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SCIENCE sciencemag.org
phene, also allows one to selectively inject carriers
propagating in the same direction and to probe
pseudospin-polarized quasi-particles. In principle,
the technique can be extended to tunneling devices in which surface states of topological insulators are used as electrodes; then, all-electrical
injection of spin-polarized current (28) with noninvasive tunneling contacts could reveal a number
of exciting phenomena (29?31).
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This work was supported by the European Union FP7 Graphene
Flagship Project 604391, European Research Council Synergy
Grant, Hetero2D, Engineering and Physical Sciences Research
Council (EPSRC) (Toward Engineering Grand Challenges and
Fellowship programs), the Royal Society, U.S. Army Research
Office, U.S. Navy Research Office, and U.S. Air Force Office of
Scientific Research. M.T.G acknowledges support from the
Leverhulme Trust. A.M. acknowledges support of EPSRC Early
Career Fellowship EP/N007131/1. S.V.M. was supported by
NUST ?MISiS? (grant K1-2015-046) and Russian Foundation for
Basic Research (RFBR15-02-01221 and RFBR14-02-00792).
Measurements in high magnetic field were supported by High Field
Magnet Laboratory?Radboud University/Foundation for
Fundamental Research on Matter (HFML-RU/FOM) and
Laboratoire National des Champs Magnétiques Intenses?Centre
National de la Recherche Scientifique (LNCMI-CNRS), members of
the European Magnetic Field Laboratory (EMFL), and by EPSRC
(UK) via its membership to the EMFL (grant no. EP/N01085X/1).
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Materials and Methods
Supplementary Text
Figs. S1 to S9
References (32?49)
11 February 2016; accepted 13 July 2016
Outburst flood at 1920 BCE supports
historicity of China?s Great Flood and
the Xia dynasty
Qinglong Wu,1,2,3*? Zhijun Zhao,2,13 Li Liu,4? Darryl E. Granger,5 Hui Wang,6
David J. Cohen,7? Xiaohong Wu,1 Maolin Ye,6 Ofer Bar-Yosef,8 Bin Lu,9 Jin Zhang,10
Peizhen Zhang,3,14§ Daoyang Yuan,11 Wuyun Qi,6 Linhai Cai,12 Shibiao Bai2,13
China?s historiographical traditions tell of the successful control of a Great Flood leading to
the establishment of the Xia dynasty and the beginning of civilization. However, the
historicity of the flood and Xia remain controversial. Here, we reconstruct an earthquakeinduced landslide dam outburst flood on the Yellow River about 1920 BCE that ranks as one
of the largest freshwater floods of the Holocene and could account for the Great Flood.
This would place the beginning of Xia at ~1900 BCE, several centuries later than
traditionally thought. This date coincides with the major transition from the Neolithic to
Bronze Age in the Yellow River valley and supports hypotheses that the primary state-level
society of the Erlitou culture is an archaeological manifestation of the Xia dynasty.
hina?s earliest historiographies, including Shujing (Book of Documents) and
Shiji (Records of the Grand Historian,
by Sima Qian), tell of the Great Flood, a
lengthy, devastating flood of the Yellow
River. The culture hero Yu eventually tamed
this flood by dredging, earning him the divine
mandate to establish the Xia dynasty, the first in
Chinese history, and marking the beginning of
Chinese civilization. Because these accounts laid
5 AUGUST 2016 ? VOL 353 ISSUE 6299
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The projected states are composed of two sublattice components in the emitter and collector.
As a result, momentum-dependent constructive
(fe(c) = 0) or destructive (fe(c) = p) interference
between sublattice components is governed by
jyA þ yB j2 º1 þ cosfe(c), for the states both in
emitter (fe) and collector (fc) and manifests itself
in the tunneling characteristics I(Vb). Because the
magnetic field selects the pairs of particular plane
wave states probed by tunneling at a particular
gate or bias voltage (Fig. 4, A and B), the measured
asymmetry provides a direct visualization of the
pseudospin polarization of the Dirac fermions.
In the presence of the magnetic field, each resonance peak represents tunneling from a particular corner of the BZ. This allows one to inject
electrons with a particular valley polarization, and
from a selected corner of the BZ. We use the experimental parameters to calculate the amount
of polarization achieved in our experiment (Fig.
