• Otávio Santiago

A Huge Subterranean ‘Tree’ Is Moving Magma to Earth’s Surface

Updated: Oct 13

RÉUNION, A FRENCH island in the western Indian Ocean, is like a marshmallow hovering above the business end of a blowtorch. It sits above one of Earth’s mantle plumes—a tower of superheated rock that ascends from the deep mantle and flambées the bases of tectonic plates, the jigsaw pieces that make up the ever-changing face of the world. The plume’s effects are hard to miss: One of the island’s two massive volcanoes, the aptly named Piton de la Fournaise, or “Peak of the Furnace,” is one of the most hyperactive volcanoes on the planet.

But the plume’s modern-day punch is nothing compared to its past.

Around 65 million years ago, when the plume was under what is now India, a series of lava floods named the Deccan Traps smothered 1.5 million square kilometers of land—enough to bury Texas, California, and Montana—in a mere 700,000 years, a geologic heartbeat. A giant asteroid strike would be the coup de grâce for the dinosaurs, but the Deccan Traps have long muddled the picture of the climatic conditions the dinosaurs had to contend with.

In 2012, a team of geophysicists and seismologists set out to map the plume, deploying a giant network of seismometers across the vast depths of the Indian Ocean seafloor. Nearly a decade later, the team has revealed that the mantle is stranger than expected. The team reported in June in Nature Geoscience that the plume isn’t a simple column. Instead, a titanic mantle plume “tree” rises from the fringes of the planet’s molten heart, with superheated branchlike structures appearing to grow diagonally out of it. As these branches approach the crust, they seem to sprout smaller, vertically rising branches—super hot plumes that underlie known volcanic hot spots at the surface.

The discovery of this massive structure beneath Réunion nearly coincides with another recent discovery, reported in November, that found additional structures in the plumes under Africa. Taken together, the two findings represent a significant scientific advance: They suggest that plumes can be more idiosyncratic, and can have more elaborate backstories, than traditional models presumed.

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