SAND storms in northwest China's Gansu Province are reducing sections of the Great Wall to mounds of dirt and may cause them to disappear in about 20 years, archaeologists say.
Zhou Shengrui, a former curator of the Minqin County museum, said a national survey in the 1980s showed there were more than 60 kilometers of the Great Wall in the county but they were rapidly disappearing.
This section of the Great Wall, built in the Han Dynasty (206BC-220AD) and extended in the Ming Dynasty (1368-1644), is on the main trunk of the Wall, which runs from the Shanhaiguan Pass in north China's Hebei Province westward to Gansu's Jiayuguan Pass, about 500 kilometers west of Minqin.
"This section of Great Wall was made of mud rather than brick and stone and is more prone to erosion. Over time, the wall has become brittle and the mud has been sanded down and blown away," Zhou said.
"Similar erosion happened to the Great Wall in other places but the situation is much more worse here," he added.
Extensive farming since the 1950s sapped underground water reservoirs in Minqin and destroyed the local ecology. The 400-sqare-kilometer, 60-meter Qingtu Lake began drying out in the 1960s and by the early 1990s the lake had been smothered by creeping yellow sand and became part of the Badain Jaran Desert, which covers more than 40,000 square kilometers.
Minqin has since then become a major source of sand storms in northwestern China.
"Frequent storms not only eroded the mud but also cracked the Wall and caused it to collapse or break down," Zhou said.
More than 40 kilometers of the Wall have disappeared in the past 20 years and only about 10 kilometers remain.
Its height has been reduced from five meters to less than two meters and square lookout towers have disappeared completely.
Wei Zhaobai, 61, a resident in Chengxi Village, in the Daba Township of Minqin, said: "The Great Wall gets shorter every year.
"When I was seven or eight years old, the section of the Great Wall about 1,000 meters west of my village was still as new. We used to walk on it like the ancient soldiers," Wei said.
Zhou said unless the local vegetation recovered and the sand storms contained, the damage was irreversible.
Local workers were covering the Wall's remains with sand and dirt.
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