Typhoon-induced megarips as triggers of turbidity currents offshore tropical river deltas

Gaetano Porcile,Octavio E Sequeiros,Michele Bolla Pittaluga,Alessandro Frascati

doi:10.1038/s43247-020-0002-1

Gaetano Porcile, Octavio E Sequeiros + Show 2 more

Open Access

https://doi.org/10.1038/s43247-020-0002-1

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Abstract

Tropical cyclones impose stresses on narrow and shallow continental shelves. The interaction of strong wind- and wave-induced currents with the local topography near the shore gives rise to complex flow and sediment transport patterns. Considerable uncertainty remains on the initiation mechanisms of turbidity currents, particularly in coastal oceanic settings subject to extreme weather events. Here we use state-of-the-art numerical models to investigate the implications of tropical cyclone-induced coastal circulation patterns for the generation of turbidity currents. In our simulations tropical cyclones induce megarip currents associated with shoreline curvature and rotation of incoming wave directions. These currents flush water and sediment towards submarine canyons, ultimately triggering turbidity currents into deep waters. Evidence of sediment-laden underflows, which resulted in subsea pipeline displacements, supports our hypothesis that tropical cyclone-induced megarip currents can trigger turbidity currents offshore from tropical river deltas.

Highlights

Tropical cyclones impose stresses on narrow and shallow continental shelves
Turbidity currents in submarine canyons initiate as sedimentladen underflows controlled by the suspended-sediment supply at the canyons’ heads and the triggering of the flow is the key for their development
Despite the ongoing advancing of turbidity current modelling, considerable uncertainty still remains regarding the formulation of realistic boundary conditions for their field-scale numerical simulation, in coastal oceanic settings

Summary

Introduction

Tropical cyclones impose stresses on narrow and shallow continental shelves. The interaction of strong wind- and wave-induced currents with the local topography near the shore gives rise to complex flow and sediment transport patterns. In our simulations tropical cyclones induce megarip currents associated with shoreline curvature and rotation of incoming wave directions These currents flush water and sediment towards submarine canyons, triggering turbidity currents into deep waters. Sediment continually evacuated from river deltas to the inner shelf are suspended over the seabed during these events by intense wave stirring and distributed by coastal circulation patterns to be eventually transported offshore by rip-current cells that can potentially transition into turbidity currents along submarine canyon systems[10]. This study is intended to unravel the conundrum of the initiation mechanism responsible for the triggering of a recently detected turbidity current event associated with the landfall of an intense typhoon For this purpose, the root cause of the lateral displacement occurred on a submarine pipeline has been analysed. Our simulations reveal a typhoon-induced megarip current generated in-between two neighbouring river deltas and extending well beyond the shelf-break as the trigger of a strong turbidity current down the largest canyon that the pipeline crosses and where its displacement was observed

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