Why do mudslides occur?

Debris flow-a special heterogeneous torrent, which is generated in ravines or slopes and is filled with a lot of solid substances (mud, sand, stones and boulders). It has the characteristics of sudden outbreak, short duration, fierce strength and great destructive power, and is a common natural disaster in mountainous areas. Research Introduction-In the study of debris flow, the Soviet Union is in a leading position. The study of the Soviet Union began in 1859, with a wide range of research contents, comprehensive research, a unified national coordinating body and remarkable achievements. Japan is an island country with many mudslides. 1966, fixed-point observation and laboratory experimental study of debris flow began, which made rapid progress and played an important role in the study of debris flow in the world. Other countries, such as Austria, the United States, Britain, France, Democratic Germany and the Federal Republic of Germany, Yugoslavia, Romania, Norway, Canada, Australia, New Zealand and Indonesia, have carried out research on the prevention and control of debris flow disasters to varying degrees. Our ancient ancestors accumulated some experience in fighting against debris flow, but the scientific research on debris flow began from 1950s to mid-1980s, and accumulated rich and precious debris flow data, preliminarily grasped the distribution, formation, movement, accumulation, development and evolution of debris flow in China, and explored some effective methods for comprehensive or single control of debris flow in different mountainous areas, different types and different control requirements. Compared with foreign countries, China has conducted a comprehensive investigation and research on regional debris flow, and conducted field observation and experimental research.

The research on early warning and comprehensive management has accumulated significantly. Formation conditions-Debris flow is the product of interaction and contradiction among sediments, stones and water. Its formation and development are controlled and influenced by a series of factors such as geology, geomorphology, hydrology and meteorology, and the rationality of human activities greatly inhibits or intensifies the formation and development of debris flow. To sum up, the formation of debris flow must meet three conditions at the same time: there are abundant loose solid substances in the basin, which can be transferred to the ravine through block movements such as landslides and collapses, and directly interact with the rushing water to form debris flow, which is the material basis for the formation of debris flow; The steep valley slope and large vertical slope of the gully bed in the basin are conducive to the collection of water flow and the collapse of loose deposits, which are mixed with debris flow and flow down quickly. In the middle and upper reaches, there are heavy rains and floods, or glaciers, snow melt water and lakes and reservoirs burst, providing rich water sources. Under the favorable confluence terrain, the loose materials on the valley slope or gully bed are eroded and excavated, which is the hydrodynamic condition for the formation of debris flow. The above three conditions are complementary to each other. The general rule is that the regional distribution and development degree of debris flow are controlled by geological structure and landform combination, the outbreak frequency and activity intensity of debris flow are controlled by water supply and hydrodynamic excitation factors, and the nature and scale of debris flow are controlled by loose solid material reserves and supply methods. Therefore, in terms of spatial distribution, debris flows are mainly formed in mountainous areas where fault structures are developed or neotectonic movements are active, earthquakes are frequent, precipitation is concentrated, local rainstorms and soil erosion are serious, and mountainous areas where ancient glaciers are developed and modern glaciers are entrenched (especially mountainous areas where modern marine glaciers are developed). In terms of time, most debris flows are formed in rainy or rainstorm years after years of drought or unreasonable development and utilization of mountain resources by human beings; A year of climate warming, glaciers retreating, snow melting and frozen soil thawing. Morphological zoning-Debris flow mostly develops in the branch ditches on both sides of the mountain rivers. A typical debris flow gully is similar to a goldfish, and it is divided into three sections from upstream to downstream: debris flow formation area, circulation area and accumulation area. Formation area-located in the upper reaches of the basin, mostly funnel-shaped terrain surrounded by mountains, where there are landslides, collapses or ice collapses, avalanches, etc. Most of them are centralized. The mountain is high and the slope is deep, the slope is steep, and the gravity erosion and slope erosion are strong, which is the birthplace of debris flow, and the solid substances and water sources that form debris flow are mainly replenished from here. Circulation area-located in the middle reaches of the river basin, mostly in bedrock canyon terrain, with large longitudinal slope of gully bed, often scarps, waterfalls or waterfalls, which is the passage for debris flow to rush out of the mountain. The accumulation area is mostly located in the lower reaches of the river basin, and the debris flow swings frequently and overflows quickly, forming fan-shaped and cone-shaped landforms. Large and small stones are dense, and the ridges on the ground are undulating. Mountain towns, villages, factories, mines, railways and highways are mostly located here, which is the main area hit by mudslides. Distribution and harm-Debris flows are widely distributed in mountainous areas all over the world, and there are mudslides on six continents except Antarctica. The most active areas are mountainous areas between the Tropic of Cancer and 50 north latitude, such as Alps-Himalayas, Pacific Rim Mountains, and some folded and fractured mountains in Eurasia. , followed by some mountainous areas in Latin America, Oceania and Africa. In the area south of the Tropic of Cancer, mudslides sometimes occur. Debris flow disasters have affected more than 60 countries and regions in the world, with the most severely affected countries including the Soviet Union, Japan, the United States, Austria, Indonesia, Peru, Chile, New Zealand, India, Pakistan, France, Italy and Nepal. According to published data, there are more than 60,000 debris flow gullies in Japan, more than 6,000 in the Soviet Union and more than 4,000 in Austria, which cause huge economic losses and personal injuries every year. Almaty, the Soviet Union, has been hit by mudslides many times in history. 192 1 year, the catastrophic mudslide caused 500 deaths and 6 million rubles of property losses. 1966, a mudslide broke out in Italy, killing more than 100 people, burying 300,000 hectares of cultivated land and 50,000 large livestock. 1in July and August, 1973, heavy rains in Japan caused large-scale mudslides in more than 230 valleys, causing great disasters. The debris flow in the United States is mainly distributed in the arid mountainous areas in the west, and there are more than 100 debris flow gullies near Los Angeles in the Sierra Nevada.

