7/7/21  By the time hurricanes strike, they have official names and landing date so people have a name to a tag all the damage, which will be well chronicled by video. Last year, however, there was a memorable natural disaster, only this one did not have a name, an official starting time or much of anything in the way of widespread media attention. Then again, this avalanche took place at depths as great as 2.8 miles, and the only sign that it had even happened was that two subsea cable systems were KOed.

Per a BBC report, the avalanche, officially called a turbidity current, was initially triggered by a large flood on the Congo River in December 2019. The fast-moving water shifted a vast amount of sand and mud to the Congo Submarine Canyon off the West African coast, but that alone did not cause the avalanche. Early spring tides in mid-January 2020, water pressure in the sediment and low tide triggered the turbidity current. The slide traveled for a full two days, starting out at 11.6 miles/hour then sped up to nearly 18 miles/hour, covering 683 miles across the floor of the Atlantic Ocean, reaching depths there as much as 2.8 miles.

A U.K. team led by Professor Peter Talling discovered the event through sensors in the area that measure current and sediment velocities. The slide damaged two submarine telecommunications cables, the South Atlantic 3/West Africa (SAT-3/WASC) cable and the West Africa Cable System (WACS), knocking out Internet and other data traffic. A French cable-laying vessel, the Léon Thévenin, repaired the cable breaks within two weeks, but the movement of sediment caused more breaks in early 2021.

Talling and his colleagues later wrote a paper (Novel sensor array helps to understand submarine cable faults off West Africa) printed at eartharxiv.org. In it, the professor explained that not all turbidity currents work the same. Some deposit large amounts of sand and mud onto cables, while other slides burrow deep into the seafloor. The Talling team provided some of the first measurements made of cable-breaking sediment flows. He explained how such flows can affect multiple cables simultaneously over large areas, and how deep erosion can damage subsea cables.

Dr. Mike Clare, marine geoscientist at the U.K.’s National Oceanography Centre and advisor to the International Cable Protection Committee, said that the goal was to best understand how to position and reroute cable repair ships into areas where undersea cable is more vulnerable to damage.
More than 99% of all data traffic between continents goes through the global submarine cable network. Participating in the Congo Canyon research was IFREMER (Institut Français de Recherche pour l'Exploitation de la MER) in France and GEOMAR Helmholtz Centre for Ocean Research in Germany. The project is co-led from Durham and Angola Cables.