Bright pink granite boulders on Antarctica's Hudson Mountains have unveiled a massive buried granite body beneath Pine Island Glacier. The structure measures nearly 100 km wide and 7 km thick. Researchers linked the rocks, dated to 175 million years ago, to this subglacial feature using gravity surveys.
For decades, pink granite boulders perched on the dark volcanic peaks of the Hudson Mountains in West Antarctica puzzled scientists. A team from the British Antarctic Survey (BAS) dated the rocks to around 175 million years ago in the Jurassic period by analyzing radioactive decay in mineral crystals. To trace their origin, they turned to gravity data from aircraft, including BAS's Twin Otter, which detected an anomalous signal under Pine Island Glacier matching a granite mass nearly 100 km wide and 7 km thick—roughly half the size of Wales in the UK. This connected the surface boulders to the underground formation, explaining how thicker ice during the last ice age, about 20,000 years ago, pulled rocks from the glacier's base and carried them uphill. The discovery sheds light on past ice sheet flow and aids models predicting responses to climate change, particularly in a region with rapid ice loss. Pine Island Glacier's subglacial geology influences ice sliding and meltwater movement, relevant to sea level rise projections. Dr. Tom Jordan, lead author and BAS geophysicist, stated: > 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. Dr. Joanne Johnson, a co-author and BAS geologist who collected samples during the International Thwaites Glacier Collaboration, added: > 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. The study appears in Communications Earth (2025).
