The Collapse of the North Song Dynasty and the AD 1048–1128 Yellow River Floods : Geoarchaeological Evidence from Northern Henan Province, China

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The collapse of the North Song dynasty and the AD 1048–1128 Yellow River floods : geoarchaeological evidence from northern Henan Province, China

Storozum, Michael J.; Zhen, Qin; Xiaolin, Ren; Haiming, Li; Yifu, Cui; Kui, Fu; Haiwang, Liu

2018

Storozum, M. J., Zhen, Q., Xiaolin, R., Haiming, L., Yifu, C., Kui, F., & Haiwang, L. (2018). The collapse of the North Song dynasty and the AD 1048–1128 Yellow River floods : geoarchaeological evidence from northern Henan Province, China. The Holocene, 28(11), 1759‑1770. doi:10.1177/0959683618788682 https://hdl.handle.net/10356/137334 https://doi.org/10.1177/0959683618788682

Downloaded on 02 Oct 2021 18:20:39 SGT The AD 1048-1128 Yellow River Floods and the Collapse of the Northern Song Dynasty: Geoarchaeological evidence from northern Henan Province, China Michael J. Storozuma*, Qin Zhenb, Ren Xiaolinc, Li Haimingd, Cui Yifud, Fu Kuie, Liu Haiwangf a Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore b School of History and Culture, Henan University, Kaifeng, P.R. China c Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, P.R. China d Key Laboratory of Western China's Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, P.R. China e College of Humanities, Zhejiang Normal University, Jinhua P.R. China f Archaeology, Henan Provincial Institute of Cultural Relics and Archaeology, Zhengzhou, P.R. China Corresponding author: Michael Storozum, [email protected] 50 Nanyang Avenue, Block N2-01a-15, Singapore 639798

Abstract

From AD 1048 to 1128, Yellow River flooding killed over a million people, left many more homeless and destitute, and turned parts of the once fertile North China Plain into a silted-up agricultural wasteland. Brought on in part by climate change and the Northern Song dynasty’s (AD 960-1127) mismanagement of the environment, the Yellow River floods likely hastened the collapse of the Northern Song dynasty. Despite the magnitude of this flood event, no sedimentary deposits have yet been linked to these historically recorded floods. In this research paper, we provide archaeological, sedimentary, and radiocarbon evidence of the AD 1048-1128 Yellow River floods at the Dazhanglongcun, Xidacheng, and Daguxiancun sites in Neihuang County, Henan Province. Based on our data, we argue that the AD 1048-1128 Yellow River floods deposited over 5 meters of alluvium on villages in the North China Plain, radically changing both the physical and political landscape of Northern Song dynasty China.

Keywords: floods, North China Plain, Yellow River, land use, Song dynasty, geoarchaeology

Introduction

The drama that surrounds the collapse of empires has enraptured both scholars and the lay public since the beginning of the modern study of history and archaeology (Tainter 1988; Diamond 2005; Butzer 2012). Scholars have generally relied on historical documents to determine the many social, economic, and environmental conditions that surround the collapse of historic empires. New advances in scientific techniques now enable archaeologists to recover more detailed environmental and economic data that can further clarify earlier explanations of imperial collapse. Although climate change, warfare, and disease are frequently invoked in narratives of imperial collapse, sedimentary archives of extraordinary natural disasters found at archaeological sites may provide a more direct link to the role that wide-spread environmental change has in leading to societal collapse.

Through the judicious use of the extant historical record, historians of premodern China have argued that devastating flood events helped create conditions ripe for dynastic collapse (Dubbs 1955; Skinner 1985; Elvin and Liu 1998; Zhang 2009; Lee 2018). Until recently, finding archaeological and sedimentary evidence of ancient flood events related to dynastic collapse has remained a persistent challenge for archaeologists working in China. However, a team of archaeologists, geographers, and historians has worked together at the Sanyangzhuang site in Neihuang County, northern Henan Province, China to link sediments to the AD 11-70 Yellow River floods that contributed to the collapse of the short-lived Xin dynasty (AD 9-23) (Kidder et al. 2012a; Kidder et al. 2015). Similarly, another collaborative team has searched for “The Great Flood” that legend claims led to the founding of China’s first dynasty, the Xia (c. 2070-1600 BC) (Wu et al. 2016). The results of these multi-disciplinary projects suggest that stratigraphic evidence for many historically-attested large Yellow River floods remain to be discovered and linked to periods of dynastic transition.

We bring together evidence from archaeology, geology, and history, to discuss the role the AD 1048-1128 Yellow River floods had in hastening the collapse of the Northern Song dynasty (AD 960-1127), a period that is often regarded by historians as the apogee of Medieval China’s economic and cultural influence (Jones 1990; Deng 2013; Deng and Zheng 2015; Figure 1). Historians have recently shown that people living in the agricultural heartland of the North China Plain bore the brunt of the devastation brought on by the AD 1048-1128 floods, leaving the Northern Song dynasty’s breadbasket of modern day Henan and Hebei Provinces unable to recover for hundreds of years (Lamouroux 1998; Zhang 2009, 2016; Mostern 2016). The AD 1048-1128 floods were an overwhelming geomorphic event that not only devastated millions of people’s lives in the North China Plain but also may have significantly contributed to the collapse of the Northern Song dynasty. In this paper, we amplify both primary and secondary historical accounts of this event by presenting stratigraphic, archaeological, and radiocarbon evidence from several locations in Neihuang County, Henan Province that were likely in the path of the AD 1048-1128 floods.

