South Eight Immortals

Nanbaxian is one of the largest and most typical Yadan landscapes in the world, with a distribution area of more than 1000 square kilometers.

This is a geomorphic combination of a series of long strip-shaped soil mounds and concave trenches.

Because the local rocks are rich in iron and the geomagnetism is strong, the compass often fails, which leads to the inability to distinguish the direction and get lost.

It is undeveloped and sparsely populated, so it is recommended to travel together.

Yardang landform

synonym

Nanbaxian generally refers to Yadan landform

This entry is compiled and applied by "popular science China" Science Encyclopedia

to examine

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Yadan landform is a special landform in Lop Nur area of Xinjiang, which is a typical wind erosion landform. The term "Yadan" has a history of more than 100 years since Sven Hedin was formally put forward in 1903 and gradually accepted by geoscientists.

"Yadan" in Uyghur language means "hill with steep wall". This event was later selected by National Geographic of China magazine and Chinese geographic society to jointly launch the "Centennial discovery of Chinese Geography".

Yadan landform refers to a kind of wind erosion landform in dry area. The surface formed by fluvial and lacustrine soil deposits, through weathering, intermittent water erosion and wind erosion, forms a combination of wind erosion mounds and wind erosion depressions (grooves) which are parallel to the prevailing wind direction and arranged alternately.

The origin of naming

The development of the definition of Yadan had many appellations before it was widely used in geosciences. It is called "Longcheng", "bailongdui" and "longdui" in volume 28 of Hanshu · geographical records written by Ban Gu, a historian of the Eastern Han Dynasty. Stapff called them "aerodynamic landforms"

And Sphinx hills

"Bugra vyduvanije; erosion hill", "Shahr LUT; desert cities"

"Mud lions"

"Tu Fu" and so on.

From 1899 to 1903, Swedish Explorer Sven heding, during his investigation in Lop Nur, Xinjiang, China, distributed the ancient lakes in groups, hundreds of meters long and more than 2-3 meters high, heading northeast to southwest. The landforms formed by water erosion first and then wind erosion were called Yardang according to the local Uyghur Language

. Later, with the wide spread of his book Central Asia and Tibet in academic circles at home and abroad, it was transliterated as "Yadan" in China. Since then, the term "Yardang" has been officially accepted by the scientific field. Following the discovery of Yadan landform in Luobu wasteland, many similar landforms have been found in many parts of arid regions in the world, which are collectively referred to as Yadan landform.

In 2009, on the occasion of the 60th anniversary of the founding of new China, the 100th anniversary of the founding of the Geographical Society of China, and the 100th anniversary of the founding and development of China's modern geography, China National Geographic magazine and the Geographical Society of China jointly launched the selection activity of "the Centennial discovery of China's geography". Including: in the early 20th century, Chinese and foreign scholars discovered and named the Yadan landform.

Age of formation

There are four methods to study the formation age of Yadan

(1) Based on field investigation and observation of modern wind erosion rate, its formation age can be calculated indirectly. For example, Xia Xuncheng thinks that the wind erosion rate of Loulan ancient city in Lop Nur is 0.24-0.47 cm / year, where Yadan is the product of wind erosion for nearly a thousand years; and Guti é rrez Elorza and others think that Yadan formed on the gypsum waste dumped in Yadan area in Ebro lowland of Spain is less than 100 years old.

(2) The formation age of Yadan landform can be calculated by obtaining the stratigraphic age at the top of Yadan landform. For example, Clarke et al. Used the infrared luminescence method to date the 1-meter-high small Yadan in the Mojave Desert of the United States, and found that its formation time was less than 250 years.

(3) By dating the cultural relics in Yadan area, we can infer the formation age of Yadan. Bohlin and hoerner dated the pottery in the fine sand near Lop Nor and Dunhuang, respectively. They believed that the medium-sized Yadan began to form 1.5-2.0 thousand years ago.

