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Widespread and progressive seafloor-sediment failure following volcanic debris avalanche emplacement: Landslide dynamics and timing offshore Montserrat, Lesser Antilles

Record type: Article

Landslides associated with flank collapse are volumetrically the most significant sediment transport process around volcanic islands. Around Montserrat, in the Lesser Antilles, individual landslide deposits have volumes (1 to 20 km3) that are up to two orders of magnitude larger than recent volcanic dome collapses (up to 0.2 km3). The largest landslide deposits were emplaced in at least two stages, initiated by the emplacement of volcanic debris avalanches which then triggered larger-scale failure of seafloor sediment, with deformation propagating progressively downslope for up to 30 km on gradients of <1°. An unusually detailed seismic, side-scan sonar and bathymetric dataset shows that the largest landslide off Montserrat (forming Deposit 8) incorporated ~ 70 m of in-situ sediment stratigraphy, and comprises ~ 80% seafloor sediment by volume. Well-preserved internal bedding and a lack of shortening at the frontally-confined toe of the landslide, shows that sediment failure involved only limited downslope transport. We discuss a range of models for progressively-driven failure of in-situ bedded seafloor sediment. For Deposit 8 and for comparable deposits elsewhere in the Lesser Antilles, we suggest that failure was driven by an over-running surface load that generated excess pore pressures in a weak and deforming undrained package of underlying stratigraphy. A propagating basal shear rupture may have also enhanced the downslope extent of sediment failure. Extensive seafloor-sediment failure may commonly follow debris avalanche emplacement around volcanic islands if the avalanche is emplaced onto a fine-grained parallel-bedded substrate. The timing of landslides off Montserrat is clustered, and associated with the deposition of thick submarine pyroclastic fans. These episodes of enhanced marine volcaniclastic input are separated by relatively quiescent periods of several 100 ka, and correspond to periods of volcanic edifice maturity when destructive processes dominate over constructive processes.

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Citation

Watt, S.F.L., Talling, P.J., Vardy, M.E., Masson, D.G., Henstock, T.J., Huhnerbach, V., Minshull, T.A., Urlaub, M., Lebas, E., Le Friant, A., Berndt, C., Crutchley, G.J. and Karstens, J. (2012) Widespread and progressive seafloor-sediment failure following volcanic debris avalanche emplacement: Landslide dynamics and timing offshore Montserrat, Lesser Antilles Marine Geology, 323-325, pp. 69-94. (doi:10.1016/j.margeo.2012.08.002).

More information

Published date: 1 September 2012
Keywords: seafloor-sediment slide, progressive landslide, frontal confinement, undrained loading, volcanic debris avalanche, Montserrat
Organisations: Geology & Geophysics, Marine Geoscience

Identifiers

Local EPrints ID: 343546
URI: http://eprints.soton.ac.uk/id/eprint/343546
ISSN: 0025-3227
PURE UUID: a59e2972-e776-45a8-a6eb-ba25e1a64044
ORCID for T.J. Henstock: ORCID iD orcid.org/0000-0002-2132-2514
ORCID for T.A. Minshull: ORCID iD orcid.org/0000-0002-8202-1379

Catalogue record

Date deposited: 04 Oct 2012 12:39
Last modified: 18 Jul 2017 05:22

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Contributors

Author: S.F.L. Watt
Author: P.J. Talling
Author: M.E. Vardy
Author: D.G. Masson
Author: T.J. Henstock ORCID iD
Author: V. Huhnerbach
Author: T.A. Minshull ORCID iD
Author: M. Urlaub
Author: E. Lebas
Author: A. Le Friant
Author: C. Berndt
Author: G.J. Crutchley
Author: J. Karstens

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