Abstract
Volcanic eruptions shape Earth’s surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond and ascend through the lithosphere is, however, still poorly understood. Since 10 May 2018, magmatic activity has occurred offshore eastern Mayotte (North Mozambique channel), associated with large surface displacements, very-low-frequency earthquakes and exceptionally deep earthquake swarms. Here we present geophysical and marine data from the MAYOBS1 cruise, which reveal that by May 2019, this activity formed an 820-m-tall, ~5 km³ volcanic edifice on the seafloor. This is the largest active submarine eruption ever documented. Seismic and deformation data indicate that deep (>55 km depth) magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subvertical faults in the mantle were reactivated beneath an ancient caldera structure. We locate the new volcanic edifice at the tip of a 50-km-long ridge composed of many other recent edifices and lava flows. This volcanic ridge is an extensional feature inside a wide transtensional boundary that transfers strain between the East African and Madagascar rifts. We propose that the massive eruption originated from hot asthenosphere at the base of a thick, old, damaged lithosphere.
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Data availability
The authors declare that most of the data supporting the findings of this study are available within the paper and its Supplementary Information files. GNSS data are available on the website (http://mayotte.gnss.fr) and can be downloaded from ftp://rgpdata.ign.fr/pub/gnss_mayotte/. Ship-borne geophysical data from the MAYOBS1 cruise can be obtained through the French national oceanographic data centre SISMER (http://en.data.ifremer.fr/SISMER, https://doi.org/10.17600/18001217), but restrictions apply to the availability of these data. The compilations of older bathymetric and topographic data are available on the SHOM website (http://www.shom.fr, https://doi.org/10.17183/S201406900). Rock samples are referenced at https://wwz.ifremer.fr/echantillons/Echantillons/Carte#/map (https://campagnes.flotteoceanographique.fr/prl?id=BFBGX-134187). Samples are accessible on site at IFREMER, Plouzané, France. Map were created using Globe software (https://doi.org/10.17882/70460)75, ArcGIS software by Esri (https://www.arcgis.com/index.html), Generic Mapping Tools86, Adobe illustrator (https://www.adobe.com/) and MATLAB. In addition to MAYOBS1 cruise multibeam data (resolution: 30 m)18, Figs. 1, 2, 4, and 5 and Extended Data Figs. 1–3 and 6–9 include topographic and bathymetric compilation16,87,88 (https://doi.org/10.17600/14000900, https://doi.org/10.17183), the General Bathymetric Chart of the Oceans (https://www.gebco.net) and global topography from SRTM GL1 (https://catalog.data.gov/dataset/shuttle-radar-topography-mission-srtm-gl1-global-30m); Litto3D Mayotte (https://diffusion.shom.fr/presentation/litto3d-mayot2012.html). Topography and bathymetry of Fig. 5b from GeoMapApp (www.geomapapp.org) CC BY. In Fig. 5 and Extended Data Figs. 6, 8 and 9, focal mechanisms for M > 5 earthquakes are from ref. 40. In Fig. 5, M > 2.5 earthquakes are from ref. 4.
Code availability
Ship-borne multibeam data were processed with the GLOBE software75. The 3D acoustic water-column data were processed using SonarScope https://wwz.ifremer.fr/flotte_en/Facilities/Shipboard-software/Analyse-et-traitement-de-l-information/SonarScope and GLOBE software: https://doi.org/10.17882/7046075. GNSS solutions were computed using the GipsyX/JPL software available at https://gipsy-oasis.jpl.nasa.gov. Deformation source modelling codes (Mogi and Nikkhoo) are available at https://github.com/IPGP/deformations-matlab, and data processing has been achieved using the WebObs open-source system available at https://ipgp.github.io/webobs/. Pressure-gauge data were processed with Python89. VLF event analysis has been performed using ObsPy90, NumPy91 and Matplotlib92. Earthquake phase picking was performed with SeisComP393, and initial locations used Hypo7183. Final locations were performed with NonLinLoc76, and results were converted back to SeisComP3 using ObsPy90.
