processes, their driving force, are floods - intense surface runoff as a result of rainstorms, rapid melting of snow and glaciers in the mountains, and sometimes water breakthroughs from natural and artificial reservoirs.

Chapter 3. Mudflow disasters

There are many known mudflow disasters. For example, on the night of August 17-18, 1891 in Tyrol, a mudflow wave from a gorge in the Austrian Alps reached a height of 18 m, as a result of which a vast area was covered in a short time with a thick layer of mud-stone material. One of the largest cities on the Pacific Coast of the United States - Los Angeles (January 25, 1914, January 1, 1934 and March 1, 1938). The mudflow of 1938 carried out a mud-stone mass from the mountains with a volume of more than 11 million m8 at an average flow rate of 2000 m8/sec and caused colossal losses, killing more than 200 people.

July 1921, after a heavy rainfall in the Trans-Ili Alatau mountains, a mud-stone mudflow struck the city of Alma-Ata, passing in waves every 30-60 seconds. He brought more than 3.5 to the city. million m* of solid material. At the Medeo site, its consumption amounted to 1-1.5 million m3.

Over the past decades, numerous mudflow events have been observed in the mountainous regions of Central Asia, the Caucasus, Crimea, the Carpathians, and Transbaikalia.

Among foreign examples, the most famous are the mudflow disasters of 1970 in Peru, as a result of which more than 60 thousand people died and 800 thousand were left homeless. Several cities were destroyed.

It is worth mentioning the village that occurred in 1973 on the river. Malaya Almaatinka. The mudflow hazard in this area has been known for a long time. Therefore, in order to protect the city of Almaty, along with other measures, a stone-earth dam with a height of approximately 115 m was built in the Malaya Almaatinka valley in the Medeo tract. It was erected with two directed explosions, followed by filling with mechanisms to the design profile.

Figure 3 Passport for the Medeu mudflow control dam

Figure 4 Cross and longitudinal sections of the dam. Medeu

On July 1973, at 17:55 local time, as a result of the breakthrough of moraine lakes in the upper reaches of the basin, a mudflow was formed, which rushed along the Mynzhilka trough valley into the bed of Malaya Almaatinka.

The formed mud-stone flow filled the reservoir in front of the Medeo dam in 2 hours and brought 4 million m3 of mudflow deposits. The maximum flow rate of the mudflow reached 2-3 thousand m*/sec, the average - 500 m*/sec.

On the evening of July 16, two more mudflow waves passed along the bed of Malaya Almaatinka. On July 18, about 0 m remained to the lower point of the dam crest. This, as well as the possibility of repeated mudflows, created a threat of overflowing the dam and required urgent measures. The government commission recommended the following as priority measures:

a) pumping out water and suspended matter accumulated in front of the dam;

b) filling the sinus with rock mass in the left abutment of the dam, left for the construction of a mudflow;

c) organizing regular observations of dams and glacial lakes;

d) preventing the filling of glacial lakes;

e) timely discharge of water from them in the event of a tendency for such filling.

The first two recommendations made it possible to quickly obtain additional mass storage capacity of up to 4 million m9, i.e. the same volume as the mudflow that occurred on July 15, 1973. Thus, the mudflow protection dam in the Medeo tract made it possible to completely accumulate the masses of the mudflow, reliably protect the city of Alma-Ata located below the gorge and prevent a disaster.

As a result of heavy rains, in the territory Black Sea coast Several incidents occurred.

August, a mudflow descended on a section of the M-27 federal highway Dzhubga - Sochi. Due to heavy rainfall, a mudflow blocked the road at the Agoi Pass.

Chapter 4. Protection of territory and structures from mudflows

Protecting areas and structures from mudflows is a difficult task. It can only be solved with an integrated approach, i.e. with a combination of both engineering (active) and preventive measures. Otherwise, the formation of powerful mudflows and numerous destructions is possible.

4.1 Preventive measures

Preventive measures include measures that prevent the formation of mudflows or weaken their effect at the very beginning of their development. The list of these measures includes:

· stopping deforestation on mudflow-prone mountain slopes,

· afforestation and shrub planting,

· restriction of livestock grazing,

· advance release of existing reservoirs (moraine and glacial lakes),

· terracing of mountain slopes,

and other forest reclamation and agrotechnical measures.

4.2 Engineering protection

For engineering protection of territories, buildings and structures from mudflows, mudflow retention, mudflow passage, mudflow control and stabilizing structures and measures are used (SNiP 22-02-2003).

They are designed and erected to retain a mudflow in the upstream and to form mudflow reservoirs, pass mudflows through an object or bypass it, direct a mudflow through an object or bypass it, direct a mudflow into a mudflow passage structure, stop the movement of a mudflow or weaken it (cascade of dams, retaining walls, drainage devices, etc.).