A Brief Overview of the Climate, Environment, and History of the North China Plain and Loess Plateau

One of the primary challenges of linking flooding with dynastic collapse in China and elsewhere is that floods are often the result of climatic changes, environmental degradation, and shifts in the policies and philosophies guiding the human management of the watershed in question. Given that each of these processes are dynamic and highly interdependent, we present a brief overview of the climatic regime, the physiographic regions of northern China, and the history of the Northern Song dynasty to place the Yellow River floods of AD 1048-1128 within their broader socio-ecological context.

Many historians and climate scientists have tried to correlate changes in climate and monsoon strength with China’s periodic dynastic collapse (Zhang et al. 2007; Fan 2010; Wei et al. 2015). Two monsoon systems dominate the climate system of northern China, the East Asian summer monsoon and the East Asian winter monsoon. The East Asian summer monsoon brings moisture to continental Asia from the sea, mainly from June to September (June to September 1971-2000 average monthly rainfall at Anyang City, 102 mm). In many parts of northern China, the average annual precipitation during these summer months is 100 mm higher than during the winter months when the East Asian winter monsoon takes moisture away from northern China, leaving the air cold and dry (October to May, 1971-2000 average monthly rainfall at Anyang City, 19 mm). Fluctuations in the strength of these two monsoons can have significant ramifications for agricultural productivity, river flood stages, and erosion (An et al. 2000). The analysis of the oxygen isotopes within speleothems at Dongge cave indicates that the East Asian summer monsoon strength over northern China was highly variable from the period of c. AD 800 to 1200, alternating between the “Late Tang Weak Monsoon Period” and the “Northern Song Strong Monsoon Period” (Zhang et al. 2008; Zhang et al. 2018). This period of prolonged natural variability in the monsoon driven climate over continental Asia occurred concurrently with the Yellow River floods of AD 1048-1128 and the collapse of the Northern Song dynasty.

The oscillating strength of the East Asian summer monsoon from weak to strong may have indirectly accelerated erosion on the Loess Plateau. The Loess Plateau is the name for the loessic hills that were formed from wind-blown deposition of silt during the glacial periods of the Pleistocene and Pliocene in the northwest of China (Liu et al. 1996). Thousands of years ago, the Loess Plateau was a partly forested area that supported both pastoral and agricultural lifeways (Huang et al. 2003; Huang et al. 2004; An, Feng, and Tang 2004). However, as agricultural technology developed and the strength of the summer monsoon increased, agricultural populations brought more of the Loess Plateau’s easily erodible soil under cultivation. From the Han dynasty onwards, dynastic governments established agricultural settlements on the Loess Plateau to protect strategic passes and valuable trade routes from neighboring nomadic kingdoms as well as increase agricultural output to support growing cities in the North China Plain and other small tributary basins (Dong et al. 2012; Mostern 2016). Although these outposts supported the short to medium term ambitions of dynastic powers, the expansion of agricultural activity disturbed the vegetation of the Loess Plateau which ultimately increased the rate of erosion on the Loess Plateau (Xu 2001; He, Tang, and Zhang 2004; Wang et al. 2006; Shi et al. 2010; Zhao et al. 2013; Kidder and Zhuang 2015).

As the rate of erosion on the Loess Plateau accelerated during the Northern Song dynasty because of climatic change and agricultural expansion, the lower reaches of the Yellow River became increasingly susceptible to more frequent and intense episodes of flooding (Ren and Zhu

1994; Chen et al. 2012). Although the dynastic government was concerned with the growing risk of Yellow River floods, other matters of state were arguably more pressing. After Emperor Taizu (Zhao Kuangyin AD 927-976, reigned from AD 960-976) conquered the warring factions of the Five Dynasties and Ten Kingdoms Period (AD 907-960) and established the Northern Song dynasty capital at Bianjing, modern day Kaifeng (Fairbank and Goldman 2006, 88), he ushered in an era of unprecedented economic prosperity and population growth that required him and his successors to fiercely defend the Northern Song dynasty’s northwestern and northeastern borders against the Western Xia Kingdom and the Liao Dynasty, respectively. However, these frequent military campaigns against both nomadic kingdoms weakened the Northern Song dynasty’s status as an economic and military power and indirectly took funds and personnel away from dealing with the growing flood risk of the Yellow River (Deng 2013; Deng and Zheng 2015).

