Named The East Antarctic Fan-Shaped Basin Province, The Structure Was Found By Accident By A Team Led By Egidio Armadillo Of The University Of Genoa While Reconstructing What East Antarctica Would Look Like Without Its Ice — The Basins Open Outward From A Central Pivot Point Near The South Pole Across 2,000 Kilometres Of Coastline, Like A Giant Geological Fan
According to ScienceAlert and a paper published June 9, 2026 in Nature Geoscience by Egidio Armadillo of the University of Genoa and co-researchers including colleagues at Durham University, scientists have identified an enormous geological structure hidden beneath Antarctica’s ice; a fan-shaped arrangement of approximately 30 connected basins covering roughly half the East Antarctic Ice Sheet.
The structure has been named the East Antarctic Fan-Shaped Basin Province, or EAFBP, and its discovery was not planned. The researchers were doing something else entirely.
What the researchers were actually trying to do. The team set out to reconstruct what East Antarctica would look like if its ice were removed; a question that sounds straightforward but is significantly more complex than it appears. Antarctica holds an estimated 27 million cubic kilometres of ice.
That ice is not merely a layer sitting on top of the bedrock; it is an enormous mass exerting continuous downward pressure on the underlying crust. The weight is so substantial that it has depressed the bedrock by a significant amount and if the ice were removed, the land would rebound upward by as much as a kilometre in altitude through a process called isostatic rebound.
This means that radar images showing what is directly below the ice do not show what the bedrock would actually look like in the absence of that ice. To reconstruct the true shape of Antarctica’s buried landscape, the team combined radar data with gravity measurements, seismic data, magnetic surveys, and models of isostatic rebound to generate a corrected topographic picture of the bedrock below.
As they examined this reconstructed topography, they noticed something peculiar. Many of the major subglacial basins in the region were not arranged randomly. They shared a common geometry; fanning outward from a single central point near the South Pole toward the coast, widening toward the coast, as though someone had taken a corner of Antarctica and tugged it apart around a central inland pivot point.
The structure and its geometry. The EAFBP spans approximately 2,000 kilometres of Antarctic coastline, with the fan opening progressively wider toward the sea. The arrangement is not subtle; the researchers describe it as a “coherent continent-scale radial pattern” of ridges radiating outward like the ribs of a handheld fan.
The geometry bears a striking resemblance to a tectonic feature type formally described in 1955 as a sphenochasm; “the triangular gap of oceanic crust separating two cratonic blocks with fault margins converging to a point, and interpreted as having originated by the rotation of one of the blocks with respect to the other.”
The process the researchers propose to explain the EAFBP is called rotational extension; a tectonic mechanism in which the crust spreads outward from a pivot point, exactly as a handheld fan opens when the ribs rotate away from each other around the riveted joint at the bottom. The radial arrangement of the Antarctic basins, together with patterns in crustal thickness and topography, matched most closely with this process of rotational extension, in which the crust spreads outward from a pivot point like an opening handheld fan.
Why Antarctica’s buried bedrock matters. The shape of the land hidden under Antarctica’s ice is not purely a matter of historical geological curiosity. It has direct practical implications for our understanding of the present and future behaviour of the ice sheet above it.
“Because these basins underlie about half of the East Antarctic Ice Sheet, they are likely to heavily influence both ice-flow and landscape evolution, making them essential to Antarctic glacial and hydrological processes,” the researchers write in their paper.
Ice sheets do not flow uniformly in all directions; they flow along channels and routes defined by the contours of the bedrock beneath them. If a subglacial basin creates a depression, it can accelerate or redirect the movement of ice above it. If a subglacial ridge creates a barrier, it can slow or divert flow. Understanding where the ice will go as Antarctica’s climate changes and how quickly, depends on knowing where these features are and how they interact with the overlying ice.
Antarctica represents approximately 10 percent of Earth’s total landmass. It holds about 60 percent of all fresh water on Earth in the form of its ice sheets. If the West Antarctic Ice Sheet alone collapsed, global sea levels would rise by approximately 3.3 metres. If both ice sheets collapsed, sea level rise would be measured in tens of metres. The difference between those outcomes and the timelines over which they might occur depends substantially on the bedrock topography that now has the EAFBP in it.
The Gondwana connection. The EAFBP may also be a geological record of events that occurred hundreds of millions of years ago. The researchers propose that it formed before the breakup of the Gondwana supercontinent, creating a zone of weakness that may later have helped steer the separation of Antarctica and Australia. Gondwana was the massive supercontinent that, before its breakup beginning approximately 180 million years ago, held together what is today Antarctica, Australia, South America, Africa, India, and the Arabian Peninsula.
The separation of Antarctica and Australia; the last major split, occurred roughly 33 to 35 million years ago and is considered one of the most climatically consequential events in Earth’s history, as it opened the Drake Passage and allowed the circumpolar current to form, thermally isolating Antarctica and triggering its glaciation. The EAFBP may have played a direct structural role in that separation, providing a pre-existing zone of crustal weakness along which the rifting eventually occurred.
The accidental discovery. One of the most scientifically satisfying elements of this story is that the researchers were not looking for the EAFBP. They were looking at the reconstructed topography of Antarctica without ice, examining the overall shape of the buried landscape, when the radial pattern emerged from the data.
The fan was hidden not just by the ice but by the pattern’s scale; too large to be apparent from examining individual basins, visible only when the full reconstructed topography was assembled and viewed as a whole.
It may also help explain Antarctica’s other features, such as the towering Gamburtsev Subglacial Mountains and Transantarctic Mountains that border the EAFBP. As the fan opened up, the researchers propose, the motion could have increased uplift in those regions, raising mountain ranges that today rank among Antarctica’s most prominent hidden features.
The Gamburtsev Subglacial Mountains; a range that rivals the Alps in scale but lies entirely buried beneath the ice, have puzzled researchers for decades because their existence is difficult to explain under standard tectonic models. The EAFBP provides a potential mechanism for their formation, generated by the same rotational extension that created the surrounding basins.
What remains uncertain and what comes next. The researchers are careful about the limits of their current interpretation. The timing of the process is difficult to constrain, and the feature could represent multiple episodes of extension that superimposed each other. Future investigation will focus on refining this aspect.
This uncertainty is fundamental rather than cosmetic. The difference between a single rotational extension event and multiple superimposed episodes has significant implications for the tectonic model, for how long the process occurred, what drove it, and what its relationship to Gondwana’s breakup actually was. Resolving it will require additional data from the most inaccessible continent on earth.
The verdict. Antarctica still represents a frontier that is difficult to penetrate. Little by little, however, scientists are discovering its secrets and with them opening a window to a long-lost ancient world. The EAFBP is the largest geological structure discovered beneath Antarctica’s ice. It was found by accident, in data collected for a different purpose, by researchers examining a reconstruction of a landscape buried under kilometres of frozen pressure.
The structure is older than the Atlantic Ocean, larger than most countries, and hidden so effectively that it took this long to find. It may also be one of the reasons Antarctica looks the way it does, flows the way it does, and separated from Australia when and where it did. The window to that ancient world has widened.
The research has been published in Nature Geoscience, June 9, 2026. To check out our previous coverage on Antarctica, geology, and Earth science, read our articles here.
