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Preconditioning by sediment accumulation can produce powerful turbidity currents without major external triggers

Bailey, Lewis P. and Clare, Michael A. and Rosenberger, Kurt J. and Cartigny, Matthieu J.B. and Talling, Peter J. and Paull, Charles K. and Gwiazda, Roberto and Parsons, Daniel R. and Simmons, Stephen M. and Xu, Jingping and Haigh, Ivan D. and Maier, Katherine L. and McGann, Mary and Lundsten, Eve (2021) 'Preconditioning by sediment accumulation can produce powerful turbidity currents without major external triggers.', Earth and Planetary Science Letters, 562 . p. 116845.

Abstract

Turbidity currents dominate sediment transfer into the deep ocean, and can damage critical seabed infrastructure. It is commonly inferred that powerful turbidity currents are triggered by major external events, such as storms, river floods, or earthquakes. However, basic models for turbidity current triggering remain poorly tested, with few studies accurately recording precise flow timing. Here, we analyse the most detailed series of measurements yet made of powerful (up to 7.2 m s−1) turbidity currents, within Monterey Canyon, offshore California. During 18-months of instrument deployment, fourteen turbidity currents were directly monitored. No consistent triggering mechanism was observed, though flows did cluster around enhanced seasonal sediment supply. We compare turbidity current timing at Monterey Canyon (a sandy canyon-head fed by longshore drift) to the only other systems where numerous (>10-100) flows have been measured precisely via direct monitoring; the Squamish Delta (a sandy fjord-head delta), and the Congo Canyon (connected to the mud-dominated mouth of the Congo River). A common seasonal pattern emerges, leading to a new model for preconditioning and triggering of turbidity currents initiating through slope failure in areas of sediment accumulation, such as canyon heads or river mouths. In this model, rapid or sustained sediment supply alone can produce elevated pore pressures, which may persist, thereby predisposing slopes to fail. Once preconditioned, a range of minor external perturbations, such as moderate storm-waves, result in local pore pressure variation, and thus become effective triggers. Major external triggers are therefore not always a prerequisite for triggering of powerful turbidity currents.

Item Type:Article
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Available under License - Creative Commons Attribution 4.0.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1016/j.epsl.2021.116845
Publisher statement:©2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Date accepted:17 February 2021
Date deposited:13 May 2021
Date of first online publication:03 March 2021
Date first made open access:13 May 2021

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