Northern Song dynasty scholars and civil servants understood that the flood risk of the Yellow River was particularly great around Kaifeng because the sediment in the Yellow River falls out of suspension as it comes out of the Taihang Mountains, raising the height of the Yellow River’s main channel above the floodplain. Here, a sudden and heavy storm can cause the Yellow River’s water level to rise high enough to breach its banks, making northern Henan Province an epicentre for channel switching and large avulsions (Chen et al. 1996). To deal with these conditions, Northern Song dynasty civil servants raised the dikes along the Yellow River between the towns of Chanzhou and Huazhou (Xu 1988). However, Zhang (2009, 2016) argues that the Northern Song dynasty civil servants’ attempts to control the river were often misguided and may have even exacerbated the flood’s severity. Eventually, the overwhelming forces of gravity and erosion caused the Yellow River to breach the dikes and levees in AD 1048 at Puyang, creating a prolonged environmental catastrophe for the people living in the agricultural heartland of the Northern Song dynasty’s empire (Marks 1998; Zhang 2016).

Historians rely on the numerous chapters (called Zhi) from the Songshi (History of the Song Dynasty) (Tuo, 1977), particularly the Songshi Hequ Zhi (History of the Song Dynasty: Chronicles of the River Course) to recreate the sequence of flood events during the Northern Song dynasty (Zou, 2013). From AD 1048-1128, the Yellow River frequently breached the dikes in Henan and Hebei Provinces, causing widespread flooding to occur throughout northern Henan Province. By AD 1128, the Jurchen Kingdom had usurped the Liao dynasty and successfully conquered most of the North China Plain causing the Northern Song dynasty governor of Kaifeng to breach the dikes along the Yellow River in a last ditch attempt to halt their advancing armies. The dike breach caused the Yellow River to flow south and stopped the widespread flooding in the north. Of all of the early flood events and major channel switches, the AD 1128 channel switching event at Shangqiu is probably one of the most clearly documented. Less clear, however, is the spatial extent and magnitude of the AD 1048-1128 Yellow River floods that preceded this major channel switching event of AD 1128. Given that the AD 1048-1128 Yellow River floods occurred in multiple places along the lower course of the Yellow River over the course of nearly a century, the environmental and economic consequences of the flood events are likely highly variable and incompletely recorded in the Songshi Hequ Zhi.

Study Area

Starting in 2011, our team of archaeologists, historians, and geographers from Washington University in St. Louis and the Henan Provincial Institute of Cultural Relics and Archaeology investigated Neihuang County, the location of the AD 1099 flood, to better understand the intertwined nature of the archaeological record and the sediments of the Yellow River (Kidder et al. 2012b; Kidder and Liu 2014; Kidder and Zhuang 2015; Storozum et al. 2017). Located to the north of Kaifeng, Neihuang County is situated in the center of the “nodal avulsion zone” of the Yellow River (Slingerland and Smith 2004). Here, the Yellow River is especially prone to channel switching and avulsions, creating a highly complex subsurface depositional environment that contains buried land surfaces, river channels, and crevasse splays that date to many different points in time during the Holocene. Most recently, our survey in Neihuang County has identified several locations, namely Dazhanglongcun, Xidacheng, and Daguxiancun that contain evidence of the Northern Song dynasty Yellow River flood events (Figure 2).

Methods

In 2013, we investigated a site named Dazhanglongcun (DZLC) after the nearby village (50N, 307869.90 m E, 3985626.30 m N). Villagers mining clay dug a large, stepped, pit about 6 meters deep. Their excavations revealed the wall of a buried village. We cleaned off five profiles at Dazhanglongcun to get a better sense of both the natural and archaeological stratigraphy at the site. Most of the artefacts recovered from the excavation were found out of their original context.

In 2013 and 2014, we visited several other archaeological sites after a team of salvage archaeologists finished their excavations. In 2013, we cleaned off two profiles to expose a sequence at the Daguxiancun (DGXC) site (50N, 297310.4 m E, 3978054.8 m N) where local archaeologists exposed an ancient road. In 2014, we opened an excavation unit at Xidacheng (XDC) site (50N, 298974.1 m E, 3953776.7 m N) in an attempt to find stratigraphic and archaeological evidence of a buried city, but these excavations did not yield any significant archaeological material. Nonetheless, our profiling work revealed detailed sequences of historic sedimentary processes. We sampled each stratigraphic layer identified at Xidacheng and conducted particle size analysis, loss-on-ignition, and magnetic susceptibility on each sample. Particle size analysis was done using a Micromeritics Saturn II digisizer. We conducted loss on ignition at 550 °C and 950 °C to estimate the percentage of organic matter and inorganic carbon in each sample (Nelson and Sommers 1996; Heiri et al. 2001). We also used a Bartington MS2 Magnetic Susceptibility Meter to determine each samples high field magnetism (4.7 kHz) and frequency dependence (Dalan and Banerjee 1996).

The results presented here are derived from salvage field work conditions, limiting our ability to present accurate geodetic information. Our descriptions and measurements of the lithostratigraphy and archaeostratigraphy at each site use standardized soil science terminology (Schoeneberger et al. 1998). We collected radiocarbon samples from charcoal found within these profiles and sent them for accelerator mass spectrometry radiocarbon dating at National Ocean Sciences Accelerator Mass Spectrometry laboratory, Woods Hole Oceanographic Institute.

Results

Detailed lithostratigraphic and archaeostratigraphic descriptions from Dazhanglongcun, Daguxiancun, and Xidacheng, are presented in supplemental material (ST1,ST2, and ST3). Radiocarbon dates are presented in Table 1.