Reference: China Encyclopedia Wisdom Collection163.24.155.45/newlib/cpedia/content? ID=74996。 Query =6

After the catastrophic mudslide disaster in Danba, Sichuan in July, 2003, experts from Chengdu Mountain Research Institute of China Academy of Sciences came to the conclusion that apart from irresistible natural forces, one of the main reasons for this mudslide disaster is that the local people's awareness of debris flow disaster prevention is very weak, and their self-protection and self-rescue abilities are too poor. Several villages, such as Qiongshan Second Village, were built on a large area of mud and stone accumulation land; The village is 4.2 kilometers away from the gully mouth, and the debris flow has precious 20 minutes to avoid disasters during this 4.2-kilometer movement. However, due to the lack of communication equipment, it is impossible to contact, which makes it too late for villagers and tourists in Mizoguchi to evacuate; Some people also follow the direction of mudslides, which leads to bad luck. Debris flow disaster in Danba reminds us once again that we should vigorously carry out popular science education on mountain disasters, mainly mudslides and landslides, strengthen tourists' awareness of disaster prevention and mitigation, and improve people's self-protection and self-help ability. Mountain disasters are fierce and powerful, far more sudden and tragic than floods. Therefore, staying away from disasters and avoiding dangers is the best disaster prevention method. When traveling to mountain valleys, we must know the recent weather situation, weather forecast and geological disaster meteorological forecast in the next few days in advance. Visitors should try to avoid going to these scenic spots in rainy days or continuous rainy days. If it coincides with bad weather, it is better to suffer economic losses and adjust the tourist route than to rush there. Geological experts tell us that there are traces of mudslides, landslides and collapses here. The steep slope or the slope is an isolated mountain mouth or concave steep slope, with obvious cracks on the slope, open space in front of the slope, or collapse, indicating that landslide or collapse has occurred before and may happen again in the future; The river suddenly stopped flowing or the water potential suddenly increased, and there were more firewood trees. There was a sound like the roar of a train or muffled thunder coming from a deep valley or ditch, and the deep valley was suddenly dark and slightly shaken. These signs can confirm that mudslides have occurred in the upper reaches of the valley. If you encounter a mudslide while traveling in mountainous areas, tourists should not panic, and must abide by the rules and take the following emergency measures: according to various phenomena, you should escape immediately after the mudslide occurs, and choose the shortest and safest path to run to the hillside or highland on both sides of the valley to avoid running in the direction of the mudslide; Don't stay in depressions with steep slopes and thick soil layers; Don't climb trees to avoid, because debris flow can sweep away all obstacles along the way; Avoid curved concave banks or narrow convex banks with low height of rivers (ditches); Don't hide under steep mountains to prevent mudslides or hillside collapses; After a long period of rain or rainstorm, or just after the rain stopped, it is impossible to return to the dangerous area immediately, and debris flow often lags behind the outbreak of rainfall; After there is more rain during the day, pay close attention to the rain at night or at night, and it is best to transfer and evacuate in advance; When people play in the valley, it is forbidden to build camping tents in the ditch or in the low-lying places in the ditch. Visitors should not stay near the dangerous rocks, avoid getting caught in the rain, rest, walk and climb the dangerous rocks on the concave steep slope. In mountain tourism, besides mountain torrents, mudslides, landslides and collapses, lightning disasters in summer and ice and snow disasters in winter all pose a threat to the personal safety of tourists. How to escape from debris flow: 1. When hiking along the valley, in case of heavy rain, you should quickly move to a safe highland nearby, stay away from the valley as far as possible, and don't stay at the bottom of the valley for too long. Pay attention to the surrounding environment, and pay special attention to whether you hear the thunder coming from the distant valley. If you hear it, be on high alert. 3. Choose a flat highland as a camp, avoid the hillside with rolling stones and a lot of deposits as much as possible, and don't camp at the valley bottom and river ditch. 