Mudflow classification and types mudflows. The type of mudflow is determined by the composition of mudflow-forming rocks. The main types of mudflows: water-stone; mud; mudstone. Mudflows are characterized by linear dimensions (length and width), speed, duration and power (volume). By power (volume), mudflows are divided into catastrophic, powerful, medium and low power. Catastrophic mudflows are characterized by the removal of material of more than 1 million cubic meters. m, most often formed as a result of earthquakes and volcanic eruptions. Powerful mudflows are characterized by the removal of material from 100 thousand to 1 million cubic meters. m and rarely occur. During mudflows of medium thickness, the removal of material from 10 to 100 thousand cubic meters is observed. m and occur once every 2-3 years. In mudflows of low power, the removal of material does not exceed 10 thousand cubic meters. m and occur annually, sometimes several times a year. Mudflow classification. Classification of mudflows according to the height of the sources. Classification of mudflows by composition.
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"Earthquake Lesson" - Earthquakes. Secondary lesions. 5. 3. Which services are the first to arrive at the scene of a disaster? Man cannot prevent an earthquake! Lesson in the 7th grade of the N-Rotaevskaya school. 2. Primary lesions. Prepare to evacuate. Turn on the means of receiving information available in the house - TV, radio point.
"Natural disasters" - Volcanic eruption. Flood. Drought. Avalanche. Natural disasters. Natural disasters have threatened the inhabitants of our planet since the beginning of civilization. Tornado. Somewhere more, elsewhere less. The presentation was made by Kristina Papyan, a 3rd grade student. Earthquake. Tsunami. Fire in the steppe. Fire in the forest.
"Landslides and landslides" - Collapse of glaciers. Sel (sail - "turbulent stream") - a mountain stream, consisting of a mixture of water, mud, stones (there are mud, stone, mud-stone). Mudflows are formed in the mountains. The descent of an avalanche is accompanied by the formation of an air pre-shock wave, which produces the greatest destruction. An avalanche is a rapid, sudden movement of snow and (or) ice down the steep slopes of mountains, posing a threat to human life and activity.
"Situations of a natural nature" - What are the causes and possible consequences of an earthquake? Important to remember! How to provide first medical care? What are general rules transporting the victim? Group 1 "Rescuers" Earthquake. Earthquakes Floods Forest and peat fires. I. Goethe. V. Hugo. Is it possible to save the life of yourself and those around you in dangerous situations?
"Tsunami in the ocean" - Tsunami. Activities in the event of a tsunami. Emergencies natural character. Test yourself. Wave height is the vertical distance between the wave crest and the wave trough. Unusual drift of ice and other floating objects, formation of cracks in fast ice. Organization of the evacuation of the population. Volcanic eruptions(around 5%).
In general terms, the process of formation of mudflows of storm origin proceeds as follows. At first, water fills the pores and cracks, while rushing down the slope. In this case, the cohesive forces between the particles are sharply weakened, and the loose rock comes into a state of unstable equilibrium. Then the water begins to flow over the surface. The first to move are small particles of soil, then pebbles and rubble, finally, stones and boulders. The process is growing like an avalanche. All this mass enters the log or channel and involves in the movement of new masses of loose rock. If the water consumption is insufficient, then the mudflow seems to run out of steam. Small particles and small stones are carried down by the water, large stones create a self-bridge in the channel. A mudflow stop can also occur as a result of the attenuation of the flow velocity with a decrease in the slope of the river. No definite repeatability of mudflows is observed. It is noted that the formation of mud and mud-stone flows is promoted by the previous dry long weather. At the same time, masses of fine clay and sand particles accumulate on the mountain slopes. They are washed away by the rain. On the contrary, the formation of water-rock flows is favored by the preceding rainy weather. After all, solid material for these flows is mainly located at the foot of steep slopes and in the channels of rivers and streams. In the case of good previous moisture, the bond of stones to each other and to the bedrock is weakened.
