Salt is the main component of salt (sand) dust storm, which is often accompanied by salt (sand) dust storm. Salt (sand) dust storm is a common form of sandstorm disaster in desert areas of Central Asia, Iran, India and the western United States (such as Great Salt Lake or Salt Desert). Salt dust storms with pure salt particles are rare. Due to the strong wind mixed with a lot of salt (mainly gypsum and rock salt), salt (sand) dust storms are often white or light gray. White salt (sand) dust storm or salt storm is a kind of wind-blown sand salt dust storm, which is produced by salt desert, salt lake deposition or other loose rocks weathering, eroded and moved by strong wind and dispersed with the wind. This kind of salt (sand) dust storm makes the air turbid. The most active salt dust comes from grassland topsoil and deep saline soil sediments, accounting for 10% of salt desert in arid and semi-arid areas.
These salt desert soils are the accumulation areas of salt substances and wind erosion, or the migration areas of salt substances, and the surface soil of these salt desert soils is thick in salt. In spring and autumn, the soluble salt content in grassland topsoil and deep salt desert 0~ 10 cm soil accounts for more than 50% of the total salt content in 50 cm soil layer. The loose saline soil structure with high salt content and the surface without vegetation protection are easily eroded, transported and drifted by strong winds. The salt deserts in Central Asia are basically distributed in basins or low-lying areas, where groundwater is mostly concentrated in brackish water and salt substances are deeply deposited. Salt deserts are mainly distributed in the Amu Darya Delta, Murgab River, Kaska River, seraph Mountains and Rivers, the eastern part of the piedmont plain of Kopite Mountain, Caspian Sea, Aral Sea and Balkhash Lake.
Before the 1970s, salt (sand) dust storms were relatively rare. In the early 1960s, with the intensive development of Aral Sea basin resources, the frequency of sandstorms and salt dust storms increased greatly, which was caused by both natural factors and human factors.
In most cases, salt dust storms are mixed with sandstorms, which can be seen in Central Asia, western Kazakhstan and the northern Caspian Sea. However, naturally occurring white salt (sand) sandstorms are only recorded in the middle and lower reaches of the Volga River for the following reasons: ① These areas are densely populated; (2) Almost all these areas are located in the areas where the Aral Sea-Caspian Sea sedimentary area produces a lot of dust and salt substances.
According to Orova's estimation, there are 86,890 square kilometers of loose salt desert grasslands in the world, which can transport 520 million tons of salt dust to the atmosphere every year. Other deserts are 45,365,438+100000 square kilometers, including those potential salt deserts, which can transport 780 million tons of salt deposits every year, and all arid areas in the world can transport1300 million tons of various salt substances to the atmosphere every year. Therefore, according to the latest forecast, the salt reserves in the salt desert of Central Asia account for about 10% of the salt reserves in all arid and semi-arid areas.
It is estimated that about1.1million tons of salt is blown away from the salt desert in Central Asia every year, which is only a rough estimate, because the severity of blowing erosion can be clearly seen from the surface of the salt desert.
Central Asia consists of a series of basins and lowlands, which developed from the lake depressions left by the retreat of the ancient Mediterranean to the west. There are also some smaller deserts, such as Karakum Desert, Kizilkum Desert, Muyunkum Desert, Sareikh Cautrat Desert, Tawukum Desert and Sendukri Desert. There are 45 deserts in Kazakhstan alone, covering an area of 336,000 square kilometers. Deserts are widely distributed, and lowland salt deserts are also widely distributed. Desert and salt desert crisscross, and together * * * constitutes the Central Asian desert. For example, the weathered rock gypsum desert occupies most of the territory of northwest Kazakhstan. Therefore, sandstorms in Central Asia are mixed with more salt, mainly gypsum sulfate, which can be called salt (sand) dust storms.
The outstanding feature of the ecological situation in the 20th century is that the pressure of human beings on nature has increased, and the affected area has expanded. The purpose of human "transforming nature" is to change the ecological conditions, but in the end it seriously destroys and interferes with the ecological balance and worsens the ecological situation. Large-scale human transformation and development activities in Central Asia include: ① virgin land development in Kazakhstan in the 1960s; ② The construction of Karabogazgor Reservoir in 1970s; (3) Large-scale development of irrigated land in Aral Sea Basin leads to rapid expansion of salt desert and increase of salt dust storms.
