An expedition consisting of experts from nine countries started Tuesday, to traverse the world 's largest doline group in Leye County in south China's Guangxi Zhuang Autonomous Region.

The objective of the expedition is to make clear the path of an underground river running through the dolines and its geological relation to the doline group, said Zhu Xuewen, director of the China Cave Research Association.

Dolines are special geological landscapes found in karst regions, formed by repeated cave-ins of the tops of the underground caves.

The underground river found in the dolines is estimated to cover 850 square kilometers.

The first expedition carried out last year only covered 20 kilometers of the river, but found 20 big dolines of different types in Leye, 460 kilometers from Nanning, capital of Guangxi.

The expedition this year has gathered together over 50 members from nine countries including China, Britain, the United States and France.

Peter Hall from Britain said that he had explored many dolines in Europe and Malaysia, as well as the world's largest doline -- in Fengjie County in Chongqing Municipality. However, the dolines in Leye are distinguished from all the others, with a strongly- flowing river and a dense forest underground.

The county received a downpour yesterday, which created difficulties for the expedition. The scientific work of last year' s expedition was interrupted by the flooding of the river.

Scientists have found that the river consists of a hot current and a cold current, the reason for which is a mystery.

The expedition is expected to last five weeks. The scientists hope to end the trip before the annual rainy season sets in.

The Leye doline group was discovered in 1998 during a national survey carried out by the Ministry of Land and Resources.

Experts explained that a drastic raising of the earth's crust or movement of the Himalayas led to its formation. The same movement also shaped the Yunnan-Guizhou Plateau in southwest China. Leye is situated in the transitional zone from the plateau to the lower land to the east.

The area is home to more than 1,000 varieties of plants, including many rare and precious species, and some small creatures such as blind fish, crabs, shrimp and flying squirrels.

(Xinhua News Agency March 13, 2002)