4. After you find the debris flow, you should immediately climb to the hillside on both sides along the vertical direction of the debris flow. Climb as high as possible. The faster you run, the better. Never go downstream of the mudslide. A two-phase flow of liquid and solid filled with clay and gravel produced in valleys and slopes. Because of its sudden outbreak, rapid movement, great influence and large handling capacity, it destroys all kinds of buildings and facilities, silts up villages and farmland and blocks rivers, which is a serious natural disaster. In China, Sichuan, Yunnan, * *, Gansu, Shaanxi, Shanxi, Beijing and other 26 provinces (cities, autonomous regions) are more serious. There are mudslides in more than 60 countries and regions in the world, such as the Soviet Union, Japan and Austria. There are many ways to classify the types of debris flow. According to the composition of entrained substances, it can be divided into three categories: mud flow. The entrained material is mainly sediment below coarse sand, and sometimes there is a small amount of gravel chips. Debris flow is a fluid composed of a large number of fine particles (silt, clay, etc.). ) and huge stones, boulders and water. Water and stone flow. It is mainly composed of large stones and water or dilute mud. According to the dynamic conditions of debris flow, it can be divided into hydraulic debris flow. Due to the strong erosion of surface runoff or water body burst, a large number of solid substances enter the channel, forming debris flow. Belonging to the research field of sediment movement mechanics. Gravity debris flow. Because the water content in the soil exceeds saturation, the soil loses its balance and leads to sliding. According to the physical and mechanical characteristics, debris flow can be divided into turbulent type (sparse debris flow or high-concentration flash flood) and laminar type (viscous debris flow or structural debris flow). The conditions for the formation of debris flow should be rich in loose solid matter, steep terrain and certain intensity of precipitation. Human factors also have a serious impact on the occurrence of mudslides in some areas. The composition, quantity and recharge mode of loose solid matter determine the type, nature and scale of debris flow. The composition, storage and accumulation of loose solid matter depend on geological structure, neotectonic movement, earthquake, stratigraphic lithology and adverse physical and geological phenomena. The terrain forming debris flow has the characteristics of steep and funnel-shaped height difference, and loose solid materials on the slope are easy to gather in valleys, forming debris flow under the action of hydrodynamic force. Water is an important condition to trigger the outbreak of debris flow, and it is also a component and transport medium of debris flow. The water sources of debris flow include rainstorm, ice and snow, meltwater and water body burst, in which rainstorm is the most important factor. Man-made factors, such as destroying natural conditions and increasing loose solid matter, will lead to the occurrence, development, revival or aggravation of debris flow. Motion characteristics Debris flow appears in the form of intermittent bursts, and dozens to dozens of bursts are formed in the process of a debris flow. The front peak of the water flow is high and steep, and it is mostly composed of boulders, commonly known as bibcock. Sometimes the faucet rushes out of the canyon from the peak of a few meters to a dozen meters. The loss of movement along the debris flow makes the water flow thinner and slower, and finally stops in the ditch bed in the form of blades. The process of moving forward more than once in paroxysmal water flow is called bed-building process. After the bed-making process is completed, the debris flow behind it moves at a faster speed on the mud surface. Because of the high velocity and large inertia, the concave bank has obvious superelevation phenomenon when it flows through the bend, and it is easy to cut and straighten. In case of reverse slope, you can climb over and go forward, sometimes even over terraces, scarps or diversion dams as high as 5 ~ 10 meters. After the debris flow stops, the debris flow structure remains unchanged, forming many gravel piles parallel to the mainstream direction, which are tongue-shaped, ridge-shaped and island-shaped, with flat or slightly protruding top surface, steep sides and steep front ridges. Because of this movement feature and accumulation form of debris flow, the ground of accumulation fan is uneven, which is very different from that of foothill accumulation fan formed by general mountain torrents or glaciation. Preventive measures and protection works. Slope protection, retaining walls, dikes, etc. in mountainous areas where mudslides are concentrated. Build along the stream to resist or eliminate the erosion, impact, lateral erosion and siltation of debris flow. Drainage works. Its function is to improve the flow potential of debris flow and increase the flood discharge capacity of debris flow ditch (see technical measures of soil and water conservation engineering). Stop the project. It is used to control the solid matter and flash flood runoff that constitute debris flow, weaken the flow, flow and energy of debris flow, and reduce the harm of debris flow to downstream buildings such as scouring, impact and siltation. Biological measures. It is used to protect the hillside slope, maintain soil and water, prevent the continuous development of debris flow, and even eventually eradicate debris flow.

