Scientists have solved a long-standing geological mystery in West Antarctica, discovering a massive granite formation hidden beneath the ice. The discovery explains the puzzling presence of strange boulders found scattered across a remote mountain range and provides crucial new data on the history of the region’s vast ice sheet, improving researchers’ ability to predict its future in a warming climate.
The vast body of rock, known as a batholith, is located deep beneath the Pine Island Glacier, one of the fastest-melting glaciers on the continent. It measures nearly 100 kilometers across and 7 kilometers thick. By linking this buried granite to surface rocks found decades ago, researchers from the British Antarctic Survey (BAS) have reconstructed past ice sheet behavior, offering a vital historical baseline to understand current and future ice loss that contributes to global sea-level rise.
A Decades-Old Geological Puzzle
For years, geologists were perplexed by the presence of distinctive pink granite boulders perched high in the Hudson Mountains. This region is predominantly volcanic, making the granite boulders a geological oddity. Their origin was a complete mystery, leaving scientists to wonder how these rocks, foreign to the local geology, came to rest in such an improbable location. The boulders sat in plain sight, but the story of their journey remained locked away until new technology allowed researchers to peer beneath the immense thickness of the West Antarctic Ice Sheet.
Mapping the Unseen Beneath the Ice
The breakthrough came from a combination of modern aerial surveying techniques and laboratory analysis of the unusual boulders. A BAS-led team managed to connect the rocks on the mountain peaks to a source hidden miles below the glacier’s surface.
Airborne Gravity Surveys
To create a picture of the subglacial landscape, researchers used aircraft equipped with instruments that measure minute variations in gravity. Flying in a grid pattern over the Pine Island Glacier region, the sensors detected a large area of higher gravity, indicating the presence of a dense rock mass concealed by the ice. Dr. Tom Jordan, a geophysicist at BAS, analyzed this data and found that the gravitational signature was consistent with that of a large granite batholith. The location of this buried mass provided the first major clue to the boulders’ origin.
Dating the Ancient Rocks
The next step was to determine if the surface boulders were related to the newly discovered subterranean formation. Geologists analyzed the composition of the pink granite boulders from the Hudson Mountains, using radioactive dating techniques on microscopic crystals locked within the rock. The results showed the granite formed approximately 175 million years ago, during the Jurassic period. The consistency in age and composition strongly suggested the boulders were indeed fragments of the giant batholith identified in the gravity survey.
Reconstructing a Thicker Ancient Ice Sheet
With the source of the boulders identified, the team could piece together the story of their transport. The only force powerful enough to pluck giant boulders from a solid rock bed and carry them to the tops of mountains is a moving ice sheet. The discovery provides compelling evidence that the West Antarctic Ice Sheet was significantly thicker and more extensive during the last ice age, around 20,000 years ago.
At that time, the ice surface would have been much higher than it is today, completely burying the Hudson Mountains. As the Pine Island Glacier flowed over the landscape, it scraped and pulled rocks from the underlying granite batholith. These boulders were then frozen into the base of the glacier and transported for miles before being deposited on top of the mountains as the ice sheet receded and thinned over thousands of years.
Implications for Future Sea-Level Rise
The findings extend far beyond solving a geological riddle. Understanding the past behavior of the ice sheet is critical for making accurate predictions about its future stability and its potential contribution to rising sea levels.
Refining Predictive Models
Computer models that forecast the effects of climate change rely on accurate historical data to test their reliability. This discovery provides a concrete physical benchmark for the thickness and flow patterns of the ice sheet during a past climatic period. By inputting this new geological information, scientists can refine their models to create more robust projections of how Antarctica will respond to future warming. This helps reduce uncertainty in global sea-level rise predictions, a critical issue for coastal communities worldwide.
Bedrock’s Role in Modern Ice Loss
The geology under a glacier plays a significant role in how it behaves. The shape of the bedrock and its composition affect how easily the ice can slide and how meltwater drains away at its base. The Pine Island Glacier is already losing ice at an alarming rate, and knowing that it rests partly on this large, stable granite formation will help scientists better understand the mechanics of its flow. This information is vital for comprehending the region’s rapid ice loss and predicting how it might change in the coming decades.
A Window into Continental Breakup
The 175-million-year-old granite provides a glimpse into a period of dramatic planetary change. The rock was formed during the Jurassic period, when the supercontinent of Gondwana was in the process of breaking apart. This magmatic activity was associated with the crustal thinning and rifting that eventually separated Africa, South America, Australia, India, and Antarctica. The Pirrit Hills granite, found in another part of West Antarctica, also dates to this period and is linked to the same large-scale tectonic events. The newly discovered batholith is another piece in the puzzle of West Antarctica’s complex geological history, confirming the intense magmatism that shaped the continent as we know it today.
