24. R. P. Dziak et al., Geophys. Res. Lett. 42, 1480–1487(2015).

25. Y. J. Tan, M. Tolstoy, F. Waldhauser, W. S. D. Wilcock, Nature10.1038/nature20116 (2016).

26. R. A. Sohn et al., Nature 453, 1236–1238 (2008).27. C. Helo, M.-A. Longpré, N. Shimizu, D. A. Clague, J. Stix, Nat.

Geosci. 4, 260–263 (2011).28. T. J. Wright et al., Nat. Geosci. 5, 242–250 (2012).29. F. Sigmundsson et al., Nature 517, 191–195 (2015).30. A. Ahmed et al., Geophys. J. Int. 205, 1244–1266 (2016).31. O. Roche, O. T. H. Druitt, O. Merle, J. Geophys. Res. 105,

395–416 (2000).32. B. Kennedy, J. Stix, J. W. Vallance, Y. Lavallee, M.-A. Longpré,

Geol. Soc. Am. Bull. 116, 515–524 (2004).33. S. Buchardt, T. R. Walter, Bull. Volcanol. 72, 297–308

(2010).

34. V. Acocella, Earth Sci. Rev. 85, 125–160 (2007).35. A. Gudmundsson, L. B. Marinoni, J. Marti, J. Volcanol.

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B12404 (2006).37. L. Michon, F. Massin, V. Famin, V. Ferrazzini, G. Roult,

J. Geophys. Res. 116 (B3), B03209 (2011).

ACKNOWLEDGMENTS

The seismic data used for this study are archived at theIncorporated Research Institutions for Seismology DataManagement System and the Ocean Observatories Initiative(OOI) Data Portal. The earthquake catalogs are archived in theInterdisciplinary Earth Data Alliance Marine GeoscienceData System (DOI: 10.1594/IEDA/323843). This work wassupported by the National Science Foundation under awards

OCE-1536219, OCE-1536320, OCE-1635276, OCE-1357076,and DGE-1256082. The seismic network was installed and isoperated by the OOI Cabled Array team, led by J. Delaney andD. Kelley. This paper is Pacific Marine Environmental Laboratorycontribution no. 4522.

SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/354/6318/1395/suppl/DC1Materials and MethodsFigs. S1 to S11Movies S1 and S2References (38–40)

15 July 2016; accepted 28 October 201610.1126/science.aah5563

VOLCANOLOGY

Inflation-predictable behavior andco-eruption deformation atAxial SeamountScott L. Nooner1* and William W. Chadwick Jr.2

Deformation of the ground surface at active volcanoes provides informationabout magma movements at depth. Improved seafloor deformation measurementsbetween 2011 and 2015 documented a fourfold increase in magma supply andconfirmed that Axial Seamount’s eruptive behavior is inflation-predictable, probablytriggered by a critical level of magmatic pressure. A 2015 eruption was successfullyforecast on the basis of this deformation pattern and marked the first time thatdeflation and tilt were captured in real time by a new seafloor cabled observatory,revealing the timing, location, and volume of eruption-related magma movements.Improved modeling of the deformation suggests a steeply dipping prolate-spheroidpressure source beneath the eastern caldera that is consistent with the location ofthe zone of highest melt within the subcaldera magma reservoir determined frommultichannel seismic results.

Successful volcanic eruption forecasting istraditionally based on short-term (minutesto hours) increases in seismicity, surfacedeformation, or both during the time thatmagma is already moving toward the sur-

face (1, 2). Successful forecasts made days toweeks in advance are much rarer because thepatterns of geophysical signals are generally notclear or repeatable enough. However, some notablesuccesses at volcanoes such as Mount St. Helensand in Iceland have been documented (3, 4). Sev-en months in advance of an April 2015 eruptionat Axial Seamount, we made a successful forecastthat it would occur within a 15-month time win-dow, on the basis of long-term deformation mon-itoring. The deformation measured during the2015 eruption also provides important constraintson the location and depth of magma reservoirsand conduits.