A Dazhanglongcun

At Dazhanglongcun, we cleaned off five profiles. Given the extent of modern and historic landscape modification in the area, determining the exact location of the modern land surface is problematic. To solve this problem, we consider the surface of the upper most profile, Profile 5, to be the modern land surface. We first discuss the natural lithostratigraphy starting from Profile 2 at the bottom, Profile 3 in the middle, and Profile 5 at the top. Then, we discuss the complex archaeostratigraphy revealed in Profile 1 and Profile 4. In Figures 3 and 4, we provide photographs of each profile and detailed stratigraphic drawings of the lithostratigraphy and archaeostratigraphy at Dazhanglongcun.

Lithostratigraphy B Profile 2 (300-600 cmbs). Profile 2 is the lower most profile. The first stratigraphic unit is 400 to 600 cm below the modern land surface. This lithostratigraphic unit (2C) is an alternating deposit of silty clay loam and silty loam that likely represents a flood event. The flood deposit abruptly ends at 400 cm below the modern ground surface. A thick and well developed buried A horizon (2Ab) formed on top of the flood deposit 2C. The buried soil 2Ab has abundant redoximorphic features that extend into the underlying 2C deposit. The redoximorphic features are in the form of root casts (< 2 cm in diameter), indicating that the soil was once biologically active. A piece of charcoal found in the buried soil 2Ab returned a raw radiocarbon age of 1050 ± 15 yr BP, with a calibrated probability distribution of cal yr AD 1018-1052 (41.9%) and cal yr AD 1081-1153 (53.5%). Above 2Ab is a thick flood deposit (C) with alternating beds of silty loam and reddish silty clay loam. In Profile 2, C starts above the buried soil 2Ab and continues to about 350 cm below the modern surface. At 350 cm below the modern land surface, the flood deposit C gradually grades into the modern soil seen on the surface of the lower most terrace.

Profile 3 (100-300 cmbs). Profile 3 is located on the middle terrace and is adjacent to the archaeological features found in Profile 1 and 4. The buried soil 2Ab is located approximately 50 cm beneath the bottom most deposit of Profile 3. The same lithostratigraphic sequence of red silty clay loam and silt loam seen in 2C at Profile 2 is present beneath the buried soil 2Ab in Profile 3. Profile 3 primarily consists of a thick bed of silt loam with thin beds red silty clay and silty clay loam (C) that extends from the bottom of the profile to about 130 cm beneath the modern ground surface where modern soil development starts. The multiple bands of red silty clay indicate that the energy of the depositional environment was variable. A piece of charcoal found within the thick bed of silty loam returned a date of 990 ± 25 yr BP (DZLC-2), with a calibrated probability distribution of cal yr AD 974-930 (95.4%).

Profile 5 (0-100 cmbs). Profile 5 is the highest profile and is located closest to the modern land surface. The pattern of sedimentation seen in Profile 5 starts as a continuation of C found in Profile 3. At Profile 5, C starts at 100 cm beneath the modern ground surface and continues up to about 70 cm beneath the modern ground surface and contains the diagnostic centimeter thick

beds of red silty clay embedded within a thick bed of silty loam. At around 70 cm beneath the modern ground surface, the deposit transitions into blocky angular silty loam, probably windblown loess. At approximately 30 cm below the modern surface, these flood deposits grade into the modern soil.

Archaeostratigraphy B The archaeostratigraphy revealed at Profile 1 and Profile 4 as well as presence of an ancient well provide good evidence for prolonged occupation at Dazhanglongcun (Figure 4).

Profile 4. Profile 4 is approximately 15 m long and 4 m high (Figure 4a and b). Profile 4 contains the majority of the archaeological evidence found at Dazhanglongcun. The archaeological sequence found in Profile 4 has three major types of features, rammed earth walls, hearths or combustion features that are imbedded within the wall, and a final layer of brick construction. Overtopping the wall is lithostratigraphic unit C with its characteristic red silty clay or silty clay loam and thick beds of silty loam.

The first phase of wall construction is characterized by many rotated angular clods (< 5 cm) that come from the underlying 2C deposit. These clods are mixed into the disturbed 2Ab buried soil. Above these silty loam clods, the first phase of wall construction consists of many finely layered levels of rammed earth that have a blocky angular structure and silty loam texture. In some areas within the rammed earth walls, there are several small pockets of sediment that have a clayey texture and crumbly structure that is different than the surrounding rammed earth. On top of the last layer of rammed earth are four bricks that are in situ. These bricks might have been a type of crenellation atop the wall. A thin bed of reddish silty clay (< 5 cm) and a much thicker silty loam bed overlies the second phase of wall construction (C). Several pits cut into C and the underlying archaeostratigraphy from the modern land surface.