4.2.1 Extract from SNiP 02/22/2003

Type of structure and eventPurpose of the structure, event and conditions for their use I Mud-retainingConcrete, reinforced concrete, masonry dams: spillway, through. Dams made of soil materials (blind) Detention of debris flow in the upper pool. Formation of mudflow reservoirs II MudflowChannels. MudflowsPassing mudflows through an object or bypassing it III Selena guidesGuide and containment dams. SpursDirection of mudflow into the mudflow control structure IV StabilizingCascades of dams. Retaining walls. Drainage devices. Terracing of slopes. AgroforestryCessation of mudflow movement or weakening of its dynamic characteristics V Debris-preventingDams for regulation of mudflow-forming floods. Spillways on lake damsPrevention of mudflow-forming floods VI Organizational and technicalOrganization of monitoring and warning serviceForecast of mudflow formation

4.2.1.1 Debris retention structures

6.10 Mudflow retention dams, the destruction of which threatens catastrophic consequences, must be checked for the impact of a mudflow caused by a flood with a probability of exceeding 0.01%. In this case, the project should provide for the installation of surface mudflow structures that ensure the discharge of excess (compared to the calculated) volume of mudflow or raising the elevation of the dam crest, ensuring the accumulation of the entire volume of mudflow.

6.11 When designing mudflow retention dams, it is necessary to provide culverts for the passage of domestic river flow into the lower pool, as well as for the discharge of the water component of sediment-borne mudflows. In this case, the discharge flow should not exceed the critical mudflow flow determined for the area below the dam site.

6.12 As a rule, mudflow retention dams should be designed without anti-filtration devices and without gates at culverts. For the accumulation of mudflows, it is allowed to provide dams with a through design. Loads on through dams should be taken as on dead ones.

6.13 The elevation of the crest of blind mudflow retention dams made of soil materials above the level corresponding to the design volume of the mudflow storage facility should be taken to be no less than the height of the last mudflow shaft, determined at the maximum design mudflow flow rate and the average slope angle equal to the angle of inclination of the area in front of the mudflow storage facility. In this case, for mud-stone mudflows, the height of the mudflow levee at the dam is assumed to be equal to the depth of the mudflow at the entrance to the mudflow reservoir.

2.1.2 Mudflow control structures

6.14 The main types of mudflow control structures are:

channels - for passing mudflows through populated areas, industrial enterprises and other objects, allowing mudflows to be passed through the object or bypassing it at the same level as them;

mudflows - for passing mudflows through linear objects (cars and railways, canals, gas pipelines, oil pipelines, etc.).

Note - The use of pipes to pass mudflows is not allowed.

6.15 The use of mudflow passage structures to pass mud-stone mudflows is allowed only if the longitudinal slope of the structure is at least 0.10.

6.16 The dimensions of mudflow passage structures with inlet and outlet sections, as well as the outlet tract, should be determined based on the condition of ensuring the necessary transporting capacity of the flow, in this case:

the slope of the bottom of the structures must be taken to be no less than the average slope of the approach section of the mudflow channel, the length of which is taken to be equal to at least twenty widths of the mudflow;

the width of structures, as a rule, is assumed to be equal to the average width of the mudflow in the approach section of the mudflow channel;

the longitudinal axis of the mudflow control structure must be aligned with the dynamic axis of the mudflow; if it is necessary to rotate the structure, the angle between the axes should be no more than 8°;

the elevation of the walls (floors) of mudflow structures above the maximum level of mudflow should be taken equal to 0.2 Nmax, where Hmax - the maximum depth of the mudflow, but not less than 1 m for trays and not less than 0.5 m for channels.

6.17 It is recommended to orient the entrance section of the mudflow passage structures in such a way that the installation angle of the mating walls relative to the axis of the main channel does not exceed 11°.

The elevation of the walls above the maximum mudflow level in the inlet areas is recommended to be at least 0.5 Nmax.

mudflow engineering protection

Figure 5 Mudflow control structure at PC 5+80. Rosa Khutor plateau. Krasnodar region.

4.2.1.3 Sewer control structures

6.18 Debris flow control structures should be provided to direct the flow to mudflow passage structures, divert mudflow from the protected object or prevent erosion of the protected area.

6.19 The angles of rotation of guide dams in plan should be taken, as a rule, in accordance with the requirements of 6.17<#"238" src="doc_zip13.jpg" />

2.1.4 Stabilization structures

6.22 The design of slope stabilizing structures (retaining walls and drainage devices) should be carried out in accordance with the requirements of section<#"527" src="doc_zip14.jpg" />

2.1.5 Debris control structures

6.30 Dams are used in conditions when the source of formation of a rain or glacial mudflow is located below the source of formation of a mudflow-forming flood and the relief between these areas allows the creation of a regulating capacity. The dam must be equipped with a water outlet that ensures automatic emptying of the control tank with a flow rate not exceeding the mudflow, as well as a catastrophic spillway.

The required capacity of the control tank should be determined by the volume of the flood with a probability of exceeding 1% minus the volumes discharged into the downstream during the period of accumulation of this flood.

6.31 Spillways should be implemented to prevent lake outbursts. The type of spillway (trench, siphon, tunnel, etc.) is determined by the construction conditions and the nature of the lake dam.

Spillways should be designed for discharge with a probability of exceeding 2%.