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Acknowledgements
We thank A. Eyssautier and the officers and the crew of the RV Marion Dufresne (TAAF/IFREMER/LDA), GENAVIR’s coordinator, M. Boudou D’hautefeuille and the shipboard operations engineers. We thank the captain and crew of the MV Ylang (SGTM company). This research was supported by the French Ministries of Environment, Research and Overseas under a research project to N.F. (proposal INSU-CT3 TELLUS SISMAYOTTE 2019). The French National Geographic Institute (IGN) provided the Mayotte GNSS data. The la Réunion university (Laboratory of Atmosphere and Hurricanes) provided data from the DSUA station in Madagascar (contract INTERREG-5 Indian Ocean 2014–2020 "ReNovRisk-Cyclones"). We thank CNRS/INSU, IPGP, IFREMER, BRGM for additional support under internal funds. We thank our colleagues F. Tronel, A. Roulle, E. Dectot, A. Colombain, C. Doubre, Daniel Sauter, A. Dofal and A. Villié for assistance in the field, previous data acquisition, processing and model development. We thank O. Desprez de Gesincourt, L. Testut and T. Tranchant for loan and data processing of the seafloor pressure sensors. We thank the French National Marine Hydrographic and Oceanographic Service (SHOM) for providing us with previous data from the area. We thank G. Barruol for discussions. This is IPGP contribution number 4233.
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Contributions
N.F., S.J., W.C.C., C.D., I.T., E.J., J.M.S., A. Lemoine, F.P., R.D., A.G., C.A., O.F., P.K., A. Laurent, J.-P.D., L.G., J.G., V.G., P.P. and E.R. participated on the MAYOBS1 cruise (N.F., S.J. and W.C.C. as principal investigators), acquired and processed the geophysical and seismological data. C. Satriano, A. Laurent and P. Bernard. detected and located the VLF events. A.P. was in charge of the GNSS installation in Glorieuse Island and processed and modelled the GNSS data with F.B. and R.G. V.B. was in charge of the APGs installed on the OBSs and processed their data. S.B. participated in the first OBS deployment on the Ylang vessel with W.C.C. and R.D. D.B., A. Lemarchand and J.V.d.W. were responsible for the installation of new seismological and GNSS stations in Mayotte and for data acquisition on shore. J.-P.D., V.G., E.R. and C.C. performed the geochemical analysis and interpretation of the water-column data. C. Scalabrin and A.G. processed the EM122 acoustic data. C.D. and A.G. performed the depth changes calculation. C. Scalabrin provided the interpretation of the water-column acoustic data. P. Bachelery and Y.F. furnished the rock sample descriptions and petrological analysis. N.F., S.J., C.D., P. Bachelery, Y.F., I.T., F.P., J.V.d.W. and E.J. provided the geological interpretation. N.F. wrote the paper with the contribution of all other authors. P. Bernard, J.M.S., E.J., W.C.C., C. Satriano, P. Bachelery, A. Lemoine, A. Laurent, C.A., V.B., A.G., A.P., F.B., R.G., E.R., C.C. and C. Scalabrin wrote the Methods section and the Supplementary Information.
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Extended data
Extended Data Fig. 2 Volcanic features offshore Mayotte.
a) 30-m resolution EM122 multibeam bathymetry (MAYOBS 1 cruise) and16,87 with locations of Fig. 2. b,c,d indicated. b), c) Interpreted MAYOBS1 shipboard bathymetry and backscatter of the upper slope east of Mayotte (location in a). Cones, lava flows and canyons as in Fig. 1b. Black dots: bathymetric depression. Dashed red lines: pre-existing caldera structure. d) Interpreted bathymetry of the lower slope east of Mayotte (localisation in a). e) zoom on d) showing monogenetic cones and lava flows.
Extended Data Fig. 3 The new volcanic edifice.
a) 2014 EM122 multibeam seafloor backscatter19. b) 2019 reflectivity (MAYOBS 1 cruise)18. c) Depth changes between the 2014 and 2019 surveys, superimposed on 2019 reflectivity. The white areas of the 2019 backscatter map exceeding the bathymetric difference map indicate the extent of new volcanic material.
Extended Data Fig. 4 CTD (conductivity temperature-depth)-Rosette measurements.
a) Nephelometry and b) temperature vertical profiles. c–g) sample analyses from 8L ®Niskin bottles. c–e) Gas concentrations(CH4, H2, CO2); f) pH, g) total alkalinity and total CO2.
Extended Data Fig. 5 Acoustic plumes over the Horseshoe volcanic structure.
a) Southward 3D view of the horseshoe morphology and two water column acoustic plumes observed on the western internal flank. b) Processed polar echogram from one EM122 multibeam ping of the data set displayed in (a) acquired on May 18th (05:41 UT) horizontal and vertical-axes correspond respectively to the cross-track distance and the water depth, in meters) – see also Acoustic plume movie 2.
