Known as the “Chinese Stone Age Venice,” the Liangzhu excavation in eastern China is considered one of the most significant testimonies of advanced Chinese civilization. More than 5,000 years ago, the city already had an elaborate water management system. Until now, it has been controversial what led to the sudden collapse. Huge floods caused by unusually intense monsoon rains caused the collapse, as an international team of Innsbruck geologist and climate researcher Christoph Spötl has now demonstrated in Science Advances.
In the Yangtze Delta, about 160 kilometers southwest of Shanghai, lie the archaeological ruins of the city of Liangzhu. There, a highly advanced culture flourished some 5300 years ago, which is considered to be one of the first evidences of a monumental aquatic culture. The earliest evidence of large hydraulic engineering structures in China originates from this late Neolithic cultural site. The walled city had a complex system of navigable canals, dams and water reservoirs. This system enabled the cultivation of large agricultural areas throughout the year.
In the history of human civilization, this is one of the earliest examples of highly developed communities based on a water infrastructure. Metals, however, were still unknown in this culture. Thousands of elaborately worked jade funerary objects were found during the excavations. Long unknown and underestimated in its historical significance, the archaeological site is now considered a well-preserved record of Chinese civilization dating back more than 5,000 years.
Liangzhu was declared a UNESCO World Heritage Site in 2019. However, the advanced civilization of this city, which has been inhabited for nearly 1000 years, came to an abrupt end. To this day, what caused it remains controversial. “A thin layer of clay was found in the preserved ruins, which points to a possible connection between the end of advanced civilization and the floods of the Yangtze River or the floods of the East China Sea. No evidence has been found of human causes, such as military conflicts,” explains Christoph Spötl, head of the Quaternary Research Group at the Department of Geology. “However, no clear conclusions about the cause were possible from the mud layer itself.”
Dripstones store the answer
Caves and their deposits, such as dripstones, are among the most important climate archives in existence. They allow for the reconstruction of climatic conditions above the caves up to several 100,000 years ago. As it is still unclear what caused the sudden collapse of the Liangzhu culture, the investigation team searched for suitable archives to investigate a possible climatic cause of this collapse.
Geologist Haiwei Zhang of Xi’an Jiaotong University in Xi’an, who spent a year at Innsbruck University as a visiting researcher in 2017, collected stalagmite samples from the two Shennong and Jiulong caves, located southwest of the excavation site.
“These caves have been well explored for years. They are located in the same area affected by the Southeast Asian monsoons as the Yangtze Delta and its stalagmites provide an accurate view of the time of the collapse of the Liangzhu culture, which, according to archaeological data discovered, happened about 4300 years ago”, explains Spötl. Stalagmite data show that between 4345 and 4324 years ago there was an extremely high rainfall period. Evidence for this was provided by carbon isotope records, which were measured at the University of Innsbruck.
Precise dating was done by uranium-thorium analyzes at Xi’an Jiaotong University, whose measurement accuracy is ± 30 years. “This is incredibly accurate in light of the temporal dimension”, says the geologist. “The heavy monsoon rains likely led to such severe flooding of the Yangtze and its branches that even the sophisticated dams and canals could no longer support these bodies of water, destroying the city of Liangzhu and forcing people to flee.” The very wet weather conditions continued intermittently for another 300 years, as geologists show from cave data.
Source: Science Advances