Novel Acoustic Method Provides First Detailed Measurements of Sediment Concentration Structure Within Submarine Turbidity Currents

Abstract

 First high-resolution measurements of the sediment concentration and velocity structure for multiple oceanic turbidity currents.  Flow duration and sediment volume are strongly bimodal, and some flows are sustained for 5-10 days.  All flows are mainly dilute (< 10 g/L), but some flows have brief (~15 min) initial period of coarser-grained or denser flow near the bed.

Anatomy of subcritical submarine flows with a lutocline and an intermediate destruction layer

“…Classical jets and plumes increase in thickness as they flow downstream by entraining and mixing with the ambient fluid, and as a result they eventually dilute themselves to extinction. In contrast, it has been observed that turbidity currents can have long runouts of over thousands of kilometers within submarine channels 7,10,[24][25][26] . Surge-type turbidity currents in erosional mode can travel long distances and not dilute themselves to extinction due to the continuous supply of sediment from the bed.…”

“…The simulations consider dilute concentration of sediment within the body of the current, which allows Boussinesq approximation in the governing mass and momentum balance equations. By restricting to the dilute body of the current, the present simulations do not model the dense near-bed layer observed near the front of the current in recent field measurements [6][7][8]10 . Suspended sediment is assumed to be non-cohesive and sufficiently small in size that its settling velocity can be either ignored in comparison to the flow velocity (i.e., sediment treated as washload) or can be taken to be the sum of local fluid velocity plus still fluid settling velocity of the sediment (i.e., equilibrium Eulerian approximation [40][41][42] ).…”

“…Unlike the much studied problem of sediment transport by rivers, our current understanding of sub-aqueous turbidity currents is lagging, due to limited availability of direct field measurements and observations (e.g., refs. [6][7][8][9][10] ). Much of our understanding is derived from interpretations of sediment deposits resulting from these flows, laboratory experiments that are necessarily limited to much smaller scale, and computer simulations that involve unavoidable assumptions and approximations.…”

Deep-sea water displacement from a turbidity current induced by the Super Typhoon Hagibis

“…For example, dating of the repeated turbidite sequences in the accretionary prism provide decisive evidence for tectonic evolution at the convergent plate boundary ( Taira, 2001 ). Despite these multidimensional interests, direct observation of turbidity currents in the deep sea had been rare until the beginning of this century ( Talling, Paull & Piper, 2013 ) due to their unpredictable nature and the limited accessibility resulting from challenges and ship time costs of deep-sea expeditions although numbers of the observation have increased during the last decade ( Xu, 2010 ; Liu et al, 2012 ; Khripounoff et al, 2012 ; Hughes Clarke, 2016 ; Paull et al, 2018 ; Wang et al, 2020 ; Heerema et al., 2020 ; Hage et al, 2019 ; Normandeau et al., 2019 ; Lintern, Hill & Stacey, 2016 ; Simmons et al, 2020 ).…”

Peer Review #3 of "Deep-sea water displacement from a turbidity current induced by the Super Typhoon Hagibis (v0.1)"

“…For example, dating of the repeated turbidite sequences in the accretionary prism provide decisive evidence for tectonic evolution at the convergent plate boundary [Taira 2001]. Despite these multidimensional interests, direct observation of turbidity currents in the deep sea had been rare until the beginning of this century [Talling et al 2013] due to their unpredictable nature and the limited accessibility resulting from challenges and ship time costs of deep-sea expeditions although numbers of the observation have increased during the last decade [Xu, 2010;Liu et al, 2012;Khripounoff et al, 2012;Hughes Clarke, 2019;Paull et al, 2018;Wang et al, 2020;Heerema et al, 2020;Hage et al, 2019;Normandeau et al, 2020;Lintern et al, 2016;Simmons et al, 2020].…”