One of the oldest known Chinese civilizations disappeared approximately 3000 years ago. However, some evidence suggests it relocated, rather than collapsing, and a new theory suggests this was driven by a distant earthquake redirecting the river that once fed the valley in which the people once lived.
The first artifacts from the Sanxingdui civilization near Chengdu, Sichuan, were found in 1929, but it was only in 1986 that the astonishing richness of the culture came to light. Bronze statues 2.4m tall were larger than anything produced elsewhere in the world at the time, and a formidable set of canals provided irrigation and defence.
Sanxingdui would hardly be unique in reaching an awe-inspiring peak before being destroyed by war or environmental disaster. However, the cause in this case has not been clear.
"The current explanations for why it disappeared are war and flood, but both are not very convincing," Niannian Fan of Sichuan University told LiveScience.
The discovery of the ancient city of Jinsha 40km southwest of Sanxindui deepened the mystery, but may also help solve it. Objects at Jinsha have very similar images on it to those found at Sangxingdui, suggesting the two civilizations were at least connected, and their ages suggest Jinsha have been Sangxingdui's successor.
At the annual meeting of the American Geophysical Union Fan presented evidence that Sanxingsui was watered by a river much larger than the one that now flows through its valley. The high walls over the valley would have required a powerful force to form them. There are geological signs of a major earthquake in the region, although the date cannot be placed more accurately than plus or minus 565 years.
However, historical records from neighboring civilizations record a major geological event in 1099BC, although of course at the time it was not possible to locate the exact epicenter.
Fan proposes that the 1099BC earthquake triggered a rockslide, which “beheaded” the Jian River, directing most of the into what is now the Minjiang River. Now draining a much smaller area, the Jian River was no longer reliably able to support Sangxingdui, leading the population to decamp to Jinsha on the new river's banks.
Fan et al. The current river systems around Chengdu (right) and the proposed paths prior to the 1099BC earthquake.
Such a shift would not have been easy, and Fan's theory would fit with the impression that Jinsha never obtained the heights of complexity of its predecessor.
To bolster their case, Fan and colleagues explored the Minjian river upstream of the two cities. The Yanmen Ravine, located 3800m above sea level was carved by glaciers towards the end of the last ice age. However, one stretch of the ravine is missing the basins known as cirques, which elsewhere serve as an indication of glacial formation. An avalanche would have buried the cirques, potentially rerouting the river at the same time.
Fan admits the theory needs more work, both from the geological side to demonstrate the changing river direction, and further exploration of the two cities to prove that one followed the other, rather than existing side by side.