Palaeoenvironmental implications of the prehistorical catastrophes in relation to the Lajia Ruins within the Guanting Basin along the Upper Yellow River, China

Abstract

Archaeological excavations have exposed a shocking picture of the prehistorical catastrophes in the Lajia Ruins in the upper Yellow River. The grouped skeletons resting on the dwelling floors show a vivid scene of the mortal struggle of human being during catastrophes. Geological records of the major disasters in relation to the devastation of this prehistorical settlement were investigated by detailed field observations, sedimentological analysis and optically stimulated luminescence (OSL) and 14C dating. The results show that the prehistorical community of the Qijia Culture migrated into the Guanting Basin at c. 4200 yr BP. They chose the loess-blanketed riverbanks to build their settlement and cultivate millet crops. At c. 3950 yr BP, immediately followed by a major earthquake, the settlement was overtaken by immense mudflows coming along the tributary gullies from the hillsides behind. The enormous mudflows suddenly buried and destroyed the dwellings and killed the women and children at their homes. The source of the catastrophic mudflows was traced upslope to the gully heads behind the ruins, where the palaeoearthquake together with the rainstorms and flash floods induced enormous mass wasting on the hillsides. Referring to the causations of the catastrophic debris flows and landslides in the region, it is inferred that the soil erosion, mass wasting and accumulation of debris on the hillsides were intensified largely by human disturbance of the landscape by bush clearance from 6000 yr BP to 3950 yr BP. During the climate event of 4200–4000 yr BP, enhanced human activities and over-exploitation of natural resources increased the vulnerability of the communities to detrimental environmental change and catastrophe. This means that the prehistorical catastrophic mudflows were created partly by the early settlers themselves. These results are of important implications in understanding the prehistorical environmental change in the environmentally sensitive zones over the world.