The beauty of sand dunes is at Hami South Lake

At the 94th Academy Awards, "Dune" won six major awards including Best Cinematography, Best Editing, Best Visual Effects, Best Sound, Best Original Score, and Best Art Direction. Although it ultimately won the Best Picture award, it became the biggest winner of the night.

In fact, as early as the premiere of Dune, the film was expected to be a "Star Wars-level film of this era". A wave of orange desert fever swept the theaters, and watching it on the big screen can better feel its magnificent, delicate and unique. The seemingly surreal "desert planet" scenery in the film was shot on location without the use of green screen technology.

The shocking scenes in the movie make people think, what would happen if the earth in the real world turned into a "sand ball"? Over the past century, the Sahara Desert has expanded by 10%. Human factors and climate change have accelerated the natural cycle of Sahara expansion. The speed of human sand control will never catch up with the speed of desertification.

▲Stills from "Dune", from the Internet

my country is one of the countries with the most deserts in the world. It stretches across the northwest, north and east China in an arc-shaped belt, stretching thousands of miles. This arc-shaped desert belt is 600 kilometers wide from north to south and 4,000 kilometers long from east to west, covering an area of ​​more than 710,000 square kilometers, mainly distributed in Xinjiang, Gansu, Qinghai, Ningxia and western Inner Mongolia.

Judging from the distribution area of ​​deserts in various provinces and regions, Xinjiang is the province with the largest desert distribution area in my country, reaching 404,000 square kilometers, accounting for 63% of the country's desert area and 25% of Xinjiang's total land area.

▲Distribution map of major deserts in my country

Among the many deserts in Xinjiang, there is a pocket desert with an area of ​​only 36 square kilometers. Although it is small in size, it is an ideal place to study the formation and evolution of deserts because it is easy to enter and has a complete range of sandy landforms. This pocket desert is the Nanhu Gobi Desert, located 20 kilometers south of Hami City.

The Hami Nanhu Desert is located on the east side of Nanhu Township, Hami City, in the lower part of the terraced Gobi plain. Geographically, it belongs to the Hami Basin. The Hami Basin is located in the Hami area of ​​Xinjiang, with an area of ​​about 50,000 square kilometers. It is high in the north and low in the south, and slopes from northeast to southwest. The northern part of the basin is the alluvial inclined plain on the southern slope of the Tianshan Mountains, the eastern and western parts are hills and Gobi, and the southern part is the Nanhu Gobi Desert.

▲Satellite image of Nanhu Desert

The sand dunes are distributed along a seasonal river called Kuruk Gol, and are deposited in a belt-like manner in a near east-west direction. The desert distribution area is about 25 kilometers long and about 10 kilometers wide at its widest. It is divided into two large areas, east and west, with a break in the middle, and is mainly semi-fixed sand dunes.

Although the Nanhu Desert is relatively small in scale, it has a complete range of sandy landform types, including crescent-shaped dunes, parabolic dunes, composite dune chains, pyramid-shaped dunes, giant dunes, ridge dunes, sand patterns and sand ridges in sand waves, and flat sand land. It is a natural sandy landform museum.

▲The 2013 Xinjiang geological relics survey team conducted a survey in the Nanhu Desert in Hami. Photo by Li Zhongdong.

01 Sand Dunes

Sand dunes are hill-like or ridge-like landforms formed by the accumulation of sand particles under the action of wind. They are the most basic landform of aeolian beds, with heights ranging from a few meters to tens of meters, and sometimes exceeding 100 meters. Sand dunes have various shapes, including crescent, parabola, dome, honeycomb, etc.

▲Nanhu Desert, Photo by Li Zhongdong

Barchan Dunes

The simplest type of sand dune. It is widely distributed in desert areas of my country. As the name suggests, the most notable feature of the barchan dune is that its plane features have the shape of a crescent moon, with the two tips of the crescent moon (called horns or wings) pointing downwind.

▲Sketch of crescent-shaped sand dunes, drawing by Yang Jinshan

▲Crescent-shaped sand dunes, photo by Li Zhongdong

Parabolic dunes

Parabolic dunes are a special type of fixed and semi-fixed dunes. Their morphological characteristics are just the opposite of crescent dunes, that is, the two animal horns (also called dune arms) of the dune point to the upwind direction. The windward slope is gentle and convex, while the leeward slope is steep and arc-shaped. The plane figure is similar to a horseshoe and a parabola. Therefore, it is called a parabolic dune.

