Scientists Record the Longest Underwater Avalanche Ever

Scientists have measured an underwater mud avalanche that lasted two days and crossed more than 1,100 kilometers across the Atlantic Ocean floor.

The sediment avalanche, or turbidity current as the phenomenon is known, occurred underwater off West Africa and shifted huge amounts of sand and mud.

Scientists noticed it had taken place because it broke two underwater data cables, which slowed down internet traffic between Nigeria and South Africa.

However, they also had instruments in place that were capable of measuring the movement of underwater sediment.

The huge sediment flow actually occurred in January 2020, followed by another in March, but the team needed time to pore over their data.

Peter Talling, a professor of submarine geohazards at Durham University in the U.K., led the team of researchers behind the avalanche detection efforts.

He told the BBC: "This thing gradually got faster and faster. Because it erodes the seabed as it goes, it picks up sand and mud, which makes the flow denser and even quicker."

In a preprint whitepaper detailing the event, that has not yet been peer-reviewed, Talling and the team said the turbidity current was the furthest traveled sediment flow ever measured on Earth.

Such flows are generally poorly understood due to a lack of data, meaning they are hard to predict. Yet, they have the potential to disrupt underwater data cables over very large areas.

Fiber-optic cables bedded into the seafloor are responsible for carrying almost all inter-continental global data traffic. This helps keep crucial networks, such as financial trading and the internet itself, running.

The team states their new data on the West Africa ocean avalanche will provide insight into cable-breaking turbidity currents, and help engineers better understand the hazards they pose.

The paper reads: "Our overall purpose is to understand the implications of these measurements for assessing and mitigating the hazards to seabed telecommunication cables.

"This includes insights into how turbidity currents are triggered at river mouths, and hence their likely future frequency, including the impacts of climate change."

The researchers say more data is needed before they can determine how exactly the huge sediment flow was triggered, but they think two main factors were at play.

The first was a large flood along the Congo River that rapidly deposited flood sediment at the river mouth in December 2019. The second factor was what the team called "unusually large spring tides" that occurred some weeks later and released the sediment that had been deposited.

The team concluded that their measurements "help to assess and potentially mitigate hazards to submarine cables, such as by identifying a relationship between river floods, tides and cable-breaking turbidity currents."

Fiber optic cable
An operator works on an undersea fiber-optic data cable on Arrietara beach near the Spanish Basque village of Sopelana, June 2017. Undersea cables carry huge amounts of inter-continental data. Ander Gillenea/AFP/Getty