Simultaneous breaks in two critical undersea cables that connect South Africa to the Internet were likely caused by a massive mudslide that originated at the mouth of the Congo River, new research has found.
South Africans found their Internet speeds to overseas services dramatically slowed down at the start of last year when breaks occurred in two undersea cables off the western coast of Africa — SAT-3/WASC and WACS.
These simultaneous cable breaks left many Internet service providers scrambling to activate backup bandwidth to ensure customers remain connected during the disruption.
On 16 January 2020, the South Atlantic 3/West Africa (SAT-3/WASC) cable and the West Africa Cable System (WACS) were hit by cable breaks.
SAT-3, which links Africa to Portugal and Spain was hit by a breakdown in Gabon, while WACS, which connects South Africa to the United Kingdom, saw an outage off the coast of the Democratic Republic of Congo.
Researchers noted that the mudslide happened ten days after the Congo River was hit by the largest flood since the 1960s.
Prof Peter J. Talling from the Department of Earth Sciences and Geography at the University of Durham in the UK led the team of researchers who conducted study.
The research was co-led by Angola Cables and supported by the Vodafone Group, British Telecom, and NERC Environmental.
According to the researchers, sand and mud from the river flood was presumably remobilised and triggered a submarine mudslide that flowed through the offshore Congo Canyon.
The canyon is one of the largest underwater canyons on earth, cutting across the continental shelf of West Africa for 85 kilometres until it reaches the shelf edge, then continues down the slope and ends 280 kilometres from its origin.
At its deepest point, the V-shaped canyon walls are 1100 meters in height.
These powerful mud slides that damage seabed cables are notoriously difficult to measure in action, and are therefore poorly understood, the researchers said.
They explained that this study involved the placement of a series of sensors along the canyon, and that these sensors recorded unique information on this type of mud slide.
The mudslide in January 2020 caused nine of the oceanographic moorings to surface. By combining the timings of when moorings reached the sea surface and the cable breaks, Talling and his team were able to calculate the flow speed of the massive undersea avalanche.
They estimated that following the initial mudslide in the canyon, the moving sediment increased in speed from 5 meters per second (m/s) in Angolan waters in the upper canyon, to reach 8m/s in the deep ocean, at water depths of 4-5 km – running out some 1,200 km from the river mouth.
“The data that we recovered from the seabed sensor and mooring data sets within the Congo Canyon have revealed that the undersea mudslide is possibly the longest recorded sediment flow yet measured in action on our planet,” the researchers stated.
The evidence gathered provided valuable scientific insights into how major flows are triggered; the frequency, speed and potential impact of mudslides or runout events.
The longer the runout, the more hazardous these mudslides can be for undersea cables, the researchers warned.
Another important conclusion was that although cables do not break during the mudslide, adjacent cables can experience faults if they are next to deeply eroded knickpoints.
“Depending on the proximity of cable repair vessels, outages can often take a number of weeks to repair resulting in costly losses to economies impacted by such breaks,” Talling said.
“Gathering evidence and the recorded data in studies such as these are critical to understanding the nature of such subterranean events, and how the subsea cable industry can better provide more durable solutions in keeping the cables – and the world connected.”