V last years Anthropogenic factors, that is, those types of human activity that cause the formation of mudflows or their activation, have been added to the natural causes of the formation of mudflows. These factors include:
Deforestation on mountain slopes;
Degradation of soil cover by unregulated grazing;
Improper placement of waste rock dumps by mining enterprises;
Explosions during the construction of railways and roads and various structures;
Insufficient land reclamation after stripping and unregulated discharge of water from irrigation facilities on slopes;
Deterioration of soil and vegetation cover by waste from industrial enterprises.
Thus, the destruction of vegetation, the development of quarries, the cutting of slopes by roads, the mass construction on the slopes led to the development of mudflow phenomena in almost all Black Sea coast Caucasus (from Novorossiysk to Sochi).
Mudflow classification.
According to the granulometric composition of the solid component:
Water stone - a mixture of water with mostly large stones, including boulders and rock fragments. Volume weight 1.1 -1.5 t/m3. It is formed mainly in the zone of dense rocks. - Mud - A mixture of water with a solid phase of clay and silt particles with a small concentration of stones. Volume weight 1.5-2.0 t/m3. - Mudstone - a mixture of water, fine earth, pebbles, gravel, small stones; there are also large stones, but there are not many of them, they either fall out of the stream, or again begin to move along with it. Volume weight 2.1-2.5 t/m3. - Water-snow-stone - a transitional stage between the mudflow itself, in which the transport medium is water, and an avalanche. From this classification, it can be seen that the mudflow is very heavy, as a result of which the impact of the mudflow reaches 5-12 t/m2.
By genesis:
- Alpine type - characteristically rapid seasonal snowmelt (USA, Canada, Andes, Alps, Himalayas)
- Desert type - occurs in arid or semi-arid areas with sudden torrential downpours (Arizona, Nevada, California)
- Lahars - volcanic mudflows that occur after heavy rain on the slopes of volcanoes, recently covered with thick deposits of dust and ash that are still in an unstable position.
According to the frequency of mudflows, there are 3 groups:
High mudflow activity (recurring once every 3-5 years and more often);
Medium mudflow activity (with a frequency of once every 6 - 15 years);
Low mudflow activity (with a frequency of once every 16 years or less).
According to their impact on structures:
Low power - small washouts, partial clogging of openings of culverts.
· Medium power - heavy washouts, complete blockage of holes, damage and demolition without foundation structures.
Powerful - great destructive force, demolition of bridge trusses, destruction of bridge supports, stone buildings, roads.
Catastrophic - complete destruction of buildings, road sections along with the roadbed and structures, burial of structures under sediments. By water source:
By water source:
Rain - They are typical for mid-mountain and low-mountain mudflow basins that do not have glacial nutrition. The main condition for the formation of such mudflows is the amount of precipitation that can cause a washout of the products of destruction of rocks and involve them in movement.
Glacial - characteristic of highland basins with developed modern glaciers and glacial deposits (moraines). 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 when glacial or moraine lakes break through. The formation of glacial mudflows significantly depends on the ambient temperature.
Volcanic - can be formed during earthquakes. In some cases (during volcanic eruptions), when there is a joint formation of the liquid and solid components of mudflows.
According to the state of the water:
Associated (structural) flows - consist of a mixture of water, clay and sand particles. The solution has the properties of a plastic substance. All water is in the shells of micelles. The stream moves as a whole. Unlike a water stream, it does not follow the bends of the channel, but destroys and straightens them or crosses over obstacles.
Unconnected streams - they move at high speed; there is a constant collision of stones, their rolling and abrasion. There is a large amount of water, which acts as vehicle. The flow basically follows the bends of the channel, sometimes destroying it.
Mudflows are subdivided, based on the main factors of occurrence, into three classes (Table 2.18) and, based on the root causes of occurrence, into eight types (Table 2.19).
