Timing and processes of tsunamigenic debris avalanche emplacement in the Lesser Antilles Volcanic Arc: insights from offshore drilling (Expedition IODP 340) and implication for hazard assessment. – CARIB

CARIB project will focus on volcanoes of Martinique and Dominica. However we will be involved in collaboration with UK scientists for research on cores from Montserrat. CARIB intends to provide a complete record of the contrasted style, impact of volcanic activity and sedimentation record along the arc over at least the last Ma. The main objectives are: Task 1/ extend the knowledge of the geologic history of the arc over a much longer eruptive record; Task 2/ determine the dynamics of tsunamigenic debris avalanche emplacement, mobility, erosive potential and related deformation; Task 3/ constrain numerical simulations for hazard assessment. To reach the objectives, we will: 1/ characterize the geochemistry, petrology, mineralogy, sedimentology, geochronology (laser heating Ar/Ar) of all volcanic layers; 2/ provide a detailed 18O stratigraphy with some 14C ages from key pelagic sediment layers to date eruptive activities and mass transport deposits; 3/ undertake fabric, stratigraphic and morpho-structural and mechanical analysis of geophysical data and cores to determine the transport processes, the volume of mass transport deposits and incorporated sediments and the stability conditions; 4/ develop onland-offshore correlative analysis; 5/ improve numerical codes (including erosional processes) for hazard assessment.

Main results (9 July 2015) have already been presented in international congress:
- New model to explain landslides around Lesser Antilles volcanoes (Le Friant et al., 2015).
- New model of evolution of Montagne Pelée volcano (Brunet et al., in prep).
- Numerical simulation of Montagne Pelée debris avalanches emplacement (Brunet et al., in prep).
- Analogical simulation (in collaboration with E.Hallot and T.Nalpas, Géosciences Rennes) to characterize marine sediment deformation resulting from loading.
- Chronostratigraphy of drilling sites U1399 and U1397 (Emmanuel et al., in prep)
- Petro-geochemistry of recent magmatic activity of Martinique (Villemant, Caron et al., in prep).
- Tephrochronology study of the first tens of meters of drilling sites U1397 A, U1401A, U 1400A, U 1399A et U1398B (Boudon et al., in prep).
- Chronostratigraphy and tephrochronology of the drilling site U1401 (Solaro et al., in prep)
- International Post-cruise meeting organised in Martinique in january 2015 (scientific meeting, outreach and education activities).

First, the project will characterize the evolution of volcanic systems (Martinique, Dominica) that can extend to a few million years in better details than from on-land studies thanks to the more comprehensive record in offshore deposits. It will allow diagnosis of the return periods of infrequent volcanic events of very large magnitude and high environmental consequences, such as explosive eruptions and major flank-collapses.
Second, our project will study the first drilling ever performed through seismically chaotic deposits. This area is particularly favourable because it records a frequency of flank collapse events larger than has been recognized in other regions and thus will provide unprecedented data to understand the mechanisms controlling the trigger, transport, and deposition of volcanic debris avalanches and associated sediments deformation. Documenting internal facies architecture is crucial for quantifying the mobility of debris avalanche and for realistic parametrization of numerical flow simulations.
Third, the project will provide a systematic and unique data set to characterise volcano flank-collapses at the scale of a volcanic island and to define a range of scenario and parameters for Lesser Antilles flank-collapses to consider for numerical simulation. The details of the collapse process in space and time determine the amplitudes of the tsunami waves and influence energy dissipation.
During the project, an effort will be made for education outreach activities and dissemination to the wider public and selected schools.

9 July 2015:
Lafuerza S., A. Le Friant, M. Manga, G. Boudon, B. Villemant, N. Stroncik, B. Voight, M. Hornbach, O. Ishizuka and the Expedition 340 Scientific Party (2014), Geomechanical characterizations of submarine volcano flank sediments, Martinique, Lesse Antilles Arc. S. Krastel et al., (Eds.), Sumarine mass movements and consequences, Advances in Natural and Technological Hazards Research, Springer Inten. Publishing, Switzerland, 2014, 37, doi 10.1007/978-3-319-00972-8_7.

