From natgeo.com: “Huge Bubble of Hot Rock May Be Rising Under New England”

National Geographic

National Geographics

December 5, 2017
Erin Blakemore

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Colorful forests fill the landscape in the Berkshires of western Massachusetts. Photograph by Berthold Steinhilber, laif, Redux

At first glance, New England doesn’t seem like a hotbed of geologic activity. The region doesn’t have any rumbling volcanoes. Earthquakes are almost unheard of. And its mountains are mere hills compared to ranges like the Rockies or the Sierra Nevada in the western U.S.

But don’t underestimate what’s going on beneath the surface: It turns out this idyllic pocket of the northeastern U.S. may sit atop a rising mass of warm rock—a smaller, slower version of the magma pockets under well-known volcanic zones.

The findings, recently published in the journal Geology, suggest that New England may not be so immune to abrupt geological change.

A team of researchers at Rutgers University and Yale University made this surprising discovery using an advanced array of seismic sensors, which show what lies in the otherwise hidden rock below our feet.

“Ten years ago, this would not have been possible,” says study coauthor Vadim Levin, a professor at Rutgers University-New Brunswick’s department of Earth and planetary sciences.

“Now, all of a sudden, we have a much better eye to see inside the Earth.”

Rising Rock

Inside our planet, heat from the volatile core makes its way up through the mantle—the hot, high-pressure zone that lies below the planet’s crust. That heat causes the crust’s tectonic plates to slip and slide around. Where those plates collide or divide is where we most often see mountains, earthquakes, and volcanoes.

The tectonic plates of the world were mapped in 1996, USGS.

Since we can’t see that deep into the planet, geologists use seismic vibrations caused by earthquakes to visualize the features within rock. Sensing how fast seismic ripples move, for instance, provides details about the structure and temperature of Earth’s mantle.

In this case, Levin’s team studied data from EarthScope, a National Science Foundation program that deploys hundreds of geophysical instruments across the United States. The project’s Transportable Array, a temporary network of seismic sensors, made its way around the country starting in 2007. The array picked up readings from small earthquakes and observed the motions of seismic waves in various regions.

The team piggybacked off previous research showing a relatively hot spot beneath New England’s upper mantle. Using data from EarthScope, they then observed a localized plume of warm rock beneath central Vermont, western New Hampshire, and western Massachusetts—and found geologic evidence that it’s on the move.

Less dense areas are where the rock is hotter, and seismic waves move more slowly. That’s what the team saw under New England. They also observed wave patterns that suggest deformations in the rock itself.

Normal plate motion leaves the geologic equivalent of skid marks in its wake, which seismic sensors can detect. In this region, however, the skid marks were gone—erased by the upward movement of warmer rock.

Shifting Perspectives

New England residents don’t need to panic. The upwelling is likely tens of millions of years old, which would make it a relatively recent development in geological terms, and it’s moving very slowly. For now, it certainly hasn’t gotten close enough to the surface to shape New England’s geography or create a volcano.

“Maybe it didn’t have time yet, or maybe it is too small and will never make it,” says Levin. “Come back in 50 million years, and we’ll see what happens.”

Instead, the discovery is a sign that it may be time to rethink the region’s geology.

The big takeaway from this paper is that Earth’s structure is even more intricate and dynamic than anyone realized, says Meghan S. Miller, a structural seismologist and associate professor at the Australian National University’s Research School of Earth Sciences who was not involved in the project.

“I think that kind of sounds simple and obvious in retrospect, but the Transportable Array data has allowed us to visualize how complex Earth’s structure really is,” she says.

The find also helps put the planet in perspective, says Levin. New England has traditionally been considered a place of little geologic change, but EarthScope data suggests that the subsurface reality is anything but stagnant.

“People think of mountains and lakes and geology as forever—there’s a general sense that Earth is a permanent thing,” says Levin. “Well, it’s not.”

See the full article here .

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The National Geographic Society has been inspiring people to care about the planet since 1888. It is one of the largest nonprofit scientific and educational institutions in the world. Its interests include geography, archaeology and natural science, and the promotion of environmental and historical conservation.