▲Parabolic sand dunes, photo by Li Zhongdong

Composite Dune Chain

The sand dunes are basically in a flowing state, formed by two or more sand dunes connected parallel to each other or connected front and back, and they move forward in a swinging motion.

▲Sketch of a composite dune chain, drawing by Yang Jinshan

Nanhu Sand Dunes - Composite Sand Dune Chain, Photo by Li Zhongdong

Pyramid-shaped sand dunes

It is named because its shape is similar to the pyramids on the banks of the Nile River in Africa. It is also called pyramidal dune because of its overall pyramidal shape.

▲Nanhu Sand Dunes - Pyramid-shaped sand dunes, photo by Li Zhongdong

Shapo

Aeolian sand waves (or sand marks) are undulating micro-topography created by wind on the sandy surface. According to the particle size, scale and arrangement orientation, aeolian sand waves can be divided into three categories: sand ripples, sand ridges and sand strips.

▲Sketch of Shabo, drawing by Yang Jinshan

▲Nanhu Sand Dunes - Veined Sand Waves, Photo by Li Zhongdong

▲Nanhu sand dunes - grain-ordered sand waves, photo by Li Zhongdong

Sand Texture

Sand ripples are the most common micro-topography on sandy surfaces, especially on the surface of quicksand. Wind-blown sand ripples generally have long and parallel ridges, and the two slopes of the cross-section are obviously asymmetrical. The ripples are varied, with a wavelength generally between 7.5 and 15 cm, a maximum wavelength of 25 cm, and a minimum wavelength of 2.5 cm. The height of the ripples is generally between 0.5 and 1.0 cm.

▲Nanhu Sand Dunes - Zebra Sand Patterns, Photo by Li Zhongdong

Sand Ridge

Also known as big sand waves, the maximum wavelength can reach 20 meters and the wave height can reach several meters. Sand ridges are usually composed of coarse sand, but may also contain gravel. Large sand waves composed of gravel can be called gravel waves. Aeolian sand patterns and sand ridges form continuous wave crests perpendicular to the wind direction in the lateral arrangement, and the appearance is relatively regular.

▲Sand Ridge, Photo by Li Zhongdong

02 Formation of Nanhu Sand Dunes

The formation of Nanhu sand dunes is mainly due to four conditions.

Dry climate with little rainfall

Deserts are located in the driest areas of the earth's continents. Drought is a prerequisite for the formation of deserts. Hami is located in the heart of the Eurasian continent, far away from the sea, with closed terrain. It belongs to the warm and arid area with an average annual precipitation of only 34 mm.

▲Nanhu Sand Dunes, Photo by Li Zhongdong

Rich sand source

Abundant sand is the necessary material basis for the formation of deserts. The Hami Basin received a large amount of river and lake sediments in the Paleogene and Neogene, forming pink, gray-white sand, conglomerate and other sediments, which are the main sources of sand. The river sediments of the ancient river channel also provide a rich source of sand for the desert.

▲Nanhu Sand Dunes, Photo by Li Zhongdong

Sufficiently strong wind in a relatively fixed direction

Hami City has many strong winds. The main section of the "Hundred Mile Wind Zone" is located in Hami City. The average wind speed in Thirteen Rooms in western Hami even reached 13.2m/s in April. Nanhu Desert is located in the southwest of Hami City. The main winds in this area are northerly and northwesterly.

▲Nanhu Sand Dunes, Photo by Li Zhongdong

Suitable terrain conditions and storage space

The Nanhu sand dunes in Hami are mainly distributed along the ancient river channel, which is a strip-shaped space. The ancient river channel is the accumulation space of the Nanhu sand dunes. The arid plants nurtured by a small amount of seasonal flowing water, as well as the muddy materials and a small amount of accumulated water accumulated at the bottom of the lower part of the ancient river channel, are conducive to the accumulation of sand, becoming a natural gathering place for gravel.

▲Nanhu Sand Dunes, Photo by Li Zhongdong

▲The 2013 Xinjiang geological relics survey team conducted a survey at the Nanhu Sand Dunes in Hami. Photo by Li Zhongdong

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Compiled by/Xia Kejun

Photo/Li Zhongdong