Le Friant, A., Ishizuka, O. , Boudon, G. , Palmer, M.R. , Talling, P. , Villemant, B. , Adachi, T., Aljahdali, M., Breitkreuz, C., Brunet, M., Caron, B., Coussens, M., Deplus, C., Endo, D., Feuillet, N., Fraas, A.J., Fujinawa, A., Hart, M. B., Hatfield, R.G., Hornbach, M., Jutzeler, M., Kataoka, K. S., Komorowski, J-C., Lebas, E., Lafuerza, S., Maeno, F., Manga, M., Martínez-Colón, M., McCanta, M., Morgan, S., Saito, T., Slagle, A., Sparks, S., Stinton, A., Stroncik, N., Subramanyam, K. S.V., Tamura, Y., Trofimovs, J., Voight, B., Wall-Palmer, D., Wang, F., Watt, S.F.L. (2015). Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340. Geochem., Geophys., Geosyst, 16, doi:10.1002/2014GC005652.

Flank collapse with emplacement of voluminous and potentially tsunamigenic debris avalanches is the key recurrent process controlling the evolution of Lesser Antilles volcanoes. In the context of island arcs where small size edifices are built, most debris avalanche material is deposited offshore. On land studies provide only a very limited part of the information necessary to study these major volcanic events of considerable potential hazard. Furthermore, analysis of available piston sediment cores offshore Martinique and Montserrat identified many more explosive eruptions than deduced from on-land studies, showing that marine sediments contain a more complete record of volcanic history. However, due to the short lengths, these cores only provide a very short part of the Lesser Antilles volcanic history.
CARIB project is conceived to take advantage of the unprecedented dataset (9 drilling cores and logging data) that have been obtained in Expedition IODP (Integrated Ocean Drilling Program) 340 (R/V JOIDES Resolution, March-April 2012). A complete record of eruptive activity and volcanoclastic sedimentation of the most active volcanic complexes of the Lesser Antilles arc over more than the last 1 Ma (Martinique, Montserrat) has been collected and seismically chaotic units (interpreted as mass transport deposits) have been drilled for the first time. All costs associated with the offshore expedition (ship time, minimum onboard analysis) were covered by the program funds. The CARIB project is dedicated to the post-cruise research plans. CARIB project is a unique opportunity for the French community (which is leader of the Expedition 340 project) to gain unprecedented information necessary for understanding the behaviour of volcanic debris avalanches and the actual role of flank collapses in the evolution of a volcanic arc which displays a remarkable frequency of flank collapses (15 in the last 12 ka) higher than in other regions (e.g. Hawaii: 1/ 350 ka).
CARIB project will focus on volcanoes of Martinique and Dominica. However we will be involved in collaboration with UK scientists for research on cores from Montserrat. CARIB intends to provide a complete record of the contrasted style, impact of volcanic activity and sedimentation record along the arc over at least the last Ma. The main objectives are: Task 1/ extend the knowledge of the geologic history of the arc over a much longer eruptive record; Task 2/ determine the dynamics of tsunamigenic debris avalanche emplacement, mobility, erosive potential and related deformation; Task 3/ constrain numerical simulations for hazard assessment. To reach the objectives, we will: 1/ characterize the geochemistry, petrology, mineralogy, sedimentology, geochronology (laser heating Ar/Ar) of all volcanic layers; 2/ provide a detailed 18O stratigraphy with some 14C ages from key pelagic sediment layers to date eruptive activities and mass transport deposits; 3/ undertake fabric, stratigraphic and morpho-structural and mechanical analysis of geophysical data and cores to determine the transport processes, the volume of mass transport deposits and incorporated sediments and the stability conditions; 4/ develop onland-offshore correlative analysis; 5/ improve numerical codes (including erosional processes) for hazard assessment.
CARIB project will involve 3 partners: 1/ IPGP (Expedition IODP 340: P.I; expertises: volcanology, tectonic, flank collapse events), 2/ ISTEP (Expedition IODP 340: participant; expertises: geochemical analysis, magmatology), 3/ UAG (Expertises: physical properties).
Results from this project will significantly improve our understanding of the eruptive history of some of the most active Caribbean volcanoes. Caribbean active volcanoes remain inherently unstable and thereby constitute a significant risk to circum-Caribbean region characterized by a rapidly expanding population, densely populated shorelines and small island nations that are particularly vulnerable to hazards.