So, it turns out that there’s a brand-new supervolcano appearing under New Hampshire, Vermont, and Massachusetts – at least, that’s what the headlines are saying all of a sudden.
Turns out that (surprise surprise) this isn’t true, and this is based off a study that was published late last year, one that explicitly said that we should not expect a new Yellowstone-esque caldera (a large crater left by a volcanic explosion) anytime soon, or even in the future. Here’s what’s actually happening.
A heat glow beneath those three states, first discovered back in the 1970s, was long thought to be the afterglow of a dead, once-upwelling plume of mantle material termed the “Great Meteor”. Using fresh seismic waves to determine what material resided down below, a paper in 2016 concluded that there’s an active, independent upwelling of very hot rock taking place right now.
Although the so-called North Appalachian Anomaly (NAA) was already known about, its high temperature and independence from the Great Meteor came as a surprise. The authors suspected, then, that one day, millions of years from now, there would be baby volcanoes of some sort cropping up in the northeastern United States.
In late-2017, Rutgers University – whose researchers co-authored that 2016 paper – used two years’ worth of data from EarthScope, a massive array of seismic instruments, to better constrain what was beneath New England. They zeroed in on those elevated temperatures in the upper mantle, and their data suggested a ballooning-like shape, characteristic of the top of a mantle plume.
It’s narrow, slow-moving, and based on the lack of surface activity – volcanism or deformation – it’s likely to be geologically young. Eventually, this could lead to an eruption at the surface in perhaps 50 million years, but it’s a small plume compared to others, so we shouldn’t expect anything supervolcanic.
In fact, it may be so small that it will never manage to make volcanoes at the surface. So – what’s with the supervolcano shenanigans then? It’s clearly broken volcanologists’ brains on social media:
Supervolcanoes are defined by the United States Geological Survey (USGS) as those that have at some point erupted more than 1,000 cubic kilometers (240 cubic miles) of fresh volcaniclastic material in a sudden and violent way. When they do so, they leave a huge crater known as a caldera.
Yellowstone, which has erupted catastrophically three times in the past 2.1 million years – and no, it isn’t about to erupt and kill everyone; see here – can be called a supervolcano as two of those eruptions produce the required amount of material.
Yellowstone’s eruptive past and geologically active present is fueled by an upwelling plume of solid mantle material. As it reaches the crust, it decompresses, which causes it to melt. The crust melts to a considerable degree, plenty of magma is generated, and voila, you have a sizeable volcano.
This heat signature, by the way, is termed a hotspot.
Mantle plumes and upwellings happen all over the planet. They can occur along divergent plate boundaries (hello, Iceland!), and in the middle of oceanic and continental plates. Having a plume doesn’t mean you’re going to get a supervolcano; you could get a series of shield volcanoes, like over in Hawaii, whose Kilauea has been stealing the spotlight for months now.
With that in mind, it’s not clear how some news outlets are so sure a supervolcano is appearing in the northeastern United States. This becomes especially baffling when the study’s lead author – Prof. Vadim Levin, a geophysicist at Rutgers – clearly ruled that possibility out.
The upwelling “is not Yellowstone (National Park)-like, but it’s a distant relative in the sense that something relatively small – no more than a couple hundred miles across – is happening,” he said.
Here’s the thing: what’s happening under New England is far cooler than any silly supervolcano formation. This part of the world was long thought to be geologically passive, one big meh in terms of tectonic activity.
Now there’s a chance that a somewhat fiery future awaits it because something down below has just, geologically speaking, started to take shape, and we don't know why. As ever, Earth isn’t quite what we thought it was – it’s more puzzling and dynamic than we’d yet dreamed.