This 500-year-old landslide found in the Red Sea could trigger a future tsunami

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The Red Sea hides powerful geological forces that could endanger coastal communities in Egypt and Saudi Arabia.

The thought hit Sam Purkis like a wave, as he stared out the window of a submarine 900 meters (3,000 feet) deep in the Strait of Tiran.

There, in the light of the vehicle’s flashlight, stood a gaping chasm three meters wide and eight meters high (that is, 10 by 26 feet).

“Immediately, I realized what we were looking at was the result of some geological force, which had broken up the seabed,” recalls Purkis, a marine geoscientist from the University of Miami.

Further research revealed that it was the work of an underwater landslide, which likely triggered 10-meter-high waves that hit the Egyptian coastline around 500 years ago.

Today, this piece of land is still teetering and if it slips, models suggest it could trigger a second tsunami twice as large as its predecessor. Even when earthquakes do occur in the region, they rarely generate tsunamis of this magnitude.

“Just a small jolt in the wrong place and the whole wall could collapse, resulting in a much larger tsunami than the one that happened 500 years ago,” Purkis says.

“This region of Egypt, as well as Saudi Arabia, which is urbanizing so rapidly, presents certain risks that have not been recognized before, but must be recognized to avoid future catastrophe.”

A map of where the old landslide occurred. (University of Miami/OceanXplorer)

The Red Sea is a maritime fault, that is to say that it moves apart as the two tectonic plates that border it gradually move.

This makes the area highly susceptible to earthquakes, but the discovery of an undersea landslide suggests that there are other tsunami-triggering forces at play that we have overlooked.

Breaks in slope along parts of the Red Sea coastline could be particularly dangerous in straits or other narrow passages, where a wave can quickly make landfall with very little warning.

In the Strait of Tiran, for example, the authors say a 20-meter-high tsunami could “seriously threaten the rapidly urbanizing coastline” of Egypt and Saudi Arabia. According to the models, an Egyptian seaside resort is located directly in the path of the wave.

The research trip that discovered this underwater landslide was actually funded by a company that develops the Saudi coastline.

Turns out the risk assessment was a good idea. Despite only sliding 30 meters (100 feet), the landslide that occurred half a millennium ago caused powerful waves to hit the shore in just minutes.

If at some point in the future the terrain slides another 50 meters, models show that the first impacts will be felt by the Egyptian resort of Sharm El Sheikh, located slightly to the southwest. In one minute and thirty seconds, the waves breaking on the shore could reach 21 meters high.

If the land slides another 100 meters, the waves hitting Sharm could reach 35 meters high. A little further north, at Mousa Bay, the waves could actually exceed 45 meters, reaching the coast in less than three minutes.

A few minutes later, the Saudi coast across the strait would be impacted, but with slightly smaller waves. In the worst case, the researchers believe the waves could reach 15 meters high.

“The way the strait bathymetry confines and directs the tsunami is remarkable in all simulations,” the authors write.

“The wide, deep waters to the north allow the wave front to progress unimpeded into the Gulf of Aqaba. To the south, the narrow, shallow strait limits wave entry into the Red Sea.”

It’s no surprise that the historical record somehow missed the undersea landslide that triggered a tsunami 500 years ago. Not only was the event earthquake-free, but the coastline where Sharm currently sits was only an occasional base for fishermen at the time, meaning few people would likely have saw the waves.

Today, the reality is quite different. This is why underwater studies of this type are so important; they can reveal vulnerabilities in coastal infrastructure that could put communities at risk.

The underwater slopes off Sharm, for example, are very steep. If these walls also slide further into the depths, it could trigger a ripple of waves that could easily reach the Saudi coast.

Being able to predict when these tsunamis will hit could save lives and infrastructure. Underwater landslides in the Red Sea should be monitored like earthquakes in the future, researchers say.

The study was published in Geophysical Research Letters.


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