Extended Data Fig. 6 Seismicity.
Top: map views, bottom: cross-sections (A-A’) projection along azimuth N115°E; (B-B’) along azimuth N45°E. a) Earthquakes recorded by onshore seismological stations before the deployment of the Ocean bottom seismometers (OBS). Colored circles are events occuring in the first six weeks of the crisis, white circles are earthquakes in the intervening 8 months. b) Earthquakes recorded by the OBS+land stations between February 25 and May 6 2019 (pink dots). Yellow diamonds: location of the Very Low Frequency (VLF) events located in this study (see supplementary 2.3). c) Focal mechanisms of the largest earthquakes from the Harvard CMT catalog40 with color scale as in a).
Extended Data Fig. 7 Global Navigation Satellite System (GNSS) data modelling and seafloor subsidence estimated from seafloor pressure variations.
a) Stations locations. Arrows with colors and names: GNSS velocity vectors (mm/yr) and station names. Coloured numbers: vertical deformation (mm/yr). Inset: yellow dots : pressure sensors on ocean bottom seismometer stations (see supplementary Fig. 2.1), red arrows: Mayotte GNSS velocity vectors (mm/yr), white arrows: far field GNSS velocity vectors. b) GNSS Time series with relative displacements recorded on the east (top), north (middle) and vertical (bottom) components of the stations between January 2018 and January 2020. c) Best fit-models with 1σ uncertainties of the GNSS data for one isotropic point source and a triple volumetric discontinuity pCDM source. d) Top panel: Pressure recorded by Seabird SBE37 gauges at the six ocean-bottom seismometer stations (Yellow dots inset Figure 7a and supplementary Fig. 2.1) de-tided and converted to vertical motion. Middle panel: vertical deformation estimated at each seafloor instrument location, using the best isotropic source model obtained from the GNSS data for the March 1st to May 1st 2019 period.
Extended Data Fig. 8 Conceptual model for the Mayotte seismo-volcanic event.
Circles and diamonds are events as in Extended Data Fig. 6. Focal mechanisms of main earthquakes are from Harvard CMT catalog40) with the same color scale as the May 10 to June 30, 2018 Volcano-Tectonic (VT) earthquakes, Yellow circle and blue patch: Location, with 3 sigma uncertainties, of the most robust isotropic source deformation model. a) Map view: The redish ellipse: Mayotte ridge, dashed circular area: old caldera structure in the morphology. Double black arrows: local extension Dashed red arrow: dyke intrusion b) Cross-section (projection along azimuth 115 degree, location on a)). Symbols as in a). Red lines: magma migration (dykes). Red ellipses and circle: magma reservoirs or mushes. Pink arrow: possible downsag along caldera structures. Redish zone: Eastern segment of the Mayotte ridge.
Extended Data Fig. 9 Regional volcano-tectonic setting of the submarine eruption offshore Mayotte.
a) Volcano-tectonic setting of the new volcanic edifice (NVE). Volcanic cones and ridges (purple) from this study and13,16,51,71. Beach balls: focal mechanisms for M>5 earthquakes40. Dotted white arrow: dyking event along the N130° E trending eastern segment of the volcanic ridge. Pink ellipse: inferred main volcano-tectonic ridges. Purple ellipses: highly damaged zones in between the en echelon ridges. Dashed grey lines: Mesozoic fracture zones6. Inset: sandbox model adapted from58 illustrating the possible arrangement of the main volcano-tectonic structures in Comoros. Thick black arrows: local extension direction.
Supplementary information
Supplementary Information
Supplementary Sections 1–3, Figs. 2.1–2.18 and Tables 1.1, 1.2, 2.1, 2.2 and 3.1–3.3.
Supplementary Movie 1
3D flight-through over the NVE and the acoustic plume.
Supplementary Movie 2
3D flight-through over the upper insular shelf of Mayotte, the Horseshoe and the acoustic plumes.
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Feuillet, N., Jorry, S., Crawford, W.C. et al. Birth of a large volcanic edifice offshore Mayotte via lithosphere-scale dyke intrusion. Nat. Geosci. 14, 787–795 (2021). https://doi.org/10.1038/s41561-021-00809-x
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DOI: https://doi.org/10.1038/s41561-021-00809-x
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