Reference: Online

1. Debris flow is the fastest (up to 80km/h).

As fast as a desperate minibus on Pokfulam Road)

Liquid surface sliding is a kind of landslide. 2. Debris flow is a kind of loose soil caused by a lot of water. After the surface absorbs water, the weight increases and the structural force weakens.

Form an unstable soil layer. Once further * * * such as flash floods.

Tashu

Even the vibration of the truck passing by.

Debris flow was triggered. Soil dissolved water washes down the hillside in the form of fluid to form debris flow, which is a kind of landslide. The main cause of debris flow is water.

Including sudden high rainfall.

Melting snow

River flooding

Or the slope has not been repaired for a long time. The size of the surface material also has an influence.

The bigger the stone is, the more it can stick together to form a structural force. Weathering is more serious.

The finer the soil layer, the easier it is to be washed away by water and become fluid. 3. As mentioned above, the places where it happened include high rainfall.

High slope

There is a river/lake nearby.

At the bottom of the iceberg

Severe weathering

It may occur in places with small soil and few stones. The rainfall in China and Hongkong is heavy and uneven.

Large temperature difference

Severe weathering

Sanduo

There are many man-made slopes with extremely steep slopes.

A place full of streams/ditches/ponds.

There are frequent mudslides.

Reference:. qid=700603240064 1