Scientists studying an ancient, unusually hot “blob” of rock slowly shifting in the direction of New York City have uncovered another puzzling structure deep beneath the region.
The feature they were investigating, known as the Northern Appalachian Anomaly (NAA), is a roughly 250-mile-wide zone of abnormally hot rock buried far below New England.
According to a 2025 study, the NAA is moving southwest at about 12 miles every million years, putting it on a path that could carry it beneath New York City in roughly 10 to 15 million years.
To examine it more closely, researchers analyzed seismic waves generated by faraway earthquakes, using them to build the most detailed three-dimensional view yet of the anomaly and the mantle around it.
Those images show the hot blob stretches from around 37 miles to 124 miles below New England, remaining within the upper mantle rather than reaching deeper into Earth.
Yet the same scans also revealed something unexpected: a thin, separate column beneath Connecticut that descends hundreds of miles farther into the planet.
While the NAA slows seismic waves as they pass through it, this newly identified column does the opposite, allowing the waves to move unusually fast — a sign it is likely made of colder, denser material.
Researchers suspect the deep column may be either a fragment ripped from the rocky base of North America or the downward-moving limb of a vast mantle circulation system.
Scientists believe a nearly 250-mile blob called the Northern Appalachian Anomaly is still moving and shaping mountains in the US
The latest study was led by researchers from Yale University and the University of Minnesota and published in the Journal of Geophysical Research: Solid Earth.
The team created the underground images using seismic tomography, which works in a similar way to a medical CT scan.
Instead of X-rays passing through a human body, the technique measures the time taken for seismic waves from distant earthquakes to travel through different parts of the planet.
Those waves slow down or accelerate depending on the temperature, density and composition of the rock they encounter.
The researchers combined readings from USArray, the Canadian National Seismograph Network and other permanent monitoring stations with data from three temporary networks deployed across New England.
The temporary stations were positioned approximately three to 16 miles apart, allowing the scientists to see smaller features that might have been blurred or missed by earlier surveys.
At its most extreme point, P-waves, the fastest seismic waves created by earthquakes, traveled approximately four percent slower through the NAA than expected.
The slower speeds support the conclusion that the blob is made from hotter or otherwise altered mantle material, although it is not a hollow chamber or a giant underground lake of liquid magma.
The team has recently idnetified a column made from colder, denser material near the blob
The scans also showed that the NAA appears to end within the upper mantle and is not physically connected to other slow-wave anomalies detected in the deeper mantle transition zone.
However, the mysterious Connecticut column is different.
Researchers described it as a small, nearly vertical structure positioned adjacent to the NAA, rather than enclosed inside the blob.
The column appears to extend through the upper mantle to the bottom of the mantle transition zone, potentially reaching approximately 410 miles below the surface.
It is also not a tunnel or opening inside the Earth, but a three-dimensional volume of rock identified because seismic waves travel through it faster than they do through the surrounding material.
The researchers’ leading theory is that the column represents a piece of continental lithosphere, the rigid layer formed by the crust and the uppermost mantle, that detached and began sinking under its own weight.
If that occurred, hotter and more buoyant material may have risen from below to replace the missing fragment, potentially creating or contributing to the neighboring hot blob.
The scans revealed that the blob extends from approximately 37 to 124 miles beneath New England and is confined to the upper mantle
Scientists refer to that process as lithospheric delamination, or lithospheric loss.
Another possibility is that the blob and the column are opposite sides of an edge-driven convection cell, a gigantic loop of slowly circulating mantle rock.
Under that scenario, hot material would rise beneath the blob while colder, denser rock descended through the column, much like a conveyor belt operating over millions of years.
However, the study does not prove that the structures are connected or that one created the other.
Researchers conducted tests intended to determine whether the column might be an artificial feature caused by gaps or limitations in the seismic data, but its precise composition and origin remain uncertain.
The NAA has puzzled geologists because regions of anomalously hot mantle are normally associated with volcanoes or active tectonic plate boundaries.
New England has neither and has remained far from an active plate boundary for approximately 180 million years.
‘This thermal upwelling has long been a puzzling feature of North American geology,’ Professor Tom Gernon, an Earth scientist at the University of Southampton, said following the 2025 study.
The blob is moving about 12 miles every million years, putting it beneath New York City in about 15 million years
Gernon and researchers from the Helmholtz Center for Geosciences in Germany proposed that the anomaly is part of a slow-moving ‘mantle wave’ triggered by an ancient continental breakup.
Their computer simulations suggested that the process began approximately 80 million years ago as Canada and Greenland separated and the Labrador Sea opened between them.
The disturbance destabilized the rocky underside of the tectonic plate, causing dense material to form drips that sank into the deeper mantle.
As those drips descended, lighter and hotter rock moved upward to replace them, creating slow-wave anomalies similar to blobs rising and falling inside a lava lamp.
Scientists call this process a Rayleigh-Taylor instability.
The 2025 model suggested that the NAA formed approximately 1,100 miles from its current location before slowly migrating southwest beneath North America.
The instability may also explain why the Appalachian Mountains remain unusually elevated despite hundreds of millions of years of erosion.
Heat at the base of the continent can weaken and remove portions of its dense root, making the land above lighter and more buoyant.
That process could have lifted parts of the ancient mountain range during the past several million years, counteracting some of the effects of erosion.
Neither the blob nor the newly imaged column poses an immediate threat to Connecticut, New York or surrounding states.