Profile 1. Profile 1 is approximately 8 m wide and 3 m deep and located at the south-eastern edge of the Dazhanglongcun pit. Buried soil 2Ab is around 300 cm beneath the modern surface (Figure 4c, d, and e). Buried soil 2Ab contains two archaeological features, a pit on the left side of Profile 1 and a thin ash lens and charcoal in the middle of Profile 1. The pit feature is dug into the underlying 2C unit from 2Ab and is filled with a crumbly red silty clay. Several thin lenses (< 1 cm) of charcoal and ash line segments of the pit feature. To the right of the pit is a combustion feature filled with charcoal and ash that returned a date of 970 ± 20 yr BP (DZLC-3; Figure 4d), with a calibrated probability distribution of cal yr AD 1082-1128 (63.7%), 991-1051 (25.1%), and 1136-1152 (6.2%). This date is roughly contemporaneous with DZLC-1 and DZLC-2 from the 2Ab recovered from Profile 2. A thick red silty clay bed that contains deep red redoximorphic features rests directly on top of these two features. These thick red silty clay beds abruptly transition into flood deposits with the thick beds of silty loam and thin beds of red silty clay that are diagnostic of unit C.

Xidacheng A The profile at Xidacheng is approximately 20 m long and 6 m deep (Figure 5). From the bottom to the top of the Xidacheng sequence, the sediments alternate between silty loam and silty clay

loam. The results of the sediment analysis from Xidacheng are presented in supplemental material (ST4). We labelled each horizon with elevated clay content an Ab horizon, however there are few indicators of landform stability like root casts or redoximorphic features. The pit features that cut through 2Ab, 2C and 2C2, suggest some recent periods of land form stability. The one charcoal sample recovered from Xidacheng’s layer 7C1 returned am uncalibrated date of 1240 ± 20 yr BP (XDC-1), with a calibrated probability distribution of cal yr AD 687-779 (72.4%), and 790-870 (23%). This radiocarbon date indicates that the 6 m of deposition accumulated over a 1200 year timespan.

Daguxiancun A The Daguxiancun site is located close to Dazhanglongcun and is comprised of two profiles, one at the bottom, Profile 1, and one at the top, Profile 2 (Figure 6). Profile 1 is 15 m long and 1.5 m deep. At the base of Profile 1 is a yellow silty loam deposit (2C) that has many root traces from the overlying buried soil (2Ab). The overlying buried soil contains at least two surfaces that were likely rapidly buried by a small flood. The boundary between the first brownish red buried soil (2Ab2) and the underlying silty loam is clear (< 5 cm) and has been subjected to bioturbation, much like the underlying silt (2C). A dark grey soil (2Ab1) overlies the brownish red buried soil and contains brick fragments and sediments that the local archaeologists say are typical of an ancient trampled road. Several small pits of greyish silty clay loam with redoximorphic features in the form of root casts also cut into the dark grey layer (2Ab1). A thick bed of silt (C2) overlies the final phase of 2Ab.

Profile 2 contains the second half of the sequence of the flood deposit that buries the dark grey buried soil (2Ab1). Profile 2 is approximately 4 m deep. A thick silty loam bed with fine reddish silty clay laminations spans the bottom of Profile 2 to about 200 cm beneath the modern ground surface (C2). At 150 cm below the modern land surface, the sediment abruptly transitions into a reddish silty clay (C1) that looks like a slackwater deposit or a buried soil capped with red silty clay. A thick bed of silty loam that has no apparent laminations or other sedimentary features overlies this reddish silty loam layer (Bw), likely wind-blown loess. The deposit transitions into the modern soil at approximately 40 cm below the modern land surface (Ap).

Discussion

A The Sedimentary and Chronological Evidence of the AD 1048-1128 Yellow River Floods

The sedimentary and archaeological records of Neihuang County provides a glimpse at the extent that the physical landscape has changed over the past several thousand years. Our data from Dazhanglongcun, Xidacheng, and Daguxiancun suggest that in slightly less than a thousand years around 5 meters of sediment buried inhabited land surfaces. We argue that the lithostratigraphic and radiocarbon evidence recovered from Dazhanglongcun, Xidacheng, and Daguxiancun are connected to the historic Yellow River floods of AD 1048-1128.

The lithostratigraphy of Yellow River flood events is well documented in both the middle and lower reaches of the Yellow River watershed (Huang et al. 2010; Huang et al. 2011; Kidder et al. 2012b; Shi et al. 2010; Storozum et al. 2017a). The stratigraphy at the nearby sites of Anshang

9 and Sanyangzhuang in Neihuang County reveal a similar process of Yellow River flooding that help place the findings at Dazhanglongcun, Xidacheng, and Daguxiancun into a sedimentary context. At Sanyangzhuang and Anshang, alternating beds of red silty clay / silty clay loam and yellow silt / silty loam are ubiquitous. Kidder, Liu, and Li (2012b) argue that the red silty clay at Sanyangzhuang represents an initial pulse of low energy flood water from the Yellow River. As the energy of the flood increased, the grain size of sediments at Sanyangzhuang also increased from red silty clay / silty clay loam to yellow silt / silty loam. In several instances, the red silty Commented [MJS1]: Add in data clay became a meta-stable land surface that gradually and then rapidly accumulated sediment as the flood waters alternated between low and high energy depositional regimes. Within the red silty clay beds, redoximorphic features are prevalent, suggesting that there was enough landform stability for vegetation to establish itself. Within the yellow silt / silty loam beds, the near complete absence of redoximorphic features suggests the landscape rapidly changed and did not give new stands of vegetation enough time to successfully infiltrate the sedimentary column.

