Two distinct types of turbidity currents observed in the Manila Trench, South China Sea

Abstract Sediment gravity flows are the most direct and efficient transport mechanisms for moving terrestrial sediments into deep oceans. Scarcity of firsthand measurements, however, has hindered quantitative, even qualitative characterization such flows. Here we present a unique year-long data record from ~4000 m depth in Manila Trench that captured two very different terms their hydraulic sedimentary properties. The first flow was slow speed (~40 cm s −1 ) long duration (~150 h), thus nicknamed ‘Tortoises’, carried fine sediment with low concentration (~0.01%). fast but short-lived h) flow, ‘Hares’, much coarser higher (~1.2%). Clay mineral compositions suggest ‘Tortoises’ originated upstream canyon wall slumping, whereas ‘Hares’ likely submarine canyons southwest Taiwan Island due to typhoon. Grain size is key factor determining evolution turbidity currents.