(4) Through the analysis of the formation age of the desert around Yadan, the climate change in the regional geological history recorded by cave deposits and the previous research results of climate change, the formation age of Yadan can be inferred indirectly, which is one of the methods that scholars use more. For example, El Baz and others believe that the wind erosion history of the large Yadan in the desert of Western Egypt can be traced back to the late Miocene or early Pliocene according to the climate change in the regional geological history period; Beadnell, peel and Hagedorn believe that the medium Yadan in the Sahara of Africa was formed after the Neolithic pluvial period; Haynes thinks that the Yadan landform in the eastern Sahara began to be extremely dry 4.5 thousand years ago It is believed by Washington that the 4-meter-high Yadan in the bodele lowland of Chad may have been formed 1.2-2.4 thousand years ago; goudie inferred that the large Yadan on the Namib Desert of Africa may have been formed millions of years ago; INBAR et al. Believed that the Yadan on the basalt in payun matru volcanic area of Argentina may have been formed in the late Pleistocene At the beginning of Holocene, Vincent et al inferred that the Yadan landform of Cambrian Ordovician sandstone in northwestern Saudi Arabia began to form 400 thousand years ago according to the climate change recorded by cave deposits; Zheng Benxing et al considered that the Yadan landform of Dunhuang Yadan Geopark began to cut in the middle and late Pleistocene by analyzing the geological evolution of surrounding areas and previous research results Yes.

In addition to the single application of the above methods, there are also scholars combined to use these methods to infer the formation age of Yadan. For example, Al dousari et al. Calculated that the formation age of Yadan in the UM al rimam lowland of keweite was 44-1500 years ago based on previous regional climate studies and field observation of wind erosion rate.

Yadan landform is an erosion landform, which is different from the accumulation landform. Its formation age is different from that of Yadan stratum. The age when the stratum began to be cut is the age when Yadan began to form. Therefore, it is very difficult to determine the formation age of Yadan, and there is no direct method to determine its formation age, which is also the difficulty in the study of Yadan landform. Only a series of indirect methods can be used to infer the approximate age of its formation, but the accuracy is not good. Due to the differences of lithology, dynamics, climate and scale in different or the same area, the formation age of Yadan landform is also very different.

China

The Yadan landform group in the western Qaidam Basin of China has the longest extension in the world. Yadan landform in China covers an area of about 20000 square kilometers, mainly distributed in the northwest of Qaidam Basin in Qinghai Province, the middle and lower reaches of Shule River in the west of Yumen pass, Wuerhe and jiangjunmiao in the west of Junggar Basin in Xinjiang, Wubao and Shisanjianfang in Tuha basin, north of Lop Nur and Loulan ancient city in the east of Tarim Basin, Kizil ghost city in Baicheng County in the north.

In 1962, fan Xipeng divided the Yadan landform into three types: pyramid, ridge and streamline.

In 1988, Mustafa harimov divided the Yadan landforms into eight types: Fangshan, canines, cones, pyramids, long ridges, arches, whales and low streamline.

Geomorphological classification

The purpose of Yadan classification is to classify many Yadan landforms with different morphology, scale, age, development stage and origin, and to determine their position and relationship in the classification system of Yadan landforms. Due to the different classification principles adopted, various classification systems are also different.

There are three classification systems in China. According to the size and age of formation, Chen zongqi divided Yadan into mesas (Pingdingshan) and yadangs (yardangs) according to their morphology; Xia Xuncheng divided Yadan into three types according to their genesis: wind erosion dominated Yadan, water erosion dominated Yadan and water erosion followed by wind erosion; Zheng Benxing divided Yadan into red Yadan, white Yadan and yellow Yadan according to their geochemical composition Dan.

There are two kinds of classification systems in foreign countries. In addition to Cooke's classification of small, medium and large types of Yadan according to the shape and size of Yadan, halimov's classification system of Yadan landform in Qaidam Basin is worth learning in the current classification research of Yadan landform.

Cause of formation

Lithologic conditions

Lithologic conditions are the basis of the formation and development of Yadan. Because of different definitions of Yadan, Yadan can be formed and developed on rocks of different hardness and ages. Some scholars believe that in addition to

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