The most reliable means for protecting settlements and territories from possible mudflows are high, massive dams and dams that block the beds of mountain rivers. An example is the 115 m high dam built in 1971 on Malaya Almaatinka in the Medeo tract. The dam was created from local stone materials by the method of directed explosion with subsequent build-up of the exploded material in the form of an embankment. With its help, in 1973, a catastrophic mudflow with a volume of up to 4.0 million m3 of mud-stone mass and up to 1.5 million m3 of flood water was stopped. Thus, the city of Alma-Ata was saved from great destruction and loss of life.

It must be emphasized that the fight against mudflows is one of the most important issues of protection and rational use of the geological environment. The design and construction of anti-mudflow structures without proper consideration of the features of this dangerous geological process and without forecasting its possible negative consequences may not only be ineffective, but also cause significant harm to the environment.

Bibliography

1.L.V. Peredelsky, O.E. Prikhodchenko "Engineering Geology".

2.V.P. Ananyev, L.V. Peredelsky "Engineering geology and hydrogeology".

.V.P. Ananyev, A.V. Potapov "Engineering Geology"

.A.I. Artsev "Engineering-geological and hydrogeological research for water supply and sanitation."

.V.F. Perov "Mudflow phenomena. Terminological dictionary" Lahars of Kamchatka

) Desert-type mudflows in arid or semi-arid areas with sudden heavy rainfall (most common in Arizona, Nevada, California);) Lahars? mudflows of volcanic origin.

Mudflow (mudflow) is a temporary rapid mountain flow of a mixture of water with a high content of stones, sand, clay and other particles (50-60% of the flow volume). 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. 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 is 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. Due to the high speed of the current, the time from the moment a mudflow occurs in the mountains to the moment it reaches the foothills is sometimes calculated in 20-30 minutes. The entire area of origin and impact of a mudflow is called a mudflow basin. The type of mudflow is determined by the composition of the mudflow-forming rocks. The main types of mudflows: water-stone (a mixture of water with predominantly large stones, y = 1.1-1.5 t/m3) mud (a mixture of water with fine earth with a small concentration of stones, volumetric weight y = 1.5-2 t/ m3) mud-stone (mixture of water, pebbles, gravel, small stones, y==2.1-2.5 t/m3) For a mudflow to occur, three mandatory conditions must simultaneously coincide: the presence on the slopes of the mudflow basin of a sufficient amount of easily transportable products of mountain destruction rocks (sand, gravel, pebbles, small stones); the presence of a significant volume of water to wash away stones and soil from the slopes and move them along the riverbed; sufficient steepness of the slopes (at least 10-15°) of the mudflow basin and water flow (mudflow bed). The direct impetus for the occurrence of a mudflow can be: intense and prolonged rainfall; rapid melting of snow and glaciers; earthquakes and volcanic activity, etc. Anthropogenic factors often lead to the occurrence of mudflows: deforestation carried out on slopes, blasting, quarrying, mass construction . How to prepare for a mudflow Usually, the places where mudflows can occur are known. Before going to the mountains, study these places along your route and avoid them, especially after heavy rains. Always remember that it is almost impossible for someone caught in a mudflow to escape. You can only escape from a mudflow by avoiding it. Before leaving home, during early evacuation, turn off electricity, gas and water supply. Close doors, windows and vents tightly. Early measures to prevent mudflows In mudflow-prone areas, anti-mudflow dams and dams are built to retain solid runoff and pass a mixture of water and fine rock fractions, a cascade of dams to destroy the mudflow and free it from solid material, retaining walls to strengthen slopes, upland runoff interception and drainage ditches for drainage of runoff into nearby watercourses, etc., bypass canals are constructed, the level of mountain lakes is reduced, the soil on the slopes is strengthened by planting trees, observations are carried out, a warning system is organized and evacuation is planned. How to act in case of a mudflow Having heard the noise of an approaching mudflow, you should immediately rise from the bottom of the ravine up the drainage, at least 50-100 m. You must remember that stones of great weight can be thrown out of the roaring flow over long distances, threatening your life. Actions after a mudflow Provide assistance to the victims and assistance to the formations and authorities clearing debris and drifts along the path of the mudflow and in places where the bulk of the mudflow was carried out. If you are injured, try to provide yourself with first aid. If possible, the affected areas of your body should be kept in an elevated position, ice (wet cloth) and a pressure bandage should be applied to them. See your doctor. There are currently no methods for predicting mudflows. At the same time, for some mudflow areas, certain criteria have been established to assess the likelihood of mudflows occurring. Thus, for areas with a high probability of mudflows of storm origin, the critical amount of precipitation is determined for 1-3 days, mudflows of glacial origin (i.e., formed during outbursts of glacial lakes and intraglacial reservoirs) - the critical average air temperature for 10-15 days or a combination of these two criteria. Source of information: Wikipedia - village; www.linkout.ru - natural disasters: Mudflow;ww.bti.secna.ru - life safety;www.booksite.ru - mudflow;bestreferat.ru - emergencies natural character; www.5ballov.ru - sat down - abstracts.