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Ghost cities mystical landscapes of the far west

STRANGE landforms in the barren lands of Xinjiang, Gansu and Qinghai may look like abandoned cities, but they are really natural sculptures carved by the wind. Shi Lei and Si Ruo report.

Scattered across the barren lands of China's far west are mysterious cities of rock and sand, wind-blown labyrinths known as "ghost cities" built not by man but by nature.

For thousands of years, the wind carrying sand and grit has carved the rock into ridges called yardangs, which follow the direction of the prevailing wind. Some are shaped like pyramids, towers, canine teeth or grotesquely shaped ridges.

Travelers can often hear a crackling sound, like that of firecrackers. That's the sound of "construction" in the ghost cities, the cracking of rocks caused by repeated temperature changes, expansion and contraction. Surface temperatures can reach 70 degrees Celsius at midday, enough to melt wax, but it can be freezing at night.

Many explorers have lost their way in these massive labyrinths, including Swedish explorer Sven Hedin, who first described yardang formations. In 1899 he discovered the lost kingdom of Loulan in what is now Xinjiang Uygur Autonomous Region. Several of his assistants perished in the dried salt lake of Lop Nor. These mazes also claimed the lives of renowned Chinese explorers Yu Chunshun and Peng Jiamu.

The arid west and northwest were not always this dry. Millions of years ago, crustal movement caused land to subside and numerous basins were formed; these attracted the flow of many rivers and subsequently lakes were formed. The sediment carried by rivers was deposited in layers in the basins. Eventually tectonic uplift and climate change caused the lakes to dry up and the remaining sediment provided the "building materials" of the ghost cities that followed.

Lop Nur is home to several ghost cities. But the area was a lake that dried up only in relatively recent times. Around 2,000 years ago, the area was an oasis of life and vegetation, with horses and cattle grazing. The lake nourished the ancient kingdom of Loulan on its western banks. In fact, Sven Hedin wrote of the mirror-like surface of the lake just a century ago.

Lop Nur slowly "died" due to a drier climate, as well as damming of the Konqi River that fed the lake. By the 1960s the lake was dry. The ghost city in Dunhuang (Gansu Province) was part of the ancient Lop Nur.

Amazing colors

The Urho ghost city in northern Xinjiang was once a haven for dinosaurs. Around 100 to 200 million years ago, the area was a large freshwater lake, and the climate was warm and wet. The Wuerhosaurus (a stegosaur with dorsal plates and a spiked tail) grazed on lush vegetation, while the Dsungaripterus (a winged pterosaur or flying lizard) flew in the skies above. Fossils found include those of the Kelmayisaurus (a bipedal carnivore).

Amazing colors can be found. At the foot of the Karamairi Mountains, the Qitai ghost city in the eastern Junggar Basin looks from afar like a giant silk banner with layers of red, yellow and purple. There's also a profusion of color in the Rainbow Beach of Xinjiang's Burqin County where sand is colored red, green, purple, yellow and brown.

The colors are caused by mineral content in the sedimentary rock. Red, for example, is typical of iron oxide. These landforms were made of layers of different sedimentary rocks that were exposed during upheavals in the Earth's crust.

It takes ferocious and sustained winds to create ghost cities. Historical texts speak of sand-carrying winds or "walls of sand" that could easily engulf a person. The fury of the winds was documented by Sven Hedin and the Buddhist monk Faxian.

On the Alataw Pass in Xinjiang, powerful winds blow for up to six months a year, leaving mountains of granite riddled with holes, like a piece of cheese. Without vegetation to slow the wind down, the wind is strong enough to carry pebbles of three centimeters in diameter. The effect of wind and sand is like a sandblaster.

In the formation of a ghost city, the land is subjected to a constant strong wind that scrapes the surface like a steel rake. Loose sand is removed, leaving behind ridges and troughs that extend along the prevailing wind. It is easy to tell the wind direction by looking at the city's layout.

In a bottleneck in the Turpan-Hami Basin, the gale-force wind blew a passenger train off its rails in April 2007.

Many windy areas are formed when the basin experiences extreme heating in spring, summer and autumn. Convection from the rising hot air creates a low pressure cell; the higher-pressure cooler air outside the basin rushes in as windstorms. An episode can last for more than a month; sometimes it blows for 95 percent of a year. Telephone poles are often broken and paint on trains is often sandblasted away.

Shaped by water

Although the wind is the major shaper of yardang landforms, water too plays a role. It seldom rains in the region but when it does, a downpour can cause major erosion.

Professor Peng Hua from Sun Yat-sen University in Guangdong Province saw massive erosion and destruction of roads and villages after a torrent in July 2007.

"There is hardly any vegetation to absorb or buffer the force of the water, so you can imagine the powerful erosive effect," says Peng, referring to the exposed sedimentary rock from the geologic past.

These yardangs are always changing and the ghost cities are always a work in progress. There's a saying that one can never step into the same river twice. Likewise, it is virtually impossible for anyone to walk into the same ghost city twice, as it is always being weathered and eroded by the twin forces of wind and water.


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