The length and dimensions of submarine channels can rival or exceed the largest rivers on land, and they produce the largest sediment accumulations on Earth. However, there were previously no direct flow-measurements at the end of a submarine channel in the deep-sea. This led to the assumption that sediment transport to the end of submarine channels occurred for only a small (< 0.5%) fraction of the time, via infrequent but unusually powerful and erosive ‘canyon-flushing’ flows. However, here we show the termination of the Congo Submarine Channel is active for ~15% of the time, during a 14-month period without canyon-flushing flows, with individual flows lasting for a week to a month. This is despite the channel’s termination being situated >1,000 km from shore (measured along the channel-axis) at a water-depth of ~5 km. The flux of sediment from the end of this submarine channel rivals that supplied by the Congo River to its head. Frequent, sustained and exceptionally (~100%) efficient transfer of sediment and organic carbon transfer thus occurs over extremely long distances. This leads to unusual deep-sea ecosystems, and rapid (~10 km/yr) submarine channel extension due to a previously unknown mechanism involving non-erosional mud-flows rather than coalescing erosional scours.
A turbidity current measured at the end of the Congo Canyon-Channel at 5,000m water depth and some 1,000 km from the coastline