Axial Seamount is a heavily instrumented sub-marine volcano that is part of the Ocean Ob-servatories Initiative (OOI) Cabled Array (5, 6).Axial Seamount is distinguished from other sub-marine volcanoes in that it has a long-term vol-cano deformation time series that spans threeeruptions. A combination of bottom pressurerecorders (BPRs) and mobile pressure recorders(MPRs) (7–11) providedmeasurements of verticaldeformation from 2000 to 2015. Both methodsuse changes in the overlying water pressure todetect vertical displacements of the seafloor witha resolution of ~1 cm. BPRs record continuouslyto capture sudden events (such as eruptions)over minutes to days, but these instruments arenot ideal for longer-termmeasurements becauseof sensor drift. MPR campaign-style surveys re-quire a remotely operated vehicle (ROV) to de-ploy the instrument at seafloor benchmarks (fig.S1) and, after correcting for sensor drift, candocument gradual deformation over months toyears (9, 10). MPR data can constrain BPR driftwhere the two are colocated. Autonomous, battery-powered BPRs have been used at Axial since themid-1980s (12, 13) and, in September 2014, theOOI

Cabled Array began providing real-time data fromthree BPR-tilt instruments (5, 6). At the time ofthe 2015 eruption, three autonomous BPRs, threecabled BPRs, and 10 MPR benchmarks were de-ployed at Axial (Fig. 1 and fig. S2).After the 2011 eruption at Axial Seamount (14),

a time- or inflation-predictable model was pro-posed in which the volcano erupts at or near athreshold level of inflation (15, 16). The 2015eruption provided a test for this model and itsusefulness in forecasting. The average linearrate of inflation measured at the caldera centerbetween 2000 and 2010 was 15 ± 0.2 cm/year(Fig. 2), with higher ratesmeasured in themonthsafter the 1998 eruption and before the eruption in2011 (14). After 2011, we initially expected the nexteruption to occur in 2018 if the pattern of de-formation repeated itself (14). However, fromcontinued monitoring we found that the rate ofinflation increased substantially after the 2011eruption. We observed that the average inflationrate at the caldera center was 61 ± 1.4 cm/yearbetween August 2011 and September 2013 (Fig.2). A marked increase in the magma supply mayexplain the fourfold increase over the 2000–2010inter-eruption rate (11). Continuation of this high-er rate of inflation during 2013–2014 was observedafter aMonterey BayAquariumResearch Instituteautonomous underwater vehicle (AUV) collectedrepeat high-resolution bathymetry (17) and withdata recovered from a prototype self-calibratingBPR (18) inAugust 2014. Thus, in September 2014,we revised our forecast that Axial would eruptsometime during 2015 (19, 20). The expected erup-tion began on 24 April 2015, detected in real timeby the OOI Cabled Array (21).This long-term forecast was unusually success-

ful for any volcano (1, 2). The level of inflation asthe 2015 eruption began was only 30 cm higherthan in 2011 (Fig. 2). This observation supportsthe model of a pressure threshold in the shallowmagma reservoir above which diking events aretriggered, but it also suggests that the thresholdmay increase with time because of accumulatingtectonic stress, as observed in Iceland and Ethi-opia (22, 23). Nevertheless, the volcanic system atAxial may be unusually repeatable due to thecontinuous magma supply and the thin oceancrust in amid-ocean ridge setting. The increaseinmagma supply rate documentedby the inflationdata led to a marked decrease in the eruption

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1University of North Carolina Wilmington, Wilmington, NC28403, USA. 2Oregon State University/Cooperative Institutefor Marine Resources Studies, Hatfield Marine ScienceCenter, Newport, OR 97365, USA.*Corresponding author. Email: nooners@uncw.edu

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recurrence interval (1998–2011 versus 2011–2015),as well as a change in lava composition eruptedat the summit (24).Pre-eruption inflation changed abruptly to co-

eruption deflation at ~06:00 on 24 April 2015(all times GMT), more than an hour after seis-micity began to increase (21), due to magmaintruding out of the summit reservoir (fig. S4).The 2015 eruption extended >20 km from thenortheastern edge of the caldera and along thenorth rift zone (24), in contrast to the last twoeruptions, which were on the south rift (25, 26).The total subsidence at the caldera center wassimilar in 2015 and 2011 (–2.45 and –2.43 m,respectively), which suggests that roughly thesame volume of magma was removed from themagma reservoir. However, the rate of deflationwas noticeably higher in 2015 than in 2011. Forexample, the total subsidence in the first 24 hoursamounted to –2.22 m in 2015 (91% of the total),compared with only –1.57 m in 2011 (65% of thetotal). In 2015, the rate of deflation decreasedquasi-exponentially until 5 May and was followedby a transitional period of alternating minor in-flation and deflation until 19 May, when rapid re-inflation resumed (fig. S5). Thus, the deflationlasted much longer in 2015: 25 days comparedwith only 6 days in 2011. Notably, this is similarto the duration of the impulsive seismoacousticevents detected on the north rift zone (21) thatcould be interpreted as steam explosions duringlava flow emplacement (24).We captured co-eruption deformation during

