A crack in the Earth’s crust seen from the airplane. Credit: rabiem22 / Flickr / CC BY 2.0
Scientists have, for the first time, documented a tectonic plate collapse beneath another, offering a rare view into how Earth’s crust breaks apart deep below the surface. This slow, step-by-step process causes the plate to fragment into smaller sections known as microplates.
The discovery sheds new light on subduction zones, where one plate sinks beneath another into the mantle. These regions are among the most powerful geological forces on Earth. They drive the movement of continents, fuel major earthquakes and volcanic eruptions, and recycle crustal material back into the planet’s interior.
The research team, led by geologist Brandon Shuck of Louisiana State University, focused on a subduction zone in the Pacific Ocean off the coast of Vancouver Island. Here, the Juan de Fuca and Explorer plates are gradually sliding beneath the North American plate.
As the oceanic plates descend, they begin to tear apart, forming deep fractures in the crust. The process appears to unfold over millions of years.
Breakdown in motion beneath Vancouver Island
Using seismic reflection imaging and earthquake records, scientists identified cracks in the subducting plates. These faults mark the early stages of collapse as the plate loses structural strength.
Shuck compared it to a train that slowly derails one car at a time rather than crashing all at once. He explained that breaking the plate reduces the downward force that drives subduction, eventually halting the entire process.
A convergent boundary of tectonic plates in Earth’s crust. Credit: domdomegg / Wikimedia Commons / CC BY 4.0
The team believes this is the clearest evidence yet of an active subduction zone breaking down. Although the collapse happens gradually, the region remains capable of producing powerful earthquakes and tsunamis. Understanding how Earth’s crust behaves during these transitions can improve hazard forecasting and disaster preparation.
Historic clues behind Earth’s crust collapse
The findings also help explain features in North America’s geological past. The study suggests that the gradual tearing of the Farallon plate, which once subducted beneath the continent, may have created microplates separated by fissures.
These gaps could act as pathways for magma, explaining why volcanism persists in regions like the Cascades and Yellowstone despite the thickened continental crust that would typically block it.
Seismic surveys along the West Coast have revealed areas where the crust is nearly twice its usual thickness. This raised questions about how magma continues to reach the surface. The updated model proposes that fragmented plates and open faults allow molten rock to rise through the otherwise dense crust.
The full study, titled Slab tearing and segmented subduction termination driven by transform tectonics, appears in Science Advances.