Particle size data from Xidacheng demonstrates that floods from the Northern Song dynasty exhibit a similar depositional pattern flood of “coarsening upward” and “fining upward” successions that are often produced by crevasse splays (Miall 2013). The specific fluvial dynamics that created deposits found at Sanyangzhuang, Anshang, and Xidacheng are likely different from one another but each deposit has similar physical characteristics, suggesting that these sediments come from the same source. Smaller, more local streams in northern Henan Province likely contain more sand than the Yellow River’s reworked loessic deposits. Although more work is needed to differentiate local and regional sources of sediment deposition, our particle size results of sediments from Xidacheng closely match previous studies at Sanyangzhuang and Anshang that suggests a similar sediment source.

In addition to the lithological similarities between deposits at Xidacheng, Anshang, and Sanyangzhuang, the radiocarbon dates obtained from Dazhangloncun and Xidacheng provide strong support for the contemporaneity of sedimentation at these sites and the start of the AD 1048-1128 flood events. After calibration, two radiocarbon dates (DZLC-1 and DZLC-3) from the buried land surfaces at Dazhanglongcun overlap from the periods of AD 1020-1050 and AD 1080-1150. Oddly, the charcoal dated from the flood deposit (DZLC-2) returned a calibrated date of AD 979-1021, dating before the period of historically recorded widespread flooding. The date from the flood deposit at Dazhanglongcun may be an older piece of charcoal that got mixed in with the flood sediment (Wang et al. 2012). At Xidacheng, the charcoal sample (XDC-1) returned a calibrated date of AD 687-779 or AD 790-870, predating the buried land surface at Dazhanglongcun by several hundred years. Regardless of some of the uncertainties in matching radiocarbon dates with historically recorded events, the ancient land surfaces found at Dazhanglongcun, Xidacheng, and Daguxiancun are deeply buried but still fairly recent. When the lower course of the Yellow River shifted to the south in AD 1128, sedimentation rates likely dropped to nearly zero because the main source of deposition, the Yellow River, was no longer geographically proximate. Therefore, the 5 meters of sediment likely buried these sites in less than 100 years.

The dates reported here are relatively consistent with the chronology of the AD 1048-1128 Yellow River floods, especially given the difficulty of precisely matching radiocarbon dates to historical events (Butzer 1980). Additional chronological data from radiocarbon and

luminescence dates are necessary to clarify the exact timing of these flood events. A developed absolute chronology, in combination with the use of relative stratigraphic dating, historical documentation, and Bayesian statistics, may make it possible to identify specific areas that were flooded more heavily than others at different points in time (Chiverrell et al 2011; Cunningham and Wallinga 2012). Moreover, advances in paleoflood hydrology may enable geomorphologists to calculate the magnitude and extent of the AD 1048-1128 based on the rate of sedimentation found across Henan and Hebei Province (Baker 1987, 2008).

For these reasons, future work at archaeological sites in northern Henan and Hebei Province should incorporate geomorphological researchers into their excavations to answer crucial questions regarding the past fluvial dynamics of the Yellow River, especially because many archaeological sites across northern Henan and Hebei Province likely contain a record of ancient Yellow River flood events. Archaeological surveys have already demonstrated that catastrophic Yellow River floods have buried large portions of Henan and Hebei Provinces (Kidder et al. 2012b; Storozum et al. 2017a; Jing, Rapp, and Gao, 1995, 1997). In eastern Henan Province, archaeologists found evidence of a buried city that likely dates to the Zhou dynasty (Jing, Rapp, and Gao 1995, 1997). Over the years, the site has become so deeply buried that it is completely obscured from view. Farther to the north in Hebei Province, archaeologists found the ancient city of Borencheng, an ancient town that was supposedly buried by a historically recorded Yellow River flood event in AD 738 (Hebei Xinwenwang 2016). Buried sites such as Dazhanglongcun, Sanyangzhuang, and Borencheng, are a consequence of environmental turmoil that frequently afflicted premodern China. A closer integration of geological methods and perspectives into investigations may help archaeologists identify catastrophic geological events in association with archaeological sites that rapidly changed the physical and political landscape of premodern China.

The Roles of Demography, Geography, and Agency in Dynastic Collapse A The combined investigation of historical, geological and archaeological records can reveal the social and environmental complexities that eventually led to the dissolution of the Northern Song dynasty. Much like the collapse of the Western Han dynasty a thousand years earlier, many social and natural factors contributed to the collapse of the Northern Song dynasty’s empire (Kidder and Zhuang 2015; Kidder et al. 2015; Zhuang et al. 2016), but eventually the dynastic machinery that worked for hundreds of years became encumbered with past successes and failures, leaving those in charge of managing the Northern Song dynasty less adaptable to changing geopolitical and environmental realities. We echo historians’ arguments that the cumulative consequences of hundreds of years of human actions accelerated the geomorphic processes that caused the AD 1048-1128 flood events (Elvin 2004; Zhang 2009, 2016). As economic, environmental, and social stresses mounted, agents were increasingly locked into decision-making processes that ultimately fractured and then dissolved the capacity for the Northern Song dynasty to effectively govern.