the submarine dike intrusion and eruption within situ tiltmeters at two sites on the OOI CabledArray (11). The tilt signals can be closely relatedto the seismicity generated by the initial dikeintrusion (21). Tilt magnitudes and directionsbegan to change at 05:25 (Fig. 3), soon after theseismic crisis began. At this time, most of theearthquakes were located beneath the north-eastern edge of the caldera (21), where the dikeintrusion initiated and the southernmost erup-tive fissures are located (24). Between 06:00 and08:00, the earthquakes propagated 3 to 4 kmsouthward along the eastern edge of the caldera.The tilt signals changed substantially (Fig. 3) dur-ing this time period in a way that is consistentwith a dike intruding southward but not reach-ing the surface in this area (21).We observed>100microradians (mrad) of down-

ward tilt toward the south in ~1 hour, which thenabruptly reversed at 07:10 (Fig. 3A) in the centralcaldera tiltmeter [Axial caldera center (AXCC)]record. This behavior is consistent with modelingof lateral dike propagation past the instrument(27), because the tilt component parallel to thedirection of dike propagation (north-south at Ax-ial) is most sensitive to the lengthening of thedike. The initial tilt is in the direction of dikepropagation, and the reversal in tilt directionoccurs when the dike tip passes the tiltmeter. Atthe same time, the east-west component of theAXCC tiltmeter also reversed direction from sloweastward tilt (toward the dike axis) to a rapidwestward tilt (away from the dike axis) (Fig. 3, Aand B). Dike modeling (27) shows that the tilt

component perpendicular to the dike axis (east-west at Axial) ismost sensitive to the depth to thetop of the dike, and the initial tilt is downwardtoward the dike axis, which reverses to tilt awayfrom the dike axis when the top of the dike nearsthe surface. This tilt record suggests that the dikepropagated to the south for 3 to 4 km before

stalling out and continuing to the north alongthe north rift zone.We observed several large and nearly instan-

taneous easterly jumps in tilt magnitude between06:13 and 07:10 from the eastern caldera tiltmeter[Axial eastern caldera (AXEC)] located closer tothe dike axis. By 07:10, the net tilt amounted to

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>1000 mrad before it reversed and started grad-ually decreasing (Fig. 3, C and D). In contrast tothe AXCC tiltmeter, which recorded smoothlyvarying tilt signals, we interpreted the large sud-den offsets in the AXEC tilt record as either in-elastic deformation (perhaps cracking or faultingnear the dike axis) or slight movements of theinstrument caused by earthquake shaking dur-ing the peak of the seismic swarm. This makesthe AXEC tilt signals more difficult for us tointerpret in the context of dike models. How-ever, after 08:00, both tilt records were againsmooth and became dominated by deformationdue to the ongoing deflation rather than fromthe dike intrusion (fig. S6).We used the MPR results from September

2013 to August 2015 for the net vertical dis-placement at seafloor benchmarks in and nearthe summit caldera to model the source of theinflation and deflation signals (Fig. 1). This timeperiod includes some pre-eruption inflation, theco-eruption deflation, and some post-eruption re-inflation (Fig. 2). The 10 MPR stations in 2015,compared with only 6 in 2011, provided betterconstraints for ground deformation models. Wefit the MPR data from all 10 MPR stations to asuite of models, including a point-source (28), apenny-shaped sill (29), and a prolate spheroid(30) (figs. S7 to S9 and table S1). The best-fittingsource for the 2013–2015 time period ðc2reduced ¼34:2Þ is a prolate spheroid with the major axisdipping at 77° in the direction of 286°, with majorand minor axes of 2.2 and 0.38 km, respectively,and a depth to center of 3.81 km (Fig. 4 and fig.S8). The fit of the observed data to this model ismuch better than the fit to previous sill or point-source models (9, 10, 14).

