Pink Granite Boulders in Hudson Mountains Reveal Massive Subterranean Structure Beneath Antarctica’s Pine Island Glacier

BAS scientists discovered a 100km-wide granite deposit under the Pine Island Glacier, solving a mystery that explains the history of Antarctica's ice flow.

By: AXL Media

Published: May 1, 2026, 11:39 AM EDT

Source: Information for this report was sourced from Earth.com

The Mystery of the Hudson Mountain Erratics

Antarctica’s landscape is often perceived as a monolithic expanse of white, yet its most significant geological activity occurs at the interface where ice meets the continental bedrock. For decades, the Hudson Mountains have presented a geological puzzle: a scattering of pink granite boulders resting atop much younger, dark volcanic rock. Because these "erratics" did not match the local mineralogy, their origin remained a mystery until a team from the British Antarctic Survey initiated a specialized investigation. By measuring the radioactive decay within the mineral crystals of these stones, scientists determined the granite formed approximately 175 million years ago during the Jurassic period, far predating the surrounding volcanic terrain.

Gravity Sensors Detect a Sub-Glacial Giant

The search for the source of these pink stones shifted from the surface to the deep interior of the continent using aerial geophysical surveys. Aircraft equipped with high-precision gravity sensors flew over the Pine Island Glacier, detecting a massive anomaly beneath the ice sheet. The data revealed a gargantuan granite deposit nearly half the size of Wales, measuring 100 kilometers in width and seven kilometers in thickness. This hidden structure has remained obscured for millions of years, and its identification confirms that the pink boulders found in the Hudson Mountains were actually torn from this subterranean giant by the raw force of moving ice.

Reconstructing Ancient Glacial Movements

The discovery provides a vital window into the behavior of the West Antarctic Ice Sheet during the last ice age. Thousands of years ago, the Pine Island Glacier was significantly thicker and more powerful than its current state. As it flowed across the continent, it eroded the granite bed, transporting fragments of the 175-million-year-old rock across the landscape. When the ice eventually thinned and retreated, it deposited these boulders—now known as "clasts"—on the slopes of the Hudson Mountains. By mapping these deposit sites, geologists can accurately reconstruct the historical speed and direction of ancient ice flows, which is essential for calibrating modern climate models.