From a purely demographic perspective, the Northern Song dynasty was an exceptional period in China’s history. Census records indicate that China’s population swelled to nearly 100 million people for the first time ever, double the population of the Han dynasty (Table 2). The rapid increase in the number of people that the Northern Song dynasty ruled over put an unprecedented

11 strain on both the environment and the economy (Durand 1960; Deng and Zheng 2015). According to the Songshi Bing Zhi (History of the Song Dynasty, Journal of Military Vol. 190), Emperor Shenzong (Zhao Xu AD 1048-1085, reigned AD 1067-1085) realized that the abundant fields in the frontier zone of the Loess Plateau were fallow and therefore he aimed to recruit farmers and soldiers to help store grain at frontier outposts. Those who cultivated the fields were exempted from military service (History of Song Dynasty, History of Population and Territorial Resource, Vol. 176). Gradually, this agricultural system called tuntian supplied the vast majority of grain for soldiers in Shannxi which reached an estimated total of 300,000 at its height (Han 1993). Not only did these policies aim to relieve population pressure on the North China Plain but they also hoped to increase agricultural surplus and create a buffer zone between the dynastic core in the North China Plain and the Western Xia kingdom (Mostern 2016). As thousands of people moved from their ancestral homes to the borderlands of the Northern Song dynasty state, they likely brought with them many preconceptions of “correct” agricultural practice that proved detrimental to the long-term stability of the Loess Plateau.

After the implementation of these policies, the rate of erosion of the Loess Plateau like accelerated, increasing both the sediment load of the Yellow River and the Yellow River’s propensity to flood. Current evidence from geological coring has revealed that sedimentation rates in the North China Plain rapidly increased during the Northern Song dynasty. From AD 1034-1127, Shi et al. (2010) estimates that the amount of deposition in the lower course of the Yellow River was 663 million tons a year, compared to 224 million tons per year from the period AD 11-1033. Rather than address the rampant erosion on the Loess Plateau, Northern Song dynasty politicians instead decided to raise the levees that constrained the lower course of the Yellow River in an effort to reduce flood risk. Administrators requisitioned extraordinary amounts of wood from the hills in Henan and Hebei Provinces to create fascine rolls that supported short term flood prevention measures but continued to exacerbate the erosion problem (Zhang, 2009, 20). Meanwhile, climatic conditions continued to oscillate from a weak summer monsoon to a strong one, increasing the potential for summer flooding to entrain more of the silt eroded off of the Loess Plateau. The rapid acceleration of erosion from the Loess Plateau and deposition onto the North China Plain is likely related to the deforestation of the Loess Plateau and higher levees along the Yellow River (Milliman et al. 1987). After building towards a geomorphic threshold event for years, the levees along the Yellow River finally gave way as the river breached its banks near Puyang in AD 1048, starting a near century long period of flooding and channel destabilization.

Starting in AD 1048, a series of Yellow River floods devastated northern Henan and Hebei Provinces. Dynastic administrators took over eight years to respond to the flooding widespread throughout the region (Zhang 2009, 20). In AD 1056, hundreds of thousands of laborers tried to repair the dikes at several locations in northern Henan Province but the flood waters drowned many of them. By AD 1068, around a million people had died from the flooding (Zhang 2009, 21). Episodic and devastating flooding continued until the governor of Kaifeng decided to breach the banks of the Yellow River in an attempt to slow the invading Jurchen army in AD 1128. The levee breach had the anticipated effect of directing the floodwaters to the east, but it also had the unanticipated effect of diverting the Yellow River southward out to the Bohai Sea, a course the Yellow River would more or less maintain until AD 1855 (Lamouroux 1998). The rapid change in base level of the Yellow River likely caused many smaller tributary streams in the middle

12 reaches of the Yellow River to rapidly incise their channels, further increasing the sedimentation rate downstream into the Yellow River’s lower reaches while simultaneously destabilizing some of the built infrastructure that supported urban centers in the middle reaches of the Yellow River (Storozum et al. 2017b).

Climate change, environmental degradation, and human actions, all conspired to create the AD 1048-1128 Yellow River floods that contributed to the collapse of the Northern Song dynasty’s empire. In particular, changes in land use policies that encouraged large populations to migrate to new and unfamiliar areas, bringing with them agricultural techniques not suited for the new environment, had significant geomorphic ramifications. The rapid erosion of the Loess Plateau and the increasing risk of overbank flooding of the Yellow River exacerbated many systemic problems along the Yellow River as the massive amount of sediment eroding out the Loess Plateau silted up the dams and canals that were the main arteries of trade, commerce, and military power (Fang and Xie 1994; Elvin 1998; Shi et al. 2010). Rather than address the root cause of the problem, many Northern Song dynasty decision makers responded by doubling down on their expansionist policies in the Loess Plateau and levee construction along the banks of the Yellow River. These solutions had the limited positive effect of reducing the agricultural strain on the North China Plain as the Northern Song dynasty’s demographic, economic, environmental, and military situation became more tenuous. As a result of social and geomorphic processes set in motion for hundreds of years, the socio-ecological system of the Northern Song dynasty became increasingly rigid, granting little flexibility to the few individual decision makers who might have been able to successfully prevent or mitigate the AD 1048-1128 Yellow River floods.