The best-fitting deformation source for theinter-eruption period between the previous MPRsurveys (an inflation-only period with data fromsix stations from July 2011 to September 2013)is very similar, a steeply dipping prolate spheroidwith the major axis dipping at 75° in the di-rection of 290°, major and minor axes of 2.2 and0.33 km, and a depth of 3.77 km (fig. S7). Wesuggest that the source of the deformation is thesame for time periods dominated by inflation ordeflation. The location of the 2013–2015 source iseast-southeast of the caldera center, but its steepdip to the west-northwest causes the maximumuplift or subsidence to be observed near the cal-dera center (Fig. 4). The prolate spheroid shapeapproximates a nearly vertical conduit, and thelocation of its top (at 1.6 km depth beneath theeastern edge of the caldera) is almost the same

as the shallowest part of the magma body imagedby multichannel seismic (MCS) surveys (31). Thesouthern half of the caldera was also where theMCS data showed the highest percentage of melt,interpreted as the locus of magma supply fromthe underlying hot spot (31). The eastern edge ofthe caldera was the source area of the dikes thatfed the 2015 eruption (21, 24), as well as the twoprevious eruptions (25, 26). The best-fitting de-formation model does not necessarily show thegeometry of the entire magma body, which isapproximated by a horizontal ellipsoid underlyingthe caldera from MCS data. The deformationmodel instead shows where the greatest volumechange occurred during inflation and deflation.Inflation and deflation at Axial Seamount appearsto be concentrated in a nearly vertical conduitthat feeds the high-melt core of the magma body

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imaged by Arnulf et al. (31), and the surroundingmush zones of the magma body have less of aninfluence on surface deformation.To calculate the volume of magma removed

from the subcaldera reservoir during the 2015eruption, we used the prolate spheroid sourceparameters obtained from modeling the 2013–2015 MPR data to solve for the volume changedue to the co-eruption subsidence only (11), asrecorded by BPR instruments at five locations(fig. S9 and table S1). The volume change was2.88 × 108 m3, which is 1.95 times the volumeof lava erupted in 2015 (24). This implies that1.40 × 108 m3 of magma was in the dike thatintruded along the north rift zone. The lengthof the dike was ~24 km from seismicity and thelocation of 2015 eruption sites (21, 24), so with

an average dike height of 2 to 3 km, as wasassumed for the previous eruptions at Axial (14),the required dike thickness would be 2 to 3 mto match the estimated dike volume. This ismuch greater than the 1-m dike thickness fromsimilar calculations for the 1998 and 2011 erup-tions. A thick dike could explain the high de-flation rate and the longer duration in 2015compared with 2011. Axial did not have an erup-tion on its north rift zone in decades or more,whereas at least the last three eruptions havebeen on the south rift zone (32). Larger accu-mulated extensional stress on the north riftmay have resulted in the intrusion of a widerdike that accommodated a higher rate of mag-ma transport from the summit reservoir andtook longer to solidify (22, 33, 34). Inflation re-

sumed as soon as co-eruption deflation stopped(Fig. 1), with 33 cm of uplift at the caldera cen-ter from the 25 August 2015 MPR survey andanother 80 cm as of 19 May 2016 from OOI data,indicating that more than one-third of the mag-ma volume lost in 2015 was recovered in thefirst year (table S1).We successfully forecast the 2015 eruption of

Axial Seamount from seafloor deformation dataand captured the eruption in real time from tiltand pressure instruments on the OOI CabledArray. The tilt data showed that the dike ini-tially propagated 3 to 4 km south before stallingout and continuing to the north, consistent withthe seismic data (21). Improved modeling of themagma source for the eruption revealed a steep-ly dipping magma conduit beneath the eastern

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caldera, in agreement with the location of a high-melt zone from recent seismic results (31). Upliftrates have gradually decreased with time sincethe 2015 eruption, so it is unclear whether thehigher magma supply rate evident from 2011–2015 will continue. If reinflation continues at~60 cm/year, the next dike intrusion could occuras early as 2019 but will occur later if the in-flation rate slows or if higher tectonic stressesfrom previous dike intrusions need to be over-come (22). Variations in the magma supply ratecomplicate forecasts but may be at least partial-ly explained by a deeper magma body hydrau-lically connected to the shallow magma reservoir(35). These complexities could be overcome usinga generalized time-predictable model after severalmore eruption cycles have been observed (16).However, for the first time, we will be able tocontinuously update the next eruption and/or in-trusion forecast for Axial Seamount with real-timedata from the OOI Cabled Array.