3, J and M), and estimate that the valley polarization, P ¼ ðIK – IK ‘ Þ=ðIK þ IK ‘ Þ [where IK (IK ‘ )
is the current injected into the K(K’) valley] can
be as high as 30% (40%) for the particular Gr/3hBN/
Gr (Gr/5hBN/BGr) devices. The main limit to the
degree of polarization is the energy broadening of
states at the Fermi levels caused by inelastic tunneling processes. However, even for the current
level of disorder, with the resonances at around
Vb ? 0 V (e.g., resonances marked by yellow dashed
lines on Fig. 2D at Vg > 50 V), which maximizes the
number of states participating in tunneling and
sensitive to magnetic field, a polarization close to
75% could be achieved (19). By using devices with
smaller misalignment between the graphene electrodes [on the order of 0.2°, now within the reach
of the current technology (19)], valley polarization
close to 100% is possible (19).
The same mechanism can also be used to select electrons with a particular pseudospin polarization. In Fig. 4, C to R, we present results of a
calculation of the contribution of different electronic states in k-space to the tunnel current for
the Gr/3hBN/Gr (Fig. 4, C to I) and Gr/5hBN/
BGr (Fig. 4, J to R) devices. We choose the position of the Fermi levels in the emitter and collector to be very close to a resonance at B = 0 T.
Then, for certain directions of B, the resonant
conditions are achieved only in one valley and
for only a very narrow distribution in k-space
(Fig. 4, G to I). Tunneling of the electrons from
other parts of k-space is prohibited either because
they are off-resonance or because of the pseudospin selection rule. Alternatively, for the Gr/5hBN/
BGr device and exploiting the difference in curvature of monolayer and bilayer electronic bands,
we can choose the overlap between the bands in
such a way that the magnetic field reduces the
overlap in one valley and increases it for the
other (Fig. 4, M to R). In this case, momentum
conservation at B = 0 T is fulfilled for the
states marked by white dashed lines (Fig. 4O).
However, only one of those lines contributes
to tunneling, owing to pseudospin interference
(Fig. 4, M and N).
Our technique, which enables tunneling of valleypolarized electrons in monolayer and bilayer gra-
the ideological foundations for the Confucian
rulership system, they had been taken as truth
for more than 2500 years until challenged by the
?Doubting Antiquity School? in the 1920s. Within
a decade, archaeological excavations demonstrated the historicity of the second dynasty,
Shang, and the search for similar evidence for
Xia began (1, 2). Archaeological fieldwork since
the 1950s on the Early Bronze Age Erlitou culture
(~1900 to 1500 BCE) has led many scholars to
associate it with the Xia (1?6) because it overlaps
with the spatial and temporal framework of
the Xia dynasty. Traditionally, historians have
dated the start of Xia to ~2200 BCE, whereas
the government-sponsored Xia-Shang-Zhou Chronology Project adopted the date as 2070 BCE
(5), leaving a chronological gap in associating
Erlitou with Xia (7?9). Other scholars see Xia purely as a myth fabricated to justify political succession
(10, 11).
Scholars also have long sought a scientific
explanation of the Great Flood (12?14), with
even Lyell mentioning it (15), yet no evidence
for it has been discovered. Here, we present
geological evidence for a catastrophic flood in
the early second millennium BCE and suggest
that it may be the basis of the Great Flood, thereby lending support to the historicity of the Xia
dynasty. The evidence found in our investigations
along the Yellow River in Qinghai Province includes remains of a landslide dam, dammed lake
sediments (DLS) upstream, and outburst flood
sediments (OFS) downstream (Fig. 1 and figs. S1
to S5) that allow us to reconstruct the size of the
lake and flood (16).