From AD 1048-1128, a torrent of water and mud slurry buried villages like the one found at Dazhanglongcun under meters of sediment. The thick sediment deposits left in the wake of the flood rendered much of northern Henan and Hebei Provinces agriculturally unusable for generations. Moreover, the Jurchen army invaded and conquered the North China Plain around AD 1125, leading to the direct collapse of the North Song dynasty and it’s reformation as the Southern Song dynasty (Fairbank and Goldman 2006, 115). In retreat, the Song elite abandoned Bianjing and headed towards the southern city of Lin’an, now known as Hangzhou, where they established a new capital for the Southern Song dynasty (AD 1127-1279) (Marks 1998). Demographic data obtained from ancient census records suggests that the bulk of the population from the North China Plain relocated to the south during this time period, a consequence of the complete destruction of millions of people’s livelihoods through rampant warfare and flooding (Table 2). Although Northern Song dynasty civil servants tried to stop the gradual accumulation of errors leading to the AD 1048-1128 Yellow River floods, centuries of climatic volatility, unsustainable human activities on the Loess Plateau, the mismanagement of the Yellow River, and widespread geopolitical crisis all contributed to the collapse of the Northern Song dynasty.

Conclusion

Historians have argued that the Chinese dynasties’ failure to manage erosion on the Loess Plateau and maintain the increasingly complex network of levees and canals devastated the lives of millions, promoted social instability, and irrevocably changed the social and natural landscape of the North China Plain. We have attempted to amplify the historical evidence that documents

13 the Yellow River floods of AD 1048-1128 through the discussion of sedimentary evidence found at several archaeological sites in northern Henan Province. Specifically, lithostratigraphic evidence from several sites in northern Henan Province indicates that Yellow River floods often follow a similar sequence of low to higher energy pulses of floodwater and could bury entire villages within short periods of time. The radiocarbon dates we obtained from Dazhanglongcun, Xidacheng, and Daguxiancun all indicate that over 5 meters of alternating beds of silty loam and silty clay buried a stable landscape in possibly less than a 100 years. In particular, the buried wall of the Northern Song dynasty village at Dazhanglongcun shows the rapidity and magnitude of the Yellow River floods of AD 1048-1128. In conclusion, a combination of climatic volatility, disastrous homesteading polices on the Loess Plateau, and geopolitical crisis along the Northern Song dynasty’s northern borders all contributed to the AD 1048-1128 Yellow River floods that set the stage for the eventual collapse of the Northern Song dynasty.

Acknowledgements

We are grateful for the assistance of the Henan Provincial Institute of Cultural Relics and Archaeology for providing us with logistical support while conducting this work. Mr. Zhang’s detailed knowledge of the local archaeology of Henan Province has been invaluable in identifying appropriate areas for excavation. We are equally indebted to the townspeople of Sanyangzhuang who have skillfully excavated many of the profiles described here. Many fruitful conversations with T. R. Kidder have helped shape this manuscript. This work is supported by the National Science Foundation BCS #1458136 and #1614330, the National Basic Research Program of China (Grant no. 2016YFA0600504), and the National Natural Science Foundation of China (Grant no. 41472319).

Figures and Table captions

Figure 1. a) World map with China outlined b) Political map with Henan Province shaded c) Physical map (dark is high, light is low) with key locations mention in the text on the map

Figure 2. a) Physical map of North China Plain with study area b) digital elevation model of northern Henan Province c) location of archaeological sites mentioned in text

Figure 3. Dazhanglongcun’s lithostratigraphy with photographs of each profile, composite stratigraphic diagram, and map of the site. See supplemental table 1 for more details.

Figure 4. Dazhanglongcun’s archaeostratigraphy a) Photograph of Profile 4, b) drawing of Profile 4, c) Photograph of Profile 1, d) close-up photograph of combustion feature, e) drawing of Profile 1, f) photograph of the context of Profiles 1, 3, and 4.

Figure 5. a) Xidacheng stratigraphic drawing and photograph with b) stacked area and ternary plot of particle size data from each stratigraphic unit at Xidacheng and graphs for magnetic susceptibility and loss on ignition. See supplemental table 2 and 4 for more details.

Figure 6. Daguxiancun’s lithostratigraphy with photographs of each profile, composite stratigraphic diagram, and photograph of the site. See supplemental table 1 for more details.

Table 1. Accelerator mass spectrometry radiocarbon dates in stratigraphic order from the pits at Dazhanglong and at Xidacheng. Dates are calibrated with OxCal 4.2 (Bronk Ramsey 2009) using the IntCal13 dataset (Reimer et al. 2013).

Table 2. Population estimates from the southern and northern extent of the Song dynasty. Note the change in distribution of population in the south and the north from AD 980 to 1291. Translated and adapted from (Ge 2005, 625).

Supplemental Table 1. Descriptions of Dazhanglongcun Supplemental Table 2. Descriptions of Xidacheng Supplemental Table 3. Descriptions of Daguxiancun Supplemental Table 4. Sedimentary data from Xidacheng

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