In 1969, a massive underwater earthquake sparked a tsunami off the coast of Portugal, but for years scientists didn’t understand what was going on. The site itself was calm, flat and featureless, according to National Geographic. Normally after a high magnitude earthquake, you might expect to see signs of tectonic activity, such as underwater mountains.
This piqued the interest of marine geologist João Duarte, whose 50 years of work with Lisbon’s Instituto Dom Luiz suggests the bottom of the tectonic plate off the country’s coast may actually be peeling away from its top. He tested his hypothesis using numerical models.
At the European Geosciences Union meeting in April, Duarte and his colleagues presented their findings: About 155 miles below the site’s seafloor is a drip-shape anomaly in what’s known as a subduction zone. This zone is caused by one part of the tectonic plate grinding beneath another.
According to Live Science, “a subduction zone is the biggest crash scene on Earth,” marking a collision of two of the planet’s tectonic plates. “Where two tectonic plates meet at a subduction zone, one bends and slides underneath the other, curving down into the mantle,” the site reported.
Because oceanic crust is denser than continental crust, oceanic crust in a subduction zone usually sinks into the mantle beneath continental crust. And, Live Science notes, scientists think that sometimes oceanic crust may grow so old and dense it collapses, spontaneously forming a subduction zone. This never, however, has been documented in pristine oceanic plates.
Subduction zones are common around the Ring of Fire, an area of the basin of the Pacific Ocean known to produce the world’s worst disasters—tsunamis, earthquakes and volcanic eruptions.
If there really is a subduction zone off the coast of Portugal, “it may mark one of the earliest stages of the Atlantic Ocean shrinking, sending Europe inching toward Canada as predicted by some models of tectonic activity,” according to National Geographic.
University of Oslo’s Fabio Crameri, who was not part of Duarte’s team but attended the April lecture, told NatGeo that while the arguments are strong, more testing is needed.
“Most of what we know so far is that new subduction tends to stay in the places where we already have ongoing subduction,” Crameri added. “But that doesn't mean it won't happen.”
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