Although it can perhaps be an alluring notion, there’s very little convincing evidence that seismic waves – generated by earthquakes, or even nuclear weapons – can trigger volcanism. Could an asteroid impact, though? There are plenty of competing ideas about how valid such a concept is, but a new study in Science Advances puts it front and center at the most famous apocalypse in history: the demise of the dinosaurs.
The curtain call for the time of the Tyrannosaurus was a complex one. The non-avian dinosaurs had, in general, entered a 40-million-year-long period of decline, and at some point, a colossal volcanic event over in India began, and the profusion of what became known as the Deccan Traps wouldn’t stop for tens of thousands of years.
Then, of course, the coup de grâce: a 10 to 15-kilometers-wide (6 to 9.3-mile-wide) asteroid hit the Yucatan Peninsula, excavating a crater 180 kilometers (110 miles) across and sending debris 25 kilometers (15.5 miles) into the sky. It triggered a rapid, frigid climate change that brought the Cretaceous crashing down.
This new paper, by a pair of researchers from the Universities of Oregon and Minnesota, suggests that the impact was so energetic that its seismic waves boosted volcanism across the planet, specifically at mid-ocean ridges (MORs) within the world’s oceans. The team also infer that the aforementioned, ongoing, prolific eruption at the Deccan Traps was likely enhanced by the impact event.
If true, this paroxysm, and its associated uptick in climate and hydrosphere changing volcanic gases, would have contributed to the end-of-days environmental crises that were already happening at the time.
The team looked at publically available datasets focusing on the changes in gravity in Earth’s oceanic crust across a million years, both before, during and after the impact occurred. Small changes in local gravitational fields are good indicators of mass changes, and mass changes at MORs – where tectonic plates are separating – suggest changes in magmatic production.
The pair found that there was a transient change in MOR productivity around the time of the impact. Anomalies at MORs, found all over the world, from India to the Pacific Ocean, suggest that the volume of melt increased.
In fact, the team estimated that the amount of additional magma produced at MORs was at least comparable to that of the Deccan Traps, which was already known to have produced so much magma that it would have completely covered Spain.
“We put the volume of excess volcanic product at 100,000 to 1 million cubic kilometers of material,” co-author Dr Joseph Byrnes, a postdoctoral researcher at the University of Minnesota, told IFLScience. “This is a global episode of volcanism.”
Incidentally, the environmental impact of this pulse of global volcanism can’t yet be properly established. As this paper only used gravity data, Byrnes pointed out that “environmental changes in the ocean are a perfectly plausible consequence, but at this time the connection has not been quantitatively established.”
So what caused it? The team suggest that it cannot be down to mantle plumes, because the signal was on a planetwide scale. It’s probably not a change in plate spreading rates either, as they’re not associated with gravity anomalies.
They suggest that it must have been the Chicxulub impact, and the seismic waves generated by it. Is that really possible, though?
Earthquakes can potentially trigger volcanic eruptions if they're already primed to erupt, but the underlying mechanism is unclear. In fact, there’s arguably little compelling evidence currently available that shows a direct cause-and-effect relationship between seismic events and significant volcanism. Suggestions crop up from time to time, but a healthy skepticism is welcome.
Byrnes emphasized that their paper “is about a very unusual earthquake, the Chicxulub impact, and a different sort of volcanism – not explosive, like Mount St. Helens.” Chicxulub was undeniably a lot more energetic than any nuclear weapon blast or natural earthquake, so it's possible it could induce volcanism if earthquakes sometimes can.
This asteroid-volcanism link has been the focus of plenty of pre-existing scientific research, and a study back in 2015 supported the hypothesis. Both the 2015 study and this new one, though, rely on coincidental timing and indirect links, as do many of those linking earthquakes and volcanic eruptions.
It’s not at all clear how seismic waves would trigger the uptick at MORs. Describing the mechanism as “fuzzy,” Byrnes argues that “right now, the evidence for these sorts of triggered events is empirical,” but adds that “we are far from attaining a satisfying theory as to how it works.”
The idea that a giant impact could also accelerate a conflagration from the planet’s hellish depths is a thrilling narrative. Right now, though, it's one that’s wide open for debate, rather than a tale with an absolute conclusion.