Bright pink granite boulders dotting the dark volcanic peaks of West Antarctica’s Hudson Mountains have led scientists to a surprising discovery. Beneath the Pine Island Glacier is a huge chunk of granite, some 100 km wide and 7 km thick, about half the size of Wales in the UK.
For decades, these unusual rocks have baffled researchers. High on a mountain ridge, they seemed out of place, raising questions about where they came from and what they reveal about Antarctica’s past and future.
Dating ancient rocks of the Jurassic period
A research team led by the British Antarctic Survey (BAS) analyzed granite by looking at the radioactive decay of elements trapped within tiny mineral crystals. The technique showed rocks that were formed during the Jurassic period, about 175 million years ago.
Even if their ages were determined, it remained unclear whether they had made the journey to the summit until scientists gathered new data from aircraft surveys over the area.
Aerial survey reveals buried structure
The researchers used sensitive gravity measurements collected by BAS’s Twin Otter aircraft and others to detect the unusual signal beneath the glacier. The data matched what scientists would expect from a giant granite object hidden beneath the ice.
By connecting rocks on the Earth’s surface to this deep underground formation, a long-standing mystery has been solved. They also found that Pine Island Glacier once had a much different behavior, pulling rock from its base and transporting it upwards, when the ice sheet was much thicker.
Clues about ice sheet behavior and sea level rise
The discovery provides important insight into how glaciers behaved during the last ice age, about 20,000 years ago. Understanding past ice thickness and movement patterns will allow scientists to improve computer models used to predict how the Antarctic ice sheet will respond to future climate change.
BAS lead author and geophysicist Dr. Tom Jordan analyzed the aerial data. he said:
“It is remarkable that the pink granite rocks found on the surface led us to the giants hidden beneath the ice. By combining geological dating and gravity surveys, we not only solved the mystery of where these rocks came from, but also revealed new information about how the ice sheet flowed in the past and how it will change in the future.”
Why subglacial geology matters today
The discovery also reveals how the geology beneath Pine Island Glacier is influencing its current conditions. This region has experienced the most rapid ice loss in Antarctica in recent decades. The type of rock underneath affects how slippery the ice is and how melt water moves beneath the ice.
A deeper understanding of these processes will help improve models that predict future sea level rise.
Rocks as a record of Antarctic history
BAS co-author and geologist Dr. Joanne Johnson collected the rocks during fieldwork in the Hudson Mountains as part of the International Thwaites Glacier Collaboration. she says:
“Rocks provide an incredible record of how our planet has changed over time, particularly how ice has eroded and changed the landscape of Antarctica. Rocks like these are a treasure trove of information about what lies deep beneath the ice sheets and just out of reach.”
“Identifying their sources can reveal how they got to where they are and provide clues about how the West Antarctic Ice Sheet may change in the future. This is essential information for determining the impact of rising sea levels on people in coastal areas around the world.”
This research shows how combining geology and geophysics can uncover hidden features beneath Antarctica and deepen our understanding of the forces that shape our planet.