In 1950s, the former Soviet Union built Lenin Canal between the Volga River and the Don River, leading the Volga River in Hainan to the Black Sea, which made the regional hydrology unbalanced. With the decline of the Caspian coastline, the port facilities of Odessa, a famous port city on the northern shore of the Caspian Sea, are 0/20 km away from the current coast. Karabogazgor Bay is shrinking, and 1980 is smaller than 1952 1/2 or more. In order to control the decline of the Caspian coastline, the Karabogazgor Reservoir was implemented in the spring of 1980 to separate the Caspian Sea from Karabogazgor Bay. This was a "victory" in conquering nature. Since then, people have once again started to fight their own bane. The reservoir separated the "Bay" from the "Sea", and the Karabogazgor Bay became shallow rapidly. After only four years, Karabogazgor Bay dried up completely, and a huge and dangerous salt desert environment was formed on the spot like a dead valley. Under the influence of human activities, "artificial salt source" appeared. The salt dust in Karabogazgor is deposited in front of the Pamirs. 1984, a pipeline was built on the dam to deliver water to Karabogazgor Bay. 1992, the dam was finally destroyed. 1In May, 1995, the water level of Karabogazgor Bay rose by 7 meters, and the whole Karabogazgor Bay was restored to the former "Liangshan Mountain in Shui Bo".
After the "artificial salt source" in Karabogazgor Bay is successfully eliminated, there will be more and more artificial components in the salt source of white salt (sand) sandstorm in Aral Sea area. There have been obvious environmental changes here, and it has great regional characteristics. Because of irrigation, the river has been artificially changed, and the river flow has changed, resulting in serious ecological changes in most areas of the basin.
The sharp decline of the recharge of the Amu Darya River and the Syr Darya River began at 196 1, which led to the rapid decline of the water level in the Aral Sea. In the past decades, the total recharge of the above rivers has decreased by about 4000 ~ 5000 cubic meters per year, while 1960 has decreased by 55000 ~ 460000 cubic meters per year. Such a large flow is equal to the annual precipitation (9,000 ~ 65,438,000+0,000 cubic meters) and obvious groundwater recharge and evaporation, which makes the water surface of the Aral Sea close to the average sea level of 53 meters, with an average depth of 1.6 meters, and the water area of the Aral Sea reaches 66,000 ~ 67,000 square kilometers. By 1999, the sea level had dropped by 18m, and now it has reached the average sea level mark of 33.8m The width of the exposed and dry lake exceeds 120km, and the total water area is only 40300km2. The Aral Sea will disappear from the earth in front of us, and the youngest sandy salt desert on the earth, the Aral Sea Desert, is forming in situ.
The decline of the Aral Sea surface has led to the change of marine geochemical process. Before the sea level fell, the Aral Sea was a salt-accumulating basin, and about 23.8 million tons of salt substances flowed into the Aral Sea with surface runoff every year, which was equal to the total groundwater flow. At present, the dry coastal zone has become a salt storage place for transporting salt to other areas, because the exposed seabed has become a huge salt desert surface.
According to its morphological characteristics, the dry seabed soil is crusted soil and loose saline soil, and swamp saline soil with an area of 2000 square kilometers has been formed. Light structural soil is easy to produce strong wind erosion process and form aeolian terrain. In the aeolian landform, the sand in the inter-hill depressions basically belongs to mild and moderate salinization sand, and the salt content of crescent dunes is less than 0. 1%~0.3%, and the dust content is 4% ~ 6%. The drying up of the Aral Sea, the intense salt accumulation on the seabed and the evolution of wind-blown sand determine that it plays an important role in enriching the sources of salt dust and sand dust, which seriously worsens the ecological situation in the surrounding areas in the form of erosion, transportation and floating dust.
