Scientists have uncovered two distinct geological features deep beneath New England: a massive, hot anomaly and a separate, fast-moving column of colder rock. The discoveries, made using seismic tomography, offer new insights into the complex geological processes occurring beneath a region considered stable for millions of years.
The primary discovery is the Northern Appalachian Anomaly (NAA), a roughly 250-mile-wide mass of unusually hot rock situated in the upper mantle, extending from approximately 37 to 124 miles below the surface. Researchers observed that seismic waves slow down significantly as they pass through the NAA, indicating hotter or altered mantle material. This anomaly has been previously noted to be drifting southwest at about 12 miles per million years, with a potential to pass beneath New York City in 10 to 15 million years.
Using advanced seismic wave analysis from distant earthquakes, researchers from Yale University and the University of Minnesota created highly detailed three-dimensional images. These scans revealed not only the extent of the NAA but also a separate, narrow column of material located beneath Connecticut. This column behaves differently, allowing seismic waves to travel unusually quickly, suggesting it is composed of colder, denser rock.
This mysterious column plunges hundreds of miles deeper than the hot blob, potentially reaching approximately 410 miles below the surface. It appears to be a nearly vertical structure adjacent to, rather than within, the NAA.
Scientists theorize that the column could be a fragment of the Earth's rigid outer layer, the lithosphere, that detached and sank. This process, known as lithospheric delamination, might have caused hotter, more buoyant material to rise from below, potentially forming or contributing to the nearby hot blob. Another hypothesis suggests both features are part of a massive convection cell in the mantle, with hot material rising beneath the anomaly and cold material descending through the column.
Geologists have long found the NAA puzzling because such hot mantle regions are typically associated with active volcanic areas or tectonic plate boundaries, neither of which is present in New England. The region has been far from an active plate boundary for about 180 million years.
Previous research proposed that the anomaly is a remnant of a mantle wave triggered by the ancient separation of Canada and Greenland, which occurred approximately 80 million years ago. This event may have destabilized the underside of the North American tectonic plate, causing dense material to sink and lighter material to rise. This instability is also thought to contribute to the unusual elevation of the Appalachian Mountains, as the heat at the base of the continent can make the land above lighter and more buoyant.
Neither the hot blob nor the newly identified column poses any immediate threat to the region. The research, published in the Journal of Geophysical Research: Solid Earth, utilized data from seismic monitoring stations across North America, including temporary networks deployed across New England for higher resolution imaging.