According to the composition of the transported solid material, mudflows are usually distinguished as follows:
mud flows, which are a mixture of water and fine earth with a small concentration of stones (the volumetric weight of the flow is 1.5–2.0 t / m 3);
mud-stone streams, which are a mixture of water, fine earth, pebbles, gravel, small stones; large stones also come across, but there are not many of them, they either fall out of the stream, or again begin to move with it (the volumetric weight of the stream is 2.1–2.5 t / m 3);
water-stone flows, which are a mixture of water with predominantly large stones, including boulders and rock fragments (volumetric weight of the flow is 1.1–1.5 t / m 3).
Mudflows are subdivided according to the nature of their movement in the channel into messengers and incoherent.
Table 2.18
Mudflow classification based on occurrence factors
|
Classes mudflows |
Formation factors |
Peculiarities distribution and regime |
|
Zonal manifestations |
Climatic (variability of hydrometeorological elements) |
The distribution is ubiquitous and has a zonal character. Mudflows are systematic; exit paths are relatively constant |
|
Regional manifestation |
Geological - active endogenous processes |
Limited distribution (in areas of greatest tectonic activity). Mudflows are episodic; exit paths are fickle |
|
Anthropogenic |
Economic activity - violations of the stability of mountain landscapes |
They develop in areas of the greatest economic load on the mountain landscape. Characteristic is the emergence of new mudflow basins with episodic, less often systematic mudflows. |
Connected flows consist of a mixture of water, clay and sand particles. The solution has the properties of a plastic substance. The flow seems to represent a single whole. Unlike a water stream, it does not follow the bends of the channel, but destroys and straightens them or crosses over an obstacle.
Table 2.19
Classification based on the root causes of mudflows
|
Types |
underlying formation |
Distribution areas and origin mechanism |
|
Rain |
Downpours, heavy rains |
The most massive type of mudflows on Earth, prevailing in the mountains of the equatorial, tropical and temperate climatic zones. The origin of mudflows is associated with the erosion of slopes and channels, as well as with landslides. |
|
Snow |
Intensive snowmelt in spring |
The dominant type of mudflows in the mountains of the Subarctic; the solid component of mudflows is represented by snow. The origin of mudflows is associated with the breakdown of waterlogged snow masses and with the breakthrough of snow dams. |
|
Glacial |
Intensive melting of snow and ice |
Formed in the zone of modern mountain glaciation; the most powerful are the mudflows of the Alpine highlands. The origin of mudflows is associated with the breakthrough of accumulations of melted glacial waters, as well as with the collapse of moraines and ice. |
|
volcanogenic |
Explosive volcanic eruptions |
formed in the regions active volcanoes; reach the largest sizes among all types of mudflows in terms of the length of the path and the volume of carryovers. The origin of mudflows is associated with the transformation of pyro-classical flows into mudflows due to rapid snowmelt, with the descent of crater lakes, etc. |
|
seismogenic |
high-ball earthquakes |
Formed in areas of high seismicity (8 points or more). The origin of mudflows is associated with the disruption of soil masses from the slopes into the channels |
|
limnogenic |
Development dynamics natural lake dams |
They form in areas of the Alpine highlands, which are characterized by dam lakes. The origin of mudflows is associated with the destruction of dams and the erosion of channels by a breakthrough wave. |
|
Anthropogenic impact |
Creation of accumulations of technogenic rocks in potentially mudflow basins; construction of low-quality earth dams, etc. |
Formed in dump storage areas mining enterprises, below reservoirs and elsewhere. The origin of mudflows is associated with erosion and slumping of strata of man-made rocks, with the destruction of dams and erosion of channels, etc. |
The end of the table. 2.19
Disconnected(current)streams moving at high speed. There is a constant impact of stones, their rolling and abrasion. The flow follows the bends of the channel, subjecting it to destruction in different places.
