Beneath the ocean's surface lie Earth's largest currents, sweeping away everything in their path. What are they about? (Photos included)

Turbidity currents are a significant natural process that often goes unnoticed. This phenomenon has been known to science for about 100 years, yet researchers still know too little about where and how exactly turbidity currents move, according to PHYS.org.

These powerful currents beneath the ocean's surface carve through deep underwater canyons and create vast sediment deposits, as well as potentially damaging underwater cables and pipelines. The main challenge lies in the high-energy nature of this phenomenon, which has made its measurement nearly impossible — any instruments placed in its path would be destroyed by its immense force, much like avalanches on land.

In a new study, an international team of scientists led by the Helmholtz Centre for Ocean Research Kiel (GEOMAR) and Durham University developed a new method to monitor these flows from a safe distance. The team utilized seismometers on the ocean floor, typically used for studying earthquakes — resulting in scientists uncovering the internal structure of these massive currents for the first time.

According to the lead author of the study and GEOMAR seismologist Dr. Pascal Kunath, the ocean floor seismometers used in the study detected the longest sediment flows ever recorded on Earth. It is important to note that turbidity currents are the dominant mechanism for transporting sediments and organic carbon from coastal areas to the deep sea, much like rivers carry sediments on land. However, unlike rivers, they are considered much less understood processes.

In their work, the researchers aimed to fill this gap. To do this, they placed seismometers in the Congo Canyon and the Congo Strait off the west coast of Africa — one of the largest and deepest underwater canyons in the world. The authors of the study noted that the instruments were positioned several kilometers from the canyon's axis, outside the range of destructive force. Fortunately, this allowed scientists to record seismic signals generated by the turbulence of the flow and the associated sediment transport.

As a result, the researchers were able to track two turbidity currents moving at speeds ranging from 5 to 8 meters per second over a distance of 1,100 kilometers — from the mouth of the Congo River through the deep-water cone of deposition and the Congo canyon system. These are the longest sediment flows ever recorded.

It is known that these flows damaged several underwater cables in January and March 2020, resulting in internet and data transmission disruptions. According to Kunath, he and his colleagues found that these powerful flows, sweeping everything in their path, are not continuous at all. In fact, they consist of multiple pulses, each lasting from 5 to 30 minutes.

Interestingly, the fastest pulses occur up to 20 kilometers ahead of the front. These waves ultimately outrun the leading edge, maintaining the sediment and momentum needed to sustain the flow over long distances. The researchers' discovery also challenges previous theories that the highest speeds occur at the front of the flow.