Field observations (fig. S2B) show that the
ancient landslide dam deposits reach an elevation of 240 m above present river level (arl)
and stretch for 1300 m (fig. S2A) along Jishi
Gorge (Figs. 1A and 3A). We estimate that the
saddle of the dam would have been 30 to 55 m
lower than the highest preserved remnants, so
the lake would have filled to an elevation of
185 to 210 arl [2000 to 2025 m above sea
level (asl)] (fig. S2B), impounding 12 to 17 km3
of water (16) (table S1). Based on typical river
discharge values, the dam would have completely blocked the Yellow River for 6 to 9 months
before overtopping (16). DLS distributed widely upstream of the dam are up to 30 m thick
and have a highest elevation of ~1890 m asl
(Fig. 1B and figs. S1 and S3A). We interpret
this as indicating that the catastrophic breach
dropped the water level 110 to 135 m (Fig. 1B),
releasing ~11.3 to 16 km3 of water (16) (table
S1), tens of times that estimated by a previous
study (17). After the breach, DLS infilled a residual lake behind the lowest part of the dam that
Outburst flood sediments are found downstream at elevations from 7 to 50 m arl in the
lower Jishi Gorge and in Guanting Basin (Fig.
1 and figs. S1 and S4). They are characterized by
high-concentration suspension deposition and
consist exclusively of angular clasts of greenschist and purple-brown mudrock sourced from
Jishi Gorge (table S2). At the mouth of the gorge,
where the Yellow River enters Guanting Basin,
the sediments reach 20 m thickness and include
boulders up to 2 m in diameter (Fig. 1B and figs.
S1 and S4, C and D). We also identified the OFS at
the earthquake-destroyed prehistoric Lajia site (fig.
S5), a settlement of the Qijia culture (18, 19) known
for its early noodle remains (20), 25 km downstream from the dam. OFS at Lajia covered the
settlement?s last Qijia culture occupation and
filled in collapsed cave dwellings (fig. S5, A and
B), pottery vessels (fig. S5B), and earthquake fissures (fig. S5C), mixing with pottery sherds (fig.
S5D) and other Qijia cultural materials, with
heights of up to 38 m arl.
Stratigraphic relationships of the OFS, remnant dam, DLS, loess, and other deposits in
Jishi Gorge and neighboring basins, along with
destruction features at the Lajia site (fig. S1),
allow us to reconstruct and date a sequence of
events ending in the outburst flood. First, they
show that the damming and outburst flood event
occurred during the archaeological Qijia culture period (~2300 to 1500 BCE) after the
collapse of the Lajia cave-houses. Ground fissures caused by the earthquake at the Lajia site
were entirely filled with OFS (fig. S5C) before
silts from surface runoff during the annual rains
could enter them, indicating that the outbreak
flood must have occurred less than 1 year after
the earthquake and collapse of the houses. It is
likely that the same earthquake that destroyed
Lajia also triggered the landslide that dammed
the river, along with widespread contemporaneous rock avalanches whose deposits lay directly
beneath the DLS (fig. S3A).
School of Archaeology and Museology, Peking University,
Beijing 100871, China. 2School of Geography Science,
Nanjing Normal University, Nanjing 210023, China. 3State
Key Laboratory of Earthquake Dynamics, Institute of
Geology, China Earthquake Administration, Beijing 100029,
China. 4Department of East Asian Languages and Cultures,
Stanford University, Stanford, CA 94305, USA. 5Department
of Earth, Atmospheric, and Planetary Sciences, Purdue
University, West Lafayette, IN 47907, USA. 6Institute of
Archaeology, Chinese Academy of Social Sciences, Beijing
100710, China. 7Department of Anthropology, National
Taiwan University, Taipei 10617, Taiwan (R.O.C). 8Department
of Anthropology, Harvard University, Cambridge, MA 02138,
USA. 9CCTEG Xi?an Research Institute, Xi?an 710077, China.
Institute of Geology, Chinese Academy of Geological Sciences,
Beijing 100037, China. 11Lanzhou Institute of Seismology, China
Earthquake Administration, Lanzhou 730000, China. 12Qinghai
Provincial Institute of Cultural Relics and Archaeology, Xining
810007, China. 13Jiangsu Center for Collaborative Innovation in
Geographical Information Resource Development and
Application, Nanjing, Jiangsu 210023, China. 14School of Earth
Science and Geological Engineering, Sun Yat-sen University,
Guangzhou 510275, China.
*Corresponding author. Email: wuqinglong@pku.edu.cn
?Present address: School of Geography Science, Nanjing Normal
University, Nanjing 210023, China. ?These authors contributed
equally to this work. §Present address: School of Earth Science
and Geological Engineering, Sun Yat-sen University, Guangzhou
510275, China.
