For decades, pink granite boulders scattered across the volcanic peaks of the Hudson Mountains in West Antarctica have puzzled scientists. However, a study published in October 2025 may have finally solved the mystery surrounding their origin, linking the scattered boulders with a hidden, giant granite body - almost 100km across and nearly 7km thick - beneath Pine Island Glacier.
The startling discovery was made by a team of researchers led by the British Antarctic Survey (BAS). Using a dating method known as U-Pb zircon geochronology, which measures the radioactive decay of elements locked inside microscopic crystals to give an accurate estimation of age, these researchers were able to work out the granite boulders formed roughly 175 million years ago, during the Jurassic Period.
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While it may be entirely covered in ice today, during the Jurassic Period Antarctica was a temperate, ice-free landmass covered in habitable forests of conifers and ferns. The climate was cool but mild and supported several species of dinosaurs, including the 7m-long Cryolophosaurus, a distant relative of T.rex, and Glacialisaurus, a primitive, long-necked dinosaur (sauropodomorph) that was actually capable of walking bipedally.
Today, the Hudson Mountains are home to just a handful of sparse lichens and mosses, and the occasional wandering snow petrel.
Although the age of the granite boulders gave researchers some insight into their history, it didn’t solve the mystery surrounding their origin. That was done by the presentation of new evidence from airborne surveys performed by the BAS’ Twin Otter and other science research aircraft.
These surveys picked up gravity anomalies above the Pine Island Glacier. After correcting for the surrounding topography and thickness of the crust, the researchers were able to use this data to work out the relative density of the rocks lying underneath the ice. This density signature matched that expected from a buried granite, which gave the researchers an answer as to where the overlying pink granite boulders originated from.
“It’s remarkable that pink granite boulders spotted on the surface have led us to a hidden giant beneath the ice. By combining geological dating with gravity surveys, we’ve not only solved a mystery about where these rocks came from, but also uncovered new information about how the ice sheet flowed in the past and how it might change in the future,” said Tom Jordan, lead author of the recent study and geophysicist at BAS.
This discovery gives us some insight as to how Pine Island Glacier may have behaved in the past, plucking rocks from the granite bedrock before depositing them across the Hudson Mountains, likely during a time when the ice sheet was much thicker today. It also sheds light on present-day processes and may help explain why this region has experienced some of the fastest ice loss across Antarctica in the last few decades.
The underlying geology has a strong influence on how Pine Island Glacier slides over the bedrock and how meltwater drains beneath it. The new findings from this latest study will help researchers improve models of ice sheet evolution in this vulnerable region. These models are not only vital for working out how the West Antarctic Ice Sheet may change in future, but also for determining the impact of sea level rise caused by the rapid melting of this ice sheet.
Joanne Johnson, a co-author of the recent study and a geologist at BAS, highlighted the crucial role that rocks such as these pink granite boulders play in recording major changes in Earth’s systems over extended periods of time.
“Rocks provide an amazing record of how our planet has changed over time, especially how ice has eroded and altered the landscape of Antarctica. Boulders like these are a treasure-trove of information about what lies deep beneath the ice sheet, far out of reach,” she said.
The recent study is published in the journal Nature Communications Earth and Environment.
Top image: Aerial view of Antartica. The Hudson Mountains, where the granite was found, are located in West Antartica (to the left of this image). Credit: MarcelC/Getty Images
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