Submarine fiber-optic cables have to endure a lot, so they need to be built to last. But what are all the factors in the ocean that need to be taken into account when designing submarine cables? One thing that is often overlooked is the impact of turbidity currents on submarine fiber-optic cables. In this article, we’ll tell you all about it!
What are turbidity currents?
When suspended sediment enters a body of water and this increase in density causes the water to begin moving downhill under the influence of gravity, this is called a turbidity current. There are several processes that can cause these high-energy currents, but three are the most common:
- Beyond the riverbanks during floods: This process carries large amounts of sediment out to sea, where it then begins to move down the continental slope.
- After volcanic eruptions: When the eruption column collapses, as in Tonga.
- During earthquakes: Earthquakes sometimes trigger landslides, causing the finer sediment dislodged by the main landslide to become suspended in the water.
How do turbidity currents affect undersea fiber-optic cables?
Turbidity currents pose a threat to cables laid through undersea canyons. This is particularly true off the coasts of major rivers, such as the Congo Canyon in West Africa. The reason such turbidity currents pose a risk to undersea fiber-optic cables lies in three key mechanisms:
- Turbidity currents are highly erosive near their source: They move across the seafloor, and at the same time, the currents dig into the seafloor and carry more sediment into the flow. This can cause damage to a fiber-optic cable buried in the seafloor.
- Movement of a suspended cable within the water column: This causes wear at the contact points at both ends of the suspension. If the cable is armored, the armor can wear down due to friction. The insulator can also wear through as a result, exposing the conductor and potentially damaging the optical fibers. This, of course, causes malfunctions!
- Debris: Debris carried along by the current can strike the exposed cable, damaging or even severing it.
Is this a major problem for undersea networks?
Worldwide, approximately 200 faults have been identified within the boundaries of mapped undersea canyons. If we exclude faults caused by human error, that leaves about 118 incidents since 1965. This means there would be an average of two faults per year, although faults have occurred more frequently in recent years than before. The reason they seem to occur more frequently is that more and more cable systems are being laid under the sea and that failures are better recorded today. Two failures per year may sound negligible at first, but we must remember that undersea fiber-optic networks perform extremely important tasks. So every failure is one too many!