Key Takeaway:
A study examining an ancient underwater avalanche off the coast of Morocco has challenged our understanding of these powerful events and their potential to disrupt global communications and infrastructure. These avalanches, also known as turbidity currents, are difficult to observe and measure, but their impact is undeniable, particularly on the intricate web of fiber-optic cables that carry nearly all of the world’s internet traffic. The study found that underwater avalanches can begin modestly and grow into catastrophic events as they move along the seafloor, prompting scientists to rethink how they assess the risks associated with these phenomena. The frequency of underwater avalanches varies depending on location and triggers for these avalanches are diverse, with climate change expected to intensify some of these triggers.
Beneath the vast, seemingly tranquil surface of the ocean, powerful forces are at work—forces that, while invisible to the human eye, have the potential to disrupt global communications and wreak havoc on critical infrastructure. Among these forces are underwater avalanches, natural events that occur with surprising frequency yet remain shrouded in mystery due to their elusive nature.
These underwater avalanches, also known as turbidity currents, are difficult to observe and measure, which means our understanding of how they operate is still limited. However, their impact is undeniable, particularly on the intricate web of fiber-optic cables that lie on the ocean floor, carrying nearly all of the world’s internet traffic.
A recent study examining an ancient underwater avalanche is challenging what we thought we knew about these powerful events and could reshape how scientists assess their risks.
Today, the seabed is crisscrossed by over 550 active fiber-optic cables stretching a combined length of 1.4 million kilometers—enough to circle the Earth 35 times. These cables form the backbone of global communication, but they are vulnerable to the destructive power of underwater avalanches.
The 2006 Pingtung earthquake off the coast of Taiwan is a stark reminder of this vulnerability. The quake triggered a series of underwater avalanches that severed multiple seabed cables, cutting off much of Southeast Asia’s internet access to the rest of the world. China reported a 90% loss in internet traffic to the United States, while Taiwan saw between 74% and 100% of its connections to neighboring islands disrupted. The financial impact was significant, as global markets struggled with a reduced capacity for transactions. Restoring the network to full functionality took 39 days and cost millions of dollars.
The avalanche responsible for this disruption reached speeds of up to 72 kilometers per hour. Yet, compared to some of the massive underwater avalanches documented in other parts of the world, it was relatively small.
Fortunately, the vast number of seabed cables makes it highly unlikely that a single underwater avalanche could cause a global internet blackout. The Pingtung event demonstrated that even when primary routes are severed, alternate pathways can keep data flowing, albeit at reduced speeds.
In a groundbreaking study, researchers have now mapped the aftermath of a colossal underwater avalanche that occurred 60,000 years ago off the coast of Morocco. This ancient event traveled 400 kilometers through the largest submarine canyon in the world and continued for another 1,600 kilometers across the Atlantic seabed. It stands as the second-largest underwater avalanche ever recorded.
Using advanced seafloor mapping and sediment core analysis, the researchers traced the path of this avalanche and determined its age. The sediment samples revealed fossils that dated the event to 60,000 years ago, allowing the team to correlate the deposits across thousands of kilometers.
The scale of this underwater avalanche is almost unimaginable. It displaced enough sediment to fill 140,000 Wembley Stadiums—a staggering 162 cubic kilometers of material. The avalanche carved a trench 30 meters deep and 15 kilometers wide over a distance equivalent to the journey from London to Liverpool, obliterating everything in its path. Eventually, it spread out over an area the size of Germany, burying the seafloor under a meter of sand and mud.
What makes this event even more remarkable is that it started as a relatively small landslide. As the avalanche traveled, it grew more than 100 times larger, a rate of expansion far beyond what is observed in land-based avalanches, which typically grow by a factor of four to eight. This discovery challenges the long-held belief that only large initial slope collapses can produce massive avalanches.
The study’s findings suggest that underwater avalanches can begin modestly and grow into catastrophic events as they move along the seafloor. This insight may prompt scientists to rethink how they assess the risks associated with these phenomena, shifting the focus from the initial landslide zone to the entire pathway the avalanche might travel.
The frequency of underwater avalanches varies depending on location. Seafloor canyons near river mouths with high rainfall can experience multiple small avalanches each year, while other systems, such as the Agadir Canyon off northwest Morocco, might see a giant avalanche only once every 10,000 years.
Triggers for these avalanches are diverse, ranging from earthquakes and tides to typhoons, river floods, and volcanic eruptions. Climate change is expected to intensify some of these triggers, potentially increasing the frequency and severity of underwater avalanches.
However, not every trigger leads to a significant event, and the size of an avalanche is not necessarily related to the magnitude of its trigger. For instance, a massive earthquake in 1755 devastated Lisbon, Portugal, but only caused a minor underwater avalanche. In contrast, a 1929 earthquake off the coast of Newfoundland, Canada, triggered the largest underwater avalanche ever documented, which snapped 11 seabed cables and even generated a tsunami that claimed 28 lives along the coast.
The study of underwater avalanches is still in its early stages, but ongoing research continues to shed light on these powerful and destructive forces hidden beneath the waves. These discoveries remind us of the untapped mysteries lying deep within our oceans, waiting to be explored and understood.