Mudflows are classified and by volume of transferred solid mass or, in other words, by power, and are divided into three groups:
powerful (strong power) - with the removal of more than 100 thousand m 3 of materials to the foot of the mountains, they happen once every 5–10 years;
medium power - with the removal of 10 to 100 thousand m 3 of materials, they happen once every 2-3 years;
weak power (low power) - with the removal of less than 100 thousand m 3 of materials, they happen annually, sometimes several times a year.
Very powerful (exceptionally strong power) mudflows are often emitted, with the removal of more than 1 million m 3 of clastic materials; happen once every 30-50 years.
Classification by the volume of one-time removals characterizes both the power of the mudflow and the potential of this mudflow basin. According to the volume of one-time removals, mudflows are divided into 6 groups (Table 2.20).
There are times when quiet and harmless-looking streams turn into terrible water-mud-stone streams, the so-called mudflows are a formidable natural phenomenon that often causes disasters to the local population.
Maria Dacosta from California describes the mudflow on February 8, 1991 in the vicinity of the city of Dodson.
“February 8, 1991, we woke up and saw that our house was surrounded on all sides by dirt. It was quiet, the rain had stopped. The dirt rose to the top step of the porch. Road workers could be seen trying to clear a path down pasture. The tap water in the kitchen did not flow. I put on rubber boots and went out into the yard. The fence at the back of the house was knocked down, the greenhouse was broken.
Finding that there was no electricity in the house, we turned on the house generator to get the news on TV. Suddenly a hum was heard. At first we thought that it was the noise of the included generator. I looked out into the yard and noticed that our horses were looking fearfully in the direction of the mountains. Feeling the vibration, I said to my sister, “Something is wrong,” and went to the kitchen window, which overlooked the garden behind the house. What was revealed to my eyes made me go cold with horror. A huge wall of dirt and rock fragments, as high as a three-story house, raced along the slope of the mountain straight at us.
We ran out into the yard, and the sister unleashed the horses, which immediately rushed away in different directions. As I ran across the pasture to the road, I suddenly remembered that Hershey, our dog, had stayed in the house. “Run, I'll catch up!” I shouted to my sister, rushing back. Hershey stood up on her hind legs and scratched at the glass of the closed door. I had to break the glass, as the door jammed. It became difficult for me to breathe - an asthma attack was approaching. The medicine was in the bathroom, I rushed there and suddenly heard a terrible rattle. From the window, I could see a wall of dirt covering our garage. Stones creaked on the roof of the garage. I rushed to the door, but it was too late. Waves of heavy mud, similar to cement, half closed the windows and the door. I was trapped! Window panes burst, viscous tongues of dirt inexorably crept up to my feet. I rushed to the attic. The door leading to the roof was jammed.
The dormer window is my salvation! Breaking the glass and skinning my hands in blood, I climbed out onto the roof. The stream beat against the walls of the house, reaching the level of the second floor. From the roof it was possible to see how the mud stream was carrying a horse. She wanted to get out of the mud, neighing. In the next second, the stream hit the horse against the wall of the house, and he no longer moved.
The dirt rose higher and higher. I stood next to the pipe. Blood gushed from my cut arm, but I felt no pain. My sister thought that day that I was dead. Mudflow, having reached the road, became wider and slowed down its movement. People were running, many carrying crying children. Abandoned cars stood on the highway: they could not pass. Turning back, people watched as tongues of mud slowly flooded the green lawns in front of their houses. Before reaching a few meters to the highway, the mudflow stopped its movement.
By three o'clock in the morning the next day, the flow began to subside, the rescuers were able to remove me from the roof. I almost fainted from blood loss…”
The California mudflow of 1991 destroyed houses in the suburbs of Dodson, a building materials plant, cut off the power line, railway washed away cars and trucks from the highway. Then 40 people died, 120 were missing.
This mudflow was triggered by an earthquake of two on the Richter scale and rapid snowmelt in the mountains. The mudflow speed was six meters per second on the slopes of the mountains and four in the valley. The volume of the transferred mud reached 25 thousand cubic meters.
