Wu Qinglong

Cai Linhai

Cai Linhai

Ancient Chinese legends tell of a catastrophic flood along the Yellow River that led to the founding of the Xia dynasty, roughly 4,000 years ago. A legendary hero named Yu is said to have established the Xia dynasty after figuring out how to stop the flood waters by dredging, thus marking the dawn of Chinese civilization with a feat of landscape engineering. Now, a group of geoscientists and archaeologists in China has discovered that this flood actually happened.

The group's recently published findings in Science magazine explain how they found traces of this historic deluge. For more than a century, archaeologists have looked for evidence that could shed light on historical accounts of early Chinese civilization, such as those in first century BCE book Shiji (史記, traditionally translated as Records of the Grand Historian). Many accounts in the Shiji have turned out to be fairly accurate, especially when it came to the Shang dynasty that followed the Xia. Because the Shang dynasty civilization had writing, scientists have been able to verify the Shiji's accuracy from written records as well as material remains.

Reconstructing a flood

Much about the Xia dynasty, however, remains mysterious. Although this Bronze Age civilization was highly sophisticated, it did not use writing, and the only accounts we have of it come from stories of the great flood that Yu controlled. Now, scientists are certain there was a megaflood on the Yellow River in roughly 1900 BCE. Ancient Chinese historiographers placed the rise of the Xia dynasty during the 2200s BCE, so their dates were about 300 years off. But whenever it happened, the flood was so devastating and enormous that the archaeologists who discovered it have no doubt that it would have left a lasting impression on any civilization that experienced it.

Purdue geoscientist Darryl Granger, who worked with the research team in China, described the flood at a press conference earlier this week. The flood waters, he said, "reached up to 38 meters above the modern river level." We know that because the scientists found distinctive sediments released by the flood in the Jishi Gorge and elsewhere downriver. Knowing the water levels helped the group figure out the volume of water, which, Dr. Granger said, "tells us that the flood was [flowing] about 300 to 500 thousand cubic meters per second... It's among the largest known floods to have happened on Earth during the past 10,000 years."

But how did it happen? Answering that meant combining archaeology with an understanding of flood mechanics. Downstream from Jishi Gorge are the remains of a Neolithic settlement called the Lajia site, which the scientists noted is part of a culture "known for its early noodle remains." There, in caves, archaeologists found evidence of a massive earthquake that killed dozens of these ancient noodle eaters. The skeletons of the quake victims, dated to roughly 1900 BCE, were covered in the same kind of flood sediments that the researchers found upstream. On top of the flood sediments they found another layer of sediment that was from a typical rainy season. That told the researchers two things: one, there was a deadly earthquake before the flood; and two, the flood happened less than a year after the quake, because there is no rainy season sediment in between the skeletons and the flood sediment layer.

Based on that evidence, the research team modeled a scenario based on data from similar quakes and floods. Most likely, the quake caused a massive landslide that dammed the Yellow River (indeed, there are remains of a dam upstream from Jishi Gorge). The dam created a lake that was "about 200 meters deep," Granger said. He added: "To put this into perspective, it’s somewhere between the height of the Three Gorges Dam in China and Hoover Dam in the United States." Eventually, under continuous assault from the river, the dam was overwhelmed by rising waters and overtopped. This type of failure would have instantly destroyed the structure of the dam, leading to an "outburst flood" that gushed into the river valleys downstream, destroying villages and farms.

A radical change in Chinese civilization

There is no evidence of Yu or his dredging, but the researchers note in their paper that the flood would have destroyed the natural levees carved by the river over time. With no steep banks to hold the waters on their course, the Yellow River likely flooded the lands downstream every year after the dam shattered. For people living in the region, there would have been a desperate need for dredging techniques. If Yu led the locals in an engineering effort to rebuild the banks of the Yellow River, it's clear why he achieved culture hero status.

Though the researchers caution that we have no material evidence of a leader named Yu founding the Xia dynasty, we do know for certain that this flood came at a time of radical transformation in Chinese civilization. National Taiwan University anthropologist David Cohen said there was a brief period of social collapse at the end of the Neolithic period when this flood happened, and then we see the emergence of a much more complex social order during the Erlitou culture of the Bronze Age. "The story of Yu taming the flood is the story of a new political order emerging out of the chaos of the flood," he explained. Cohen said the Neolithic culture at the Lajia site disappears, and "we have a transitional period that we don't understand too well." But then, after that:

The Erlitou, and later the sites associated with the Shang dynasty, emerge. And when they do, things are at a new level of development. The cities that are built jump from 10, 20, 30 hectares in size up to 300 or more hectares in size. We have more complex administrative structures, we have a writing system that emerges, we have workshops manufacturing bronzes that require the long-distance transport of metals from various parts of China into these centers in the Yellow River. So things are just being done at a higher order of complexity and organization... And this is what's occurring around 1900 BC.

Of course, a massive flood around the time of China's Bronze Age transition might just be a coincidence. "We don't have causation," Cohen said plainly. That said, these events do fit a pattern described in the Shiji. We could really be looking at what the researchers call in their paper "a profound and complicated cultural response to an extreme natural disaster."

What is perhaps most satisfying, for those with a technical or scientific bent, is that the flood at the dawn of Chinese civilization was apparently perceived as an engineering problem. Yu saved the world with hydrology. And that makes the legend of the Xia dynasty more relevant than ever in our world of rising waters and broken levees.

Science, 2016. DOI: 10.1126/science.aaf0842

Listing image by Wu Qinglong