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ACKNOWLEDGMENTS

The BPR and tilt data presented here are archived at theIntegrated Earth Data Applications Marine GeoscienceData System (12, 13) and at the OOI Data Portal (6). Thiswork was supported by NSF awards OCE-1356216 and 1546616and by the National Oceanic and Atmospheric Administration,Pacific Marine Environmental Laboratory (NOAA-PMEL),Earth-Ocean Interactions Program. We thank M. Fowler andthe crews of R/V Thomas G. Thompson, ROV Jason, and AUVSentry for logistical support at sea during expedition TN327. Thiswork would not have been possible without the support of theNOAA-PMEL Engineering Division and the University ofWashington OOI Cabled Array team, led by J. Delaneyand D. Kelley. The paper benefited from helpful inputfrom two anonymous reviewers. This is PMEL contributionnumber 4509.

SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/354/6318/1399/suppl/DC1MethodsSupplementary TextFigs. S1 to S9Table S1References

30 June 2016; accepted 28 October 201610.1126/science.aah4666

GEOCHEMISTRY

Large gem diamonds from metallicliquid in Earth’s deep mantleEvan M. Smith,1* Steven B. Shirey,2 Fabrizio Nestola,3 Emma S. Bullock,4

Jianhua Wang,2 Stephen H. Richardson,5 Wuyi Wang1

The redox state of Earth’s convecting mantle, masked by the lithospheric plates and basalticmagmatism of plate tectonics, is a key unknown in the evolutionary history of our planet.Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phasein the deep mantle.These sublithospheric diamonds contain inclusions of solidifiediron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane ± hydrogen, andsometimesmajoritic garnet or former calcium silicate perovskite.Themetal-dominatedmineralassemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions.We verify previous predictions that Earth has highly reducing deepmantle regions capable of precipitating a metallic iron phase that contains dissolved carbonand hydrogen.

Earth has a metallic liquid outer core, andit has been predicted from theory and ex-periments that the deep mantle could pre-cipitate iron alloys. The presence of suchmetallic iron phases, especially in high

enough abundance, would have profound effectson the physical and chemical properties of Earth’sdeep mantle. However, the inaccessibility of thedeep Earth makes it challenging to observe. Up-welling mantle regions melt adiabatically, pro-

ducing prolific basaltic volcanism and silicatemantle residues, both of which appear too oxi-dized to have originated from a deeper regionof metal saturation. Thus, physical evidence forsuch reducing regions—essential for understand-ing mantle evolution—has been virtually absent.Wehave identified a genetically distinct diamond

population that samples these metal-saturatedregions of Earth’s mantle. These diamonds aretypified by the 3106-carat (1 carat = 0.2 g) Cul-linan diamond and are almost always classifiedas type II, referring to their minimal nitrogencontent (<5 to 20 parts per million). More spe-cifically, diamonds that are Cullinan-like tendto be large, inclusion-poor, relatively pure, ir-regularly shaped, and resorbed (1–3). Combiningthe traits into an acronym leads us to term themCLIPPIR diamonds to distinguish them fromother populations of diamond, especially other

SCIENCE sciencemag.org 16 DECEMBER 2016 • VOL 354 ISSUE 6318 1403

1Gemological Institute of America, New York, NY 10036,USA. 2Department of Terrestrial Magnetism, CarnegieInstitution for Science, Washington, DC 20015, USA.3Department of Geosciences, University of Padova, Padova35131, Italy. 4Geophysical Laboratory, Carnegie Institution forScience, Washington, DC 20015, USA. 5Department ofGeological Sciences, University of Cape Town, Rondebosch7701, South Africa.*Corresponding author. Email: evan.smith@gia.edu

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Inflation-predictable behavior and co-eruption deformation at Axial SeamountScott L. Nooner and William W. Chadwick Jr.

DOI: 10.1126/science.aah4666 (6318), 1399-1403.354Science 

, this issue p. 1395, p. 1399Sciencevastly outnumber their aboveground counterparts.inflates and erupts when the inflation hits a threshold. Both studies elucidate the dynamics of submarine volcanoes, whichshow that eruptions are predictable on the basis of deformation data. As magma pools underneath it, Axial Seamount

Chadwickthe most recent eruption in April 2015 that allow the tracking of magma before and during eruption. Nooner and present real-time seismic data fromet al.location to include in the Ocean Observatories Initiative Cabled Array. Wilcock

the western United States. Eruptions in 1998 and 2011 were followed by periods of magma recharge, making it an ideal Axial Seamount is a large and active submarine volcano along the Juan de Fuca midocean ridge off the coast of

Volcano monitoring goes into the deep

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REFERENCES

http://science.sciencemag.org/content/354/6318/1399#BIBLThis article cites 26 articles, 4 of which you can access for free

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