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There’s something large moving deep beneath New England.

This is the conclusion of a new paper by researchers from the University of Southampton, England, who have been studying a mysterious patch of unusually hot rock below the Appalachian Mountains.

This region—known as the Northern Appalachian Anomaly (NAA)—is some 200 miles wide and lies around 125 miles beneath the surface.

According to the researchers, the anomaly is part of a slow-moving underground “mantle wave” triggered by tectonic events that happened more than 90 million years ago.

“The ‘mantle wave’ refers to a newly-discovered chain reaction of convective instabilities in the mantle that begins when a continent starts to rift,” paper author and Southampton geodynamicist professor Tom Gernon told Newsweek.

“It’s not a literal wave, but a progressive flow and deformation of mantle material that behaves like a wave in how it propagates.”

This surprising find is shaking up what geologists thought they knew about the eastern U.S.—a region long considered geologically stable—and may help explain why parts of the Appalachian Mountains have been gently rising for millions of years.

What Exactly Is the Northern Appalachian Anomaly?

Appalachian Mountains in northeastern North America. Appalachian Mountains in northeastern North America. University of Southampton

Imagine taking a CT scan of the Earth. That’s essentially what geologists did using seismic tomography, a technique that tracks how earthquake waves travel through different layers of the planet. What they found under New Hampshire was a huge, slow-moving blob of hot material.

This kind of anomaly is typically seen near volcanoes or tectonic boundaries—but New England has neither.

Originally, scientists thought the NAA might be caused by “edge-driven convection,” a type of vertical stirring in the Earth’s mantle caused when thick and thin crust meet. But that didn’t fully explain why this hot zone sits far inland, beneath thick and ancient rock.

A Drip from the Distant Past

A bold new theory reimagines the NAA as a “Rayleigh–Taylor instability”—a geological term for when heavy, cold rock begins to sink into the hot, soft rock below, like molasses dripping into honey. This process forces hotter material to rise, forming a plume of heat beneath the surface.

The twist? This “drip” may not have originated beneath New England at all.

Instead, scientists now believe it began near the Labrador Sea, a site where North America began pulling away from Europe over 120 million years ago. As the continents split, stress fractured deep layers of rock, triggering convective instabilities—blobs of rock slowly dripping downward under gravity.

Gernon explained: “As the continent stretches and begins to split, space opens up beneath the rift. That space is rapidly filled by an inflow of soft, flowing asthenosphere.”

(The asthenosphere is a semi-molten part of the Earth’s upper mantle, beneath the tectonic crust.)

“This sudden movement disturbs the edge of the continent’s root, triggering a chain reaction. Much like falling dominoes, blobs of the root begin to drip downward one after another.

“These ‘drips’ migrate inland over time, away from the rift. We think this same process might explain unusual seismic patterns beneath the Appalachians. The timing lines up perfectly.

These “drips” move slowly—about 20 kilometers every million years—which matches perfectly with the NAA’s current location and age.

Not a Lone Hot Spot

The NAA may be just one part of a larger chain.

Further south, another underground heat anomaly—the Central Appalachian Anomaly (CAA)—may represent an earlier drip in this chain. That one likely dates back around 135 million years, consistent with the early stages of the Labrador Sea rift.

Together, these anomalies form a “mantle wave”: a hidden, progressive disturbance deep inside the Earth, slowly traveling westward like a chain reaction.

This idea, pioneered by Gernon’s team, is gaining traction in explaining elevated plateaus, seismic activity, and even past volcanism in areas once considered geologically “dead.”

Origin of the Northern Appalachian Anomaly. Origin of the Northern Appalachian Anomaly. University of Southampton

What It Means for the Surface

While the Northern Appalachian Anomaly lies deep underground, its presence could help explain some of the long-term uplift seen in parts of the Appalachian Mountains.

However, the region’s dry climate and low erosion rates suggest that not much visible change has occurred in recent geological time.

Earlier convective instabilities—like those possibly linked to the Central Appalachian Anomaly—may have had a greater impact, contributing to the reshaping of the landscape millions of years ago. The pattern of these features suggests that such deep mantle processes may have occurred repeatedly, moving step by step inland over tens of millions of years.

Because there’s limited seismic data in northern areas like Newfoundland and the Gulf of St. Lawrence, it’s still unclear whether more of these ancient “drips” exist along the same path.

But their potential connection hints at a larger, hidden system of mantle activity beneath the eastern edge of North America.

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about the mantle? Let us know via science@newsweek.com.

Reference

Gernon et al. (2025). A viable Labrador Sea rifting origin of the Northern Appalachian and related seismic anomalies. Geology. http://dx.doi.org/10.1130/G53588.1