The generation of debris flows, how are debris flows formed?

Debris flow is a torrent formed by heavy rain and flood to saturate and dilute the soft soil mountain containing sand and gravel, and its area, volume and flow are large, while landslide is a small area of diluted soil mountain, and the typical debris flow is composed of thick mud suspended with coarse solid debris and rich in silt and clay. Under appropriate topographic conditions, a large amount of water is soaked into the solid accumulation material in the slope or ditch bed, which reduces its stability, and the solid accumulation material full of water moves under the action of its own gravity, forming a debris flow. Mudslides are a catastrophic geological phenomenon.

Mudslides erupt suddenly and violently, and can carry huge boulders. Because of its high speed and powerful energy, it is extremely destructive.

The whole process of mudslide flow is generally only a few hours, and the short one is only a few minutes. Debris flow is a kind of natural disaster widely distributed in some areas with special topography and geomorphological conditions in various countries around the world, which is a mixed flow of soil, water and air between sand-carrying water flow and landslide triggered by heavy rain, ice and snow melt and other water sources on mountain valleys or mountain slopes. Mudslides are mostly accompanied by flooding in mountainous areas.

Mudslides refer to landslides caused by heavy rains, snowstorms or other natural disasters in mountainous areas or other ravines and areas with steep terrain, and carry a large amount of sediment and rocks. Debris flow has the characteristics of suddenness, fast flow rate, large flow rate, large material capacity and strong destructive power.

Three basic conditions are required for the formation of debris flows: there is a suitable terrain with steepness to facilitate the collection of water and sediment; Abundant loose solids accumulate upstream; There is a sudden large amount of turnover in a short period of time**. Resources.

Large-scale concentrated precipitation, steep mountains, low vegetation coverage.

The formation of debris flow must meet the following three conditions at the same time: steep topography that is convenient for water collection and material collection; abundant loose matter; There is a large amount of water in a short period of time.

1. Topography and geomorphological conditions: the terrain has high mountains and deep ravines, steep terrain, large longitudinal slopes of the ditch bed, and the form of the watershed is convenient for water flow. In terms of landform, the landform of debris flow can generally be divided into three parts: formation area, circulation area and accumulation area.

The topography of the upstream formation area is mostly surrounded by mountains on three sides, a scoop or funnel shape with an outlet on one side, the terrain is relatively open, the surrounding mountains are high and steep, the mountains are broken, and the vegetation growth is poor, which is conducive to the concentration of water and detrital materials. The topography of the middle reaches of the circulation area is mostly narrow and steep canyons, and the longitudinal slope of the valley bed is large, so that the debris flow can be rapid and straight. The topography of the downstream accumulation area is an open and flat piedmont plain or river valley terrace, which makes the debris have a place to accumulate.

2. Loose material conditions: debris flows often occur in areas with complex geological structures, developed fault folds, strong neotectonic activities, and high intensity. The fragmentation of surface rock layers, the development of undesirable geological phenomena such as landslides, collapses, and staggered falls provide abundant solid materials for the formation of debris flows. In addition, the rock formation structure is loose and weak, easy to weather, joints are developed, or the soft and hard layered areas are susceptible to damage, and can also provide rich debris for debris flows**; Some human engineering economic activities, such as soil erosion caused by deforestation, mining, quarrying and slag, etc., often also provide a large amount of material for debris flows**.

Ice and snow meltwater and reservoir (pool) outburst water bodies. The main sources of debris flow in China are heavy rain and long-term continuous rainfall.

The formation of debris flow is the result of a combination of factors, generally speaking, there are three basic conditions: topographic conditions, geological conditions and hydrometeorological conditions. 1.

Topographic conditions are simply put, there must be a suitable area for the formation of debris flows, and the topography of this area should be conducive to the accumulation of loose materials such as soil and stones, and it must also be able to collect a large amount of water and be able to produce rapid flow. According to the above requirements, the debris flow is generally formed in a semicircular wide area surrounded by mountains on three sides and an exit on one side, and the surrounding slopes are steep, generally 30° to 60° steep slopes. The steep slopes are generally fragmented and have little vegetation cover.

Such slopes are often cut by gullies and develop collapses, landslides, etc. Under such conditions, it is easier for water and loose solids to collect uphill. When there is an area where the debris flow is generated, there must be a passage for the debris flow to carry these large quantities of sediment and debris.

Most of these passages are narrow, deep-cut canyons or gullies with very steep walls. Usually, when the debris flow in the ditch, it will also wash down the soil and rocks on the ditch bed and ditch wall, increasing the flow of the debris flow. When a mudslide is washed out of a valley or deep gully, it encounters a gentle and wide area, and its kinetic energy naturally decreases and finally stops.

2.Geological conditions, topography and geomorphological conditions determine the space and location of debris flows, but if there is no large amount of sediment and stones, debris flows are no longer mudslides but ordinary floods. It is the geological conditions that determine the large amount of sediment and rock**. The areas where debris flows often occur are generally areas with complex geological structures, rock weathering and fragmentation, active tectonic movements, frequent occurrences, and frequent collapse and landslide disasters.

Such an area, on the one hand, provides a large amount of soil and rock for the debris flow, and on the other hand, because of the steep terrain, the huge height difference provides a strong kinetic energy for the debris flow. 3.

Meteorological and hydrological conditions have sand and rocks, and there are places for activities, and mudslides cannot be formed without water. The occurrence of debris flow is closely related to the large amount of flowing water in a short period of time. In one case, a heavy rainstorm in a short period of time or the melting of glaciers and snow, or the sudden collapse of a mountain lake or reservoir.

These sudden currents of water rush down to make it easy to form mudslides. In addition, the frequent changes in temperature, alternating between hot and cold, and the erosion of precipitation will accelerate the weathering and fragmentation of rocks on the hillside, which will increase the broken material and facilitate the generation of debris flows. From the above, it can be seen that the occurrence of debris flow has a certain temporal and spatial distribution law.

In terms of time, it mostly occurs during the rain-flood season when the rainfall is concentrated or in the season when the alpine ice and snow melt strongly, mainly in the summer of each year. Spatially, it is mostly distributed in steep mountainous areas with strong tectonic strength.

If they hadn't cut down the trees on the mountain, there would have been no mudslides, and people wouldn't have been buried. This is a lesson, and may those who are greedy understand it.

It is usually caused by someone cutting down trees, and without trees, the land cannot be fixed and becomes a mudslide!

Mudslides are made of mud and sand.

The vegetation on the hillside was destroyed, and the soil could not be consolidated during the rainfall, which caused mudslides.

Floods (mudslides) are formed by loose earth and rocks on the slope that are saturated by heavy rain or long-term immersion of ice and snow meltwater