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SYFY WIRE volcanoes

Scary tectonic plate's past could tell us if volcanism is in Earth's future

By Elizabeth Rayne

While some astronomers are nervously looking to the sky for signs of a lethal asteroid before we go the way of the dinosaurs, there are geologists who believe the planet has a better chance of breaking out in killer volcanoes.

Clouds of volcanic smoke and ash that were belched out with rivers of hot magma are thought to be one of the main culprits behind dinosaur extinction — with the asteroid that smashed into Earth provoking them. Volcanoes vomit the guts of the planet at the edges of tectonic plates. They form on the surface like planetary acne when plates either sink deep beneath other plates and melt to form magma, or when two plates pull apart and release magma. Resurrection is a prehistoric tectonic plate which was assumed to be forever lost or, in some cases, not even exist. Now new research has brought Resurrection back from the dead.

Subduction can explain why Resurrection vanished in the first place. Earth’s lithosphere (its ridgid outer shell) is broken into tectonic plates. In a subduction zone, where the edge of one plate head-butts another, the loser of this fight moves sideways and downward into the mantle, melting as it plunges into liquid magma and giving rise to angry volcanoes.

“When the Resurrection oceanic plate and North American continental plate were smashed together by tectonic forces 60 million years ago, the oceanic plate lost the plate tectonic tug-of-war and sank down into the deep Earth,” University of Houston geologists Jonny Wu and Spencer Fuston, who recently published a study in Geological Society of America Bulletin, told SYFY WIRE. “Today, the vanished Resurrection plate has sunk to 400 to 600 km depths in the mantle and will likely continue to slowly sink through the mantle over time.”

Wu and Fuston’s modeling suggested that the Resurrection plate did some serious damage while it was still near the surface during the Cenozoic era. As a plate subducts, huge, gaping cracks bubble with lava, heating the continent above more and more. When plates separate, that lava gushes to the seafloor and erupts into an enormous outburst of basalt, which spreads and results in mid-ocean ridges. Some of these undersea volcanic belts can be found stretching from the Alaskan coast through Washington state.

The two plates that are known to have existed at the time are Kula and Farallon. Resurrection would have been right between them, and it has the potential to answer why that volcanic belt between Alaska and Washington formed.

To potentially solve this mystery, the scientists used a technique called slab unfolding, which was developed at the UH Center for Tectonics and Tomography, to reconstruct what the tectonic plates in the Pacific Northwest must have looked like during the period right after the dinosaurs went extinct. Wu and Fuston applied this technique to tomography images that show cross-sections of the mangle. 3D mapping technology is used to pull out subducted plates in theses images and place them where they once were before “unfolding” and stretching them to the shapes they used to be.

“Our reconstruction of the vanished Resurrection plate, which was not based on volcanism but on tomographic images of the mantle, explains these unique volcanic belts very well by showing that they match the boundaries of the ancient Resurrection plate,” Wu and Fuston said. “These volcanoes spewed greenhouse gases into Earth’s ancient atmosphere, but may not have been fully accounted for in climate models.”

So could we be seeing a volcanopocalypse? Maybe not from Resurrection, which only keeps sinking deeper into the bowls of the Earth, but how it interacted with other plates can tell us what to expect. Mid-ocean ridges are not unique to just one area. They have occurred in the past and continue to occur all over the planet, with the same processes creating ridges that spawn new volcanoes. What was thought to be an anomaly is happening off the coast of southern Chile right now. Wu and Fuston believe that geological changes in the deep past could help us see if there really is anything to dread.

“Having plate tectonic reconstructions that include these volcanoes allow climate models to better understand the effect they had on Earth’s ancient climate change,” they said. “It provides key information on how it will respond in the future.”