The arid zone around Aral Sea was formed in 196 1, but it was not until 1975 that obvious strong sandstorms and salt dust storms appeared. 1In April, 975, the salt (sand) dust storm first occurred on the northeast coast of Aral Sea and extended to the south of the Syr Darya River Delta. From the satellite photos of the earth, it can be clearly seen that the salt (sand) dust storm formed a dry sand belt with a width of 20~25 km and a length of 100 km. 1975 Only 8 salt (sand) dust storms occurred from April to June; Among them, it happened 5 times in April, 2 times in May and 1 time in June. During the period of 1975~ 198 1, there were 29 salt (sand) dust storms in this area, which basically extended to the west and southwest, with an extension length of 200~450 kilometers.
During the five years from 1985 to 1990, the average days of salt (sand) dust storms increased to 5.5 days per year.
The deposition of aeolian salt dust in grassland topsoil and loose salt desert is about 5000~7000 tons /km2. In the patch salinization area with high salt content near the surface, about 728 tons of saline soil, salt dust and salt nitrate are blown away per square kilometer.
During the period of 1986, there were three main erosion points, namely Vostokny, Saresh Ganski and Erski, Cocala. At present, there are five artificial wind erosion dust sources on the dry seabed of the Aral Sea in Kazakhstan, which are the bottom of the former Sareshiknak Bay in the north and the beaches of the former caral and Bersa-Quelme Islands, the dry lake bottom from Syr Darya River to Akbekin Islands in the east, and the recently formed islands of Vozrockane and lazarev Islands in the west.
According to aerial observation, the dust cloud is as high as 3000 ~ 4000 meters. When dry-hot salt (sand) dust storms occur in the southeast, the ground, objects, vegetation and livestock are covered with a layer of slightly bitter white sediment, with a thickness of 1 ~ 2mm and 2~4 mm in some areas. The chemical analysis results show that the sediments are mainly sodium sulfate, sodium chloride, magnesium salt, gypsum particles and silica particles. As mentioned earlier, there was a white salt storm, and the dust storms of salt powder and salt (sand) on April 18~22 1955 had a great impact, with the damage range reaching 500,000 square kilometers.
Satellite photos can clearly see the salt (sand) dust storm floating in the Volga River basin. Salt (sand) dust storms carry a lot of dust and salt dust through this area, and the prevailing southeast and east winds often strengthen in this area, forming storms and even hurricanes. Storms and hurricanes rolled up huge columns of salt powder and dust, passed through the ancient Utzboy passage, the salt desert of Karakum Desert and the Caspian Sea coast, and moved to the Russian plain. In the vast area of Volga River basin, power failure is caused by the influence of dust, floating dust and salt dust on power generation equipment and ancillary equipment.
In Xinjiang, China, which is close to Central Asia, you can not only taste the bitter salt scraped from Northwest Central Asia, but also have a similar situation in the environment. There is a big lake-Ebinur Lake on the Chinese side of the Sino-Kazakhstan border (Alashankou) in northern Xinjiang. The lake is replenished by Kuitun River and other rivers upstream. In the past 50 years, a large number of irrigated farmland has been developed in the middle and upper reaches, and a number of emerging industrial cities such as Shihezi, Kuitun and Dushanzi have emerged. The upstream water almost completely cut off the supply source of Ebinur Lake, causing the lake to shrink rapidly. By the end of the 20th century, Ebinur Lake had completely dried up, and the salt at the bottom of the dried lake was exposed, and the early exposed part of the edge was fluffy saline soil formed by sulfate, which formed a salt sandstorm when encountering strong winds. Coincidentally, Alashankou in the northwest is a famous tuyere in northern Xinjiang, and its terrain conditions make it accumulate strong winds, often blowing strong winds of magnitude 8 or above, and there are records of 12 winds. The sand blown from Ebinur Lake area forms a desert in front of the mountain, and the sand and alkali disaster in Yili-Alashankou section of the northern Xinjiang railway is serious, which threatens the safety of the northern Xinjiang railway from time to time. This railway has become the bottleneck of Lianyungang-Frankfurt Eurasian Continental Bridge.