How are submarine cables impacted by tectonic shifts beneath the seafloor?
This week's guests on TeleGeography Explains the Internet are well-positioned to tell us. They join us from the UK’s National Oceanography Centre: Isobel Yeo, Researcher in Geology and Volcanology, and Michael Clare, Principal Researcher of Ocean BioGeoscience and Marine Environmental Adviser to the International Cable Protection Committee.
Mike and Izzy are geologists specializing in the seafloor, so their research has become vital for the submarine cable community.
While most cable faults are due to human activity, a fair number are caused by changes in the seafloor. This includes earthquakes, volcanoes, landslides, and even flooding on land.
We discuss the myriad ways that the dynamic nature of what lies under the surface can damage cables. We even get into the history of natural disasters and communications cables going back a century or more.
As a geographer, I was fascinated by how little we actually know about the geography of the ocean floor, despite the fact that water covers 70% of the globe. Mike and Izzy even get into ways that submarine cables can help provide data about the ocean floor to increase our knowledge of this dark world.
We cover a lot of ground in this episode. We get into a specific seismic event—the recent Tongan volcanic eruption—as well as ongoing threats to sub cables, including how climate change could increase risks and how we can start to mitigate them.
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These natural events, including earthquakes, underwater landslides, volcanoes, seafloor currents, and even land-based flooding from massive rainfall events like tropical cyclones, are particularly concerning because they can damage multiple cables simultaneously, unlike most human-caused faults which typically affect only a single cable.
Geological events like turbidity currents (avalanches of sand and mud) can run through underwater canyons and cause abrasion or breaks to cables crossing these paths. Even long-term processes like abrasion from currents over rough seafloor terrain can damage cables over time.
Our understanding of the seafloor is limited; for example, only about 20% of the oceans are mapped at a resolution of 150 meters, and repeat mapping to understand how the seafloor is evolving is rare.
When submarine cables break, especially in unexpected locations, it provides valuable scientific information about the deep sea's activity. Historical cable faults, like those off the Congo River mouth in the late 1800s or the 1929 Grand Banks earthquake off New Newfoundland, have provided crucial insights into underwater processes like massive landslides and fast-moving turbidity currents, proving that deep waters are not always still.
The 2022 Tonga volcanic eruption, which damaged both domestic and international cables hundreds of kilometers away from the volcano, offered unprecedented data on the speed (up to 120 km/h) and scale of volcanic flows on the seafloor.
New technologies like distributed acoustic sensing (DAS) and state of polarization/interferometry can use the optical fibers within modern cables to monitor various phenomena.
These techniques can pinpoint where faults or perturbations occur and can effectively turn cables into seismic monitoring networks. This allows detection of ground motions from earthquakes, the rumbling before volcanic eruptions, and other processes on the seafloor.
Such monitoring could provide valuable early warning information for coastal communities vulnerable to tsunamigenic (what a fantastic word) events or volcanic hazards, helping to prevent being caught by surprise by damaging natural disasters. This also contributes to understanding the hazards that potentially threaten the cables themselves. Collaboration between researchers and the submarine cable industry is facilitating this data collection and analysis to improve understanding and future resilience.