5 AUGUST 2016 ? VOL 353 ISSUE 6299
Fig. 1. Evidence of the exceptional outburst flood in the upper valley of the Yellow River. (A) Distributions of OFS, DLS, and landslide dam. Light purple and dark green shaded areas indicate purple-brown
mudrock and greenschist, respectively. Line AB across the Lajia site shows the location of the reconstructed cross section in fig. S6C. (B) The vertical distribution of the OFS, landslide dam, DLS, Lajia site
and reconstructed lake levels relative to the longitudinal profile of the present Yellow River. DLS are classified into lacustrine sediments (LS) and fan delta deposits (FD).
sciencemag.org SCIENCE
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To date the outburst flood, we collected carbon samples for accelerator mass spectrometry (AMS) 14C dating (16). Seventeen charcoal
samples from the OFS and the only charcoal
sample from a layer overlying the OFS (fig. S1)
indicate that the age for the flood is between
2129 and 1770 cal. BCE [95% confidence interval (CI)] (Fig. 2A and table S5) (16). Charcoal samples from DLS upstream of the dam
(fig. S1) yield calibrated 14C results (95% CI)
spanning 2020 to 1506 BCE (Fig. 2A and table
S5), demonstrating that the DLS is coeval with
or younger than the outburst flood and confirming that it is fill from the remnant lake.
The best dating for the flood comes from the
Lajia site (16), because it was destroyed within
1 year before the outburst flood. Radiocarbon determinations of bone samples from three
human victims, aged 6 to 13 years old, in collapsed Lajia dwellings (Fig. 2B) agree to within
uncertainty (Fig. 2A and table S5), consistent
with that of two victims reported previously (21)
as well. Because the radiocarbon calibration curve
is linear in this region and the bones are the
same age, we use the inverse variance weighted
mean of the three measurements. This yields a
calibrated age with a median of 1922 ± 28 BCE
(1 SD) and a 95% CI of 1976 to 1882 BCE (Fig.
2C). To simplify this range, we use 1920 BCE to
indicate the approximate date of the flood.
We estimate the peak discharge of the flood
in two ways. Empirical formulas considering
the volume of the lake and the height of the
dam lead to estimates ranging from 0.08 to
0.51 × 106 m3 s-1, with large uncertainties (16)
(table S3). We also reconstruct the flood channel
cross section from detailed surveys in Guanting
Basin and use Manning?s equation to estimate
a peak discharge of 0.36 to 0.48 × 106 m3 s-1 (16)
(fig. S6 and table S4), consistent with the dam
break estimations (16) (table S3). The calculated
peak discharge of ~0.4 × 106 m3 s-1 is more than
500 times the average discharge of the Yellow
River at Jishi Gorge. This ranks globally among
the largest freshwater floods of the Holocene (22).
We do not explicitly model the inundation
and effect of this outburst flood in the lower
reaches of the river, but analogous events demonstrate that outburst floods from landslide
dams can propagate long distances. In 1967, an
outburst flood with a volume of just ~0.64 km3
propagated at least 1000 km along the YalongYangtze Rivers (23), so the Jishi prehistoric
outburst flood, with a volume of ~11 to 16 km3,
could have easily travelled more than 2000 km
downstream. The Jishi flood would have breached
the natural levees of the Yellow River, resulting in rare, extensive flooding. It is possible
that this outburst flood was also the cause of a
major avulsion of the lower Yellow River (Fig.
3A) inferred from archaeological data, with a
previously estimated date of ~2000 BCE (24, 25).
Widespread destruction of levees and deposition of tributary mouth bars may have destabilized the main river channel, leading to
repeated flooding until a new river channel
was established. Extensive flooding on the lower Yellow River plain would have had a great
effect on societies there. We argue that this
event and its aftermath likely would have sur-
vived in the collective memories of these societies for generations, eventually becoming
formalized in the received accounts of the
Great Flood in the first millennium BCE. In
fact, early texts such as the Shujing and Shiji
even record that a place called Jishi (the same
characters as the gorge where the outburst flood
began) was where Yu began his dredging of the
Yellow River; whether this is a coincidence will
require further historical geographical research.
The ~1920 BCE flood shares the main characteristics of the Great Flood described in ancient texts. Apart from its huge peak discharge,
the secondary flooding on the lower plains may
have been long-lasting, just as the Great Flood
remained uncontrolled for 22 years until it

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